KR102710221B1 - Acoustic resonator - Google Patents

Abstract

The present invention discloses an acoustic resonator including a substrate including a first cavity, a first electrode formed on an upper portion of the substrate, a piezoelectric layer formed on one surface of the first electrode, and a second electrode formed on one surface of the piezoelectric layer, wherein the first electrode, the piezoelectric layer, and the second electrode include an overlapping region corresponding to one end to the other end of the first cavity, one end of the first electrode terminates in a region outside the overlapping region, an etched region is formed in which a part of the piezoelectric layer is removed and overlaps with the end of the first electrode, and the substrate further includes a second cavity overlapping a part of the etched region on an imaginary vertical line. According to the present invention, a problem of increased resistance due to parasitic capacitance between the two electrodes can be solved, thereby increasing a quality factor Q value.

Description

Acoustic resonator {ACOUSTIC RESONATOR}

The present invention relates to an acoustic resonator used in RF (Radio Frequency) communications, and more particularly, to a film bulk acoustic resonator (FBAR) having an improved Q value through an improved air bridge structure.

Wireless mobile communication technology requires various RF (Radio Frequency) components that can efficiently transmit information in a limited frequency band. In particular, filters among RF components are one of the core components used in mobile communication technology, enabling high-quality communication by selecting the signal that the user needs among multiple frequency bands or filtering the signal to be transmitted.

Currently, the most widely used RF filters for wireless communication are dielectric filters and surface acoustic wave (SAW) filters. Dielectric filters have the advantages of high permittivity, low insertion loss, high temperature stability, vibration resistance, and shock resistance. However, dielectric filters have limitations in miniaturization and monolithic microwave integrated circuit (MMIC) development, which are recent technological development trends. In addition, SAW filters have the advantages of being compact, easy to process signals, simple circuits, and mass-producible by using semiconductor processes compared to dielectric filters. In addition, SAW filters have the advantage of high-quality information exchange due to high side rejection within the passband compared to dielectric filters. However, since the SAW filter process includes a process of exposing using ultraviolet (UV), there is a disadvantage in that the line width of the interdigital transducer (IDT) is limited to about 0.5 ㎛. Therefore, there is a problem that it is impossible to cover the ultra-high frequency (over 2.5 GHz) band using a SAW filter, and there are fundamental difficulties in forming a single chip with an MMIC structure made on a semiconductor substrate using a SAW filter.

To overcome the above limitations and problems, a film bulk acoustic resonator (FBAR) filter has been proposed that can completely MMIC the frequency control circuit integrated with other active elements on a conventional semiconductor (Si, GaAs) substrate.

FBAR is a thin film device that can be used in wireless communication devices and military radars of various frequency bands (900 MHz to 10 GHz) because it is low-cost, small, and has high Q coefficient characteristics. In addition, it can be miniaturized to a size several hundredths of that of dielectric filters and lumped constant (LC) filters, and has the characteristic of having much lower insertion loss than SAW filters. Therefore, FBAR is evaluated as the most suitable device for MMIC that requires high stability and high Q coefficient.

The FBAR filter induces resonance due to piezoelectric properties by depositing piezoelectric materials such as zinc oxide (ZnO) and aluminum nitride (AlN) on a semiconductor substrate such as silicon (Si) or gallium arsenide (GaAs) using RF sputtering. In other words, FBAR can generate resonance through the deposition of a piezoelectric film between two electrodes and the induction of bulk acoustic waves.

The FBAR structure has been studied in various forms so far. In the membrane-type FBAR structure, a silicon oxide film (SiO ₂ ) is deposited on a substrate, and a membrane layer is formed through a cavity formed on the opposite side of the substrate by isotropic etching. Then, a lower electrode is formed on top of the silicon oxide film, and a piezoelectric material is deposited on top of the lower electrode layer by RF magnetron sputtering to form a piezoelectric layer, and an upper electrode is formed on top of the piezoelectric layer.

The membrane type FBAR as above has the advantage of low substrate dielectric loss due to the cavity and low power loss. However, the membrane type FBAR has a large area occupied by the device due to the directionality of the silicon substrate, and the structural stability is low during the subsequent packaging process, so there is a problem of reduced yield due to breakage. Therefore, in order to reduce the loss due to the membrane and simplify the device manufacturing process, air gap type and Bragg Reflector type BAW resonators, namely SBAR (Solidly mounted BAR), have recently appeared.

The Bragg reflector-type SBAR is a structure in which a material with a large elastic impedance difference is deposited in layers on a substrate to form a reflection layer, and a lower electrode, a piezoelectric layer, and an upper electrode are sequentially laminated, so that elastic wave energy passing through the piezoelectric layer is not transmitted toward the substrate but is entirely reflected by the reflection layer, thereby generating efficient resonance. This Bragg reflector-type FBAR is structurally solid and has no stress due to bending, but has the disadvantages of being difficult to accurately form a reflection layer with a thickness of four or more layers for total reflection, and requiring a lot of time and cost for manufacturing.

Meanwhile, a conventional thin-film bulk acoustic resonator having a structure that isolates the substrate and the resonant section using an air gap instead of a reflective layer implements a sacrificial layer by anisotropically etching the surface of a silicon substrate, and then sequentially deposits an insulating layer, a lower electrode, a piezoelectric layer, and an upper electrode after surface polishing using CMP, and then removes the sacrificial layer through a via hole to form an air gap to implement an FBAR.

In the case of the prior art, a piezoelectric layer is formed between the upper and lower electrodes in the FBAR structure, and the upper and lower electrodes are installed only in the necessary area of the piezoelectric layer, thereby utilizing the piezoelectric effect. Therefore, the structure of the prior art has a large mechanical anchor loss, which causes a decrease in mechanical energy.

For the upper or lower electrode, Mo, Ru, W, etc. are used to increase the acoustic impedance. The skin depth of the electrode material is determined according to the frequency of the filter, and since an electrode with a thickness much smaller than the skin depth is generally used, the charge charged at the resonance point of the piezoelectric layer is not sufficiently transmitted through the lead, so the quality factor at the resonance point decreases.

One way to improve the quality factor at the resonance point is to minimize the energy that escapes in the lateral direction.

In addition to improving the quality factor, there are many challenges to be solved to improve the quality of acoustic resonators, such as minimizing the increase in electrical resistance due to thinning and minimizing parasitic impedance components that affect the quality factor due to changes in the positions between electrodes.

Republic of Korea Patent Publication No. 10-2004-0102390 (published on December 8, 2004)

The problem to be solved by the present invention is to provide an acoustic resonator with improved quality factors through deformation of the lower electrode.

The problem to be solved by the present invention is to provide an acoustic resonator in which the influence of parasitic impedance occurring between two electrodes can be minimized.

The problem to be solved by the present invention is to provide an acoustic resonator capable of reducing substrate loss due to an electric field generated between two electrodes.

According to an embodiment of the present invention for solving the above-described problem, an acoustic resonator comprises: a substrate including a first cavity; a first electrode formed on an upper portion of the substrate; a piezoelectric layer formed on one surface of the first electrode; and a second electrode formed on one surface of the piezoelectric layer, wherein the first electrode, the piezoelectric layer, and the second electrode include an overlap area corresponding to one end and the other end of the first cavity, one end of the first electrode terminates in an area outside the overlap area, and an etched area is formed in which a portion of the piezoelectric layer is removed to overlap with the end of the first electrode, and the substrate may be formed to further include a second cavity overlapping the etched area.

Additionally, a third cavity can be formed between the first electrode and the piezoelectric layer in the region between the overlapping region and the etching region.

Additionally, the first electrode may be formed to include a raised frame whose thickness increases in a region in contact with the third cavity.

Additionally, the piezoelectric layer can be formed to include an air bridge region in which the upper and lower surfaces start with an upwardly inclined plane of a second acute angle (θ ₂ ), the upper surface in contact with the second electrode is interrupted with a downwardly inclined plane of a third acute angle (θ ₃ ), and the lower surface in contact with the third cavity is interrupted with a downwardly inclined plane of a first acute angle (θ ₁ ).

In addition, it is characterized in that the first acute angle (θ ₁ ), the second acute angle (θ ₂ ), and the third acute angle (θ ₃ ) are formed at 45° or less, and the third acute angle (θ ₃ ) is formed larger than the first acute angle (θ ₁ ).

Additionally, the piezoelectric layer can form a longitudinal section in the etched area with a thickness equal to the difference between the third acute angle (θ ₃ ) and the first acute angle (θ ₁ ).

Additionally, the piezoelectric layer may be divided into a first part and a second part with an etching region therebetween, the first part may be formed on one surface of the first electrode, and the second part may be formed on the substrate.

Additionally, the second electrode may be formed in a V- or U-shape or a shape similar to a V- or U-shape to cover the inclined cross-sections of the first part and the second part spaced apart from each other on the etching area.

Additionally, the second electrode may be formed so that its lower surface, which has a V- or U-shape or a shape similar to a V or U shape, is in contact with the third cavity.

Additionally, the first electrode may have a longitudinal section formed with an inclined plane having a first acute angle (θ ₁ ) at a position overlapping the etching region.

According to the present invention, quality factors can be improved through deformation of the lower electrode.

Additionally, the influence of parasitic impedance occurring between the two electrodes can be minimized.

In addition, it is possible to reduce substrate loss caused by the electric field generated between the two electrodes.

FIG. 1 is a cross-sectional view of an acoustic resonator according to one embodiment of the present invention.
FIG. 2 is an exemplary diagram illustrating the structure of an acoustic resonator according to one embodiment of the present invention.
Figure 3 is a flow chart of a method for manufacturing an acoustic resonator according to an embodiment of the present invention.
Figure 4 is an exemplary diagram comparing an acoustic resonator according to a prior art and an embodiment of the present invention.
Figure 5 is an example circuit diagram of parasitic impedance due to the electric field between the two poles.
Figure 6 is a comparative graph of the Q value of an acoustic resonator according to the dielectric loss of the substrate.
FIG. 7 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.
FIG. 8 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.
FIG. 9 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.
FIG. 10 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.
FIG. 11 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.
FIG. 12 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.
FIG. 13 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.

Before describing the present invention in detail, it should be understood that the terms or words used in this specification should not be interpreted as being unconditionally limited to their usual or dictionary meanings, and that the inventor of the present invention may appropriately define and use the concepts of various terms in order to describe his or her invention in the best possible manner, and further that these terms or words should be interpreted as meanings and concepts that are consistent with the technical idea of the present invention.

That is, the terms used in this specification are only used to describe preferred embodiments of the present invention, and are not intended to specifically limit the contents of the present invention. It should be understood that these terms are terms defined in consideration of various possibilities of the present invention.

Additionally, it should be noted that in this specification, singular expressions may include plural expressions unless the context clearly indicates a different meaning, and similarly, even if expressed in plural, may include a singular meaning.

Throughout this specification, whenever a component is described as "including" another component, this may mean that the component may further include any other component, rather than excluding any other component, unless otherwise specifically stated.

Furthermore, when a component is described as being “existing within, or installed in connection with” another component, it should be noted that the component may be installed in direct connection with or in contact with the other component, may be installed spaced apart from the other component by a certain distance, and if it is installed spaced apart from the other component by a certain distance, there may be a third component or means for fixing or connecting the component to the other component, and the description of this third component or means may be omitted.

On the other hand, when a component is described as being "directly connected" or "directly connected" to another component, it should be understood that no third component or means is present.

Likewise, other expressions that describe the relationship between each component, such as "between" and "directly between", or "adjacent to" and "directly adjacent to", should be interpreted as having the same meaning.

In addition, it should be noted that the terms “one side,” “the other side,” “one side,” “the other side,” “first,” “second,” etc., when used in this specification, are used to clearly distinguish one component from other components, and that the meaning of the component is not limited by such terms.

In addition, terms related to position, such as “upper,” “lower,” “left,” and “right,” if used in this specification, should be understood to indicate relative positions of the corresponding components in the corresponding drawings, and unless absolute positions are specified for these positions, these position-related terms should not be understood to refer to absolute positions.

In addition, in specifying the drawing symbols for each component in each drawing in this specification, the same component is given the same drawing symbol even if the component is shown in a different drawing, that is, the same reference symbol indicates the same component throughout the specification.

In the drawings attached to this specification, the size, position, connection relationship, etc. of each component constituting the present invention may be described in an exaggerated, reduced, or omitted manner in order to sufficiently clearly convey the idea of the present invention or for convenience of explanation, and therefore the proportions or scales may not be strict.

In addition, in the following description of the present invention, a detailed description of a configuration that is judged to unnecessarily obscure the gist of the present invention, for example, a known technology including a prior art, may be omitted.

Hereinafter, embodiments of the present invention will be described in detail with reference to the relevant drawings.

An acoustic resonator (100) according to one embodiment of the present invention can be formed by laminating layers of different materials, and a plurality of layers viewed in the lamination direction can have a polygonal structure shape.

FIG. 1 is a cross-sectional view of an acoustic resonator according to one embodiment of the present invention.

Referring to FIG. 1, an acoustic resonator (100) includes a substrate (111), a first electrode (121) laminated on the substrate (111), a piezoelectric layer (131) laminated on one surface of the first electrode (121), and a second electrode (141) laminated on one surface of the piezoelectric layer (131), and may be configured to optionally further include a first protective layer (113) laminated between the substrate (111) and the first electrode (121) and a second protective layer (150) laminated on one surface of the second electrode. Accordingly, at least one of the first protective layer (113) and the second protective layer (150) may be omitted from the acoustic resonator (100).

The acoustic resonator (100) does not have a certain directionality, but for the convenience of explanation, the upper and lower sides in the horizontal (x-axis) direction and the vertical (y-axis) direction are referred to based on the cross-section of the acoustic resonator (100) depicted in FIG. 1. For example, in FIG. 1, among the two sides of the piezoelectric layer (131), the side in contact with the second electrode (141) is referred to as the upper side, the side in contact with the first electrode (121) is referred to as the lower side, and the first electrode (121) may be referred to as the lower electrode and the second electrode (141) may be referred to as the upper electrode.

FIG. 2 is an exemplary diagram explaining the structure of an acoustic resonator according to one embodiment of the present invention.

Fig. 2 is an enlarged depiction of a portion of Fig. 1. The structure of the acoustic resonator (100) will be described in detail based on Fig. 2.

Referring to FIG. 2, a first trench having a width ranging from E ₁ (not shown) to E ₂ may be formed in a substrate (111). The first trench acts as a first cavity (112a). A second trench having a width ranging from E ₃ to E ₄ (not shown) may be formed in the substrate (111) spaced apart from the first trench. The second trench acts as a second cavity (112b). The first cavity (112a) and the second cavity (112b) may be formed at the same height. In addition, it is preferable that the second cavity (112b) is formed to have a smaller area than the first cavity (112a).

The first electrode (121) or the first protective layer (113) may be formed on one surface of the substrate (111) on which the first cavity (112a) and the second cavity (112b) are formed. The first electrode (121) or the first protective layer (113) may be suspended over the space of the first cavity (112a) and the second cavity (112b) without filling the bottom of the first groove and the second groove. When the first protective layer (113) is formed on one surface of the substrate (111), the first electrode (121) is formed on one surface of the first protective layer (113).

Some areas of the first electrode (121), the piezoelectric layer (131), and the second electrode (141) are positioned on the first cavity (112a), and the area of the first electrode (121), the piezoelectric layer (131), and the second electrode ( ₁₄₁ ) on the first cavity (112a) having a width from one end (E ₁ ) to the other end (E 2 ) is referred to as an overlap area. That is, the first electrode (121), the piezoelectric layer (131), and the second electrode (141) can be formed to include the overlap area.

Referring again to FIG. 2, the first electrode (121), when viewed horizontally, the first electrode (121), the piezoelectric layer (131) and the second electrode (141) are divided into a first outer region (not shown) connected to one end (E ₁ ) of the overlapping region, and a second outer region connected to the other end (E ₂ ) of the overlapping region and the overlapping region.

Referring back to FIG. 1, the first electrode (121) may be formed to terminate at a position spaced apart from the overlapping region, i.e., at the second outer region. And the piezoelectric layer (131) may also be interrupted at the same position as the first electrode (121) in the horizontal direction. And the second part (132) of the piezoelectric layer may be restarted at a point spaced apart by a certain width from the interrupted piezoelectric layer (131). The piezoelectric layer (131) may be divided into the first part and the second part (132) through etching. The portion of the piezoelectric layer (131) where a portion is removed through etching is called an etching region.

The etched area refers to an area where a portion of the piezoelectric layer (131) is removed in a U-shape, a V-shape, or a similar shape. On one side of the etched area, the piezoelectric layer is interrupted to overlap with the end of the first electrode (121), and on the other side of the etched area, the piezoelectric layer is resumed. The etched area corresponds to an area where the piezoelectric layer is removed by etching. In fact, the second electrode (141) is positioned in the etched area. The etched area is formed with the intention of forming the second electrode with a height difference and an incline.

The cross-section of the first electrode (121) may be formed in the form of a sloped surface having a first acute angle (θ ₁ ). In order to prevent cracks, which are shapes in which the edge of the first electrode (121) is broken during the process of laminating and removing a sacrificial layer on the first electrode (121), the first electrode (121) may be formed such that the angle between its cross-section and the horizontal plane becomes the first acute angle (θ ₁ ), for example, 45 degrees or less, and most preferably, about 15 degrees or less.

Referring back to FIG. 2, the piezoelectric layer (131) may be formed to include an air bridge region having a third cavity (122) between the first electrode (121) in the vertical direction and the second outer region, that is, between the other end (E ₂ ) of the first cavity (112a) and the longitudinal section of the first electrode (121) in the horizontal direction. In some regions, a sacrificial layer is laminated on one surface of the first electrode (121), and a piezoelectric layer (131) of a certain height is formed on one surface of the first electrode (121) without the sacrificial layer and one surface of the sacrificial layer, and when the sacrificial layer is removed, the region corresponding to the sacrificial layer becomes the third cavity (122).

The first electrode (121) may be formed to include a raised frame (123) whose thickness increases in some areas. The raised frame (123) is an area where the thickness of the first electrode (121) is formed thicker compared to adjacent areas.

The rising frame (123) of the first electrode (121) may be formed to overlap with the third cavity (122). Referring to FIG. 2, the third cavity (122) may be formed to have a thickness (b) that is narrower due to the influence of the rising frame (123) compared to the thickness (a) in the case where the rising frame (123) does not exist.

The third cavity (122) may be formed from the point indicated in FIG. 2 to the end point, and may further extend beyond the end point to the area between the second electrode (141) and the substrate (111) or between the second electrode (141) and the first protective layer (113). That is, the third cavity (122) may overlap with the etching area while contacting the end surface of the first electrode (121) and may be formed between the substrate (111) and the piezoelectric layer (131). According to a simulation experiment, the closer the point of the third cavity (122) gets to the other end (E ₂ ) of the first cavity (112a), that is, the more the third cavity (122) extends, the higher the Q value may be.

As described above, the piezoelectric layer (131) may be formed by being interrupted by an etching region in some areas, and thus divided into a first part (131) of the piezoelectric layer in which a third cavity (122) exists and a second part (132) of the piezoelectric layer that does not come into contact with the first electrode (121).

The piezoelectric layer (131) may be formed such that the cross-section by the etching area overlaps the cross-section of the first electrode (121). Referring to FIG. 2, the first electrode (121) may be terminated at the end point, and the piezoelectric layer (131) may be formed such that it is interrupted. Referring to FIG. 1, the end surface of the piezoelectric layer (131), that is, the end surface, is expressed as being stopped in that the second part (132) of the piezoelectric layer exists, and the end surface of the first electrode (121), that is, the end surface, is expressed as being terminated in that the first electrode does not exist under the second part (132) of the piezoelectric layer.

Specifically describing the third cavity (122) of the piezoelectric layer (131), the piezoelectric layer (131) can be formed to include an air bridge region in which the upper and lower surfaces start with an upward slope of a second acute angle (θ ₂ ), the upper surface in contact with the second electrode ends with a downward slope of a third acute angle (θ ₃ ), and the lower surface in contact with the third cavity (122) ends with a downward slope of a first acute angle (θ ₁ ).

The first acute angle (θ ₁ ) formed by the longitudinal section of the first electrode (121) with the horizontal plane, the second acute angle (θ ₂ ) formed by the meeting of the piezoelectric layer (131) and the air bridge region, and the third acute angle (θ ₃ ) formed by the longitudinal section of the piezoelectric layer (131) with the horizontal plane are formed at acute angles, for example, 45° or less, and the third acute angle (θ ₃ ) is formed larger than the first acute angle (θ ₁ ). In particular, it is most preferable that the first acute angle (θ ₁ ) and the second acute angle (θ ₂ ) are formed at 15°. Of course, there may be an error range due to the manufacturing process.

The piezoelectric layer (131) can form the longitudinal section with a thickness equal to the difference between the third acute angle (θ ₃ ) and the first acute angle (θ ₁ ).

Referring again to Fig. 2, the angle formed between the upper and lower cross-sections of the piezoelectric layer (131) is the value obtained by subtracting the first acute angle (θ ₁ ) from the angle of the third acute angle (θ ₃ ), and thus has a value of θ ₃ -θ ₁ .

Referring back to FIGS. 1 and 2, the acoustic resonator (100) can lower the electrical resistance of the electrode by expanding the thickness of the second electrode (141), thereby improving the overall conductivity. Since the second electrode (141) is paired with the first electrode (121) with the piezoelectric layer (131) interposed therebetween, the space for the thickness to be expanded is narrow. Therefore, in order to expand the thickness of the first electrode (121) and reduce the stress of the piezoelectric layer (131), it is necessary to separate the piezoelectric layer (131) into two parts.

Through the etching of the piezoelectric layer (131), i.e., the etching region depicted in FIG. 2, the piezoelectric layer (131) can be removed in some areas. That is, by forming a valley formed by an inclined surface in some areas of the piezoelectric layer (131), the piezoelectric layer (131) is not actually separated, but can be depicted as being separated into two parts (131, 132) in the cross-sectional view depicted in FIG. 2.

Since the second electrode (141) is formed on the piezoelectric layer (131), its shape can be determined according to the shape of the piezoelectric layer (131). That is, the second electrode (141) can be formed so as to cover the etching area of the piezoelectric layer (131).

Specifically, the second electrode (141) may be formed to extend in the direction of the first electrode (121) so as to cover the inclined longitudinal surfaces of the first part (131) and the second part (132) of the piezoelectric layer spaced apart from each other in the etching region, that is, to have a shape of the cross-section in the shape of a V or U or a shape similar to a V or U.

How far the second electrode (141) can extend may be an issue. The second electrode (141) may extend within a range that does not encroach on the first electrode (121). In addition, the first electrode (121) may be formed to be terminated before the second electrode (141) is extended. Even when the first electrode (121) is terminated, the first electrode (121) and the second electrode (141) must maintain a minimum distance to prevent the occurrence of noise such as parasitic capacitance. Therefore, the third cavity (122) on the first electrode (121) may extend further than the end point of the first electrode (121). Accordingly, the second electrode (141) may be formed so that the lowest surface of the V or U shape is in contact with the third cavity (122).

The third cavity (122) may be filled with air or a dielectric. In addition, the fourth cavity (142) formed below the air bridge region of the second electrode (141) may be filled with air or a dielectric. The third cavity (122) may have a function of preventing the generation of parasitic capacitance between the first electrode (121) and the second electrode (141).

The third cavity (122), which corresponds to the inter-pole cavity between the first electrode (121) and the second electrode (141), can reduce electrical loss because it has a difference in permittivity with the adjacent medium, and can increase the Q value by driving the resonator only in the active area of the resonator to minimize energy loss.

Additionally, a first protective layer (113) may be selectively formed between the substrate (111) and the first electrode (121), and a second protective layer (150) may be formed on one surface of the second electrode (141).

The acoustic resonator (100) may be configured to further include a first metal pattern layer and a second metal pattern layer, which are referred to as pads. That is, the acoustic resonator (100) may be formed to further include conductive metal pattern layers formed on the first electrode (121) and the second electrode (141) respectively on the outer side of the overlapping region based on one end of the first cavity (112a). The metal pattern layers serve to electrically connect with external components.

The substrate (111) can be implemented using a semiconductor substrate among various substrate materials, and in particular, a silicon wafer can be used, and preferably, a high-resistivity silicon substrate can be used.

A first cavity (112a) may be formed in a portion of a substrate (111). That is, the first cavity (112a) may be formed in a trench shape from one end (E ₁ ) to the other end (E ₂ ) not shown in FIG. 1 in a portion of a portion of one side, the upper surface, of the substrate (111). The first cavity (112a) may be formed through a sacrificial layer formation process or bonding of a pre-formed first electrode.

The first cavity (112a) can act as a reflective element, and its arrangement position has an important meaning in the acoustic resonator. Referring to the first cavity (112a) depicted in Fig. 1, in addition to the first electrode (121), the piezoelectric layer (131), and the second electrode (141) constituting the overlapping region, the modified structure of the second electrode (141) is related to the first cavity (112a) having one end (E ₁ ) and the other end (E ₂ ) as a width.

The first cavity (112a) may be formed by forming a trench region on one surface of the substrate (111), then forming an insulating layer in the trench region, depositing a sacrificial layer on top of the insulating layer, etching to make it planar, and then removing the sacrificial layer. In addition, a pre-formed first electrode (121) may be bonded to the upper portion after the space region of the first cavity (112) is formed.

As a material for the sacrificial layer, a material having excellent surface roughness and easy formation and removal of the sacrificial layer, such as polysilicon, TEOS (Tetraethyl orthosilicate), or PSG (Phophosilicate glass), can be used. In one embodiment, polysilicon can be employed as the sacrificial layer, and such polysilicon not only has excellent surface roughness and easy formation and removal of the sacrificial layer, but can also be removed by applying dry etching in a subsequent process.

In a state where the sacrificial layer of the overlapping region of the first cavity (112a) is not removed, a first protective layer (113) covering the surface of the sacrificial layer and the substrate (111) can be selectively formed. To implement the first protective layer (113), a thermal oxide film that can be easily grown on the substrate (111) can be employed, or an oxide film or nitride film using a conventional deposition process such as chemical vapor deposition can be selectively employed.

The first electrode (121) may be formed on one surface of the substrate (111). That is, the first electrode (121) may be formed to be suspended over the first cavity (112a) when there is no first protective layer (113) and to cover the entire area or a portion of the substrate (111) where the first cavity (112a) does not exist. FIG. 2 illustrates a first electrode (121) formed to cover the first cavity (112a) and a portion of the substrate (111). In particular, the first electrode (121) may be formed to terminate in an outer area of the first cavity (112) based on the other end (E ₂ ) of the first cavity (112a). Referring to FIG. 1, the edge of the cross-section of the first electrode (121) may be finished with a downward slope.

The first electrode (121) corresponds to the input terminal and output terminal of the electrical signal with the second electrode (141). The first electrode (121) can be implemented with a conductive material.

The first electrode (121) can be formed on the first protective layer (113) or the substrate (111). If a sacrificial layer exists in the first cavity (112a) region of the substrate (111), it can be formed on the sacrificial layer.

The first electrode (121) can be formed by patterning after a predetermined material is deposited on one surface of the substrate (111). As a material of the first electrode (121), a common conductor such as a metal, preferably one of aluminum (Al), tungsten (W), gold (Au), platinum (Pt), nickel (Ni), titanium (Ti), chromium (Cr), palladium (Pd), rustium (Ru), rhenium (Rhenium (Re)), and molybdenum (Mo) can be used. The first electrode (121) can be formed with a thickness in the range of 10 to 1000 nm.

The piezoelectric layer (131) may be formed on the surface opposite to the surface where the first electrode (121) is in contact with the substrate (111) among the two surfaces of the first electrode (121). The piezoelectric layer (131) formed on the first electrode (121) may be formed so as not to cover a portion of the first electrode (121). For example, referring to FIG. 2, a first metal pattern layer may be formed on a portion of the first electrode (121) that is exposed because the piezoelectric layer (131) does not cover it.

In addition, as the first electrode (121) is terminated, the piezoelectric layer (131) may also be interrupted to form a slanted edge. It is preferable that the piezoelectric layer (131) is formed so as not to cover the edge of the terminated first electrode (121).

The piezoelectric layer (131) may be composed of a piezoelectric element and is called a piezoelectric layer after the name of the element. When an electrical signal is applied between the first electrode (121) and the second electrode (141), the piezoelectric layer (131) generates elastic waves due to the piezoelectric material.

The piezoelectric layer (131) can be formed through patterning after a piezoelectric material is deposited on the surface opposite to the surface where the first electrode (121) comes into contact with the substrate (111) among the two surfaces of the first electrode (121). Aluminum nitride (AIN) or zinc oxide (ZnO) can be used as the piezoelectric material constituting the piezoelectric layer (131). The deposition method can be a RF magnetron sputtering method, an evaporation method, or the like. The piezoelectric layer (131) can be formed in a thickness range of 5 to 500 nm.

The second electrode (141) corresponds to the input terminal and output terminal of the electrical signal with the first electrode (121). The second electrode (141) can be implemented with a conductive material.

The second electrode (141) can be formed by depositing and patterning a metal film for an electrode on a predetermined area of one surface of the piezoelectric layer (131). The second electrode (141) can be formed by using the material, deposition method, and patterning method used for the first electrode (121). The second electrode (141) can be formed with a thickness in the range of 5 to 1000 nm.

As a material for the second electrode (141), a common conductor such as a metal, preferably one of aluminum (Al), tungsten (W), gold (Au), platinum (Pt), nickel (Ni), titanium (Ti), chromium (Cr), palladium (Pd), rustium (Ru), rhenium (Re) and molybdenum (Mo) can be used.

When an electrical signal is input to the acoustic resonator (100) through the first electrode (121) and the second electrode (141), a portion of the input electrical energy is converted into mechanical energy according to the piezoelectric effect, and in the process of the mechanical energy being converted back into electrical energy, resonance occurs at a frequency of natural vibration according to the thickness of the piezoelectric layer (131).

An acoustic resonator (100) according to an embodiment of the present invention may be formed so that the first electrode (121), the second electrode (141), and the piezoelectric layer (131) have a common overlapping area, or in other words, an active area. In addition, the substrate (111) may be formed so as to have a first cavity (112a) corresponding to a reflection area between the first electrode (121) and the substrate (111), overlapping the active area. In other words, the first cavity (112a) may be formed between the first electrode (121) and the substrate (111) while overlapping the upper active area.

Referring again to FIG. 2, a wing region of a second electrode (141) and thereby a fourth cavity (142) may be formed on the upper portion of the other end (E ₂ ) of the first cavity (112a). A fifth cavity (143) having a width C may be formed to partially overlap with the third cavity (122) near the starting point of the third cavity (122). In addition, the fourth cavity (142) and the fifth cavity (143) may be connected to each other in a horizontal direction.

The active region may be formed in a region where the first electrode (121), the piezoelectric layer (131), and the second electrode (141) commonly overlap. A wing region (not shown) of the second electrode (141) may be formed on one end (E ₁ ) of the active region, and a second air bridge region of the second electrode (141) may be arranged on the other end (E ₂ ).

When the first electrode (121) is terminated beyond the overlapping region, i.e., the active region, the piezoelectric layer (131) can be formed to be interrupted accordingly. As a result, the piezoelectric layer (131) does not cover the edge of the first electrode (121).

Among the various functions of the active region, heat generated in the active region can be transferred to the substrate (111).

As mobile communications develop, the frequency bands used are increasing, and accordingly, the size of filters is becoming increasingly miniaturized and their thickness is becoming thinner. The disadvantages of thinning include structural mechanical problems, electrical problems related to conduction, and thermodynamic problems related to heat transfer.

The thermodynamic problem is that the electrodes of the filter that handles high frequencies generate a lot of heat as the charge increases rapidly due to the use of a lot of power. And the electrical problem is that the electrical resistance of the electrodes increases as the filter becomes thinner based on Ohm's law.

As a method of compensating for the increase in electrical loss of the electrode, a method of reinforcing the thickness of the electrode can be considered based on Ohm's law.

Referring back to FIG. 1, the second electrode (141) may be formed to include an air bridge region extending to the outside of the overlapping region based on the other end (E ₂ ) of the active region, that is, the overlapping region. And the air bridge region of the second electrode (141) may be formed to have a fourth cavity (142) between the piezoelectric layers (131). That is, the fourth cavity (142) may be formed between the piezoelectric layer (131) and the second electrode (141) due to the air bridge region of the second electrode (141).

The fourth cavity (142) may also be formed as a closed type, similar to the third cavity (122). The fourth cavity (142) may also be filled with a dielectric or air.

The height of the fourth cavity (142) may be less than or equal to 1/2 of the thickness of the piezoelectric layer (131). The length of the horizontal width of the fourth cavity (142) may be more than 1/4 of the wavelength of the lateral acoustic wave leaking through the piezoelectric layer (131).

The fourth cavity (142) can be formed by depositing a sacrificial layer on top of the piezoelectric layer (131), then patterning it by planarization and etching, stacking the second electrode (141) on the piezoelectric layer (131) including the remaining sacrificial layer, and then removing the sacrificial layer. In this case, a cavity may be formed in a portion of the upper portion of the piezoelectric layer (131), and then the sacrificial layer may be deposited.

Here, a material having excellent surface roughness and easy formation and removal of the sacrificial layer, such as polysilicon, TEOS (Tetraethyl orthosilicate), or PSG (Phophosilicate glass), can be used as the sacrificial layer material. The formation process of the fourth cavity (142) can be applied equally to the third cavity (122).

An acoustic resonator (100) according to one embodiment of the present invention may be configured to further include a first conductive metal pattern layer formed to cover an edge caused by an interruption of the piezoelectric layer (131) in an area where the piezoelectric layer (131) is interrupted and the first electrode (121) is exposed.

In addition, the acoustic resonator (100) according to one embodiment of the present invention may be configured to further include a second metal pattern layer formed in an area where the second protective layer (150) is terminated and the second electrode (141) is exposed.

According to one embodiment of the present invention, a metal pattern layer can be arranged as close as possible to the active area. Through such arrangement close to the active area, electrical loss of the first electrode (121) and the second electrode (141) can be reduced.

The metal pattern layer corresponds to a metal pad to which a signal line of an external circuit device connected to the first electrode (121) and the second electrode (141) is connected. One end of the metal pattern layer may be formed to have a uniform thickness corresponding to the shape of one end of the piezoelectric layer (131).

The metal pattern layer can be formed of a conductive metal at a location outside the active region. The metal forming the metal pattern layer includes gold (Au), copper (Cu), aluminum (Al), aluminum-copper alloy (AlCu), etc. By forming the metal pattern layer, the Q value can be improved.

The second electrode (141) laminated on the piezoelectric layer (131) may be formed to be inclined toward the first electrode (121) depending on the shape of the piezoelectric layer (131). The second electrode (141) may be formed in a V or U shape depending on the angle of inclination. The second electrode (141) may have a shape in which the thickness increases in the horizontal direction depending on the inclination, and may also include a recessed frame in which the thickness increases and then becomes recessed.

In some areas, the piezoelectric layer (131) may be interrupted, and a second part of the piezoelectric layer (132) may be formed at a point spaced a predetermined distance from the interrupted point. Unlike the first part of the piezoelectric layer (131), the second part of the piezoelectric layer (132) may be formed on the first protective layer (113) or the substrate (111).

By increasing the thickness of the second electrode (141) at a location outside the active area, the resistance of the electrode with the increased thickness decreases, so that the current gathers at the edge of the electrode and flows to the electrode lead, which can increase the Q value. That is, since the resistance decreases in the area of the increased thickness of the second electrode (141), the flow of charge per unit time can increase.

Additionally, heat concentrated in the active area can be transferred to the outside through the substrate (111).

In addition, by reinforcing the thickness of the first electrode (121), heat generated in the active area can be transferred to the substrate, thereby improving heat transfer.

Referring back to FIG. 1, the acoustic resonator (100) may be configured to include a second protective layer (150). The second protective layer (150) may be formed on an opposite surface of the surface where the second electrode (141) contacts the piezoelectric layer (131).

The second protective layer (150) can perform a passivation function to protect the first electrode (121), the piezoelectric layer (131), and the second electrode (141). The second protective layer (150) can be formed so that one edge of the second protective layer matches the one edge of the second electrode (141).

According to one embodiment of the present invention, the technical features of the acoustic resonator (100) can be described by the manufacturing method. Since the specific manufacturing process of the acoustic resonator (100) has been described above, the features will be briefly described.

FIG. 3 is a flow chart of a method (S100) for manufacturing an acoustic resonator according to an embodiment of the present invention.

Referring to FIG. 3 together with FIG. 2, the main processes constituting the method for manufacturing an acoustic resonator (S100) are depicted. The method for manufacturing an acoustic resonator (S100) includes a step (S110) in which a first trench of a first cavity (112a) and a second trench of a second cavity (112b) are formed in a portion of a substrate (111), and a sacrificial layer is formed in the space between the first trench and the second trench, a step (S120) in which a raised frame (123) of a first electrode (121) is formed and the first electrode (121) is formed to be terminated on the outside of the overlapping region based on the other end of the overlapping region, a step (S131) in which a sacrificial layer is formed on a portion of a surface, a longitudinal surface, and a portion of a surface on the substrate (111), a piezoelectric layer (131) covering the first electrode (121) and the sacrificial layer is formed, and a portion of the piezoelectric layer (131) is etched, and a second electrode (141) is formed on the piezoelectric layer (131). It can be configured to include step (S150).

The first cavity (112a) and the second cavity (112b) may be formed in a trench shape in a portion of the substrate (111) (S110). The first cavity (112a) may be formed to have a width from one end (E ₁ ) to the other end (E ₂ ), and the second cavity (112b) may be formed to have a width from one end (E ₃ ) to the other end (E ₄ ).

The first electrode (121) may be formed on the upper portion of the substrate (111), including the first cavity (112a). That is, the first electrode (121) may be formed on the upper surface of the substrate (111) when there is no first protective layer (113), and may be formed on the first protective layer (113) when there is a first protective layer (113) on the substrate (111).

The first electrode (121) may include an overlapping region corresponding to one end (E ₁ ) to the other end (E ₂ ) of the first cavity (112a). In addition, the first electrode (121) may be formed to terminate on the outside of the overlapping region with the other end (E ₂ ) of the overlapping region as the standard.

The piezoelectric layer (131) may be formed on one surface of the first electrode (121), but may be formed to be interrupted on the outside of the overlapping region. The piezoelectric layer (131) may be formed to include an air bridge region in which the upper and lower surfaces start with an upward slope of a second acute angle (θ ₂ ), the upper surface in contact with the second electrode (141) is interrupted with a downward slope of a third acute angle (θ ₃ ), and the lower surface in contact with the third cavity (122) is interrupted with a downward slope of a second acute angle (θ ₁ ).

Here, the first acute angle (θ ₁ ), the second acute angle (θ ₂ ), and the third acute angle (θ ₃ ) are formed at 45° or less, and the third acute angle (θ ₃ ) is formed larger than the first acute angle (θ ₁ ).

The second electrode (141) may be formed to extend along the longitudinal section of the piezoelectric layer (131) toward the first electrode (121). A second protective layer (150) may optionally be formed on one surface of the second electrode (141). The first metal pattern layer may be formed in the area where the first electrode (121) is exposed, and the second metal pattern layer may be formed in the area where the second electrode (141) is exposed. Finally, the sacrificial layer is removed, thereby forming a cavity in the space that was filled with the sacrificial layer.

Figure 4 is an exemplary diagram comparing an acoustic resonator according to a prior art and an embodiment of the present invention.

The termination of the first electrode (121), the etching of the piezoelectric layer (131), and the formation of the second cavity (112b) and the third cavity (122) formed between the second electrode (141) and the first electrode (121) are based on a series of causal relationships.

Referring to FIG. 4, in the #1 acoustic resonator, loss occurs inside the substrate (111) due to the electric field between the first electrode (121) and the second electrode (141). In order to prevent loss due to the electric field, the length of the first electrode (121) may be formed to be reduced toward the inside of the first cavity (112a), as in the #2 acoustic resonator. In the #1 acoustic resonator and the #2 acoustic resonator, the second electrode (141) is formed to include an air bridge shape.

In order to minimize mechanical loss due to acoustic waves traveling laterally through the piezoelectric layer (131), a portion of the piezoelectric layer is removed, as in the #3 acoustic resonator, and the first electrode (121) is designed to expand in the horizontal direction again. In order to reduce loss of the electrode due to thinning, the second electrode (141) may also be designed to expand in the vertical direction. In order to reduce electrical resistance due to thinning of the electrode, the piezoelectric layer (131) may be etched to expand the thickness of the second electrode (141) in the vertical direction.

The loss occurring in the substrate (111) due to the electric field and the first electrode (121) and the second electrode (141) that are brought close together may be a problem. As the first electrode (121) and the second electrode (141) are formed close together by the etching region, a third cavity (122), which is an air bridge region between the two electrodes, and a second cavity (112b) on the substrate (111) may be formed to reduce the parasitic impedance between the two electrodes and the loss due to the substrate (111), as in the #4 acoustic resonator.

Additionally, the third cavity (122) may be initiated closer to the first cavity (112a) in the horizontal direction.

Figure 5 is an example circuit diagram of parasitic impedance due to the electric field between the two poles.

Referring to FIG. 5, an equivalent circuit of the #4 acoustic resonator depicted in FIG. 4 is depicted. In the area where the piezoelectric layer (131) is etched, an electric field is generated from the second electrode (141) to the first electrode (121) through the Si substrate (111) despite the high-resistance Si substrate (Si-wafer) (111). This electric field can be modeled as a parasitic capacitance and resistance as shown in FIG. 5, and the parasitic resistance value is related to the loss tan delta of the substrate (111) and reduces Q at the anti-resonant frequency of the acoustic resonator. Since the permittivity of air is much lower than that of the Si-wafer, in order to prevent a decrease in Q, a second cavity (112b) is formed on the substrate, as in the #4 acoustic resonator, so that the electric field intensity generated between the second electrode (141) and the first electrode (121) can be reduced, the loss due to the substrate (111) can also be reduced, and the Q value can be prevented from deteriorating.

Figure 6 is a comparative graph of measured Q values in a simulation example of an acoustic resonator according to the dielectric loss of the substrate.

Referring to FIG. 6, the simulation results of Q values of the acoustic resonators #2, #3, and #4 illustrated in FIG. 4 are depicted graphically. In the simulation example of the acoustic resonator #4, the substrate loss is less distributed due to the influence of the second cavity (112b), and therefore the highest Q value is shown. On the other hand, in the simulation example of the acoustic resonator #3, the substrate loss increases due to the horizontal expansion of the first electrode (121) and the vertical expansion of the second electrode (141), and thus the Q value decreases. In addition, in the simulation example of the acoustic resonator #2, the Q value can be recovered within a certain range through the horizontal expansion of the second cavity (112b) and the third cavity (122).

FIG. 7 and FIG. 8 are drawings related to simulation results according to the presence or absence of a second cavity (112b) on the substrate (111) corresponding to the inter-pole cavity between the first electrode (121) and the second electrode (141).

FIG. 7 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.

Referring to FIG. 7, in a simulation example in which all other conditions are the same, including a third cavity (122) formed between a piezoelectric layer (131) and a second electrode (141) and a cavity (112b) formed on a substrate by extending thereto, and a second cavity (112b) is not included on the substrate (111), the value of Qp (normalized Q at anti-resonant frequency) is 1.

Referring to FIG. 8, in a simulation example in which all other conditions are the same, including a third cavity (122) formed between a piezoelectric layer (131) and a second electrode (141) and a cavity (112b) formed on a substrate by extending thereto, and a second cavity (112b) is included on a substrate (111), the value of Qp (normalized Q at anti-resonant frequency) is 1.18.

In summary of the results of FIGS. 7 and 8, it can be seen that when the substrate (111) located on the electric field path between the first electrode (121) and the second electrode (141) includes the second cavity (112b), there is an effect of improving the Qp value. This result is due to the relationship between the permittivity of the substrate (111) and air and the electrical loss.

Figures 9 and 10 are drawings related to simulation results according to the presence or absence of a rising frame (123) of the first electrode (121) formed in the third cavity (122).

FIG. 9 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.

Referring to FIG. 9, in a simulation example where all other conditions are the same, including a second cavity (112b) formed on a substrate (111) and a third cavity (122) formed between the first electrode (121) and the second electrode (141), and the first electrode (121) does not include a rising frame (123) within the third cavity (122), the value of Qp (normalized Q at anti-resonant frequency) is 1.

FIG. 10 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.

Referring to FIG. 10, in a simulation example where all other conditions are the same, including a second cavity (112b) formed on a substrate (111) and a third cavity (122) formed between the first electrode (121) and the second electrode (141), and the first electrode (121) includes a rising frame (123) within the third cavity (122), the value of Qp (normalized Q at anti-resonant frequency) is 1.42.

In summary of the results of FIGS. 9 and 10, it can be seen that there is an effect of improving the Qp value when the first electrode (121) includes a raised frame (123). This result is due to the relationship between the thickness of the first electrode (121) and the electrical loss.

Figures 11 to 13 are drawings related to simulation results of the Zp value according to the width of the second cavity (112b) formed in the substrate (111) so as to overlap the path of the electric field formed between the first electrode (121) and the second electrode (141).

FIG. 11 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.

Referring to Fig. 11, in a simulation example in which all other conditions are the same, including the third cavity (122) formed between the first electrode (121) and the second electrode (141), and the width of the second cavity (112b) is set to about 3 μm, the value of Zp (normalized impedance at anti-resonant frequency) is 1.

FIG. 12 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.

Referring to Fig. 12, in a simulation example in which all other conditions are the same, including the third cavity (122) formed between the first electrode (121) and the second electrode (141), and the width of the second cavity (112b) is set to about 4 μm, the value of Zp (normalized impedance at anti-resonant frequency) is 1.37.

FIG. 13 is an example view of a simulation for measuring the Q value of an acoustic resonator according to an embodiment of the present invention.

Referring to Fig. 13, in a simulation example in which all other conditions are the same, including the third cavity (122) formed between the first electrode (121) and the second electrode (141), and the width of the second cavity (112b) is set to about 6.5 μm, the value of Zp (normalized impedance at anti-resonant frequency) is 1.67.

Therefore, by summarizing the results of FIGS. 11 to 13, it can be seen that the second cavity (112b) formed on the substrate (111) has the effect of improving the Zp value as its width increases. This result is due to the relationship between the space of the cavity (112b) and the intensity of the electric field.

According to one embodiment of the present invention, the quality factor can be improved through deformation of the lower electrode.

Additionally, the influence of parasitic impedance occurring between the two electrodes can be minimized.

In addition, it is possible to reduce substrate loss caused by the electric field generated between the two electrodes.

Above, although some examples have been given and various preferred embodiments of the present invention have been described, the description of various embodiments described in the “Specific Details for Carrying Out the Invention” section is merely exemplary, and those skilled in the art to which the present invention pertains will readily understand that various modifications of the present invention can be implemented or equivalent implementations of the present invention can be implemented based on the above description.

In addition, since the present invention can be implemented in various other forms, the present invention is not limited by the above description, and the above description is provided only to make the disclosure of the present invention complete and to fully inform a person having ordinary skill in the art to which the present invention belongs of the scope of the present invention, and it should be understood that the present invention is defined only by each claim of the claims.

100: Acoustic resonator
111: Substrate
112a: Cavity 1
112b: Second cavity
113: 1st protective layer
121: First electrode
122: 3rd Cavity
131: Piezoelectric layer (Part 1)
132: Piezoelectric layer part 2
141: Second electrode
142: Cavity 4
143: Cavity 5
150: Second protective layer

Claims (10)

A substrate including a first cavity;
A first electrode formed on the upper part of the substrate;
A piezoelectric layer formed on one surface of the first electrode; and
Including a second electrode formed on one surface of the above piezoelectric layer,
The first electrode, the piezoelectric layer and the second electrode include an overlap area corresponding to one end and the other end of the first cavity,
One end of the first electrode is terminated in an area outside the overlapping area,
An etched area is formed in which a portion of the piezoelectric layer is removed so as to overlap with the end of the first electrode,
The substrate is formed to further include a second cavity overlapping a portion of the etched area in an imaginary vertical line.
Acoustic resonator. In claim 1,
A third cavity exists between the first electrode and the piezoelectric layer in the region between the overlapping region and the etching region, characterized in that the third cavity extends to a section beyond the second cavity.
Acoustic resonator. In claim 2,
The first electrode is formed to include a raised frame whose thickness increases in an area in contact with the third cavity.
Acoustic resonator. In claim 2,
The piezoelectric layer includes an air bridge region in which the upper and lower surfaces start with an upward slope of a second acute angle (θ ₂ ), the upper surface in contact with the second electrode is interrupted with a downward slope of a third acute angle (θ ₃ ), and the lower surface in contact with the third cavity is interrupted with a downward slope of a first acute angle (θ ₁ ), and is formed to include a rising frame.
Acoustic resonator. In claim 4,
The first acute angle (θ ₁ ), the second acute angle (θ ₂ ) and the third acute angle (θ ₃ ) are formed at 45° or less, and the third acute angle (θ ₃ ) is formed larger than the first acute angle (θ ₁ ).
Acoustic resonator. In claim 4,
The above piezoelectric layer,
Due to the difference between the third acute angle (θ ₃ ) and the first acute angle (θ ₁ ), it becomes thinner and is formed to be interrupted in the etching area.
Acoustic resonator. In claim 2,
The above piezoelectric layer is divided into a first part and a second part with the etching region interposed between them,
The first part is formed on top of the first electrode, and the second part is formed on top of the substrate.
Acoustic resonator. In claim 7,
The second electrode is formed in a V- or U-shape or a shape similar to a V- or U-shape so as to cover the inclined cross-sections of the first part and the second part spaced apart from each other on the etching area.
Acoustic resonator. In claim 8,
The second electrode is formed so that the lowest surface of the V- or U-shaped or similar shape to the V- or U-shaped shape is in contact with the third cavity.
Acoustic resonator. In claim 1,
The first electrode has a cross-section formed with a slope of a first acute angle (θ ₁ ) at a position overlapping the etching area.
Acoustic resonator.

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