TWI866311B - Electrode-defined unsuspended acoustic resonator - Google Patents

Abstract

The present invention provides a bulk acoustic wave resonator that can operate in a bulk acoustic wave mode, which includes a resonator body mounted on a separate carrier, the carrier being not a part of the resonator body. The resonator body includes a piezoelectric layer, a device layer and an upper conductive layer, the upper conductive layer being located above the piezoelectric layer and the other side of the piezoelectric layer being the device layer. The piezoelectric layer is a LiNbO ₃ single crystal cut at an angle of 130°±30°. The surface of the device layer opposite to the piezoelectric layer is used to mount the resonator body on the carrier.

Description

Electrode-defined unsuspended acoustic resonator

The present invention relates to a bulk acoustic wave resonator, in particular to a bulk acoustic wave resonator having a resonator body and optionally one or more connection structures, wherein the connection structures can be used to supply electrical signals to one or more resonator conductive layers.

Wireless communications have progressed from the "1G" system in the 1980s, to the "2G" system in the 1990s, to the "3G" system in the 2000s, and to the current "4G" system that was standardized in 2012. In existing wireless communications, surface-acoustic-wave (SAW) filters or bulk-acoustic-wave (BAW) filters are used to filter RF signals.

Film-bulk-acoustic-resonators (FBARs) and solid-mounted-resonators (SMRs) are two types of BAW filters, which are piezoelectrically driven micro-electro-mechanical-system (MEMS) devices that enable today's 4G wireless communications to resonate at relatively high frequencies and relatively low insertion loss compared to SAW filter devices. These BAW acoustic wave resonators include a piezoelectric stack having, for example, a piezoelectric material film sandwiched between an upper electrode film and a lower electrode film. The resonant frequency of these piezoelectric stacks is thickness-based or depends on the thickness of the films of the piezoelectric stack. As the thickness of the film in the piezoelectric stack decreases, the resonant frequency increases. The film thickness of the resonator is critical and must be precisely controlled to obtain the desired resonant frequency. It is difficult and time-consuming to achieve a consistent high degree of thickness to correct different areas of the piezoelectric stack in order to achieve a target or specific RF frequency within reasonable yields in the FBAR and SMR manufacturing processes.

The 5G wireless communication systems being developed will eventually replace the earlier lower performance communication systems described above, which operate at RF frequencies between a few hundred MHz and 1.8 GHz. 5G systems will operate at higher RF frequencies, such as 3-6 GHz (below 6 GHz) or even higher, up to 100 GHz.

One of the challenges facing BAW acoustic wave resonators in the current state of the art is the need to increase the resonance frequency by reducing the film thickness of FBAR and SMR-related RF filters used in 5G applications due to the increase in frequency. The reduction in the thickness of the piezoelectric film means that the distance between the upper and lower electrodes of the piezoelectric stack is reduced, resulting in an increase in capacitance. The increase in capacitance leads to higher feed-through of the RF signal and reduces the signal to noise ratio, which is undesirable. The ideal piezoelectric coupling efficiency of a piezoelectric stack (upper electrode, lower electrode, and piezoelectric layer between the upper and lower electrodes) can come from an ideal combination of the thickness of the piezoelectric layer, the thickness of the upper electrode, the thickness of the lower electrode, and the alignment and orientation of the piezoelectric crystals. In order to achieve high RF frequency operation required for 5G communications, reducing the thickness of the piezoelectric film may not achieve the best piezoelectric coupling efficiency, which leads to higher insertion loss and higher motion impedance. The thickness of the electrode, whether the upper electrode, the lower electrode, or both, must be reduced. The reduction in electrode thickness leads to an increase in resistivity, which will lead to another undesirable limitation, namely higher insertion loss.

Furthermore, the product of frequency and the quality factor (or Q value) of FBAR and SMR devices is generally constant, which means that an increase in the resonant frequency will reduce the Q value. A reduction in the Q value is not desirable, especially as the current state of the art for FBAR and the Q of SMR are approaching the theoretical limit frequency of 2.45 GHz or lower. Therefore, doubling the frequency will result in a reduction in the Q value, making it difficult to manufacture RF devices such as RF filters, RF resonators, RF switches, and RF oscillators.

In view of this, the present invention provides a resonator body that can operate using a bulk acoustic wave mode, preferably a lateral resonance mode. The bottom of the resonator body can be mounted or coupled to a mounting substrate or carrier, and the resonator body can be used as an RF filter, RF resonator, RF switch, RF oscillator, etc.

The present invention also provides a bulk acoustic wave resonator, which includes a resonator body and one or more connecting structures, which can transmit electrical information to one or more conductive layers of the resonator body. In an ideal and non-limiting embodiment or example, the one or more connecting structures can be integrally formed and/or formed with the same layer of material as the resonator body, so that the bulk acoustic wave resonator can be a single object. The bottom of the single object bulk acoustic wave resonator can be mounted or coupled to a mounting substrate or carrier, and the resonator body can be used as an RF filter, RF resonator, RF switch, RF oscillator, etc.

The bulk acoustic wave resonator of the present invention is characterized in that it comprises: a resonator body, which comprises: a piezoelectric layer; a device layer; and an upper conductive layer, which is located above the piezoelectric layer and the other side of the piezoelectric layer is the device layer; wherein the entire surface of the device layer on the opposite side of the piezoelectric layer is substantially used to mount the resonator body on a carrier and separate the resonator body.

For the purpose of the following detailed description, it should be understood that, unless expressly indicated to the contrary, the present invention may assume various alternative situations and step sequences. It should also be understood that the specific devices and methods described in the following specification are only exemplary embodiments, examples, or aspects of the present invention. In addition, except in any operating example or with special instructions, the quantities of components mentioned in this specification and the scope of the patent application in the ideal and non-limiting embodiment, example, and aspect should be understood as the word "about" in all cases. Therefore, unless expressly indicated to the contrary, the numerical parameters set forth in the following specification and the scope of the patent application are approximate values and may vary depending on the desired properties obtained by the present invention. Therefore, each numerical parameter should be interpreted at least according to the number of reported significant digits and by ordinary rounding techniques.

Although the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in its respective testing measurements.

Furthermore, it should be understood that any numerical range described in the present invention should include all sub-ranges included therein. For example, the range of "1 to 10" is intended to include all sub-ranges between the listed minimum value 1 and the listed maximum value 10 (and including), that is, the minimum value is equal to or greater than 1 and the maximum value is equal to or less than 10.

It should also be understood that the specific devices and steps described in the drawings and the following description are merely exemplary embodiments, examples, or aspects of the present invention. Therefore, the exemplary embodiments, examples, or aspects of the present invention are not limited to specific dimensions or other related physical characteristics. Specific ideal and non-limiting embodiments, examples, or aspects of the present invention will be described by the same element codes in the drawings corresponding to the same or functionally equivalent elements.

In the present invention, unless otherwise specifically stated, the use of the singular may include the plural and the plural may encompass the singular. Also, in the present invention, unless otherwise specifically stated, the use of "or" means "and/or", even if "and/or" may be used in specific circumstances. Furthermore, in the present invention, the use of "a" means "at least one" unless otherwise stated.

For the purpose of the following description, the terms "end", "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", "lateral", "longitudinal" and their derivatives shall be related to the examples in the figures. However, it should be understood that the examples may assume various alternative situations and step orders unless otherwise specifically stated. It should be noted that the specific examples described in the drawings and this specification are only exemplary examples or aspects of the present invention. Therefore, the exemplary examples or aspects disclosed herein should not be limited thereto.

As shown in FIG1 , in an ideal and non-limiting embodiment or example, according to the principles of the present invention, an unsuspended bulk acoustic wave resonator (UBAR) 2 can operate in a bulk acoustic wave mode and includes a resonator body 4, which can include a stack of layers from top to bottom, wherein the stack includes an upper conductive layer 6, a piezoelectric layer 8, an optional lower conductive layer 10, and a device layer 12. In the example of the UBAR 2 shown in FIG1 , the bottom of the device layer 12 can be mounted, for example, directly mounted on a mounting substrate or carrier 14.

2 and continuing from FIG. 1 , in an ideal and non-limiting embodiment or example, according to the principles of the present invention, another UBAR2 example can be similar to the UBAR2 shown in FIG. 1 , wherein the difference is that the resonator body 4 of FIG. 2 can include an optional substrate 16 between the device layer 12 and the carrier 14. In one example, the bottom of the device layer 12 can be mounted, for example, directly mounted on the top of the substrate 16, and the bottom of the substrate 16 can be mounted, for example, directly mounted on the carrier 14.

3 and continuing with FIGS. 1 and 2 , in an ideal and non-limiting embodiment or example, according to the principles of the present invention, another UBAR2 example may be similar to the UBAR2 shown in FIG. 2 , wherein the difference is that the resonator body 4 of FIG. 3 may include an optional second substrate 16-1 between the device layer 12 and the piezoelectric layer 8 or the optional lower conductive layer 10, and/or include a second device layer 12-1 between the second substrate 16-1 and the piezoelectric layer 8 or the optional lower conductive layer 10. In an ideal and non-limiting embodiment or example, it is better if the resonator body 4 of FIG. 3 may further include one or more additional device layers 12 (not specifically shown) and/or one or more additional substrates 16 (not specifically shown). Another example resonator body 4 has a plurality of device layers 12 and substrates 16, and may include an exemplary sequence, from the piezoelectric layer 8 or the optional lower conductive layer 10 to the carrier 14, in order: first device layer, first substrate, second device layer, second substrate; third device layer, third substrate, etc. In an ideal and non-limiting embodiment or example, the resonator body 4 may include a plurality of device layers 12 and/or a plurality of substrates 16, each device layer 12 may be made of the same or different materials, and each substrate 16 may be made of the same or different materials. In an ideal and non-limiting embodiment or example, the number of device layers 12 and the number of substrates 16 may be different. In one example, the resonator body 4 may include a device layer 12-1, a substrate 16-1, and a device layer 12 as the bottom layer of the resonator body 4, illustratively from the piezoelectric layer 8 or the optional lower conductive layer 10 to the carrier 14. Examples of materials that can be used for each device layer 12 and each substrate 16 are described below.

In an ideal and non-limiting embodiment or example, as shown in FIGS. 1-3 , one or more temperature compensation layers 90, 92, 94 may be on the top surface of the upper conductive layer 6; between the piezoelectric layer 8 or the optional lower conductive layer 10, and the device layer 12; and/or between the device layer 12 (or 12-1) and the substrate 16 (or 16-1). Each temperature compensation layer may contain at least one of silicon and oxygen. For example, each temperature compensation layer may contain silicon dioxide, or a silicon element, and/or an oxygen element. One or more optional temperature compensation layers 90, 92, 94 may help prevent changes in the resonant frequency due to heat generated by using the resonator body 4 in each of the examples shown in FIGS. 1-3.

In plan view, the resonator body 4 and/or UBAR 2 described in the present invention may have a cube or rectangular parallelepiped shape. However, the resonator body 4 and/or UBAR 2 may have other shapes.

As shown in Figures 4A-4C and continuing all the above figures, in an ideal and non-limiting embodiment or example, one or both conductive layers 6 and the optional conductive layer 10 can be presented in the form of an interdigitated electrode 18 (Figure 4A), which can include a conductive wire or spring 20, supported by a back 22, interdigitated with a conductive wire or spring 24, supported by a back 26. In an ideal and non-limiting embodiment or example, one or both conductive layers 6 and the optional conductive layer 10 can be presented in the form of a comb electrode 27 (Figure 4B), which can include a conductive wire or spring 28 extending from a first back 30. The ends of the conductive wires or springs 28 on the opposite side of the first back 30 can be connected to an optional second back 32 (indicated by the dotted lines in Figure 4B). In an ideal and non-limiting embodiment or example, one or both conductive layers 6 and the optional conductive layer 10 can be presented in the form of a conductive sheet electrode 33 (FIG. 4C). Each wire or spring 20, 24 and 28 is presented as a straight line. In one example, each wire or spring 20, 24 and 28 can be an arc-shaped wire or spring, a spiral wire or spring, or other suitable and/or desired shape.

In an ideal and non-limiting embodiment or example, the upper conductive layer 6 may be in the form of an interdigitated electrode 18, or a comb electrode 27, or a sheet electrode 33. Independent of the form of the upper conductive layer 6, the optional bottom conductive layer 10 may be in the form of an interdigitated electrode 18, or a comb electrode 27, or a sheet electrode 33. Hereinafter, for descriptive purposes only, in an ideal and non-limiting embodiment or example, the upper conductive layer 6 will be described as being in the form of a comb electrode 27, which includes a first back 30 and an optional second back 32, and the optional bottom conductive layer 10 will be described as being in the form of a sheet electrode 33. However, the present embodiment is not limited thereto, and any one of the interdigitated electrodes 18 , the comb-shaped electrodes 27 , or the sheet-shaped electrodes 33 may be used as the upper conductive layer 6 , and may be combined with any one of the interdigitated electrodes 18 , the comb-shaped electrodes 27 , or the sheet-shaped electrodes 33 as the optional lower conductive layer 10 .

In an ideal and non-limiting embodiment or example, the resonance frequency of the resonator body 4 having at least the upper conductive layer 6 in the form of the interdigitated electrode 18 or the comb electrode 27 in each example, regardless of the form of the optional lower conductive layer 10, can be adjusted or selected in a known manner by appropriately selecting the finger spacing 38 (e.g., Figures 4A-4B), where the finger spacing 38 = finger width + finger gap (between two adjacent fingers). In one example, the resonance frequency of each resonator body 4, but not all, which is mainly desired, can be increased by reducing the finger spacing 38 in the lateral mode relative to the thickness mode. In one example, it is desirable that each, but not all, resonator bodies 4 have a resonant frequency that is reduced by increasing the inter-finger spacing 38 in the thickness mode relative to the lateral mode.

In an ideal and non-limiting embodiment or example, the resonator body 4 of each example can be in a thickness mode, a transverse mode, or a hybrid/composite mode of a combination of a thickness mode and a transverse mode. For thickness mode resonance, the acoustic wave resonates in the thickness direction of the piezoelectric layer 8, and the resonance frequency is based on the thickness of the piezoelectric layer 8, and the thickness of the upper conductive layer 6 and the optional lower conductive layer 10. The combination of the piezoelectric layer 8, the optional lower conductive layer 10, and the upper conductive layer 6 can be referred to as a piezoelectric stack. The acoustic velocity determined by the resonance frequency of the resonator body 4 of each example described herein is the composite acoustic velocity of the piezoelectric stack. In one example, the resonance frequency f can be obtained by dividing the composite acoustic velocity _Va by twice the thickness of the piezoelectric stack. to calculate.

For transverse mode resonance, the sound wave resonates in the transverse direction (x or y direction) of the piezoelectric layer 8, and the resonant frequency can be obtained by dividing the complex sound velocity V _a of the piezoelectric stack by twice the finger spacing 38, f = V _a /2 (finger spacing). _L is reduced to small pitch size _S , the percentage of frequency increase, PFI _Calculated , in one example, can be calculated by the following formula PFI _Calculated = ( _L - _S ) / _S. In one example, when the inter-finger spacing 38 is reduced from 2.2 μm to 1.8 μm, the PFI of the lateral mode _{is calculated} to be 22.2%. In another example, when the inter-finger spacing 38 is reduced from 1.8 μm to 1.4 μm, the PFI of the lateral mode _{is calculated} to be 28.5%.

The composite mode resonance may include a thickness mode resonance portion and a transverse mode resonance portion. The transverse mode resonance portion L in the composite mode resonance may be reduced by changing the finger spacing 38 from a large spacing size to a large spacing size. _L to small pitch size _S is defined as the ratio between the actual ratio or measured percentage of the increase in frequency (PFI _measurement ) and the calculated ratio of the increase in frequency (PFI _calculation ). If there are one or more uncontrolled or unpredictable changes, the transverse mode resonance L value can be greater than 100%. In one example, the resonator body 4 can resonate in thickness mode, transverse mode, or composite mode. In the example of composite mode resonance, the portion L of the transverse mode resonance can be ≥20%. In another example of composite mode resonance, the portion L of the transverse mode resonance can be ≥30%. In another example of composite mode resonance, the portion L of the transverse mode resonance can be ≥40%.

In an ideal and non-limiting embodiment or example, a resonator body 4 has an optional lower conductive layer 10 in the form of a sheet electrode 33 and an upper conductive layer 6 in the form of a comb electrode 27, wherein a finger spacing 38 of 2.2 μm can resonate in a composite mode having the following mode resonance frequencies: mode 1 resonance frequency = 1.34 GHz; mode 2 resonance frequency = 2.03 GHz; and mode 4 resonance frequency = 2.82 GHz.

In one example, a resonator body 4 having an optional lower conductive layer 10 in the form of a sheet electrode 33 and an upper conductive layer 6 in the form of a comb electrode 27, wherein a finger spacing 38 of 1.8 μm can resonate in a composite mode with the following modal resonance frequencies: Mode 1 resonance frequency = 1.49 GHz; Mode 2 resonance frequency = 2.38 GHz; and Mode 4 resonance frequency = 3.05 GHz. In this example, the lateral mode resonance L percentages of the composite mode resonance can be respectively: L mode 1 = 53%; L mode 2 = 78%; and L mode 4 = 27%. See also FIG. 10, which is a frequency-dB relationship diagram of the resonator body 4 in this example. In FIG. 10 , each resonance frequency 82 , 84 , and 88 represents the response of the resonator body 4 to a different mode, mode 1 resonance frequency = 1.49 GHz; mode 2 resonance frequency = 2.38 GHz; and mode 4 resonance frequency = 3.05 GHz.

In one example, the mode 1 resonant frequency may or may alternatively be considered or associated with a surface acoustic wave (SAW); the mode 2 resonant frequency may or may alternatively be considered or associated with the _S0 (or extensional) mode; and the mode 4 resonant frequency may or may alternatively be considered or associated with the _A1 (or flexural) mode. In addition, the mode 3 resonant frequency (described below) may or may alternatively be considered or associated with the shear mode. SAW, _S0 mode, extensional mode, _A1 mode, shear mode and flexural mode are known to those of ordinary skill and will not be further described herein.

In one example, a resonator body 4 having an optional lower conductive layer 10 in the form of a sheet electrode 33 and an upper conductive layer 6 in the form of a comb electrode 27, wherein a finger spacing 38 of 1.4 μm can resonate in a composite mode with the following mode resonance frequencies: mode 1 resonance frequency = 1.79 GHz; mode 2 resonance frequency = 2.88 GHz; and mode 4 resonance frequency = 3.36 GHz. For the resonator body 4 of this example, the lateral mode resonance percentage of the composite mode resonance L can be: L mode 1 = 70%; L mode 2 = 74%; and L mode 4 = 35%.

In one example, the aforementioned resonator body 4 in thickness mode, lateral mode, or composite mode can be applied to each UBAR 2 example shown in Figures 1-3, which can include a resonator body 4 combined with one or more connecting structures 34 and 36, as will be described below.

Next, referring to FIG. 1-3 , in an ideal and non-limiting embodiment or example, each resonator body 4 at the bottom layer shown in FIG. 1-3 can be directly mounted on the carrier 14 using any suitable and/or desired mounting technology, such as eutectic mounting, adhesive, etc. Here, “directly mounted”, “directly mounted on” and similar phrases can be understood as placing and bonding the resonator body 4 at the bottom layer of each resonator body 4 shown in FIG. 1-3 in close proximity to the carrier 14 in any suitable and/or desired manner, such as mounting, connecting, and/or by a suitable and/or desired method, such as eutectic bonding, conductive adhesive, non-conductive adhesive, etc. in one example. In one ideal and non-limiting embodiment or example, the carrier 14 may be a surface of a package, such as a conventional integrated circuit (IC) package. After the bottommost layer of the resonator body 4 is mounted to the surface of the aforementioned package, the resonator body 4, and more generally, the UBAR 2, is sealed in the aforementioned package in a known manner to protect the resonator body 4, and more generally, the UBAR 2 from external environmental conditions. In one example, the package uses a conventional ceramic IC package from Japanese company NTK Ceramic Co., Ltd. for mounting the UBAR. However, this should not be construed as limiting, as it is contemplated that the resonator body 4 and/or UBAR 2 may be mounted in any suitable and/or desired package now known or later developed.

In another example, the carrier 14 can be a surface of a substrate, such as a ceramic sheet, a conventional printed circuit board material sheet, etc. The description of each substrate example as the bottom layer of the resonator body 4 and/or UBAR 2 of Figures 1-3 can be mounted is for illustrative purposes only and should not be construed as limiting. The carrier 14 can be made of any suitable and/or desired material that is compatible with the bottom layer material of each resonator body 4 and/or UBAR 2 shown in Figures 1-3 and can be used in a known manner. The carrier 14 can have any form that a person of ordinary skill in the art considers suitable and/or desirable. Therefore, the present description is not limiting with respect to the mounting substrate or carrier 14.

1-3, in an ideal and non-limiting embodiment or example, each UBAR 2 may include one or more optional connection structures 34 and/or 36 that facilitate application of electrical signals to the upper conductive layer 6 and the optional lower conductive layer 10 of the resonator body 4. However, in an ideal and non-limiting embodiment or example, one or more optional connection structures 34 and/or 36 may be excluded (e.g., not provided), wherein the electrical signal may be directly applied to the upper conductive layer 6 and the optional lower conductive layer 10 of the resonator body 4. Thus, in one example, the UBAR 2 may include the resonator body 4 without the connection structures 34 and 36. In another example, the UBAR 2 may include the resonator body 4 and a single connection structure 34 or 36. For the purpose of describing the present invention in detail only, a desired and non-limiting embodiment or example of the UBAR 2 including the resonator body 4 and the connecting structures 34 and 36 is described below.

Each connection structure 34 and 36 can be presented in any suitable and/or desired form, can be formed by any suitable and/or desired method, and can be made of any suitable and/or desired material that can help provide independent electrical signals to the upper conductive layer 6 and the optional lower conductive layer 10. In an example, in which the upper conductive layer 6 is in the form of a comb electrode 27 having only a back 30 or 32, and the optional lower conductive layer 10 is in the form of a comb electrode 27 having only a back 30 or 32, or a sheet electrode 33, electrical signals can be provided to each upper conductive layer 6 and the optional lower conductive layer 10 via a single connection structure 34 or 36, and the single connection structure 34 or 36 can be configured to provide electrical signals to the upper conductive layer 6 and the optional lower conductive layer 10, respectively.

In another example, at least one of the upper conductive layer 6 or the optional lower conductive layer 10 has the form of an interdigitated electrode 18 or a comb electrode 27 and has two backs 30 and 32, and one or more electrical signals can be provided to the backs 22 and 26 of the interdigitated electrode 18 and/or the backs 30 and 32 of the comb electrode 27 respectively through individual connection structures 34 and 36. The form of the upper conductive layer 6 and the optional lower conductive layer 10 and the manner in which the upper conductive layer 6 and the optional lower conductive layer 10 are provided with electrical signals should not be limiting.

In an ideal and non-limiting implementation or example, without being bound by any particular description, example or theory, examples of first and second connecting structures 34 and 36 can be used with the example UBARs 2 shown in Figures 1-3, which will be described below.

In an ideal and non-limiting embodiment or example, only for the purpose of describing the present invention in detail, as shown in FIGS. 1-3 , each connection structure 34 and 36 will be described as having various examples of extensions of various layers and/or substrates forming the resonator body 4. However, this is not limiting, as it is contemplated that each connection structure 34 and 36 can have any suitable and/or desired form and/or structure that can provide one or more individual electrical signals to the upper conductive layer 6 and the optional lower conductive layer 10.

In an ideal and non-limiting embodiment or example, as shown in Figures 5A-5B, which are representative diagrams along the lines A-A and B-B in any or all of Figures 1-3, Figure 5A shows an upper conductive layer 6 in the form of a comb electrode 27 on top of the piezoelectric layer 8, including a back 30 and an optional back 32. In an example, the upper conductive layer 6 can be optionally presented in the form of an interdigitated electrode 18. In an ideal and non-limiting embodiment or example, Figure 5B shows an optional lower conductive layer 10 under the piezoelectric layer 8 in the form of a sheet electrode 33 (as shown in the dotted line of Figure 5B). In an example, the optional lower conductive layer 10 can be optionally presented in the form of an interdigitated electrode 18 or a comb electrode 27. In the following, for example only, the upper conductive layer 6 and the optional lower conductive layer 10 will be described as being in the form of a comb electrode 18, including a back 30 and an optional back 32, and in the form of a sheet electrode 33, respectively. However, this is not restrictive.

In a desirable and non-limiting embodiment or example, the connection structures 34 and 36 may include bottom metal layers 40 and 44 ( FIG. 5B ) contacting the sheet electrode 33, which is formed as an optional lower conductive layer 10 of the resonator body 4. Each bottom metal layer 40 and 44 may be sheet-shaped and covered with a piezoelectric layer 8. In one example, each bottom metal layer 40 and 44 may be formed simultaneously as an extension of the sheet electrode 33. In another example, each bottom metal layer 40 and 44 may be formed separately from the sheet electrode 33 and may be the same material or a different material from the sheet electrode 33. In one example, the connection structures 34 and 36 may also include top metal layers 42 and 46 on top of the piezoelectric layer 8 and backs 30 and 32 respectively contacting the comb electrodes 27 formed as the upper conductive layer 6 of the resonator body 4.

In one example, the bottom metal layers 40 and 44 can be connected to the contact pads 48 on the top surfaces of the first and second connection structures 34 and 36 through the conductive vias 50 formed in the piezoelectric layer 8, and the conductive vias 50 extend between the aforementioned contact pads 48 and the bottom metal layers 40 and 44. For example, each of the top metal layers 42 and 46 can have a sheet shape and be separated from the corresponding contact pads 48 by a gap (not numbered). Each of the top metal layers 42 and 46 can also include a contact pad 58. Each contact pad 48 can be connected to each other, and each contact pad 48 can be connected to a suitable signal source (not shown) as needed, which can electrically drive/bias the optional lower conductive layer 10 in any suitable and/or desired manner. Similarly, each contact pad 58 can be connected to each other, and each contact pad 58 can be connected to a suitable signal source (not shown) as needed, which can electrically drive/bias the upper conductive layer 6 in any suitable and/or desired manner.

As shown by the component codes 18 and 27 in FIGS. 5A-5B , the upper conductive layer 6 may also be in the form of an interdigitated electrode 18 , and the optional lower conductive layer 10 may also be in the form of a comb electrode 27 or an interdigitated electrode 18 .

As shown in Figures 6A-6B, which are representative diagrams along the lines A-A and B-B in any or all of Figures 1-3, in an ideal and non-limiting embodiment or example, the example in Figures 6A-6B is similar to the example in Figures 5A-5B, except for at least the following differences. Bottom metal layers 40 and 44 can each be in the form of a pair of spaced apart conductors 52 (relative to the conductive sheets shown in Figures 5A-5B), which are connected to an optional lower conductive layer 10 in the form of a sheet electrode 33 by lateral conductors 54 and tether conductors 56. Top metal layers 42 and 46 can each be in the form of conductors 60. Each conductor 60 can be connected to the back 30 or back 32 of the comb electrode 27 formed as the upper conductive layer 6 by tether conductors 62. The tether conductor 62 can be vertically aligned with the tether conductor 56 and separated from the tether conductor 56 by the piezoelectric layer 8. In one example, as shown in FIGS. 6A-6B , the width of the tether conductor 62 can be less than the width of the conductor 60, and the width of the tether conductor 56 can be approximately the same as the width of the tether conductor 62.

As shown in Figures 7A-7B, which are representative views along lines A-A and B-B in any or all of Figures 1-3, in one ideal and non-limiting embodiment or example, the example in Figures 7A-7B is similar to the example in Figures 6A-6B, except for at least the following differences: Some or all of the material of each of the connecting structures 34 and 36 on both sides of the tether conductors 62 and 56, the aforementioned connecting structure portions can be removed to form grooves, which can extend from the top of the UBAR 2 to the bottom of the UBAR 2 on both sides of the aforementioned tether conductors between the remaining portions of the aforementioned connecting structures and the resonator body 4 for part or all of the distance. In one example, a tether structure 76 is defined by removing part or all of the material of each connecting structure 34 and 36 on both sides of the tether conductor of the aforementioned connecting structure. The tether structure 76 may include the tether conductors 62 and 56 and a portion of the piezoelectric layer 8 is vertically aligned with the tether conductor 62.

Referring to FIG. 7C and continuing to refer to FIG. 7A-7B , in a desired and non-limiting embodiment or example, some or all of the material of each connection structure 34 and 36 is removed on both sides of the tether conductors 62 and 56, and the aforementioned connection structures can be used with any of the UBAR 2 examples in FIG. 1-3 . For example, FIG. 7C is a side view of the UBAR 2 example in FIG. 1 , in which the material of the first and second connection structures 34 and 36 on both sides of the tether conductors 62 and 56 is removed as shown in FIG. 7A-7B . It can be understood from Figures 7A-7C that on both sides of the tether conductors 62 and 56 of the aforementioned connecting structure, the material removed from each connecting structure 34 and 36 may include portions of the upper conductive layer 6, the piezoelectric layer 8, the optional lower conductive layer 10 and the device layer 12. Therefore, in Figures 7A-7B, there is no visible material in the grooves formed by removing each connecting structure 34 and 36 on both sides of the tether conductors 62 and 56 of the aforementioned connecting structure. In the example shown in Figures 7A-7C, each tether structure 76 may include, from top to bottom: a tether conductor 62, a portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, an optional tether conductor 56 (when the lower conductive layer 10 is present), and a portion of the device layer 12 vertically aligned with the tether conductor 62.

In another example, where the UBAR 2 includes a substrate 16 ( FIG. 2 ), represented by the dashed lines in FIG. 7C , and optionally one or more additional device layers 12-1 and/or substrate 16-1 ( FIG. 3 ), portions of each connection structure 34 and 36 may also be removed from the material forming each additional device layer 12-1 and/or substrate 16-1 ( FIG. 3 ) and substrate 16 on both sides of the tether conductors 62 and 56, so that no material is visible in the trenches formed by removing each connection structure 34 and 36 on both sides of the tether conductors 62 and 56 of the aforementioned connection structures in FIGS. 7A-7B .

In one example, FIGS. 7A-7B are diagrams of the UBAR 2 example in FIG. 2 , and each tether structure 76 may include, from top to bottom: a tether conductor 62, a portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, an optional tether conductor 56 (when an optional lower conductive layer 10 is present), a portion of the device layer 12 vertically aligned with the tether conductor 62, and a portion of the substrate 16 vertically aligned with the device layer 12. In another example, Figures 7A-7B are diagrams of the UBAR 2 example in Figure 3, and each tether structure 76 may include, from top to bottom: a tether conductor 62, a portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, an optional tether conductor 56 (when an optional lower conductive layer 10 is present), a portion of the device layer 12 and 12-1 vertically aligned with the tether conductor 62, and a portion of the substrate 16 and 16-1 vertically aligned with the tether conductor 62.

As shown in FIGS. 8A-8B , which are representative views along lines A-A and B-B in any or all of FIGS. 1-3 , in one ideal and non-limiting embodiment or example, the example in FIGS. 8A-8B is similar to the example in FIGS. 7A-7B , except for at least the following differences: That is, all or a portion of the material of at least one device layer 12 or 12-1 forming each connection structure 34 and 36 is retained on both sides of the tether conductors 62 and 56 of the aforementioned connection structure, so that the material of the aforementioned at least one device layer 12 or 12-1 is visible in the grooves on both sides of the tether conductors 62 and 56 of the aforementioned connection structure. In one example, FIGS. 8A-8C are diagrams of the UBAR 2 example in FIG. 1 , and each tether structure 76 may include, from top to bottom: tether conductor 62, a portion of piezoelectric layer 8 vertically aligned with tether conductor 62, and an optional tether conductor 56 (when an optional lower conductive layer 10 is present). In this example, the device layer 12 is retained in the trench and can be seen in FIGS. 8A-8B .

In another example, FIG8A-8B is a diagram of the UBAR 2 example in FIG2, and each tether structure 76 may include, from top to bottom: tether conductor 62, a portion of piezoelectric layer 8 vertically aligned with tether conductor 62, an optional tether conductor 56 (when an optional lower conductive layer 10 is present), and a portion of device layer 12 vertically aligned with tether conductor 62. In this example, device layer 12 is retained in the trench and can be seen in FIG8A-8B, and substrate 16 under device layer 12 is also retained (indicated by the dotted line in FIG8C), but is not visible in the trench of FIG8A-8B.

In another example, FIG8A-8B is a diagram of the UBAR 2 example in FIG3, and each tether structure 76 may include, from top to bottom: tether conductor 62, a portion of piezoelectric layer 8 vertically aligned with tether conductor 62, an optional tether conductor 56 (when an optional lower conductive layer 10 is present), and a portion of device layer 12 vertically aligned with tether conductor 62. In one example, device layer 12 is retained and visible in the trenches of FIG8A-8B, and substrate 16 under device layer 12 is also retained but not visible in the trenches of FIG8A-8B, and each tether structure 76 also includes a portion of device layer 12-1 and substrate 16-1 vertically aligned with tether conductor 62. In another example, the device layer 12 - 1 is retained and visible in the trenches of FIGS. 8A-8B , and the substrates 16 , 16 - 1 and the device layer 12 are also retained but are not visible in the trenches of FIGS. 8A-8B .

As another example, as shown in FIG. 8D , which is a diagram of the UBAR 2 example in FIG. 1 or 2 , each tether structure 76 may include, from top to bottom: a tether conductor 62, a portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, an optional tether conductor 56 (when an optional lower conductive layer 10 is present), a portion of the body of the device layer 12 vertically aligned with the tether conductor 62, and a portion of the body of the device layer 12 vertically aligned with the tether conductor 62 is exposed by partially removing the device layer 12 on both sides of the tether conductors 62 and 56 of each connecting structure 34 and 36. 8D is the UBAR 2 shown in FIG. 2 , and the substrate 16 (shown as a dotted line in FIG. 8D ) may remain below the device layer 12 but is not visible in FIGS. 8A-8B .

In another example, the UBAR shown in Figure 3 For example, each tether structure 76 may include, from top to bottom: the tether conductor 62, the portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, the optional tether conductor 56 (when the optional lower conductive layer 10 is present), the body of the device layer 12 or the portion of the device layer 12-1 vertically aligned with the tether conductor 62, and the body of the device layer 12 or the portion of the device layer 12-1 vertically aligned with the tether conductor 62 is exposed by partially removing the device layer 12 or the device layer 12-1 on both sides of the tether conductors 62 and 56 of each connecting structure 34 and 36 (similar to the partial removal of the device layer 12 in FIG. 8D). In one example, when a portion of the device layer 12 of the UBAR 2 shown in FIG3 is removed (similar to the partial removal of the device layer 12 in FIG8D ), the internal portion of the material forming the device layer 12 of the UBAR 2 in FIG3 is visible in the trenches in FIG8A-8B , and each tether structure 76 may also include a portion of the device layer 12-1 and the substrate 16-1 vertically aligned with the tether conductor 62. In this example, the substrate 16 is retained, i.e., no portion of the substrate 16 is removed and will not be shown in FIG8A-8B .

In another example, when a portion of the device layer 12-1 body of the UBAR 2 shown in FIG. 3 is removed (similar to the device layer 12 partially removed in FIG. 8D ), the internal portion of the forming material of the device layer 12-1 is visible in the trenches in FIG. 8A-8B , and each tether structure 76 may also include a portion of the device layer 12-1 vertically aligned with the tether conductor 62. In this example, the substrates 16, 16-1, and the device layer 12 are retained, that is, no portion of the substrates 16, 16-1, and the device layer 12 is removed and will not be shown in FIG. 8A-8B .

9A-9B, which are representative views along lines A-A and B-B in any or all of FIGS. 1-3, the UBAR 2 of FIG. 2 in one ideal or non-limiting embodiment or example, the example shown in FIGS. 9A-9B is similar to the example of FIGS. 8A-8B, except for at least the following exceptions. Each tether structure 76 may include a portion of the material forming the device layer 12, wherein as shown in FIGS. 9A-9C, portions of the substrate 16 are visible in the trenches formed on both sides of the tether conductors 62 and 56 of each connecting structure 34 and 36. In this example, the substrate 16 is retained and each tether structure 76 may include, from top to bottom: the tether conductor 62, the portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, the optional tether conductor 56 (when the optional lower conductive layer 10 is present), and the portion of the device layer 12 vertically aligned with the tether conductor 62.

Next, referring to Figures 9A-9B, in an ideal and non-limiting embodiment or example of the UBAR 2 shown in Figure 3, the device layer 12 and the substrates 16, 16-1 are retained as shown in Figures 9A-9B, and the substrate 16-1 can be seen in the grooves formed on both sides of the tether conductors 62 and 56 of each connecting structure 34 and 36. In this example, each tether structure 76 may include, from top to bottom: the tether conductor 62, the portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, the optional tether conductor 56 (when the optional lower conductive layer 10 is present), and the portion of the device layer 12-1 vertically aligned with the tether conductor 62.

In another example, the UBAR 2 shown in FIG. 3 wherein the substrate 16 is retained, the substrate 16 can be seen in the trenches formed on both sides of the tether conductors 62 and 56 of each connecting structure 34 and 36 in FIGS. 9A-9B , each tether structure 76 may include, from top to bottom: the tether conductor 62, a portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62, an optional tether conductor 56 (when the optional lower conductive layer 10 is present), a portion of the device layer 12-1 vertically aligned with the tether conductor 62, a portion of the substrate 16-1 vertically aligned with the tether conductor 62, and a portion of the device layer 12 vertically aligned with the tether conductor 62.

In another example shown in FIG9D , in the example of UBAR 2 shown in FIG2 , at the interface between substrate 16 and device layer 12, a portion of the material forming the substrate 16 body can be removed laterally below the resonator body 4 and the connecting structures 34 and 36, wherein as shown in FIG9D , the bottoms 64 and 70 of the connecting structures 34 and 36 are exposed, the bottoms 66 and 68 of the resonator body 4 are exposed, and the surfaces 72 and 74 of the substrate 16 body are exposed. In this example, the portion of the material forming the substrate 16 body that is removed can extend to the plane of FIG9D and the material portion of the substrate 16 is vertically aligned with each tether structure 76. In this example, each tether structure 76 may include, from top to bottom: tether conductor 62, a portion of piezoelectric layer 8 vertically aligned with tether conductor 62, an optional tether conductor 56 (when an optional lower conductive layer 10 is present), a portion of device layer 12 vertically aligned with tether conductor 62, and a portion of substrate 16 vertically aligned with tether conductor 62 and proximate to device layer 12. In this example, surfaces 72 and 74 can be seen in the trenches of FIGS. 9A-9B .

In another alternative example, in the UBAR 2 example shown in FIG. 3 , a portion of the forming material of the substrate 16-1 or 16 may be removed laterally below the resonator body 4 and the connecting structures 34 and 36, similar to the removal of the forming material of the substrate 16 in FIG. 9D , wherein the forming material surface of the substrate 16-1 or 16 (such as surfaces 72 and 74) is exposed and visible in the trenches of FIGS. 9A-9B .

In one example, when the surfaces of the forming material of substrate 16-1 of the UBAR 2 example of FIG. 3 (e.g., surfaces 72 and 74) are exposed and visible in the trenches of FIGS. 9A-9B , each tether structure 76 may also include a portion of the device layer 12-1 vertically aligned with the tether conductor 62 and a portion of the forming material of substrate 16-1 vertically aligned with the tether conductor 62 and adjacent to the device layer 12-1. In this example, only a portion of the bulk of substrate 16-1 is removed to form each trench, and device layer 12 and substrate 16 are retained, i.e., no portion of device layer 12 and substrate 16 is removed and is not visible in FIGS. 9A-9B .

In another example, when the surfaces (such as surfaces 72 and 74) of the substrate 16 forming material of the example of UBAR 2 in FIG3 are exposed and visible in the trenches shown in FIGS. 9A-9B , each tether structure 76 may also include a portion of the device layer 12-1 vertically aligned with the tether conductor 62, a portion of the substrate 16-1 vertically aligned with the tether conductor 62, a portion of the device layer 12 vertically aligned with the tether conductor 62, and a portion of the substrate 16 forming material vertically aligned with the tether conductor 62 and adjacent to the device layer 12. In this example, only a portion of the bulk of the substrate 16-1 is removed to form each trench.

In an ideal and non-limiting embodiment or example, when there is no lower conductive layer 10 in the above-discussed example, the bottom metal layers 40 and 44 of the connection structures 34 and 36 are not required.

In an ideal and non-limiting embodiment or example, each of the aforementioned tether structures 76 may include at least the tether conductor 62, the optional tether conductor 56 (when the optional lower conductive layer 10 is present), and only the portion of the piezoelectric layer 8 vertically aligned with the tether conductor 62. In another ideal and non-limiting embodiment or example, each of the tether structures 76 may include one or more of the following portions vertically aligned with the tether conductor 62: the device layer 12, the substrate 16, the device layer 12-1, and/or the substrate 16-1. However, this is not intended to be limiting.

In an ideal and non-limiting embodiment or example, in the resonator body 4 in each example shown in FIGS. 1-3 , at least the widths of the upper conductive layer 6, the optional lower conductive layer 10, and the portion of the piezoelectric layer 8 below the upper conductive layer 6 may be the same. That is, or in one example, the width of the device layer 12, the substrate 16, the device layer 12-1, and/or the substrate 16-1 may be the same as the width and/or size of the upper conductive layer 6, the optional lower conductive layer 10, and the piezoelectric layer 8.

In an ideal and non-limiting embodiment or example, any one or more surfaces of the resonator body 4 in any of the examples shown in FIGS. 1-3 and/or one or all surfaces of any one or more connecting structures 34 and/or 36 can be appropriately etched as appropriate and/or desired, in the hope of optimizing the quality factor and/or insertion loss of any of the UBAR 2 examples in FIGS. 1-3. For example, the upper surface and the lower surface of the resonator body 4 in any of the examples shown in FIGS. 1-3 can be etched. That is, or alternatively, any one or more side surfaces of the resonator body 4 in each of the examples shown in FIGS. 1-3 can be etched, wherein the aforementioned side surfaces are perpendicular to the plane.

In an ideal and non-limiting embodiment or example, the upper conductive layer 6, the optional lower conductive layer 10, or both are in the form of an interdigitated electrode 18, a back 22 or 26 of the interdigitated electrode 18 can be connected and driven by a suitable signal source, and the other back 22 or 26 may not be connected to the signal source. In another ideal and non-limiting embodiment or example, the upper conductive layer 6, the optional lower conductive layer 10, or both are in the form of an interdigitated electrode 18, a back 22 of the interdigitated electrode 18 can be connected and driven by a signal source, and a back 26 of the interdigitated electrode 18 can be connected and driven by a second signal source. In one example, the second signal source can be the same as or different from the first signal source.

In an ideal and non-limiting embodiment or example, the acoustic impedance of each device layer 12 (or 12-1) can be ≥ 60 x 10 ⁶ Pa-s/m ^3. In another example, the acoustic impedance of each device layer 12 (or 12-1) can be ≥ 90 x 10 ⁶ Pa-s/m ^3. In another example, the acoustic impedance of each device layer 12 (or 12-1) can be ≥ 500 x 10 ⁶ Pa-s/m ^3. In an ideal and non-limiting embodiment or example, the acoustic impedance of each substrate 16 can be ≤ 100 x 10 ⁶ Pa-s/m ^3. In another example, the acoustic impedance of each substrate 16 can be ≤ 60 x 10 ⁶ Pa-s/m ³ .

In an ideal and non-limiting embodiment or example, the acoustic wave reflectivity (R) of the interface of the device layer 12, the piezoelectric layer 8, or the optional lower conductive layer 10 can be greater than 50%. In another example, the acoustic wave reflectivity (R) of the interface of the device layer 12, the piezoelectric layer 8, or the optional lower conductive layer 10 can be greater than 70%. In another example, the acoustic wave reflectivity (R) of the interface of the device layer 12, the piezoelectric layer 8, or the optional lower conductive layer 10 can be greater than 90%.

In an ideal and non-limiting embodiment or example, the acoustic reflectivity (R) of the interface between the device layer 12 or 12-1 and the piezoelectric layer 8 or the optional lower conductive layer 10 can be greater than 70%. In one example, the interface reflectivity R of any two layers 6 and 8; 8 and 10; 8 or 10 and 12 or 12-1; or 12 or 12-1 and 16 or 16-1, or the interface reflectivity R of the device layer 12 or 12-1 and the substrate 16 or 16-1 can be calculated by the following equation:

R = ǀ (Zb-Za)/(Za+Zb) ǀ

Where Za = the acoustic impedance of the first layer, e.g. the piezoelectric layer 8 or the optional lower conductive layer 10, which is located above the second layer; and

Zb = acoustic impedance of the second layer, for example: device layer 12.

Other examples of the first layer and the second layer may include an example in which the device layer 12 or 12 - 1 is on the substrate 16 or 16 - 1 .

In an ideal and non-limiting embodiment or example, the overall reflectivity (R) of any example of the resonator body 4 shown in Figures 1-3 can be > 90%.

In an ideal and non-limiting embodiment or example, the device layer 12 can be a diamond layer or SiC formed by prior art. In one example, the substrate 16 can be formed of silicon.

In an ideal and non-limiting embodiment or example, the device layer 12 formed of diamonds can be obtained by chemical vapor deposition of diamonds on the substrate 16 or 16-1 or a sacrificial substrate (not shown). In an ideal and non-limiting embodiment or example, the optional lower conductive layer 10, piezoelectric layer 8, and upper conductive layer 6 can be deposited on the device layer 12 and patterned as needed (e.g., comb electrodes 27 or interdigitated electrodes 18), and the conventional semiconductor manufacturing technology used is not described here.

Here, each temperature compensation layer 90, 92, 94 may include at least one of silicon or oxygen. For example, each temperature compensation layer may include silicon dioxide, silicon element, and/or oxygen element.

In an ideal and non-limiting embodiment or example, each UBAR 2 shown in FIGS. 1-3 can have an unloaded quality factor ≥ 100. In another example, each UBAR 2 shown in FIGS. 1-3 can have an unloaded quality factor ≥ 50. In an ideal and non-limiting embodiment or example, the thickness of the piezoelectric layer 8, each device layer 12, and the substrate 16 of each example of the resonator body 4 shown in FIGS. 1-3 can be selected in any suitable and/or desired manner to optimize the performance of the resonator body 4. Similarly, in an example, the size of each example of the resonator body 4 shown in FIGS. 1-3 can be selected based on the target performance, for example, without limitation: insertion loss, power handling capability, and heat dissipation. In an ideal and non-limiting embodiment or example, when diamond is used as the material of the device layer 12, the interface of the surface of the diamond layer at the lower layer 12 can be completed by optical methods and/or it is physically dense. In one example, the diamond material forming the device layer 12 can be undoped or doped, for example: P type or N type. The diamond material can be a polycrystalline, a nanocrystalline or an ultra-nanocrystalline. In one example, when silicon is used as the material of each substrate 16 example, the silicon can be undoped or doped, for example: P type or N type, and a single crystal or a polycrystalline. The diamond material forming the device layer can have a Raman half peak width ≤ 20 cm ^-1 .

In an ideal and non-limiting embodiment or example, the piezoelectric layer 8 can be made of ZnO, AlN, InN, alkali metal or alkali earth metal niobate, alkali metal or alkali earth metal titanium oxide, alkali metal or alkali earth metal tantalum, GaN, AlGaN, lead zirconate titanate (PZT), a polymer or a doped form of any of the foregoing materials.

In an ideal and non-limiting embodiment or example, the device layer 12 can be formed of any suitable and/or desired high acoustic impedance material. For example, a material having an acoustic impedance between 10 ⁶ Pa-s/m ³ and 630 x 10 ⁶ Pa-s/m ³ or higher than 630 x 10 ⁶ Pa-s/m ³ can be considered a high acoustic impedance material. Some non-limiting examples of typical high acoustic impedance materials that may be used, for example to form any of the device layers 12 described herein, may include: diamond (~630 x 10 ⁶ Pa-s/m ³ ); W (~99.7 x 10 ⁶ Pa-s/m ³ ); SiC; a condensed phase material such as a metal, such as Al, Pt, Pd, Mo, Cr, Ir, Ti, Ta; an element from Group 3A or 4A of the Periodic Table; a transition element from Group 1B, 2B, 3B, 4B, 5B, 6B, 7B, or 8B of the Periodic Table; ceramics; glass; and polymers. This non-limiting list of high acoustic impedance materials is not intended to be limiting.

In an ideal and non-limiting embodiment or example, the substrate 16 can be formed of any suitable and/or desired low acoustic impedance material. For example, a material having an acoustic impedance between 10 ⁶ Pa-s/m ³ and 30 x 10 ⁶ Pa-s/m ³ can be considered a low acoustic impedance material. Some non-limiting examples of typical low acoustic impedance materials that can be used, such as to form any of the substrates 16 described herein, can include at least one of the following: ceramics; metals, glasses, crystals, minerals having an acoustic impedance between 10 ⁶ Pa-s/m ³ and 30 x 10 ⁶ Pa-s/m ³ ; ivory (1.4 x 10 ⁶ Pa-s/m ³ ); alumina/sapphire (25.5 x 10 ⁶ Pa-s/m ³ ); alkaline metal K (1.4 x 10 ⁶ Pa-s/m ³ ); silicon dioxide and silicon (19.7 x 10 ⁶ Pa-s/m ³ ). This non-limiting list of low acoustic impedance materials is not intended to be limiting.

In an ideal and non-limiting embodiment or example, depending on the material selection for forming the resonator body 4 in each example, one or more materials that are generally considered to be high acoustic impedance materials can be used as low acoustic impedance materials for the resonator body 4. For example, when diamond or SiC is used as the material for the device layer 12, W can be used as the material for the substrate 16. Therefore, by achieving the desired reflectivity R of the two-layer interface or the resonator body 4 (as described above), it can be determined which materials can be used as high acoustic impedance and which can be used as low acoustic impedance.

In an ideal and non-limiting embodiment or example, a bulk acoustic wave resonator may include a resonator body 4 according to the principles of the present invention. The resonator body 4 may include a piezoelectric layer 8; a device layer 12; and an upper conductive layer 6, which is located above the piezoelectric layer 8 and the other side of the piezoelectric layer is the device layer 12. The entire surface of the device layer 12 on the side opposite to the piezoelectric layer 8 is substantially used to mount the resonator body 4 on a carrier 14 separated from the resonator body 4. In this example, it is desirable but not necessary that the entire surface of the device layer on the side opposite to the piezoelectric layer is used to mount the entire resonator body on the carrier. In this example, it is desirable but not necessary that the BAW resonator may include a connection structure 34 or 36 to conduct the signal to the upper conductive layer. In one example, the device layer may include diamond or SiC. In one example, the upper conductive layer 6 may include a plurality of conductive wires or springs with spaces. In one example, the resonator body 4 may further include an optional lower conductive layer 10, which is located between the piezoelectric layer 8 and the device layer 12.

In an ideal and non-limiting embodiment or example, the resonator body 4 may further include a substrate 16 connected to the device layer 12 and the other side of the device layer is the piezoelectric layer 8. In one example, the surface of the device layer 12 may be entirely mounted in the substrate 16. In one example, the surface of the substrate 16 facing the carrier 14 may be entirely directly mounted in the carrier 14.

In an ideal and non-limiting embodiment or example, the surface of the device layer 12 facing the carrier 14 can be entirely mounted in the substrate 16. In an example, the surface of the device layer 12 facing the carrier 14 can be entirely mounted in the carrier 14.

In an ideal and non-limiting embodiment or example, the resonator body 4 may further include a second device layer 12-1 located between the substrate 16 and the piezoelectric layer 8; or a second substrate 16-1 located between the substrate 16 and the piezoelectric layer 8; or both.

In an ideal and non-limiting embodiment or example, the term "entire installation" may refer to directly installing a layer or substrate, or indirectly installing another layer or substrate. In one example, the term "entire installation" may refer to or replace the space or interval between a layer or substrate and another layer or substrate without intentional reservation. In another example, the term "entire installation" may refer to or replace the space that naturally occurs between a layer or substrate and another layer or substrate, which is naturally generated and not intentionally manufactured.

Some non-limiting implementation forms or examples of UBAR have been described, and the first to sixth UBAR examples will be described here.

First UBAR Example: A mode 3 of the device layer is enabled AND/OR Mode 4 Resonant and with temperature compensation layer.

1, in some non-limiting embodiments or examples, a first UBAR2 example (as shown in FIG. 1) may include, from the top to the carrier 14, a conductive layer 6 (as shown in FIG. 4A to 4B) including a conductive wire or spring 20 or 28 with spaces, a piezoelectric layer 8 formed of _LiNbO3 , a temperature compensation layer 92 formed of _SiO2 , and a device layer 12 formed of diamond or SiC. In one example, the finger spacing 38 (as shown in FIG. 4A to 4B) is 0.6 μm and the thickness of the piezoelectric layer 8 is 0.6 μm.

Throughout the present invention, the value of the variable "λ" can be based on one or more dimensions of the pattern or feature defined by the upper conductive layer, or based on the thickness of the piezoelectric layer 8. In some non-limiting embodiments or examples, the value of λ can be twice the finger spacing 38 or twice the thickness of the piezoelectric layer 8 (1.2µm in this example). However, this should not be interpreted as limiting, as the value of λ can be based on the thickness of one or more layers and/or any other suitable and/or desired dimensions of one or more patterns or features in each UBAR example described herein. In this example, the cutting angle of the piezoelectric layer 8 is 0° (or 180°), sometimes referred to as Y-cut or YX-cut. In some non-limiting embodiments or examples, it is envisioned that the cutting angle of the piezoelectric layer 8 is 0° (or 180°) ± 20°. Here, unless otherwise specified, the cutting angle of the piezoelectric layer 8 refers to the cutting angle relative to the X-axis rotation.

In some non-limiting embodiments or examples, to mold a first UBAR2 instance, an exemplary electrical stimulation frequency scan (e.g. _, 1 GHz to 6.2 GHz) is performed on the first UBAR2 instance to confirm the frequency response (frequency vs. vibration) for multiple or a plurality of different exemplary values of the thickness of the temperature compensation layer 92 formed by SiO2. In one molding example, the thickness of the temperature compensation layer 92 formed by _SiO2 is between (9/16)λ and (1/64)λ, and the exemplary electrical stimulation frequency performed on the first UBAR2 instance is at least between 1 GHz and 6.2 GHz for each different thickness value. In one example, frequency scanning between at least 1 GHz and 6.2 GHz can determine a first graph, diagram, or relationship of frequency vs. vibration for a temperature compensation layer 92 thickness such as (9/16)λ. In one example, frequency scanning between at least 1 GHz and 6.2 GHz can determine another graph, diagram, or relationship of frequency vs. vibration for a temperature compensation layer 92 thickness such as (3/64)λ. Frequency scanning at different thicknesses of the temperature compensation layer 92 can determine additional graphs, diagrams, or relationships of frequency vs. vibration.

At least the mode 4 resonance frequency 88 is observed in the graphs, plots or relationships of frequency vs. vibration (FIGS. 10 and 11). In the first UBAR example, however, the mode 4 resonance frequency 88 is unexpectedly observed at 5.2 GHz (FIG. 11) relative to the mode 4 resonance frequency 88 observed at 3.05 GHz (FIG. 10), and the mode 3 resonance frequency 86 is observed at 3.13 GHz (FIG. 11).

In FIG. 11 , for simplicity of representation, the resonant frequencies 82 and 84 of mode 1 and mode 2 (as shown in FIG. 10 ) are omitted to the left of the resonant frequency 86 of mode 3. However, it should be understood that when the frequency scan is between at least 1 GHz and 6.2 GHz, in addition to the resonant frequencies 86 and 88 of mode 3 and mode 4, there may also be resonant frequencies 82 and 84 of mode 1 and mode 2 (as shown in FIG. 10 ).

In some non-limiting embodiments or examples, as shown in FIG. 11 , in various graphs, diagrams or relationships of frequency vs. vibration, the mode 3 resonance frequency 86 includes a positive peak f _s1 and a negative peak f _p1 , and the mode 4 resonance frequency 88 includes a positive peak f _s2 and a negative peak f _p2 .

For illustrative purposes only, the "resonance frequency" observed at "approximately" a specific frequency described herein may be any representative frequency of the positive peak value _fs1 and the negative peak value _fp1 for the mode 3 resonant frequency 86, and may be any representative value of the positive peak value _fs2 and the negative peak value _fp2 for the mode 4 resonant frequency 88. Therefore, any resonant frequency described herein as "approximately" a specific frequency should not be limited.

In some non-limiting embodiments or examples, when the thickness of the temperature compensation layer 92 formed by _SiO2 is (1/16)λ, the mode 3 coupling efficiency (M3CE) and the mode 4 coupling efficiency (M4CE) of the resonance frequencies 86 and 88 of mode 3 and mode 4 can be determined by the following equations EQ1 and EQ2, respectively: EQ1: Mode 3 coupling efficiency (M3CE) = (π ² /4)(( f _p1 – f _s1 )/ f _p1 ) EQ2: Mode 4 coupling efficiency (M4CE) = (π ² /4)(( f _p2 – f _s2 )/ f _p2 ) Wherein, when the exemplary values of f _p1 and f _s1 are 3.738 GHz and 3.13 GHz, respectively, M3CE = 40.093%; and when the exemplary values of f _p2 and f _s2 are 5.442 GHz and 5.172 GHz, M4CE = 12.229%.

However, since a value of M3CE of ≥8%, ≥11%, ≥14%, ≥17%, or ≥20% is satisfactory, suitable, and/or desirable, the aforementioned M3CE value in this example should not be limiting. Additionally or alternatively, since a value of M4CE of ≥3%, ≥4%, ≥6%, ≥8%, or ≥10% is satisfactory, suitable, and/or desirable, the aforementioned M4CE value in this example should not be limiting.

In some non-limiting embodiments or examples, when a specific M3CE value is desired, such as ≥8%, ≥11%, ≥14%, ≥17% or ≥20%, the cutting angle of the piezoelectric layer 8 may extend beyond the above 0° (or 180°) ± 20°, for example: the cutting angle is 0° (or 180°) ≥ ± 20°, ≥ ± 30°, ≥ ± 40°, ≥ ± 50°, etc. In some non-limiting embodiments or examples, the piezoelectric layer 8 is not limited, for example, it is a LiNbO ₃ crystal, and the desired cutting angle produced from Z-cutting or X-cutting may also be sufficient to obtain a specific desired value of M3CE.

In some non-limiting embodiments or examples, when a specific M4CE value is desired, such as ≥3%, ≥4%, ≥6%, ≥8% or ≥10%, the cutting angle of the piezoelectric layer 8 can extend beyond the above 130° ± 30° (sometimes referred to as Y-cut 130 ± 30 or YX-cut 130 ± 30), for example, the cutting angle is: 130° ≥ ± 30°, ≥ ± 40°, ≥ ± 50°, etc. In some non-limiting embodiments or examples, the piezoelectric layer 8 is not limited, such as LiNbO ₃ crystals, and the desired cutting angle produced from Z-cut or X-cut may also be sufficient to obtain a specific desired value of M4CE.

In some non-limiting embodiments or examples, multiple thickness values of the temperature compensation layer 92 are obtained using equations EQ1 and EQ2 and the frequency vs. vibration graph, diagram or relationship determined above, and multiple thickness values of the temperature compensation layer 92 formed by _SiO2 and used to optimize the resonance frequencies of mode 3 and mode 4 are determined to be (3/64)λ and (1/32)λ, respectively. However, since the thickness of the temperature compensation layer 92 formed by _SiO2 can be any suitable and/or desired and non-limiting thickness, such as ≤1λ, ≤(1/2)λ, ≤(3/8)λ, ≤(1/4)λ or ≤(1/8)λ, the thickness value should not be limiting.

Second UBAR Example: A mode 3 of the device layer is enabled AND/OR Mode 4 Resonant and without temperature compensation layer.

In some non-limiting embodiments or examples, for comparison and/or modeling purposes, an exemplary electrical stimulation frequency scan (e.g., 1 GHz to 6.2 GHz) is performed on a second UBAR2 example to confirm the frequency response, and the second UBAR2 example has layers similar to the first UBAR2 example described above (as shown in FIG. 1 ), except that the second UBAR2 example does not include a temperature compensation layer 92. The frequency scan is performed to confirm a graph, diagram, or relationship of frequency vs. vibration.

Using equations EQ1 and EQ2 and a graph, plot or relationship of frequency vs. vibration identified by the frequency scan, the coupling efficiencies M3CE and M4CE for mode 3 and mode 4 resonant frequencies 86 and 88 of the second UBAR2 example can be identified as: M3CE = 40.093% for values of _fp1 and _fs1 of 3.738 GHz and 3.13 GHz, respectively; M4CE = 9.312% for values of _fp2 and _fs2 of 6.194 GHz and 5.96 GHz, respectively.

However, since M3CE values ≥8%, ≥11%, ≥14%, ≥17%, or ≥20% are satisfactory, suitable, and/or desirable, the M3CE values described above in this example should not be limiting. Additionally or alternatively, since M4CE values ≥3%, ≥4%, ≥6%, ≥8%, or ≥10% are satisfactory, suitable, and/or desirable, the M4CE values described above in this example should not be limiting.

In some non-limiting embodiments or examples, when a specific M3CE value is desired, such as ≥8%, ≥11%, ≥14%, ≥17% or ≥20%, the cutting angle of the piezoelectric layer 8 may extend beyond the aforementioned cutting angle of 0° (or 180°) ± 20°, such as a cutting angle of 0° (or 180°) ≥ ± 20°, ≥ ± 30°, ≥ ± 40°, ≥ ± 50°, etc. In some non-limiting embodiments or examples, the piezoelectric layer 8 is not limited to, for example, a LiNbO ₃ crystal, and the desired cutting angle produced from Z-cut or X-cut may also obtain the desired specific M3CE value.

In some non-limiting embodiments or examples, when a specific M4CE value is desired, such as ≥3%, ≥4%, ≥6%, ≥8% or ≥10%, the cutting angle of the piezoelectric layer 8 can extend beyond 130° ± 30° (sometimes referred to as Y-cut 130 ± 30 or YX-cut 130 ± 30), such as the cutting angle of 130° ≥ ± 30°, ≥ ± 40°, ≥ ± 50°, etc. In some non-limiting embodiments or examples, the piezoelectric layer 8 is not limited, such as LiNbO ₃ crystals, and the desired cutting angle produced from Z-cut or X-cut may also be sufficient to obtain a specific desired value of M4CE.

From the M4CE values of UBAR2 with and without the temperature compensation layer 92, it can be understood that when UBAR2 has the temperature compensation layer 92 formed of _SiO2 , its coupling efficiency is greater, and conversely, when UBAR2 does not have the temperature compensation layer 92 formed of _SiO2 , its coupling efficiency is smaller. In some non-limiting embodiments or examples, generally speaking, it is more desirable to obtain a coupling efficiency with a larger value.

Third UBAR Example: A mode 3 of the device layer is enabled AND/OR Mode 4 Resonant and has a temperature compensation layer and an aluminum nitride layer.

Referring to FIG. 12 and continuing with FIG. 11 , in some non-limiting embodiments or examples, for comparison and/or molding purposes, an exemplary electrical stimulation frequency scan (e.g., 1 GHz to 6.2 GHz) is performed on a third UBAR2 example (as shown in FIG. 12 ) to confirm the frequency response. The third UBAR2 example is similar to the first UBAR2 example described above in each layer, except that the third UBAR2 is at least as follows: That is, the third UBAR2 example includes a layer of aluminum nitride AlN 96 between the device layer 12 formed of diamond or SiC and the temperature compensation layer 92 formed of SiO ₂ , the temperature compensation layer 92 is on the aluminum nitride 96 (as shown in FIG. 12 ), the aluminum nitride 96 has a thickness of (7/16)λ, and the temperature compensation layer 92 formed of SiO 2 is formed of a temperature compensation layer 92 formed of SiO 2. The temperature compensation layer 92 formed by ₂ has a thickness of (11/128)λ, and the device layer 12 formed by diamond or SiC has a thickness of (90/16)λ. In this example, λ is equivalent to 1.6 µm. A frequency scan is then performed to confirm a graph, diagram or relationship of frequency vs. vibration.

Using equations EQ1 and EQ2 and a graph, plot or relationship of frequency vs. vibration identified by a frequency scan, the coupling efficiencies M3CE and M4CE for mode 3 and mode 4 resonance frequencies 86 and 88 of the third UBAR2 example in FIG. 12 are identified as: M3CE = 39.351% for values of _fp1 and _fs1 of 3.608 GHz and 3.032 GHz, respectively; M4CE = 10.802% for values of _fp2 and _fs2 of 5.02 GHz and 4.8 GHz, respectively.

However, the aforementioned M3CE values in this example are not limiting, as M3CE ≥8%, ≥11%, ≥14%, ≥17%, or ≥20% may be satisfactory, suitable, and/or desirable. Additionally or alternatively, the aforementioned M4CE values in this example are not limiting, as M4CE ≥3%, ≥4%, ≥6%, ≥8%, or ≥10% may be satisfactory, suitable, and/or desirable.

In some non-limiting embodiments or examples, when a specific M3CE value is desired, such as ≥8%, ≥11%, ≥14%, ≥17% or ≥20%, the cutting angle of the piezoelectric layer 8 may extend beyond the aforementioned cutting angle of 0° (or 180°) ± 20°, for example, the cutting angle is 0° (or 180°) ≥ ± 20°, ≥ ± 30°, ≥ ± 40°, ≥ ± 50°, etc. In some non-limiting embodiments or examples, the piezoelectric layer 8 is not limited to, for example, a LiNbO ₃ crystal, and the desired cutting angle produced from Z-cut or X-cut may also obtain the desired specific M3CE value.

In some non-limiting embodiments or examples, when a specific M4CE value is desired, such as ≥3%, ≥4%, ≥6%, ≥8% or ≥10%, the cutting angle of the piezoelectric layer 8 can extend beyond 130° ± 30° (sometimes referred to as Y-cut 130 ± 30 or YX-cut 130 ± 30), such as the cutting angle of 130° ≥ ± 30°, ≥ ± 40°, ≥ ± 50°, etc. In some non-limiting embodiments or examples, the piezoelectric layer 8 is not limited, such as LiNbO ₃ crystals, and the desired cutting angle produced from Z-cut or X-cut may also be sufficient to obtain a specific desired value of M4CE.

In the first to third examples above, the UBARs, M3CE and M4CE values of the piezoelectric layer 8 formed by the LiNbO ₃ crystal cut at 0° (or 180°) are confirmed. In some non-limiting embodiments or examples, the applicant has found that the piezoelectric layer 8 formed by the LiNbO ₃ crystal cut at 130° (sometimes referred to as YX cut 130° or Y cut 130°) can enhance or optimize the coupling efficiency M4CE of the mode 4 resonance frequency 88. In one example, the cutting angle of the piezoelectric layer 8 formed by the LiNbO ₃ crystal can be 130° ± 30°, for example, in the range of 100° to 160°; ideally 130° ± 20°, for example, in the range of 110° to 150°; most ideally 130° ± 10°, for example, in the range of 120° to 140°. However, this ± value or range is not restrictive.

In addition, in some non-limiting embodiments or examples, the applicant has found that when UBAR2 is formed, between the piezoelectric layer 8 (formed from LiNbO ₃ crystal and cut at an angle of about 130° (± 30°, or ± 20°, or ± 10°)) and the device layer 12 (when the substrate 16 is omitted) or the substrate 16 (when the device layer 12 is omitted) or both the device layer 12 and the substrate 16, having alternating low and high acoustic impedance layers can enhance or optimize the coupling efficiency M4CE of the mode 4 resonance frequency 88. In some non-limiting embodiments or examples, the UBAR2 having alternating low and high acoustic impedance layers may include a device layer 12 formed of diamond, SiC, W, Ir or AlN and a substrate 16 formed of silicon. In some non-limiting embodiments or examples, the UBAR 2 having alternating low and high acoustic impedance layers may include a substrate 16 formed of silicon, but may exclude the device layer 12 .

Fourth UBAR Example: A stack-enabled flex mode ( Mode 4) It includes at least one low acoustic impedance layer and one high acoustic impedance layer, and optionally a device layer.

Referring to FIG. 13 and continuing to refer to FIG. 11 , in some non-limiting embodiments or examples, a fourth UBAR2 example (as shown in FIG. 13 ) is composed of alternating low and high acoustic impedance material layers, which may include: between the piezoelectric layer 8 (formed by LiNbO ₃ crystals and cut at an angle of approximately 130° (± 30°, ± 20°, ± 10°)) and the (optional) device layer 12 or substrate 16, there is a first low acoustic impedance layer 100, a first high acoustic impedance layer 102, a second low acoustic impedance layer 104, a second high acoustic impedance layer 106 and a third low acoustic impedance layer 108. In this example, the interdigital distance 38 of the conductive wires or springs 20 or 28 (as shown in FIGS. 4A and 4B) with spaces in the upper conductive layer 6 is 1.2 µm, the λ value is 2.4 µm, the piezoelectric layer thickness is λ/2, the device layer 12 thickness if present is 4λ, and the substrate 16 thickness is 20 µm. In this example, for the purpose of molding, the cutting angle of the piezoelectric layer 8 can be 100° to 160°.

In some non-limiting embodiments or examples, each low acoustic impedance layer 100, 104 and 108 can be formed from silicon dioxide ( _SiO2 ), each high acoustic impedance layer 102 and 106 can be formed from metal, such as tungsten (W), the device layer 12 can be formed from diamond or SiC, and the substrate 16 can be formed from silicon. In one example, the device layer 12 is optional, wherein the third low acoustic impedance layer 108 can directly contact the substrate 16 and the second high acoustic impedance layer 106.

In some non-limiting embodiments or examples, for the purpose of molding, exemplary electrical stimulation frequency scans (e.g., 1 GHz to 6.2 GHz) are performed on several fourth UBARs 2 examples to confirm the frequency response (frequency vs. amplitude), with and without the device layer 12, at multiple different cutting angles of the piezoelectric layer 8 from 100° to 160°, at different exemplary thicknesses of the low acoustic impedance layers 100, 104 and 108, and at different exemplary thicknesses of the high acoustic impedance layers 102 and 106, for example, in the manner of the first UBAR2 described above. In other words, exemplary electrical stimulation frequency scans (e.g., 1 GHz to 6.2 GHz) were performed on several fourth UBARs 2 examples to confirm the frequency response (frequency vs. amplitude), and the aforementioned UBARs 2 examples had different combinations of: (1) with or without the device layer 12; (2) the piezoelectric layer 8 had multiple different cutting angles from 100° to 160°; (3) different thicknesses of the low acoustic impedance layers 100, 104 and 108; (4) different thicknesses of the high acoustic impedance layers 102 and 106.

In some non-limiting embodiments or examples, the cutting angles of the piezoelectric layer 8, the thicknesses of the low acoustic impedance layers 100, 104 and 108 are set at the same value (first value), the thicknesses of the high acoustic impedance layers 102 and 106 are set at the same value (second value), and an exemplary electrical stimulation frequency scan is performed in the fourth UBARs 2 example, the frequency is, for example, 1 GHz to 6.2 GHz, and the frequency response of the fourth UBARs 2 example is recorded. Then, only the thickness of the low acoustic impedance layer (first value) or the thickness of the high acoustic impedance layer (second value) is changed, the frequency scan is repeated, and the response frequency of the fourth UBARs 2 example is recorded. To characterize the frequency response of different thickness values of the low-acoustic impedance layer and the high-acoustic impedance layer of the fourth UBARs 2 example, the process is repeated several times for different low-acoustic impedance layer and high-acoustic impedance layer thickness values. In some non-limiting embodiments or examples, the different thickness values of each low-acoustic impedance layer and/or high-acoustic impedance layer can be the same or different. In some non-limiting embodiments or examples, diamond, SiC, W, Ir, AlN, etc. can be used as high-acoustic impedance materials. A graph, chart, or relationship of frequency vs. amplitude is confirmed in each frequency scan.

By further confirming the graph, diagram, or relationship of frequency vs. amplitude using equation EQ2 and the frequency scan of the fourth UBAR2 example, the ideal coupling efficiency M4CE of the mode 4 resonance frequency 88 of the fourth UBAR2 example in Figure 13 with and without the device layer 12 is: For _fp2 and _fs2 of 5.43 GHz and 5.08 GHz, respectively, M4CE = 15.888%. For example: the cutting angle of the piezoelectric layer 8 is 130°, the thickness of each low acoustic impedance layer 100, 104, 108 is (1/16)λ, and the thickness of each high acoustic impedance layer 102, 106 is (1/16)λ.

Since M4CE values ≥ 3%, ≥ 4%, ≥ 6%, ≥ 8% or ≥ 10% may be satisfactory, suitable and/or desired, the aforementioned M4CE values in this example should not be limiting. In one example, M4CE values ≥ 3%, ≥ 4%, ≥ 6%, ≥ 8% or ≥ 10% can be achieved by adjusting the cutting angle of the piezoelectric layer 8 ± a suitable and/or desired value such as the aforementioned 130° ± 30°. In some non-limiting embodiments and examples, the piezoelectric layer 8 is not limited, such as the desired cutting angle of the LiNbO ₃ crystal produced from the Z cut or X cut, and the desired specific M4CE value may also be obtained.

In addition, the aforementioned thickness of each low-acoustic impedance layer and/or each high-acoustic impedance layer should not be restrictive, because the aforementioned thickness of each low-acoustic impedance layer and/or each high-acoustic impedance layer may be a suitable and/or desired thickness, for example, ≤1λ, ≤(1/2)λ, ≤(3/8)λ, ≤(1/4)λ or ≤(1/8)λ without limitation. The thickness of each low-acoustic impedance layer and/or each high-acoustic impedance layer may be different (or the same) as the thickness of any other low-acoustic impedance layer and/or each high-acoustic impedance layer. Therefore, it is not restrictive when the thickness of the low-acoustic impedance layer is the same, the thickness of the high-acoustic impedance layer is the same, or the thickness of the low-acoustic impedance layer is the same as the thickness of the high-acoustic impedance layer.

Fifth UBAR Example: A stack-enabled flex mode ( Mode 4) It includes at least one low acoustic impedance layer and one high acoustic impedance layer, and optionally a device layer.

Continuing with reference to FIG. 11 and FIG. 13 , in some non-limiting embodiments or examples, similar to the fourth UBAR 2 example described above, for each different cutting angle of the piezoelectric layer 8 from 100° to 160°, for the purpose of molding, an exemplary electrical stimulation frequency scan (e.g., 1 GHz to 6.2 GHz) is performed at different thickness values of the low acoustic impedance layer and the high acoustic impedance layer of the fifth UBAR 2 example to confirm the frequency response (frequency vs. amplitude), and the fifth UBAR 2 example is similar to the fourth UBAR 2 example in each layer (as shown in FIG. 13 ) except that the low acoustic impedance layer 108 is omitted. A graph, diagram, or relationship of frequency vs. amplitude is confirmed in each frequency scan.

Using equation EQ2 and the frequency vs. amplitude graph, diagram, or relationship identified in the fifth UBAR2 example, the ideal coupling efficiency M4CE of the mode 4 resonance frequency 88 of the fifth UBAR2 example is consistent with the fourth UBAR2 example with and without the device layer 12, that is: M4CE = 15.888% when _fp2 and _fs2 are 5.43 GHz and 5.08 GHz, respectively. When the piezoelectric layer 8 is cut at an angle of 130°, the thickness of each low acoustic impedance layer 100 and 104 is (1/16)λ, and the thickness of each high acoustic impedance layer 102 and 106 is (1/16)λ.

In some non-limiting embodiments or examples, the thickness of each low acoustic impedance layer and/or the thickness of each high acoustic impedance layer can be the same or different. In some non-limiting embodiments or examples, diamond, SiC, W, AlN, Ir, etc. can be used as the material of each high acoustic impedance layer.

Since the M4CE value is satisfactory, suitable and/or desired when it is ≥ 3%, ≥ 4%, ≥ 6%, ≥ 8% or ≥ 10%, the aforementioned M4CE value in this example should not be limiting. In one example, the M4CE value ≥ 3%, ≥ 4%, ≥ 6%, ≥ 8% or ≥ 10% can be achieved by adjusting the cutting angle of the piezoelectric layer 8 ± a suitable and/or desired value, such as the aforementioned 130° ± 30°. In some non-limiting embodiments or examples, the piezoelectric layer 8 is, for example, a non-restrictive LiNbO ₃ crystal, and the desired specific M4CE value may also be obtained from the cutting angle of the Z-cut or X-cut.

In addition, the thickness of each low acoustic impedance layer and/or each high acoustic impedance layer should not be restrictive, because the thickness of each low acoustic impedance layer and/or each high acoustic impedance layer can be ideally and/or expected, without limitation, ≤1λ, ≤(1/2)λ, ≤(3/8)λ, ≤(1/4)λ or ≤(1/8)λ, and the thickness of each low and/or high acoustic impedance layer may be different from or the same as the thickness of any other low and/or high acoustic impedance layer. Therefore, it is not restrictive when the thickness of the low acoustic impedance layer is the same, the thickness of the high acoustic impedance layer is the same, or the thickness of the low acoustic impedance layer is the same as the thickness of the high acoustic impedance layer.

This result suggests that there may be some advantage to having one or more additional low acoustic impedance layers between the high acoustic impedance layer 106 and the device layer 12 or substrate 16 or both.

Sixth UBAR Example: A stack-enabled flexure mode ( mode 4) includes at least one low acoustic impedance layer and one high acoustic impedance layer, and optionally a device layer. Referring to FIG. 14 and continuing to refer to FIG. 11, in some non-limiting embodiments or examples, the sixth UBAR 2 example (as shown in FIG. 14) is formed from alternating low and high acoustic impedance layer materials, and its piezoelectric layer 8 (formed from LiNbO ₃ crystal, cut at an angle of 130° (± 30° or ± 20° or ± 10°)) to the device layer 12 may include: a first bass impedance layer 100, a first high acoustic impedance layer 102, a second bass impedance layer 104, a second high acoustic impedance layer 106, a third bass impedance layer 108, a third high acoustic impedance layer 110, a fourth bass impedance layer 112, a fourth high acoustic impedance layer 114, a fifth bass impedance layer 116, a fifth high acoustic impedance layer 118, a sixth bass impedance layer 120, a sixth high acoustic impedance layer 122, a seventh bass impedance layer 124, a seventh high acoustic impedance layer 126, an eighth bass impedance layer 128, an eighth high acoustic impedance layer 130 and a ninth bass impedance layer 132.

In this example, the finger spacing 38 of the conductive wire or spring 20 or 28 (as shown in Figures 4A and 4B) with spaces in the upper conductive layer 6 is 1.2 µm, the λ value is 2.4 µm, the piezoelectric layer thickness is (0.2)λ, the thickness of each low-acoustic impedance layer is (1/16)λ, and the thickness of the device layer 12 is 4λ.

In order to mold the sixth UBAR 2 example according to several different cutting angles of the piezoelectric layer 8 from 100° to 160°, exemplary electrical stimulation frequency scans (e.g., 1 GHz to 6.2 GHz) are performed on the sixth UBARs 2 example to confirm the frequency response, at different exemplary thicknesses of the high acoustic impedance layer, such as in the manner described above for the fourth UBAR 2. In this example, for each piezoelectric layer 8 cutting angle and each frequency scan, each high acoustic impedance layer is the same thickness. A graph, diagram, or relationship of frequency vs. amplitude is confirmed in each frequency scan.

In some non-limiting embodiments or examples, each low acoustic impedance layer may be formed from silicon dioxide (SiO ₂ ), each high acoustic impedance layer may be formed from, for example, aluminum nitride (AlN), the device layer 12 may be formed from diamond or SiC, and the substrate 16 may be formed from silicon.

Using equation EQ2 and the graph, diagram or relationship of the frequency response identified in the sixth UBAR 2 example, the ideal coupling efficiency M4CE of the mode 4 resonance frequency 88 of the sixth UBAR 2 example can be identified as: When the values of _fp2 and _fs2 are equal to 5.38 GHz and 5.09 GHz, respectively, M4CE = 13.287%, when the piezoelectric layer 8 has a cutting angle of 130° and the thickness of each high acoustic impedance layer is (5/16)λ.

In some non-limiting embodiments or examples, the thickness of each low acoustic impedance layer and/or high acoustic impedance layer can be the same or different. In some non-limiting embodiments or examples, diamond, SiC, W, AlN, etc. can be used as the material of each high acoustic impedance layer.

Since the M4CE value is satisfactory, suitable and/or desirable when it is ≥ 3%, ≥ 4%, ≥ 6%, ≥ 8% or ≥ 10%, the aforementioned M4CE value in this example should not be restrictive. In addition, the thickness of each low acoustic impedance layer and/or each high acoustic impedance layer should not be restrictive, because the thickness of each low acoustic impedance layer and/or each high acoustic impedance layer can be suitable and/or desirable, non-restrictive ≤1λ, ≤(1/2)λ, ≤(3/8)λ, ≤(1/4)λ or ≤(1/8)λ, and the thickness of each low and/or high acoustic impedance layer can be different (or the same) as the thickness of any other low and/or high acoustic impedance layer. Therefore, it is not restrictive that the thickness of the low acoustic impedance layer is the same, the thickness of the high acoustic impedance layer is the same, or the thickness of the low acoustic impedance layer is the same as the thickness of the high acoustic impedance layer.

In one example, M4CE values ≥ 3%, ≥ 4%, ≥ 6%, ≥ 8% or ≥ 10% can be achieved by adjusting the cutting angle of the piezoelectric layer 8 ± a suitable and/or desired value, such as the aforementioned 130° ± 30°. In some non-limiting embodiments or examples, the piezoelectric layer 8 is not limited to, for example, a LiNbO ₃ crystal, and is cut at a specific angle of Z-cut or X-cut, and a specific desired M4CE value can also be obtained.

In some non-limiting embodiments or examples, the modeling of the first to sixth UBARs 2 examples described above is represented by computer simulation, and in some cases, in one or more actual examples.

In some non-limiting embodiments or examples, it can be seen from the aforementioned first to sixth UBARs 2 examples that the piezoelectric layer 8 formed from LiNbO ₃ and cut at an angle of 130° or approximately can obtain an ideal M4CE value. However, in some non-limiting embodiments or examples, the piezoelectric layer 8 formed from LiNbO ₃ and cut at an angle of 100° to 160° can also obtain an ideal M4CE value; the piezoelectric layer 8 formed from LiNbO ₃ and cut at an angle of 110° to 150° can obtain a more ideal M4CE value; the piezoelectric layer 8 formed from LiNbO ₃ and cut at an angle of 120° to 140° can further obtain an even more ideal M4CE value. However, the piezoelectric layer 8 formed from LiNbO ₃ and cut at an angle of 130° can obtain the most ideal (highest) M4CE value.

In any of the UBAR examples described herein, the thickness of the piezoelectric layer, such as LiNbO ₃ , can be any suitable and/or desired thickness, such as, in the flexure mode example of Mode 4, the thickness is ≤0.5λ, ≤0.4λ, ≤0.3λ, or ≤0.2λ.

In any of the UBAR examples described herein, the thickness of the piezoelectric layer, such as LiNbO ₃ , can be any suitable and/or desired thickness, such as, in the shear mode example of Mode 3, the thickness is ≤2λ, ≤1.6λ, ≤1.2λ, or ≤0.8λ.

In any of the UBAR examples described herein, the thickness of the electrode, such as Al, Mo, W, etc., can be any suitable and/or desired thickness, such as ≥0.010λ, ≥0.013λ, ≥0.016λ, ≥0.019λ, or ≥0.022λ.

For any of the UBAR examples described herein, the thickness of the device layer, such as diamond, SiC, AlN, etc., can be any suitable and/or desired thickness, such as ≥50 nm, ≥100 nm, ≥150 nm, or ≥200 nm.

For any of the UBAR examples described herein, the thickness of the low acoustic impedance layer may be a suitable and/or desired thickness, such as ≥0.05λ, ≥0.07λ, ≥0.09λ, ≥0.11λ, or ≥0.13λ.

For any of the UBAR examples described herein, the thickness of the high acoustic impedance layer may be a suitable and/or desired thickness, such as ≥0.05λ, ≥0.07λ, ≥0.09λ, ≥0.11λ, or ≥0.13λ.

For any of the UBAR examples described herein, the thickness of the temperature compensation layer can be a suitable and/or desired thickness, such as ≤2λ, ≤1.5λ, ≤1.0λ, ≤0.5λ, or ≤0.3λ. Ideally, one or more or all of the outer surfaces of any of the UBAR examples described herein are protected by an optional passivation layer. The passivation layer can be a layer of dielectric material, such as AlN, SiN, _SiO2 , etc.

The resonant frequency of any UBAR example described herein may be ≥0.1 GHz, ≥0.5 GHz, ≥1.0 GHz, ≥1.5 GHz, or ≥2.0 GHz.

The coupling efficiency of any of the UBAR examples described herein may be ≥3%, ≥4%, ≥6%, ≥8%, or ≥10%.

Any UBAR example described herein will resonate in a mode that includes a bulk acoustic wave. Shallow bulk acoustic waves may include but are not limited to _S0 mode, expansion mode, shear mode, _A1 mode, flexion mode, etc., and complex modes.

More non-limiting embodiments or examples will be described in the following numbered embodiments. [Embodiment]

Embodiment 1: A bulk acoustic wave resonator comprises: a resonant body, which comprises: a piezoelectric layer, wherein the piezoelectric layer is a single crystal of _LiNbO3 ; a device layer; and an upper conductive layer, which is located above the piezoelectric layer and the other side of the piezoelectric layer is the device layer; wherein the entire surface of the device layer on the opposite side of the piezoelectric layer is substantially used to mount the resonator body on a carrier and separate the resonator body.

Example 2: A bulk acoustic wave resonator as in Example 1, wherein the single crystal of LiNbO ₃ can be cut at an angle of 130° ± 30°, ± 20° or ± 10°.

Embodiment 3: A bulk acoustic wave resonator as in Embodiment 1 or 2, wherein the single crystal of LiNbO ₃ can be cut at an angle of 0° ± 30°, ± 20° or ± 10°.

Embodiment 4: The bulk acoustic wave resonator of any one of embodiments 1 to 3 may include a mode 3 or mode 4 resonance frequency ≥ 0.1 GHz, ≥ 0.5 GHz, ≥ 1.0 GHz, ≥ 1.5 GHz or ≥ 2.0 GHz.

Embodiment 5: The bulk acoustic wave resonator of any one of embodiments 1 to 4 may include at least one of the following: a coupling efficiency of mode 3 resonance ≥8%, ≥11%, ≥14%, ≥17% or ≥20%; and a coupling efficiency of mode 4 resonance ≥3%, ≥4%, ≥6%, ≥8% or ≥10%.

Embodiment 6: A bulk acoustic wave resonator as in any one of embodiments 1 to 5, wherein the single crystal thickness of LiNbO ₃ in mode 4 resonance may be ≤ 0.5λ, ≤ 0.4λ, ≤ 0.3λ or ≤ 0.2λ.

Embodiment 7: A bulk acoustic wave resonator as in any one of embodiments 1 to 6, wherein the single crystal thickness of LiNbO ₃ in mode 3 resonance may be ≤ 2λ, ≤ 1.6λ, ≤ 1.2λ or ≤ 0.8λ.

Embodiment 8: The BAW resonator of any one of Embodiments 1 to 7 further comprises a conductive layer between the piezoelectric layer and the device layer, the thickness of which is ≥ 0.010λ, ≥ 0.013λ, ≥ 0.016λ, ≥ 0.019λ or ≥ 0.022λ.

Embodiment 9: The bulk acoustic wave resonator of any one of Embodiments 1 to 8, wherein the thickness of the device layer is ≥ 50 nm, ≥ 100 nm, ≥ 150 nm or ≥ 200 nm.

Embodiment 10: A bulk acoustic wave resonator as in any one of embodiments 1 to 9, further comprising a low acoustic impedance material between the piezoelectric layer and the device layer, wherein the acoustic impedance of the low acoustic impedance material is between 10 ⁶ Pa-s/m ³ and 30 x 10 ⁶ Pa-s/m ³ , and the thickness is ≥ 0.05λ, ≥ 0.07λ, ≥ 0.09λ, ≥ 0.11λ or ≥ 0.13λ.

Embodiment 11: A bulk acoustic wave resonator as in any one of embodiments 1 to 10, further comprising a high acoustic impedance material between the piezoelectric layer and the device layer, wherein the acoustic impedance of the high acoustic impedance material is between 10 ⁶ Pa-s/m ³ and 630 x 10 ⁶ Pa-s/m ³ , and the thickness is ≥ 0.05λ, ≥ 0.07λ, ≥ 0.09λ, ≥ 0.11λ or ≥ 0.13λ.

Embodiment 12: The bulk acoustic wave resonator of any one of embodiments 1 to 11 further comprises a temperature compensation layer between the piezoelectric layer and the device layer, wherein the temperature compensation layer comprises silicon and oxygen and has a thickness of ≤ 2λ, ≤ 1.5λ, ≤ 1.0λ, ≤ 0.5λ or ≤ 0.3λ.

Embodiment 13: The BAW resonator of any one of Embodiments 1 to 12 further comprises a passivation layer.

Embodiment 14: The BAW resonator of any one of Embodiments 1 to 13, wherein the upper conductive layer may include at least one set of conductive springs with spaces. The finger spacing of the at least one set of conductive springs with spaces may be ≤ 70 μm, ≤ 20 μm, ≤ 10 μm, ≤ 6 μm or ≤ 4 μm.

Embodiment 15: The BAW resonator according to any one of Embodiments 1 to 14, further comprising a plurality of alternating temperature compensation layers and high acoustic impedance layers between the piezoelectric layer and the device layer.

Embodiment 16: A bulk acoustic wave resonator as in any one of embodiments 1 to 15, wherein the aforementioned device layer may further include the following: diamond; W; SiC; Ir, AlN, Al; Pt; Pd; Mo; Cr; Ti; Ta; an element of Group 3A or 4A on the Periodic Table of Elements; a transition element of Group 1B, 2B, 3B, 4B, 5B, 6B, 7B or 8B on the Periodic Table of Elements; ceramics; glass and polymers.

The purpose of the present invention has been described in detail based on the most ideal and practical and non-limiting embodiments, examples or types currently considered, but it should be understood that such details are only used for this purpose and the present invention is not limited to the disclosed ideal and non-limiting embodiments, examples or types. On the contrary, this description is intended to cover modifications and equivalent configurations within the spirit and scope of its application. For example: it should be understood that the present invention will consider any one or more ideal and non-limiting embodiments, examples, types or technologies of the attached application as much as possible, and can be combined with one or more other ideal and non-limiting embodiments, examples, types or technologies of the attached application.

2: Bulk acoustic wave resonator (UBAR) 4: Resonator body 6: Upper conductive layer 8: Piezoelectric layer 10: Optional lower conductive layer 12: Device layer 14: Carrier 16: Substrate 18: Interdigitated electrodes 20, 24, 28: Springs 22, 26: Back 27: Comb electrodes 30: First back 32: Second back 33: Sheet electrodes 34, 36: Connection structure 38: Interdigitated distance 40, 44 Bottom metal layer 42, 46 Metal layer 48, 58: Contact pads 50: Conductive vias 52, 60: Conductors 54: Lateral conductors 56, 62: chain conductor 64, 66, 68, 70: bottom 76: chain structure 82, 84, 88: resonance frequency 90, 92, 94: temperature compensation layer 96: aluminum nitride 100: first low-sound impedance layer 102: first high-sound impedance layer 104: second low-sound impedance layer 106: second high-sound impedance layer 108: third low-sound impedance layer 110: third high-sound impedance layer 112: fourth low-sound impedance layer 114: fourth high-sound impedance layer 116: fifth low-sound impedance layer 118: fifth high-sound impedance layer 120: sixth low-sound impedance layer 122: Sixth high impedance layer 124: Seventh low impedance layer 126: Seventh high impedance layer 128: Eighth low impedance layer 130: Eighth high impedance layer 132: Ninth low impedance layer

The present invention is explained through the following description in conjunction with the drawings, so that the above and other objects and technical features of the invention will be more apparent.

[FIG. 1] is a side view of an unsuspended BAW resonator according to an ideal and non-limiting embodiment or example of the principles of the present invention (e.g., used herein to illustrate the first and second examples of unsuspended BAW resonators). [FIG. 2] is a side view of an unsuspended BAW resonator according to an ideal and non-limiting embodiment or example of the principles of the present invention. [FIG. 3] is a side view of an unsuspended BAW resonator according to an ideal and non-limiting embodiment or example of the principles of the present invention. [FIG. 4A] is a plan view of an isolated interdigitated electrode according to an ideal and non-limiting embodiment or example of the principles of the present invention, which can serve as an upper conductive layer, an optional lower conductive layer, or both of an unsuspended BAW resonator. [FIG. 4B] is a separated plan view of a comb electrode according to an ideal and non-limiting embodiment or example of the principles of the present invention, which can be used as the upper conductive layer, the optional lower conductive layer, or both of the unsuspended BAW resonator. [FIG. 4C] is a separated plan view of a sheet electrode according to an ideal and non-limiting embodiment or example of the principles of the present invention, which can be used as the upper conductive layer, the optional lower conductive layer, or both of the unsuspended BAW resonator. [FIG. 5A-5B] are cross-sectional views of the ideal and non-limiting embodiments or examples of FIG. 1 to 3 along the A-A line and the B-B line. [FIG. 6A-6B] are cross-sectional views of the ideal and non-limiting embodiments or examples of FIG. 1 to 3 along the A-A line and the B-B line. [Figures 7A-7B] are cross-sectional views of the ideal and non-limiting embodiments or examples of Figures 1 to 3 along lines A-A and B-B. [Figure 7C] is a side view of the unsuspended BAW resonator of the ideal and non-limiting embodiments or examples of Figures 7A-7B, with the first and second connecting structures and the material on the two side tying conductors removed. [Figures 8A-8B] are cross-sectional views of the ideal and non-limiting embodiments or examples of Figures 1 to 3 along lines A-A and B-B. [Figure 8C] is a side view of the unsuspended BAW resonator of the ideal and non-limiting embodiments or examples of Figures 8A-8B, with the material on the first and second connecting structures and the two side tying conductors removed. [FIG. 8D] is a side view of an unsuspended BAW resonator of an ideal and non-limiting embodiment or example of FIG. 8A-8B, with the first and second connecting structures and the material on the two side tying conductors removed. [FIG. 9A-9B] is a cross-sectional view of an ideal and non-limiting embodiment or example of FIG. 1 to 3 along the A-A line and the B-B line. [FIG. 9C] is a side view of an unsuspended BAW resonator of an ideal and non-limiting embodiment or example of FIG. 9A-9B, with the material on the first and second connecting structures and the two side tying conductors removed. [FIG. 9D] is a side view of an unsuspended BAW resonator of an ideal and non-limiting embodiment or example of FIG. 9A-9B, with the first and second connection structures and the material on the two side tie conductors removed. [FIG. 10] is a graph of frequency versus decibel for a resonator body having a lower conductive layer of a sheet electrode type and an upper conductive layer of a sparse electrode type, wherein the interdigital spacing is 1.8 μm. [FIG. 11] is an exemplary graph of frequency versus normalized vibration, particularly the resonance frequencies of modes 3 and 4, which can be used to illustrate the frequency response of the first to sixth examples of unsuspended BAW resonators described in this specification. [FIG. 12] is a side view of an unsuspended BAW resonator according to an ideal and non-limiting embodiment or example of the principles of the present invention (e.g., used herein to illustrate the third example of the unsuspended BAW resonator). [FIG. 13] is a side view of an unsuspended BAW resonator according to an ideal and non-limiting embodiment or example of the principles of the present invention (e.g., used herein to illustrate the fourth and fifth examples of the unsuspended BAW resonator). [FIG. 14] is a side view of an unsuspended BAW resonator according to an ideal and non-limiting embodiment or example of the principles of the present invention (e.g., used herein to illustrate the sixth example of the unsuspended BAW resonator).

2: Bulk Acoustic Wave Resonator (UBAR)

6: Upper conductive layer

8: Piezoelectric layer

10: Optional lower conductive layer

12: Device layer

14: Carrier

34, 36: Connection structure

90, 92: Temperature compensation layer

96: Aluminum nitride

Claims (23)

A bulk acoustic wave resonator for use on a carrier, the bulk acoustic wave resonator comprising: a device layer having a surface configured to be mounted on the carrier; a piezoelectric layer located on the device layer and being a single crystal of LiNbO ₃ , the single crystal of LiNbO ₃ having a cutting angle and a thickness, the angle and the thickness being conducive to a mode 3 resonance or a mode 4 resonance with a predetermined coupling efficiency; and an upper conductive layer located above the piezoelectric layer and the other side of the piezoelectric layer being the device layer. A bulk acoustic wave resonator as described in claim 1, wherein the single crystal of LiNbO ₃ is cut at an angle of 130°±70°, 130°±60°, 130°±50°, 130°±40°, 130°±30°, 130°±20°, 130°±10°, 0°±20°, 0°±30°, 0°±40°, 0°±50°, 0°±60° or 0°±70°. The bulk acoustic wave resonator as recited in claim 1, wherein the single crystal of LiNbO ₃ is cut at an angle of 0°±10°, and wherein the frequency of the mode 3 resonance or the mode 4 resonance is

0.1GHz. A bulk acoustic wave resonator as recited in claim 1, wherein at least one of the following is true: the mode 3 resonance has

8% of the predetermined coupling efficiency; and the mode 4 resonance has

3% of the predetermined coupling efficiency. The bulk acoustic wave resonator as recited in claim 4, wherein the upper conductive layer defines a pattern or feature having a size; and wherein: for the mode 4 resonance, the single crystal of LiNbO ₃ has

0.5λ, wherein the value of λ is based on the size of the pattern or feature defined by the upper conductive layer; or for the mode 3 resonance, the first thickness of the single crystal of LiNbO ₃

2λ, where the value of λ is based on the size of the pattern or feature defined by the upper conductive layer. The bulk acoustic wave resonator as recited in claim 1 further comprises a lower conductive layer located between the piezoelectric layer and the device layer and having a thickness of

0.010λ, wherein the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or based on the thickness of the single crystal of LiNbO ₃ . The BAW resonator as recited in claim 1 further comprises a layer of low acoustic impedance material between the piezoelectric layer and the device layer, the layer of low acoustic impedance material having an acoustic impedance between 10 ⁶ Pa-s/m ³ and 30 x 10 ⁶ Pa-s/m ³ and

A thickness of 0.05λ, wherein the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or based on the thickness of the single crystal of LiNbO ₃ . The BAW resonator as recited in claim 1 further comprises a layer of high acoustic impedance material between the piezoelectric layer and the device layer, the layer of high acoustic impedance material having an acoustic impedance between 10 ⁶ Pa-s/m ³ and 630 x 10 ⁶ Pa-s/m ³ and

A thickness of 0.05λ, wherein the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or based on the thickness of the single crystal of LiNbO ₃ . The BAW resonator as recited in claim 1 further comprises a temperature compensation layer between the piezoelectric layer and the device layer, the temperature compensation layer comprising silicon and oxygen, the thickness of the temperature compensation layer being

2λ, wherein the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or on the thickness of the single crystal of LiNbO ₃ . The bulk acoustic wave resonator as recited in claim 1 further comprises a plurality of alternating temperature compensation layers and high acoustic impedance layers located between the piezoelectric layer and the device layer. A bulk acoustic wave resonator as recited in claim 1, wherein a passivation layer of a dielectric material is located on one or more external surfaces of the bulk acoustic wave resonator; wherein the upper conductive layer comprises at least one set of conductive springs with spaces; wherein the thickness of the device layer is

50nm; and/or wherein the device layer comprises at least one of the following: diamond; W; SiC; Ir, AlN, Al, Pt, Pd, Mo, Cr, Ti, Ta; an element of Group 3A or 4A in the periodic table; a transition element of Group 1B, 2B, 3B, 4B, 5B, 6B, 7B or 8B in the periodic table; ceramic; glass and a polymer. A bulk acoustic wave resonator as claimed in claim 1, wherein the piezoelectric layer is composed of: ZnO, AlN, InN, alkali metal niobate, alkali earth metal niobate, alkali metal titanate, alkali earth metal titanate, alkali metal tantalum, alkali earth metal tantalum, GaN, AlGaN, lead zirconate titanate (PZT), a polymer, or a doped form of any of the above. A bulk acoustic wave resonator for a carrier, the bulk acoustic wave resonator comprising: a device layer having a surface configured to be mounted on the carrier; a plurality of alternating layers located on the device layer, the alternating layers comprising a temperature compensation layer and a high acoustic impedance layer; a piezoelectric layer located on the alternating layers and being a single crystal of LiNbO ₃ , the single crystal of LiNbO ₃ having a cutting angle and a thickness, the angle and the thickness being conducive to a mode 3 resonance or a mode 4 resonance with a predetermined coupling efficiency; and an upper conductive layer located above the piezoelectric layer. A bulk acoustic wave resonator as described in claim 13, wherein the single crystal of _LiNbO3 is cut at an angle of 130°±70°, 130°±60°, 130°±50°, 130°±40°, 130°±30°, 130°±20°, 130°±10°, 0°±20°, 0°±30°, 0°±40°, 0°±50°, 0°±60° or 0°±70°. The bulk acoustic wave resonator as recited in claim 13, wherein the LiNbO ₃ single crystal is cut at an angle of 0°±10°, and wherein the LiNbO ₃ single crystal has a frequency

A mode 3 resonance or a mode 4 resonance at 0.1 GHz. The bulk acoustic wave resonator as recited in claim 13, wherein the single crystal of LiNbO ₃ comprises at least one of the following:

8% mode 3 resonance; and having a predetermined coupling efficiency

3% one mode 4 resonance. The bulk acoustic wave resonator of claim 16, wherein the upper conductive layer defines a pattern or feature having a size; and wherein: for the mode 4 resonance, the thickness of the single crystal of LiNbO ₃ is

0.5λ, where the value of λ is based on the size of the pattern or feature defined by the upper conductive layer; or for the mode 3 resonance, the thickness of the single crystal of LiNbO ₃

2λ, where the value of λ is based on the size of the pattern or feature defined by the upper conductive layer. The BAW resonator as recited in claim 13 further comprises a lower conductive layer located between the piezoelectric layer and the device layer, wherein the thickness of the lower conductive layer is

0.010λ, where the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or based on the thickness of the LiNbO ₃ single crystal. The BAW resonator as recited in claim 13 further comprises a layer of low acoustic impedance material between the piezoelectric layer and the device layer, the low acoustic impedance material having an acoustic impedance between 10 ⁶ Pa-s/m ³ and 30 x 10 ⁶ Pa-s/m ³ and

The thickness is 0.05λ, where the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or based on the single crystal thickness of the LiNbO ₃ . The bulk acoustic wave resonator of claim 13, wherein the high acoustic impedance layer of the alternating layers comprises a layer of high acoustic impedance material having an acoustic impedance between 10 ⁶ Pa-s/m ³ and 630 x 10 ⁶ Pa-s/m ³ and

The thickness is 0.05λ, where the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or based on the single crystal thickness of the LiNbO ₃ . The bulk acoustic wave resonator as recited in claim 13, wherein the temperature compensation layer of the alternating layer comprises a layer of temperature compensation material comprising silicon and oxygen and having a thickness of

2λ, where the value of λ is based on the size of the pattern or feature defined by the upper conductive layer, or on the thickness of the LiNbO ₃ single crystal. A BAW resonator as recited in claim 13, wherein a passivation layer of a dielectric material is located on one or more external surfaces of the BAW resonator; wherein the upper conductive layer comprises at least one set of conductive springs with spaces; wherein the thickness of the device layer is

50nm; and/or the device layer includes at least one of the following: diamond; W; SiC; Ir, AlN, Al, Pt, Pd, Mo, Cr, Ti, Ta; an element of group 3A or 4A in the periodic table; a transition element of group 1B, 2B, 3B, 4B, 5B, 6B, 7B or 8B in the periodic table; ceramic; glass and polymer. A bulk acoustic wave resonator as claimed in claim 1, wherein the piezoelectric layer is composed of: ZnO, AlN, InN, alkali metal niobate, alkali earth metal niobate, alkali metal titanate, alkali earth metal titanate, alkali metal tantalum, alkali earth metal tantalum, GaN, AlGaN, lead zirconate titanate (PZT), a polymer, or a doped form of any of the above.