TW202007079A - Solidly mounted resonator - Google Patents

Abstract

This invention provides a solidly mounted resonator that includes a substrate, a Bragg reflector disposed on the surface of the substrate, a piezoelectric film deposed on the Bragg reflector, and an electrode unit disposed on the piezoelectric film. The Bragg reflector includes a plurality of high acoustic impedance layers. And the material of the electrode unit is the same of the high acoustic impedance layers. The excited wave of the piezoelectric film is longitudinal wave. This invention also provides a solidly mounted resonator that the material of the electrode unit is different from the high acoustic impedance layers. The excited wave of the piezoelectric film is shear wave.

Description

Solid state microresonator

The invention relates to a resonator, in particular to a solid-state micro resonator.

In recent years, due to the development of wireless communication, more and more attention has been paid to the development of high-frequency acoustic wave resonators. Among them, thin-film bulk acoustic wave resonators have smaller element sizes, lower manufacturing costs, and excellent high Frequency performance and attracted much attention.

Thin film bulk acoustic resonators have two modes of propagation, longitudinal mode and shear mode. Among them, the longitudinal mode is widely used in high-frequency communication components, but it has the problem of energy dissipation when transmitted in liquid, making it less suitable for application. In the biosensor, there is no problem of energy dissipation when the shear mode is transmitted in the liquid. Therefore, if the thin film bulk acoustic resonator is to be used in the biosensor, its propagation mode needs to use pure Shear mode avoids the problem of signal dissipation when propagating in liquid, and has a high Q factor.

The thin film bulk acoustic resonator currently used to excite longitudinal waves mainly uses electrodes (upper electrode and lower electrode) formed on opposite surfaces of the piezoelectric film (hereinafter referred to as vertical electrodes), and controls the upper electrode and the The direction of the lower electrode corresponding to the piezoelectric film is the same as the c-axis direction of the piezoelectric film, and a thin film bulk acoustic resonator capable of exciting longitudinal waves is obtained.

To obtain a thin film bulk acoustic resonator that can excite a shear wave, the current common structure is to use a vertical electrode structure similar to the aforementioned thin film bulk acoustic resonator. The difference lies in that the piezoelectric thin film The c-axis direction is inclined at a specific angle with respect to the upper and lower electrodes, and a thin film bulk acoustic resonator that can excite shear waves is obtained. However, in addition to stimulating shear waves, this structure also excites longitudinal waves, thus reducing the quality factor of such thin film bulk acoustic resonators in liquids; another type of thin film bulk acoustic resonance that can excite shear waves The device uses a coplanar electrode structure, connecting two electrodes on the same surface of the piezoelectric film, thereby obtaining a thin film bulk acoustic resonator that can excite pure shear waves.

As can be seen from the above description, if a thin film bulk acoustic resonator is to excite a pure longitudinal state or a pure shear wave, the structure of the thin film bulk acoustic resonator must be changed to achieve it. In addition, when a thin-film bulk acoustic resonator capable of exciting longitudinal waves is to be fabricated by using a vertical electrode structure, the crystal direction of the piezoelectric thin film needs to be strictly controlled, so that the difficulty of manufacturing the thin-film bulk acoustic resonator is increased.

Therefore, the object of the present invention is to provide a solid-state microresonator whose excitation wave is a longitudinal wave.

Therefore, the solid-state microresonator of the present invention includes a substrate, a Bragg reflector, a piezoelectric film, and an electrode unit.

The Bragg reflector is provided on the surface of the substrate and includes a plurality of high acoustic impedance layers, and a plurality of low acoustic impedance layers stacked alternately with the high acoustic impedance layers, and the acoustic impedance of the low acoustic impedance layers is less than the high acoustic impedance Impedance layer.

The piezoelectric film is provided on the surface of the Bragg reflector away from the substrate.

The electrode unit is disposed on the surface of the piezoelectric film away from the Bragg reflection layer, and includes two ground electrodes spaced along a first direction, and two signal electrodes located between the ground electrodes. The second directions orthogonal to the first direction are arranged at a gap from each other.

Wherein, the electrode unit is selected from the same material as the high acoustic impedance layers, and the piezoelectric film can excite longitudinal waves.

In addition, another object of the present invention is to provide a solid-state microresonator whose excitation wave is a shear wave.

Therefore, the solid-state microresonator of the present invention includes a substrate, a Bragg reflector, a piezoelectric film, and an electrode unit.

The Bragg reflector is provided on the surface of the substrate and includes a plurality of high acoustic impedance layers, and a plurality of low acoustic impedance layers stacked alternately with the high acoustic impedance layers, and the acoustic impedance of the low acoustic impedance layers is less than the high acoustic impedance Impedance layer.

The piezoelectric film is provided on the surface of the Bragg reflector away from the substrate.

The electrode unit is disposed on the surface of the piezoelectric film away from the Bragg reflection layer, and includes two ground electrodes spaced along a first direction, and two signal electrodes located between the ground electrodes. The second direction orthogonal to the first direction is arranged at a gap from each other, the gap is greater than 20 microns, and the ratio of the length of the gap to the length of the piezoelectric film along the second direction is greater than 1:50.

Wherein, the electrode unit is selected from materials different from the high acoustic impedance layers, and the piezoelectric film can excite the shear wave.

The effect of the present invention lies in that: by controlling the materials of the electrode unit and the high acoustic impedance layers, the solid microresonators with the same structure can be used to obtain the characteristics that can excite pure shear waves and pure longitudinal waves, respectively. The conventional thin film bulk acoustic resonator, the solid-state micro-resonator is more widely used, and is simple to manufacture and easy to implement.

Before the present invention is described in detail, it should be noted that in the following description, similar elements are denoted by the same numbers. In addition, the drawings of the present invention are schematic diagrams, and the dimensions between the elements are not drawn to scale.

1 and 2, a first embodiment of the solid-state microresonator of the present invention includes a substrate 2, a Bragg reflector 3 disposed on the substrate 2, and a piezoelectric film 4 disposed on the Bragg reflector 3, And an electrode unit 5 provided on the piezoelectric film 4.

In detail, the Bragg reflector 3 is provided on the surface of the substrate 2 and includes a plurality of high acoustic impedance layers 31, and a plurality of low acoustic impedance layers 32 stacked alternately with the high acoustic impedance layers 31, and the high acoustic impedances The acoustic impedance of layer 31 is greater than these low acoustic impedance layers 32. The material of the high acoustic impedance layer 31 may be selected from aluminum, tungsten, nickel, or molybdenum, and the material of the low acoustic impedance layer 32 may be selected from silicon dioxide, aluminum, titanium, or silicon.

Preferably, the thicknesses of the high-acoustic impedance layers 31 and the low-acoustic impedance layers 32 meet the quarter-wavelength condition, and accordingly, the sound waves are in the high-acoustic impedance layers 31 and the low-acoustic impedance layers 32 After being transmitted and reflected at the interface between the impedance layers, constructive interference can be generated with a large reflectivity, which makes the first embodiment have a better frequency response.

It should be noted that the number of layers of the high acoustic impedance layers 31 and the low acoustic impedance layers 32 is not limited, when the number of layers of the high acoustic impedance layers 31 and the low acoustic impedance layers 32 is greater , Can improve the sound wave reflection ability of the Bragg reflector 3, and make the resonance response of the solid-state micro-resonator rise, but when there are too many layers of the high acoustic impedance layer 31 and the low acoustic impedance layer 32, it will cause the The roughness of the interface between the constant high acoustic impedance layer 31 and the low acoustic impedance layer 32 increases, so that the resonance response of the solid-state microresonator decreases. Preferably, controlling the interface roughness of the high-acoustic impedance layer 31 and the low-acoustic impedance layer 32 to be not greater than 10 nanometers may enable the solid-state microresonator to have a better resonance response, in the first embodiment In the example, the number of layers of the high-acoustic impedance layer 31 and the low-acoustic impedance layer 32 is four as an example, but the actual implementation is not limited to this.

In addition, it should be further explained that the Bragg reflector 3 serves as an acoustic wave reflector, and the impedance layer connected to the piezoelectric film 4 may be the high acoustic impedance layer 31 or the low acoustic impedance layer 32, and there is no certain limit. Both can achieve the purpose of sound wave reflection. In the first embodiment, the low acoustic impedance layer 32 is connected to the piezoelectric film 4 to further reduce the noise of the solid-state micro resonator and improve the quality factor.

The piezoelectric film 4 is disposed on the surface of the Bragg reflector 3 away from the substrate 2.

Specifically, the material of the piezoelectric film 4 may be selected from zinc oxide, aluminum nitride, magnesium-doped zinc oxide, barium titanate, or lead zirconate titanate and other materials that can generate a piezoelectric effect.

It should be noted that the thickness of the piezoelectric film 4 can be determined according to the characteristics and requirements of the device, and meets the condition of the half wavelength or the condition of the quarter wavelength. When the thickness of the piezoelectric film 4 meets the half wavelength Under conditions, the effective electromechanical coupling coefficient (Effective Electromechanical Coupling Coefficient) of the solid-state microresonator will be larger than that of the solid-state microresonator whose thickness of the piezoelectric film 4 meets the quarter-wavelength condition, and has a larger bandwidth; When the thickness of the piezoelectric film 4 meets the quarter-wavelength condition, the stress of the piezoelectric film 4 is small and it is not easy to break, so that the solid-state microresonator has better yield and the required process time is shorter , Can improve the yield of the solid-state microresonator. In the first embodiment, the thickness of the piezoelectric film 4 is exemplified by satisfying the half-wavelength condition.

In addition, it should be re-explained that the c-axis direction of the piezoelectric film 4 can be the same as the normal direction of the connection surface of the piezoelectric film 4 and the electrode unit 5, or relative to the piezoelectric film 4 and the electrode unit 5 The normal direction of the connection surface is inclined at an angle, and there is no limit. For example, the angle of inclination can range from 20 to 90 degrees. Compared with the conventional film bulk acoustic resonator that can excite the shear mode, it is splashed with an inclination method. The piezoelectric layer is coated, and the bulk acoustic resonator of the coplanar electrode is a vertically sputtered piezoelectric layer or an obliquely sputtered piezoelectric layer. In this embodiment, the c-axis direction of the piezoelectric film 4 does not affect the solid-state micro resonance Excitation wave pattern.

The electrode unit 5 is disposed on the surface of the piezoelectric film 4 away from the Bragg reflector 3. The material is selected from the same materials as the high acoustic impedance layers 31, and includes two ground electrodes 51 spaced along a first direction X , And two signal electrodes 52 located between the ground electrodes 51, and the signal electrodes 52 are spaced apart from each other along a second direction Y orthogonal to the first direction X with a gap d.

In detail, each signal electrode 52 has an electrode portion 521 adjacent to the other signal electrode 52, and an extension portion 522 extending from the electrode portion 521 toward the opposite signal electrode 52. Using the two signal electrodes 52 to apply a voltage to the piezoelectric film 4, longitudinal waves can be excited, and a solid-state microresonator with longitudinal modes can be obtained.

It should be noted that the size of the electrode portion 521 and the extension portion 522 of the signal electrodes 52, the size of the gap d, and the size of the ground electrodes 51 are adjustable according to the size of the piezoelectric film 4, There is no certain limitation, as long as the sound waves can be excited between the signal electrodes 52, however, when the gap d is too large, the transmission distance of the sound waves excited by the signal electrodes 52 will be too long, and there is a problem of energy dissipation. ; When the gap d is too small, it will cause the direction of the electric field between the signal electrodes 52 is not uniform, and noise is likely to occur, therefore, preferably, the gap d and the piezoelectric film 4 along the second direction Y The ratio of the length is between 1:50 and 1:4. For example, if the length of the piezoelectric film 4 along the first direction X and the second direction Y is 1000×1000 microns, then the gap d is between 20 and 250 microns can make the solid-state microresonator generate less acoustic noise, and the energy is not easy to dissipate, so it has a high quality factor.

In some embodiments, when the length of the piezoelectric film 4 along the first direction X and the second direction Y is 1000×1000 μm, the length L of the electrode portions 521 along the first direction X is between 300 Up to 500 microns, the width W along the second direction Y is between 20 and 250 microns, and the distance d between the electrode portions 521 is between 20 and 250 microns, accordingly, when an electric field is applied to the signal electrodes At 52 o'clock, the electric field distribution density between the electrode portions 521 is relatively uniform and the direction is consistent, so that the first embodiment has a better frequency response, and thus a better quality factor.

In addition, it should be noted that the shapes of the ground electrodes 51 and the electrode portions 521 are not particularly limited. For example, the ground electrodes 51 and the electrode portions 521 may extend linearly or in an arc shape. The ground electrode 51 may be rectangular, elliptical, or polygonal, and the electrode portions 521 may be rectangular, circular, or polygonal. In the first embodiment, the ground electrodes 51 and the electrode portions 521 are described by taking rectangles as an example, which can avoid generating additional electric fields and make the electric field distribution between the electrode portions 521 more uniform, making the first One embodiment has lower noise.

By controlling the material of the electrode unit 5 and the materials of the high acoustic impedance layers 31, the solid-state microresonator of the present invention can use longitudinal excitation of the coplanar electrode to excite longitudinal waves, which is more common than conventional ones. 1. The lower electrode and the c-axis direction of the piezoelectric film excite longitudinal waves. The solid-state microresonator has a simple manufacturing process and a high frequency response, which is beneficial to mass production and is used in communication components.

1 and 2, the structure of the second embodiment of the solid-state microresonator of the present invention is substantially the same as that of the first embodiment, except that the material of the electrode unit 5 is different from those of the high acoustic impedance 31, And the gap d of the signal electrodes 52 is greater than 20 microns, and the ratio of the length of the gap d to the length of the piezoelectric film 4 along the second direction Y is greater than 1:50.

By controlling the material of the electrode unit 5 to be different from the high acoustic wave impedance layers 31, and making the gap d of the signal electrodes 52 greater than 20 microns, and controlling the ratio of the gap d to the side length of the piezoelectric film 4 If it is greater than 1:50, the solid-state microresonator with coplanar electrodes can be used to excite the shear wave, and the frequency response is large, which can be applied to the liquid sensor.

To further explain, when the length of the piezoelectric film 4 in the first embodiment along the second direction Y is 1000 μm, controlling the gap d between 20 and 50 μm can make the first embodiment The excitation wave of is a pure longitudinal wave. When the gap d of the first embodiment is further controlled to be between 40 and 50 microns, the frequency response of the excited pure longitudinal wave can reach 30dB; when the piezoelectric film of the second embodiment 4 When the length in the second direction Y is 1000 μm, controlling the gap d to be between 40 and 50 μm can make the excitation wave of the second embodiment pure shear wave, and the frequency of the pure shear wave excited The response can reach 20dB, showing that the solid-state microresonator can excite pure longitudinal waves or pure shear by controlling the materials of the high acoustic impedance layer 31 and the electrode unit 5 and the gap d of the signal electrodes 52 Wave, and the frequency response is high and can be applied to different components.

The following describes the excitation wave characteristics of the solid-state microresonator of the present invention with specific examples 1-8.

Specific example 1

The element structure of this specific example 1 is the same as that of the first embodiment, that is, the solid micro-resonator of the electrode unit 5 and the material of the high acoustic impedance layer 31 are the same, wherein the resonance frequency is set to 2.5 GHz, and the substrate The material of 2 is silicon, the material of each high acoustic impedance layer 31 is molybdenum, the thickness is 0.629 microns, the material of each low acoustic impedance layer 32 is silicon dioxide, and the thickness is 0.52 microns, the material of the piezoelectric film 4 is Zinc oxide, with a thickness of 1.268 μm, and a side length in the first direction X and the second direction Y of 1000×1000 μm, the material of the electrode unit 5 is molybdenum, and the length L of the electrode portions 521 is 150 μm The width W is 20 microns, and the gap d is 20 microns.

Specific examples 2~4

The element structures and materials of the specific examples 2 to 4 are substantially the same as those of the specific example 1, except that the gaps d of the specific examples 2 to 4 are 30 μm, 40 μm, and 50 μm, respectively, and the electrodes The width W of the portion 521 is 30 microns, 40 microns, and 50 microns, respectively.

Specific examples 5~8

The element structure of the specific examples 5 to 8 is the same as that of the second embodiment, that is, the solid-state microresonator of which the material of the electrode unit 5 and the material of the high acoustic impedance layers 31 are different, wherein the substrate 2 and the Bragg reflection The material, thickness and side length of the device 3 and the piezoelectric film 4 are the same as those of the specific example 1, and the material of the electrode unit 5 is selected from aluminum, and the gap d of the specific examples 5-8 is 20 microns, 30 micrometers, 40 micrometers, and 50 micrometers, the width W of the electrode portions 521 is 20 micrometers, 30 micrometers, 40 micrometers, and 50 micrometers, respectively.

Referring to FIGS. 3 to 6, FIGS. 3 to 6 are the frequency response results of the specific examples 1 to 4 when the resonance frequency is set to 2.5 GHz. It can be seen from FIGS. 3 to 6 that when the gap d is between 20 and 50 μm, the solid-state microresonator can excite pure longitudinal waves, and when the gap d is between 40 and 50 μm, the solid-state microresonator’s The frequency response can reach more than 30dB, showing that by controlling the material of the electrode unit 5 to be the same as the high acoustic impedance layers 31, the solid-state microresonator can indeed excite longitudinal waves, and further control the gap d between 20 to At 50 microns, a pure longitudinal wave with a high frequency response is obtained. In addition, when the gap d of the signal electrodes 52 is between 40 and 50 microns, the solid-state microresonator can obtain a pure longitudinal wave with a frequency response of 30 dB.

7 to 10, FIG. 7 to FIG. 10 are the frequency response results of the specific examples 5 to 8 when the resonance frequency is set to 2.5 GHz. As can be seen from FIGS. 7 to 10, when the gap d is greater than 20 and not greater than 50 microns, the solid-state microresonator can excite a shear wave. Preferably, when the gap d is between 40 and 50 microns, the solid-state micro The resonator can excite pure shear waves, and the frequency response can reach more than 20dB, showing that by controlling the material of the electrode unit 5 is different from the high acoustic impedance layers 31, and the gap d is greater than 20 and not greater than 250 microns It is true that the solid-state microresonator can excite a shear wave with a high frequency response, and when the gap d of the signal electrodes 52 is further controlled, a pure shear wave with a high frequency response can be obtained.

It should be noted that the applicable resonant frequency of the solid-state microresonator is not limited, and it can be high frequency or low frequency, which can cause the solid-state microresonator to excite longitudinal waves or shear waves. In the above specific examples 1~8 In this example, the resonant frequency is 2.5 GHz as an example, but the actual implementation is not limited to this.

In summary, by controlling the material of the electrode unit 5 and the high acoustic impedance layer 31 to be the same or different, the solid-state microresonator of the present invention can cause the solid-state microresonator of the same structure to excite shear waves or longitudinal waves , And further cooperate with the control of the gap d of the signal electrodes 52, a solid-state microresonator with high frequency response and exciting pure shear wave or pure longitudinal wave can be further obtained, making the solid-state microresonator more widely used. And the process is simple and easy to implement, so it can indeed achieve the purpose of cost invention.

However, the above are only examples of the present invention, and should not be used to limit the scope of the present invention. Any simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the patent specification are still classified as This invention covers the patent.

2‧‧‧Substrate 521‧‧‧ Electrode part 3‧‧‧ Bragg reflector 522‧‧‧Extended part 31‧‧‧High acoustic impedance layer d‧‧‧Gap 32‧‧‧Low acoustic impedance layer W‧‧‧Width 4‧‧‧ Piezoelectric film L‧‧‧Length 5‧‧‧ Electrode unit X‧‧‧ First direction 51‧‧‧Ground electrode Y‧‧‧Second direction 52‧‧‧Signal electrode

Other features and functions of the present invention will be clearly presented in the embodiment with reference to the drawings, in which: FIG. 1 is a perspective view illustrating a first embodiment of the solid-state micro resonator of the present invention; FIG. 2 is a top view, The first embodiment will be described; FIG. 3 is a frequency response vs. frequency diagram illustrating the frequency response result of the signal electrode gap d of this specific example 1 being 20 microns; FIG. 4 is a frequency response vs. frequency diagram illustrating the specific The frequency response of the signal electrode gap d of Example 2 is 30 microns; FIG. 5 is a frequency response versus frequency diagram illustrating the frequency response of the signal electrode gap d of this specific example 3 is 40 microns; FIG. 6 is a frequency response For the frequency relationship diagram, the frequency response result of the signal electrode gap d of this specific example 4 is 50 μm; FIG. 7 is a frequency response vs. frequency diagram, illustrating the frequency response of the signal electrode gap d of this specific example 5 is 20 μm Results; FIG. 8 is a frequency response vs. frequency diagram illustrating the frequency response result of the signal electrode gap d of this specific example 6 is 30 μm; FIG. 9 is a frequency response vs. frequency diagram illustrating the signal electrode of the specific example 7 The gap d is a frequency response result of 40 microns; and FIG. 10 is a frequency response vs. frequency diagram illustrating the frequency response result of the signal electrode gap d of this specific example 8 is 50 microns.

2‧‧‧ substrate

3‧‧‧ Prague reflector

31‧‧‧High acoustic impedance layer

32‧‧‧Low acoustic impedance layer

4‧‧‧ Piezo film

5‧‧‧Electrode unit

51‧‧‧Ground electrode

52‧‧‧Signal electrode

Claims (11)

A solid-state microresonator, comprising: a substrate; a Bragg reflector provided on the surface of the substrate, including a plurality of high acoustic impedance layers, and a plurality of low acoustic impedance layers stacked alternately with the high acoustic impedance layers, and these The acoustic impedance of the high acoustic impedance layer is greater than the low acoustic impedance layers; a piezoelectric film is provided on the surface of the Bragg reflector away from the substrate; and an electrode unit is provided on the surface of the piezoelectric film away from the Bragg reflector , Including two ground electrodes spaced apart along a first direction, and two signal electrodes located between the ground electrodes, and the signal electrodes are spaced apart from each other along a second direction orthogonal to the first direction Setting; wherein, the electrode unit is selected from the same material as the high acoustic impedance layers, and can cause the piezoelectric film to excite longitudinal waves. The solid-state microresonator according to claim 1, wherein materials of the electrode unit and the high acoustic impedance layers are selected from aluminum, tungsten, nickel or molybdenum. The solid-state microresonator according to claim 1, wherein the ratio of the gap length of the two signal electrodes to the length of the piezoelectric film in the second direction is between 1:50 and 1:4. A solid-state microresonator, comprising: a substrate; a Bragg reflector provided on the surface of the substrate, including a plurality of high acoustic impedance layers, and a plurality of low acoustic impedance layers stacked alternately with the high acoustic impedance layers, and these The acoustic impedance of the high acoustic impedance layer is greater than the low acoustic impedance layers; a piezoelectric film is provided on the surface of the Bragg reflector away from the substrate; and an electrode unit is provided on the surface of the piezoelectric film away from the Bragg reflector , Including two ground electrodes spaced along a first direction, and two signal electrodes located between the ground electrodes, the signal electrodes are spaced apart from each other along a second direction orthogonal to the first direction , The gap is greater than 20 microns, and the ratio of the length of the gap to the length of the piezoelectric film along the second direction is greater than 1:50; wherein, the electrode unit is selected from materials different from the high acoustic impedance layers, and The piezoelectric film can excite the shear wave. The solid-state microresonator according to claim 4, wherein materials of the electrode unit and the high acoustic impedance layers are selected from aluminum, tungsten, nickel, or molybdenum, respectively. The solid-state microresonator according to claim 4, wherein the gap between the two signal electrodes is greater than 20 and not greater than 250 microns. The solid-state microresonator according to claim 4, wherein the gap between the two signal electrodes is greater than 20 and not greater than 50 microns. The solid-state microresonator according to claim 1 or claim 4, wherein each signal electrode has an electrode portion adjacent to the other signal electrode, and an extension extending from the electrode portion in the direction opposite to the other signal electrode unit. The solid-state microresonator according to claim 8, wherein the length of the electrode portions in the first direction is between 300 and 500 microns, and the width in the second direction is between 20 and 250 microns. The solid-state microresonator according to claim 1 or claim 4, wherein the material of the low acoustic impedance layer is selected from silicon dioxide, aluminum, titanium, or silicon, and the material of the piezoelectric film is selected from Zinc oxide, aluminum nitride, magnesium-doped zinc oxide, barium titanate, or lead zirconate titanate. The solid-state microresonator according to claim 1 or claim 4, wherein the thicknesses of the high acoustic impedance layers and the low acoustic impedance layers meet the quarter-wavelength condition, and the thickness of the piezoelectric film conforms to two Condition of quarter wavelength or quarter wavelength.

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