CN113890501B

CN113890501B - Method for forming surface acoustic wave resonance device

Info

Publication number: CN113890501B
Application number: CN202111449046.8A
Authority: CN
Inventors: 王斌; 李军涛; 韩兴; 周建
Original assignee: Changzhou Chengxin Semiconductor Co Ltd
Current assignee: Changzhou Chengxin Semiconductor Co Ltd
Priority date: 2021-12-01
Filing date: 2021-12-01
Publication date: 2022-04-26
Anticipated expiration: 2041-12-01
Also published as: CN113890501A

Abstract

The embodiment of the invention provides a method for forming a surface acoustic wave resonance device, which comprises the following steps: forming a first portion comprising: providing a piezoelectric pretreatment layer; forming a defect layer in the piezoelectric pretreatment layer; providing a first substrate; bonding the piezoelectric pretreatment layer and the first substrate; forming a piezoelectric layer based on the defect layer, wherein the piezoelectric layer comprises a first side and a second side opposite to the first side, and the first substrate is positioned on the first side; forming a second portion comprising: providing a second substrate; joining the first portion and the second portion, the second portion being on the second side; removing the first substrate; and forming an electrode layer on the first side contacting the piezoelectric layer. In the method, the ratio of the difference between the first thermal expansion coefficient of the piezoelectric pretreatment layer material and the second thermal expansion coefficient of the first substrate material to the second thermal expansion coefficient is less than 5%, and when the piezoelectric layer with better crystal quality is formed by adopting a high-temperature separation and high-temperature annealing mode, the condition of fracture can be reduced, and the yield of products is improved.

Description

Method for forming surface acoustic wave resonance device

Technical Field

The invention relates to the technical field of semiconductors, in particular to a method for forming a surface acoustic wave resonance device.

Background

A Radio Frequency (RF) front-end chip of a wireless communication device includes a power amplifier, an antenna switch, a Radio Frequency filter, a multiplexer including a duplexer, a low noise amplifier, and the like. The rf filter includes a piezoelectric Acoustic Surface Wave (SAW) filter, a Bulk Acoustic Wave (BAW) filter, a Micro-Electro-Mechanical System (MEMS) filter, an Integrated Passive Devices (IPD) filter, and the like.

The quality factor value (Q value) of the SAW resonator is high, and the SAW resonator is made into a radio frequency filter with low insertion loss and high out-of-band rejection, that is, a SAW filter, which is a mainstream radio frequency filter used in wireless communication equipment such as mobile phones and base stations at present. Where the Q value is the quality factor value of the resonator, defined as the center frequency divided by the 3dB bandwidth of the resonator. The frequency of use of the SAW filter is typically 0.4GHz to 2.7 GHz.

The SAW resonator has the characteristic that the frequency drifts along with the working temperature, and in order to meet the requirements of a 5G radio frequency terminal on a filter, the frequency band of which is crowded, the SAW resonator needs to have higher frequency-temperature stability. The frequency-Temperature stability of the Temperature Compensation (TC) type SAW (TCSAW) resonator is higher than that of the common SAW resonator, and in addition, the Q value of the TC-SAW resonator can also be higher than that of the SAW resonator.

Fig. 1 shows a TC-SAW resonator device 100 including: a substrate 110; a temperature compensation layer 130 on the substrate 110; a piezoelectric layer 150 disposed on the temperature compensation layer 130, the piezoelectric layer 150 including a first side 151 and a second side 153 opposite to the first side, the temperature compensation layer 130 being disposed on the first side 151; and an electrode layer 170 on the second side 153 and on the piezoelectric layer 150, wherein the electrode layer 170 includes but is not limited to an Inter Digital Transducer (IDT), the IDT includes a plurality of electrode strips 171 and a plurality of electrode strips 173, the electrode strips 171 and the electrode strips 173 have different polarities, and the electrode strips 171 and the electrode strips 173 are alternately disposed. It should be noted that the Temperature compensation layer and the piezoelectric layer of the TC-SAW resonator have opposite Temperature Frequency shift characteristics, so that the Temperature Coefficient of Frequency (TCF) of the TC-SAW resonator can be adjusted to be 0 ppm/deg.c.

The method of forming the TC-SAW resonating device 100 includes: the piezoelectric layer 150 with good crystal quality is formed by high-temperature separation and high-temperature annealing, however, the thermal expansion coefficients of the material of the piezoelectric layer 150 and the material of the substrate 110 are mismatched, so that the piezoelectric layer is easily broken during high-temperature processing, thereby reducing the product yield. Note that the mismatch in the thermal expansion coefficients means that the ratio of the difference between the thermal expansion coefficient of the material of the piezoelectric layer 150 and the thermal expansion coefficient of the material of the base 110 to the thermal expansion coefficient of the material of the base 110 is greater than 5%.

Disclosure of Invention

The invention aims to provide a method for forming a surface acoustic wave resonance device, which can reduce the situation of fracture and improve the yield of products.

To solve the above problem, an embodiment of the present invention provides a method for forming a surface acoustic wave resonator device, including: forming a first portion, the forming the first portion comprising: providing a piezoelectric pretreatment layer; forming a defect layer in the piezoelectric pretreatment layer; providing a first substrate; bonding the piezoelectric pretreatment layer to the first substrate; forming a piezoelectric layer based on the defective layer, the piezoelectric layer including a first side and a second side opposite to the first side, the first substrate being located at the first side; forming a second portion, the forming the second portion comprising: providing a second substrate; joining the first portion and the second portion, the second portion being located on the second side; removing the first substrate; and forming an electrode layer on the first side contacting the piezoelectric layer.

In some embodiments, a ratio of a difference between a first coefficient of thermal expansion of a material of the piezoelectric pretreatment layer and a second coefficient of thermal expansion of a material of the first substrate to the second coefficient of thermal expansion is less than 5%.

In some embodiments, the material of the first substrate comprises at least one of: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In some embodiments, the material of the first substrate is the same as the material of the piezoelectric pretreatment layer.

In some embodiments, forming a defect layer in the piezoelectric pretreatment layer comprises: and injecting at least one type of particles into the piezoelectric pretreatment layer, wherein the at least one type of particles form the defect layer after entering the piezoelectric pretreatment layer.

In some embodiments, bonding the piezoelectric pretreatment layer to the first substrate comprises: forming a first intermediate layer between the first substrate and the piezoelectric pretreatment layer at least for bonding the first substrate and the piezoelectric pretreatment layer. In some embodiments, the material of the first intermediate layer comprises at least one of: metal, polymer, insulating dielectric, polysilicon.

In some embodiments, the thickness of the first intermediate layer comprises: 0.2 to 1 micron. In some embodiments, the thickness of the first intermediate layer comprises: 1 micron to 10 microns.

In some embodiments, a first sub-layer and a second sub-layer are further formed in the piezoelectric pretreatment layer and located on two sides of the defect layer, respectively, wherein the thickness of the first sub-layer is greater than that of the second sub-layer.

In some embodiments, forming a piezoelectric layer based on the defective layer includes: removing the first sublayer; and repairing the defect layer. In some embodiments, removing the first sub-layer comprises: and separating the first sub-layer at a high temperature, wherein the high temperature is 250-1000 ℃. In some embodiments, repairing the defective layer comprises: and annealing the defect layer at a high temperature, wherein the high temperature is 250-1000 ℃.

In some embodiments, joining the first portion and the second portion comprises: under the normal atmospheric temperature condition, form the second intermediate level, be located the second base with between the piezoelectric layer, be used for the bonding at least the second base with the piezoelectric layer, wherein, normal atmospheric temperature means 25 degrees centigrade to 250 degrees centigrade. In some embodiments, the material of the second intermediate layer comprises at least one of: polymer, insulating dielectric, polysilicon.

In some embodiments, removing the first substrate comprises: and polishing the first substrate or etching the first substrate. In some embodiments, the method further comprises: and removing the first intermediate layer after removing the first substrate.

In some embodiments, said forming the first portion further comprises: forming a first bonding layer on the second side. In some embodiments, said forming the second portion further comprises: and forming a second bonding layer on one side of the second substrate. In some embodiments, joining the first portion and the second portion comprises: and bonding the first bonding layer and the second bonding layer at normal temperature to form a third intermediate layer, wherein the third intermediate layer is positioned between the second substrate and the piezoelectric layer and is at least used for bonding the second substrate and the piezoelectric layer, and the normal temperature is 25-250 ℃. In some embodiments, the material of the third intermediate layer comprises at least one of: polymer, insulating dielectric, polysilicon.

In some embodiments, said forming the first portion further comprises: and before the piezoelectric pretreatment layer and the first substrate are jointed, an isolation layer is formed, is positioned on one side of the first substrate, covers the first substrate and is at least used for shielding an etching agent to protect the piezoelectric layer. In some embodiments, the material of the isolation layer comprises at least one of: silicon oxide, silicon nitride, aluminum oxide, metal.

In some embodiments, bonding the piezoelectric pretreatment layer to the first substrate comprises: forming a fourth intermediate layer between the piezoelectric pretreatment layer and the isolation layer for at least bonding the isolation layer and the piezoelectric pretreatment layer, the fourth intermediate layer and the first substrate being respectively located on both sides of the isolation layer. In some embodiments, the material of the fourth intermediate layer comprises at least one of: polymer, insulating dielectric, polysilicon, metal. In some embodiments, the thickness of the fourth intermediate layer comprises: 0.2 to 1 micron. In some embodiments, the method further comprises: removing the isolation layer after removing the first substrate; and removing the fourth intermediate layer after removing the isolation layer.

It should be noted that the ratio of the difference between the first thermal expansion coefficient of the piezoelectric layer material and the second thermal expansion coefficient of the transition base material to the second thermal expansion coefficient is less than 5%, so that when the piezoelectric layer with good crystal quality is formed by adopting a high-temperature separation and high-temperature annealing mode, the occurrence of fracture can be reduced, and the yield of products can be improved.

Drawings

FIG. 1 is a schematic diagram of a cross-section A of a TC-SAW resonator device 100;

FIG. 2 is a schematic flow chart diagram of a method 200 of forming a surface acoustic wave resonator device in accordance with an embodiment of the present invention;

FIGS. 3 to 10 are schematic structural views of a cross section A of a method of forming a surface acoustic wave resonator device according to an embodiment of the present invention;

fig. 11 to 18 are schematic sectional a structures of a method of forming a surface acoustic wave resonator device according to an embodiment of the present invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.

As described in the background section, a method of forming a TC-SAW resonant device includes: the piezoelectric layer with better crystal quality is formed by high-temperature separation and high-temperature annealing, however, the thermal expansion coefficients of the piezoelectric layer material and the substrate material are mismatched, so that the piezoelectric layer is easy to break during high-temperature treatment, and the product yield is reduced.

The inventor of the invention finds that the ratio of the difference between the first thermal expansion coefficient of the piezoelectric layer material and the second thermal expansion coefficient of the transition substrate material to the second thermal expansion coefficient is less than 5%, and when the piezoelectric layer with better crystal quality is formed by adopting a high-temperature separation and high-temperature annealing mode, the occurrence of fracture can be reduced, and the yield of products can be improved.

The embodiment of the invention provides a method for forming a surface acoustic wave resonance device, which comprises the following steps:

step S201, forming a first portion, the forming the first portion including:

providing a piezoelectric pretreatment layer;

forming a defect layer in the piezoelectric pretreatment layer;

providing a first substrate;

bonding the piezoelectric pretreatment layer to the first substrate;

forming a piezoelectric layer based on the defective layer, the piezoelectric layer including a first side and a second side opposite to the first side, the first substrate being located at the first side;

step S203 of forming a second portion, the forming the second portion including: providing a second substrate;

step S205 of joining the first portion and the second portion, the second portion being located on the second side;

step S207, removing the first substrate; and

step S209, forming an electrode layer on the first side, contacting the piezoelectric layer.

In this embodiment, a ratio of a difference between a first thermal expansion coefficient of a material of the piezoelectric pretreatment layer and a second thermal expansion coefficient of a material of the first substrate to the second thermal expansion coefficient is less than 5%.

In this embodiment, in step S201, the forming a defect layer in the piezoelectric pretreatment layer includes: implanting at least one type of particles (e.g., helium ions, beryllium ions, oxygen ions) into the piezoelectric pretreatment layer, the at least one type of particles forming the defect layer upon entering the piezoelectric pretreatment layer.

In this embodiment, in step S201, the forming a defect layer in the piezoelectric pretreatment layer further includes: and forming a first sublayer and a second sublayer in the piezoelectric pretreatment layer, wherein the first sublayer and the second sublayer are respectively positioned on two sides of the defect layer, and the thickness of the first sublayer is greater than that of the second sublayer.

In this embodiment, in step S201, the bonding the piezoelectric pretreatment layer and the first substrate includes: forming a first intermediate layer between the first substrate and the piezoelectric pretreatment layer at least for bonding the first substrate and the piezoelectric pretreatment layer. In this embodiment, the material of the first intermediate layer includes at least one of: metal, polymer, insulating dielectric, polysilicon. In this embodiment, the first intermediate layer and the defect layer are respectively located on two sides of the second sublayer.

In some embodiments, the thickness of the first intermediate layer comprises: 0.2 to 1 micron. Note that, in these embodiments, the material of the first intermediate layer is less affected by an etchant (e.g., hydrofluoric acid, hydrochloric acid, tetramethylammonium hydroxide, potassium hydroxide).

In other embodiments, the thickness of the first intermediate layer comprises: 1 micron to 10 microns. Note that, in these embodiments, the material of the first intermediate layer is greatly affected by an etchant (e.g., hydrofluoric acid, hydrochloric acid, tetramethylammonium hydroxide, potassium hydroxide).

In this embodiment, in step S201, forming a piezoelectric layer based on the defective layer includes: removing the first sublayer; and repairing the defect layer. In this embodiment, removing the first sub-layer includes: and separating the first sub-layer at a high temperature, wherein the high temperature is 250-1000 ℃. In this embodiment, repairing the defective layer includes: and annealing the defect layer at a high temperature, wherein the high temperature is 250-1000 ℃. In other embodiments, step S201 further comprises: planarizing the piezoelectric layer.

It should be noted that, the ratio of the difference between the first thermal expansion coefficient of the piezoelectric layer material and the second thermal expansion coefficient of the transition base material to the second thermal expansion coefficient is less than 5%, and when the piezoelectric layer with good crystal quality is formed by adopting a high-temperature separation and high-temperature annealing mode, the occurrence of fracture can be reduced, and the yield of products can be improved.

In this embodiment, step S205 includes: under the normal atmospheric temperature condition, form the second intermediate level, be located the second side, be located the second base with between the piezoelectric layer, be used for the joint at least the second base with the piezoelectric layer, wherein, normal atmospheric temperature means 25 degrees centigrade to 250 degrees centigrade. In this embodiment, the material of the second intermediate layer includes at least one of: polymer, insulating dielectric, polysilicon. It should be noted that the acoustic impedance of the second intermediate layer is different from the acoustic impedance of the piezoelectric layer, so that leakage waves can be blocked.

In this embodiment, step S207 includes: and polishing the first substrate or etching the first substrate. It should be noted that, when the first substrate is wet-etched, the first intermediate layer can shield the piezoelectric layer from being corroded by the etchant.

In this embodiment, the method for forming the surface acoustic wave resonator further includes: after step S207, the first intermediate layer is removed.

In this embodiment, step S209 includes: forming an interdigital transducer device. In this embodiment, the forming the interdigital transducer device includes: forming a plurality of first electrode stripes; forming a plurality of second electrode stripes; wherein the polarities of the plurality of first electrode stripes and the plurality of second electrode stripes are different; wherein the first electrode stripes and the second electrode stripes are alternately arranged.

The embodiment of the invention also provides a method for forming the surface acoustic wave resonance device, which comprises the following steps:

step S201, forming a first portion, the forming the first portion including:

providing a piezoelectric pretreatment layer;

forming a defect layer in the piezoelectric pretreatment layer;

providing a first substrate;

bonding the piezoelectric pretreatment layer to the first substrate;

step S207, removing the first substrate; and

In this embodiment, step S201 further includes: forming a first bonding layer on the second side.

In this embodiment, step S203 further includes: and forming a second bonding layer on one side of the second substrate.

In this embodiment, step S205 includes: and bonding the first bonding layer and the second bonding layer at normal temperature to form a second intermediate layer, wherein the second intermediate layer is positioned between the second substrate and the piezoelectric layer and is at least used for bonding the second substrate and the piezoelectric layer, and the normal temperature is 25-250 ℃. In this embodiment, the material of the second intermediate layer includes at least one of: polymer, insulating dielectric, polysilicon. It should be noted that the acoustic impedance of the second intermediate layer is different from the acoustic impedance of the piezoelectric layer, so that leakage waves can be blocked.

step S201, forming a first portion, the forming the first portion including:

providing a piezoelectric pretreatment layer;

forming a defect layer in the piezoelectric pretreatment layer;

providing a first substrate;

bonding the piezoelectric pretreatment layer to the first substrate;

step S207, removing the first substrate; and

In this embodiment, step S201 further includes: an isolation layer is formed on one side of the first substrate for protecting the piezoelectric layer from damage by subsequent processes (e.g., etching, polishing). In this embodiment, the material of the isolation layer includes at least one of: silicon oxide, silicon nitride, aluminum oxide, metal.

In this embodiment, in step S201, the bonding the piezoelectric pretreatment layer and the first substrate includes: forming a first intermediate layer between the isolation layer and the piezoelectric pretreatment layer at least for bonding the isolation layer and the piezoelectric pretreatment layer, the first intermediate layer and the first substrate being respectively located on both sides of the isolation layer. In this embodiment, the material of the first intermediate layer includes at least one of: metal, polymer, insulating dielectric, polysilicon. In this embodiment, the thickness of the first intermediate layer includes: 0.2 to 1 micron.

In this embodiment, step S207 includes: and polishing the first substrate or etching the first substrate. It should be noted that, when the first substrate is wet etched, the isolation layer may shield a first etchant used for etching the first substrate, so as to better protect the first intermediate layer and the piezoelectric layer.

In this embodiment, the method for forming the surface acoustic wave resonator further includes: after step S207, the isolation layer is removed. It should be noted that, when the isolation layer is etched, the first intermediate layer is also used for shielding a second etchant used for etching the isolation layer from corroding the piezoelectric layer.

In this embodiment, the method for forming the surface acoustic wave resonator further includes: and removing the first intermediate layer after removing the isolation layer.

In connection with the schematic cross-sectional structure diagram of the surface acoustic wave resonator device, the following two specific methods for forming the surface acoustic wave resonator device are provided in the embodiments of the present invention to facilitate better understanding of the present invention, but the present invention may also be implemented in other ways different from the following embodiments, and therefore the present invention is not limited to the specific embodiments disclosed below.

Fig. 3 to 10 are schematic structural views of a cross section a of a method of forming a Surface Acoustic Wave (SAW) resonator device according to an embodiment of the present invention.

As shown in fig. 3, the method of forming the SAW resonator device includes: forming a first portion, wherein the forming the first portion comprises:

providing a piezo pre-treatment layer 301, said piezo pre-treatment layer 301 comprising a particle injection side 303;

at least one type of particles is injected into the piezoelectric pre-treatment layer 301 from the particle injection side 303, said at least one type of particles forming a defect layer 305 after entering the piezoelectric pre-treatment layer 301.

In this embodiment, the material of the piezoelectric pretreatment layer 301 includes, but is not limited to, at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

In the present embodiment, the depth of the defect layer 305 in the piezoelectric pretreatment layer 301 is adjusted by controlling the energy of particle implantation during the particle implantation, wherein the depth refers to the distance from the defect layer 305 to the surface of the particle implantation side 303. Note that the crystal lattice of the defect layer 305 is damaged by the particle implantation.

In this embodiment, the at least one particle includes, but is not limited to, at least one of: hydrogen ions, helium ions, oxygen ions, beryllium ions. It is noted that the particle implantation method (e.g., hydrogen ion implantation, helium ion implantation, co-implantation of hydrogen ions and helium ions, oxygen ion implantation) known to those skilled in the art can be applied to the embodiments of the present invention.

In this embodiment, after entering the piezoelectric pretreatment layer 301, the at least one particle further forms a first sub-layer 307 and a second sub-layer 309, where the first sub-layer 307 and the second sub-layer 309 are respectively located on two sides of the defect layer 305. In this embodiment, the thickness of the first sub-layer 307 is greater than the thickness of the second sub-layer 309.

As shown in fig. 4, the forming the first portion further includes: a bonding layer 401 is formed on the particle injection side 303 on the piezoelectric pretreatment layer 301.

In this embodiment, the material of the bonding layer 401 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon, metal. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 5, the forming the first portion further includes:

providing a substrate 501;

a bonding layer 503 is formed on one side of the substrate 501 and on the substrate 501.

In this embodiment, the ratio of the difference between the first coefficient of thermal expansion of the material of the piezoelectric pretreatment layer 301 and the second coefficient of thermal expansion of the material of the substrate 501 to the second coefficient of thermal expansion is less than 5%. In this embodiment, the material of the substrate 501 includes, but is not limited to, at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. It should be noted that the material of the piezoelectric pretreatment layer 301 and the material of the substrate 501 may be the same.

In this embodiment, the material of the bonding layer 503 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon, metal. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 6, the forming the first portion further includes: the piezoelectric pretreatment layer 301 is bonded to the substrate 501.

In this embodiment, bonding the piezoelectric pretreatment layer 301 to the substrate 501 includes: bonding the bonding layer 401 and the bonding layer 503 to form an intermediate layer 601 on the particle implantation side 303, wherein the intermediate layer 601 comprises a first side 603 and a second side 605 opposite to the first side 603, the substrate 501 is on the first side 603, and the piezoelectric pretreatment layer 301 is on the second side 605. It should be noted that the bonding may be normal temperature bonding or high temperature bonding, where the normal temperature refers to 25 degrees celsius to 250 degrees celsius, and the high temperature refers to 250 degrees celsius to 1000 degrees celsius.

In this embodiment, the material of the intermediate layer 601 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon, metal. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

In some embodiments, the thicknesses of the intermediate layer 601 include: 0.2 to 1 micron. It should be noted that in these embodiments, the material of the intermediate layer 601 is less affected by the etchant (e.g., hydrofluoric acid, hydrochloric acid, tetramethylammonium hydroxide, potassium hydroxide).

In other embodiments, the thicknesses of the intermediate layer 601 include: 1 micron to 10 microns. It should be noted that, in these embodiments, the material of the intermediate layer 601 is greatly affected by an etchant (e.g., hydrofluoric acid, hydrochloric acid, tetramethylammonium hydroxide, potassium hydroxide).

As shown in fig. 7, the forming the first portion further includes:

removing the first sublayer 307;

repairing the defective layer 305 to form a piezoelectric layer 701, wherein the piezoelectric layer 701 includes a third side 703 and a fourth side 705 opposite to the third side 703, the substrate 501 is located on the third side 703, and the intermediate layer 601 is located on the third side 703;

planarizing the fourth side 705;

a bonding layer 707 is formed on the fourth side 705 on the piezoelectric layer 701.

In this embodiment, removing the first sublayer 307 includes: the first sublayer 307 is separated at a high temperature, wherein the high temperature is 250 to 1000 degrees celsius. It should be noted that the high temperature separation method known to those skilled in the art can be applied to the embodiment of the present invention.

In this embodiment, repairing the defective layer 305 includes: annealing the defect layer 305 at a high temperature, wherein the high temperature is 250 to 1000 degrees celsius. Note that the high temperature anneal may repair the lattice damage in the defect layer 305 due to the particle implantation. It should be noted that the high temperature annealing method known to those skilled in the art can be applied to the embodiments of the present invention.

It should be noted that, because the ratio of the difference between the first thermal expansion coefficient of the material of the piezoelectric pretreatment layer 301 and the second thermal expansion coefficient of the material of the substrate 501 to the second thermal expansion coefficient is less than 5% (i.e., the thermal expansion coefficient of the material of the piezoelectric pretreatment layer 301 and the thermal expansion coefficient of the material of the substrate 501 are similar), the amount of thermal expansion of the piezoelectric pretreatment layer 301 and the amount of thermal expansion of the substrate 501 during high-temperature processing are similar, and the generated stress is small, thereby reducing the occurrence of fracture and improving the yield of products.

It is noted that planarization methods (e.g., chemical mechanical polishing) known to those skilled in the art can be applied to the embodiments of the present invention.

In this embodiment, the material of the bonding layer 707 includes, but is not limited to, at least one of: polymer, insulating dielectric, polysilicon. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 8, the method of forming the SAW resonator device further includes: forming a second portion, wherein the forming the second portion comprises:

providing a substrate 801;

a bonding layer 803 is formed on the substrate 801 on one side of the substrate 801.

In this embodiment, the material of the substrate 801 includes, but is not limited to, at least one of the following: silicon, silicon carbide, silicon dioxide, gallium arsenide, gallium nitride, aluminum oxide, magnesium oxide, ceramics, polymers.

In this embodiment, the material of the bonding layer 803 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 9, the method of forming the SAW resonator device further includes: joining the first portion and the second portion.

In this embodiment, joining the first portion and the second portion includes: bonding the bonding layer 707 and the bonding layer 803 to form an intermediate layer 901 located on the fourth side 705, where the intermediate layer 901 includes a fifth side 903 and a sixth side 905 opposite to the fifth side 903, the substrate 801 is located on the fifth side 903, the piezoelectric layer 701 is located on the sixth side 905, the intermediate layer 601 is located on the sixth side 905, and the substrate 501 is located on the sixth side 905. It should be noted that the bonding is normal temperature bonding, where normal temperature refers to 25 ℃ to 250 ℃, and a normal temperature bonding manner known to those skilled in the art may be applied to the embodiment of the present invention.

In this embodiment, the material of the intermediate layer 901 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 10, the method of forming the SAW resonator device further includes:

removing the substrate 501;

removing the intermediate layer 601;

an electrode layer 1001 is formed on the third side 703 on the piezoelectric layer 701.

In this embodiment, removing the substrate 501 includes: polishing the substrate 501 or etching the substrate 501. It should be noted that wet etching is adopted to etch the substrate 501, and wet etching methods known to those skilled in the art (for example, hydrofluoric acid wet etching, hydrochloric acid wet etching, tetramethylammonium hydroxide wet etching, and potassium hydroxide wet etching) may be applied to the embodiment of the present invention. It should be noted that the intermediate layer 601 can protect the piezoelectric layer 701 from being damaged when the substrate 501 is etched.

In this embodiment, removing the intermediate layer 601 includes: the intermediate layer 601 is polished or the intermediate layer 601 is etched.

In this embodiment, the forming the electrode layer 1001 includes: forming an IDT, wherein the forming the IDT comprises: forming a plurality of electrode bars 1003 on the third side 703 on the piezoelectric layer 701; forming a plurality of electrode strips 1005 on the third side 703 on the piezoelectric layer 701; wherein the polarity of the plurality of electrode bars 1003 and the polarity of the plurality of electrode bars 1005 are different; wherein the electrode strips 1003 and the electrode strips 1005 are alternately arranged. It should be noted that the embodiment of the present invention is a specific embodiment, and the present invention is not limited to the specific embodiment, and an IDT structure known to those skilled in the art may be applied to the embodiment of the present invention.

Fig. 11 to 18 are schematic structural views of a cross section a of a method of forming a Surface Acoustic Wave (SAW) resonator device according to an embodiment of the present invention.

As shown in fig. 11, the method of forming the SAW resonator device includes: forming a third portion, wherein the forming the third portion comprises:

providing a piezo pre-treatment layer 1101, said piezo pre-treatment layer 1101 comprising a particle implantation side 1103;

at least one type of particles is injected into the piezoelectric pretreatment layer 1101 from the particle injection side 1103, and the at least one type of particles forms a defect layer 1105 after entering the piezoelectric pretreatment layer 1101.

In this embodiment, the material of the piezoelectric pretreatment layer 1101 includes, but is not limited to, at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

In this embodiment, the depth of the defect layer 1105 in the piezoelectric pretreatment layer 1101 is adjusted by controlling the energy of particle implantation during the particle implantation, wherein the depth refers to the distance from the defect layer 1105 to the surface of the particle implantation side 1103. Note that the crystal lattice of the defect layer 1105 is damaged by the particle implantation.

In this embodiment, the at least one particle includes, but is not limited to, at least one of: hydrogen ions, helium ions, oxygen ions, beryllium ions. It is noted that ion implantation methods (e.g., hydrogen ion implantation, helium ion implantation, co-implantation of hydrogen ions and helium ions, oxygen ion implantation) known to those skilled in the art can be applied to the embodiments of the present invention.

In this embodiment, after entering the piezoelectric pretreatment layer 1101, the at least one particle forms a first sub-layer 1107 and a second sub-layer 1109, where the first sub-layer 1107 and the second sub-layer 1109 are located at two sides of the defect layer 1105 respectively. In this embodiment, the thickness of the first sub-layer 1107 is greater than the thickness of the second sub-layer 1109.

As shown in fig. 12, the forming the third portion further includes: a bonding layer 1201 is formed on the particle implantation side 1103 on the piezoelectric pretreatment layer 1101.

In this embodiment, the material of the bonding layer 1201 includes, but is not limited to, at least one of: polymer, insulating dielectric, polysilicon, metal. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 13, the forming the third portion further includes:

providing a substrate 1301;

forming an isolation layer 1303 on one side of the substrate 1301 and on the substrate 1301, wherein the isolation layer 1303 includes a first side 1305 and a second side 1307 opposite to the first side 1305, and the substrate 1301 is on the first side 1305

A bonding layer 1309 is formed on the second side 1307 over the isolation layer 1303.

In this embodiment, the ratio of the difference between the first thermal expansion coefficient of the material of the piezoelectric pretreatment layer 1101 and the second thermal expansion coefficient of the material of the substrate 1301 to the second thermal expansion coefficient is less than 5%. In this embodiment, the material of the substrate 1301 includes, but is not limited to, at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. It should be noted that the material of the piezoelectric pretreatment layer 1101 may be the same as the material of the substrate 1301.

In this embodiment, the material of the isolation layer 1303 includes, but is not limited to, at least one of the following: silicon oxide, silicon nitride, aluminum oxide, metal. It should be noted that the etching manner of the isolation layer 1303 is different from that of the substrate 1301, that is, the isolation layer 1303 is not damaged when the substrate 1301 is etched.

In this embodiment, the material of the bonding layer 1309 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon, metal. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 14, the forming the third portion further includes: bonding the piezoelectric pretreatment layer 1101 with the substrate 1301.

In this embodiment, bonding the piezoelectric pretreatment layer 1101 to the substrate 1301 includes: bonding the bonding layer 1201 and the bonding layer 1309 to form an intermediate layer 1401 on the particle injection side 1103, wherein the intermediate layer 1401 comprises a third side 1403 and a fourth side 1405 opposite to the third side 1403, the substrate 1301 is located on the third side 1403, the isolation layer 1303 is located on the third side 1403, and the piezoelectric pretreatment layer 1101 is located on the fourth side 1405. It should be noted that the bonding may be normal temperature bonding or high temperature bonding, where the normal temperature refers to 25 degrees celsius to 250 degrees celsius, and the high temperature refers to 250 degrees celsius to 1000 degrees celsius.

In this embodiment, the material of the intermediate layer 1401 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon, metal. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

In this embodiment, the thickness of the intermediate layer 1401 includes, but is not limited to: 0.2 microns to 1 micron.

It should be noted that the etching manner of the isolation layer 1303 is different from the etching manner of the intermediate layer 1401, that is, the intermediate layer 1401 is not damaged when the isolation layer 1303 is etched.

As shown in fig. 15, the forming the third portion further includes:

removing the first sublayer 1107;

repairing the defect layer 1105 to form a piezoelectric layer 1501, wherein the piezoelectric layer 1501 includes a fifth side 1503 and a sixth side 1505 opposite to the fifth side 1503, the substrate 1301 is located on the fifth side 1503, the isolation layer 1303 is also located on the fifth side 1503, and the intermediate layer 1401 is located on the fifth side 1503;

planarizing the sixth side 1505;

a bonding layer 1507 is formed on the sixth side 1505 on the piezoelectric layer 1501.

In this embodiment, removing the first sublayer 1107 includes: the first sublayer 1107 is separated at a high temperature, wherein the high temperature is 250 to 1000 degrees celsius. It should be noted that the high temperature separation method known to those skilled in the art can be applied to the embodiment of the present invention.

In this embodiment, repairing the defective layer 1105 includes: and annealing the defect layer 1105 at a high temperature, wherein the high temperature is 250-1000 ℃. Note that the high-temperature annealing can repair the lattice damage in the defect layer 1105 due to the particle implantation. It should be noted that the high temperature annealing method known to those skilled in the art can be applied to the embodiments of the present invention.

It should be noted that, since the ratio of the difference between the first thermal expansion coefficient of the material of the piezoelectric pretreatment layer 1101 and the second thermal expansion coefficient of the material of the substrate 1301 to the second thermal expansion coefficient is less than 5% (that is, the thermal expansion coefficient of the material of the piezoelectric pretreatment layer 1101 and the thermal expansion coefficient of the material of the substrate 1301 are similar), the amount of thermal expansion of the piezoelectric pretreatment layer 1101 and the amount of thermal expansion of the substrate 1301 during high-temperature processing are similar, and the generated stress is small, thereby reducing the occurrence of cracks and improving the yield of products.

In this embodiment, the material of the bonding layer 1507 includes, but is not limited to, at least one of: polymer, insulating dielectric, polysilicon. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 16, the method of forming the SAW resonator device further includes: forming a fourth portion, wherein the forming the fourth portion comprises:

providing a substrate 1601;

a bonding layer 1603 is formed on one side of the substrate 1601 on the substrate 1601.

In this embodiment, the material of the substrate 1601 includes, but is not limited to, at least one of the following: silicon, silicon carbide, silicon dioxide, gallium arsenide, gallium nitride, aluminum oxide, magnesium oxide, ceramics, polymers.

In this embodiment, the material of the bonding layer 1603 includes, but is not limited to, at least one of the following: polymer, insulating dielectric, polysilicon. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 17, the method of forming the SAW resonator device further includes: joining the third portion with the fourth portion.

In this embodiment, joining the third portion and the fourth portion includes: bonding the bonding layer 1507 and the bonding layer 1603 to form an intermediate layer 1701 on the sixth side 1505, wherein the intermediate layer 1701 comprises a seventh side 1703 and an eighth side 1705 opposite to the seventh side 1703, the substrate 1601 is on the seventh side 1703, the piezoelectric layer 1501 is on the eighth side 1705, the intermediate layer 1401 is on the eighth side 1705, the isolation layer 1303 is on the eighth side 1705, and the substrate 1301 is on the eighth side 1705. It should be noted that the bonding is normal temperature bonding, where normal temperature refers to 25 ℃ to 250 ℃, and a normal temperature bonding manner known to those skilled in the art may be applied to the embodiment of the present invention.

In this embodiment, the material of the intermediate layer 1701 includes, but is not limited to, at least one of: polymer, insulating dielectric, polysilicon. In this embodiment, the polymer includes, but is not limited to, at least one of: benzocyclobutene (i.e., BCB), photosensitive epoxy photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes, but is not limited to, at least one of: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

As shown in fig. 18, the method of forming the SAW resonator device further includes:

removing the substrate 1301;

removing the isolation layer 1303

Removing the intermediate layer 1401;

an electrode layer 1801 is formed on the fifth side 1503 on the piezoelectric layer 1501.

In this embodiment, removing the substrate 1301 includes: and grinding the substrate 1301 or etching the substrate 1301. It should be noted that wet etching is adopted to etch the substrate 1301, and wet etching methods (for example, hydrofluoric acid wet etching, hydrochloric acid wet etching, tetramethylammonium hydroxide wet etching, and potassium hydroxide wet etching) known to those skilled in the art may be applied to the embodiment of the present invention. It should be noted that the etching manner of the isolation layer 1303 is different from that of the substrate 1301, that is, the isolation layer 1303 is not damaged when the substrate 1301 is etched, so that the isolation layer 1303 can protect the intermediate layer 1401 from being damaged when the substrate 1301 is etched.

In this embodiment, removing the isolation layer 1303 includes: and polishing the isolation layer 1303 or etching the isolation layer 1303. It should be noted that the etching manner of the isolation layer 1303 is different from the etching manner of the intermediate layer 1401, that is, the intermediate layer 1401 is not damaged when the isolation layer 1303 is etched, so that the intermediate layer 1401 can protect the piezoelectric layer 1501 from being damaged when the isolation layer 1303 is etched.

In this embodiment, removing the intermediate layer 1401 includes: the intermediate layer 1401 is polished or the intermediate layer 1401 is etched.

In this embodiment, the forming the electrode layer 1801 includes: forming an IDT, wherein the forming the IDT comprises: forming a plurality of electrode strips 1803 on said fifth side 1503 on said piezoelectric layer 1501; forming a plurality of electrode strips 1805 on said fifth side 1503 on said piezoelectric layer 1501; wherein the plurality of electrode strips 1803 and the plurality of electrode strips 1805 are of different polarities; wherein the electrode strips 1803 and the electrode strips 1805 are alternately arranged. It should be noted that the embodiment of the present invention is a specific embodiment, and the present invention is not limited to the specific embodiment, and an IDT structure known to those skilled in the art may be applied to the embodiment of the present invention.

In summary, the piezoelectric layer with good crystal quality is formed through high-temperature separation and high-temperature annealing, and the thermal expansion coefficients of the piezoelectric layer material and the substrate material are mismatched, so that the piezoelectric layer is easy to break during high-temperature treatment, and the product yield is reduced. In the method for forming the surface acoustic wave resonator provided by the embodiment of the invention, the ratio of the difference between the first thermal expansion coefficient of the piezoelectric layer material and the second thermal expansion coefficient of the transition substrate material to the second thermal expansion coefficient is less than 5%, and when the piezoelectric layer with better crystal quality is formed by adopting a high-temperature separation and high-temperature annealing mode, the fracture condition can be reduced, and the yield of products is improved.

It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.

Claims

1. A method of forming a surface acoustic wave resonator device, comprising:

forming a first portion, the forming the first portion comprising: providing a piezoelectric pretreatment layer; forming a defect layer in the piezoelectric pretreatment layer; providing a first substrate; bonding the piezoelectric pretreatment layer to the first substrate; forming a piezoelectric layer based on the defective layer, the piezoelectric layer including a first side and a second side opposite the first side, the first base being located at the first side, a ratio of a difference of a first coefficient of thermal expansion of a material of the piezoelectric pretreatment layer and a second coefficient of thermal expansion of a material of the first base to the second coefficient of thermal expansion being less than 5%;

a first sublayer and a second sublayer are further formed in the piezoelectric pretreatment layer and are respectively positioned on the upper side and the lower side of the defect layer, wherein the thickness of the first sublayer is larger than that of the second sublayer;

forming a piezoelectric layer based on the defective layer includes: removing the first sublayer; repairing the defective layer;

forming a second portion, the forming the second portion comprising: providing a second substrate;

joining the first portion and the second portion, the second portion being located on the second side;

removing the first substrate; and

forming an electrode layer on the first side contacting the piezoelectric layer.

2. A method of forming a surface acoustic wave resonator device as set forth in claim 1, wherein forming a defect layer in said piezoelectric pretreatment layer includes: and injecting at least one type of particles into the piezoelectric pretreatment layer, wherein the at least one type of particles form the defect layer after entering the piezoelectric pretreatment layer.

3. A method of forming a surface acoustic wave resonator device as set forth in claim 1, wherein bonding the piezoelectric pretreatment layer and the first substrate includes: forming a first intermediate layer between the first substrate and the piezoelectric pretreatment layer at least for bonding the first substrate and the piezoelectric pretreatment layer.

4. A method for forming a surface acoustic wave resonator device as claimed in claim 3, wherein the material of said first intermediate layer includes at least one of: metal, polymer, insulating dielectric, polysilicon.

5. A method of forming a surface acoustic wave resonator device as set forth in claim 3, wherein the thickness of said first intermediate layer includes: 0.2 to 1 micron.

6. A method of forming a surface acoustic wave resonator device as set forth in claim 3, wherein the thickness of said first intermediate layer includes: 1 micron to 10 microns.

7. A method of forming a surface acoustic wave resonator device as set forth in claim 1, wherein removing the first sublayer includes: and separating the first sub-layer at a high temperature, wherein the high temperature is 250-1000 ℃.

8. A method of forming a surface acoustic wave resonator device as set forth in claim 1, wherein repairing the defective layer includes: and annealing the defect layer at a high temperature, wherein the high temperature is 250-1000 ℃.

9. A method of forming a surface acoustic wave resonator device as set forth in claim 1, wherein joining the first portion and the second portion includes: under the normal atmospheric temperature condition, form the second intermediate level, be located the second base with between the piezoelectric layer, be used for the bonding at least the second base with the piezoelectric layer, wherein, normal atmospheric temperature means 25 degrees centigrade to 250 degrees centigrade.

10. A method for forming a surface acoustic wave resonator device as claimed in claim 9, wherein the material of said second intermediate layer includes at least one of: polymer, insulating dielectric, polysilicon.

11. A method of forming a surface acoustic wave resonator device, as set forth in claim 1, wherein said forming the first portion further comprises: forming a first bonding layer on the second side.

12. A method for forming a surface acoustic wave resonator device as set forth in claim 11, wherein said forming the second portion further includes: and forming a second bonding layer on one side of the second substrate.

13. A method of forming a surface acoustic wave resonator device as set forth in claim 12, wherein joining the first portion and the second portion includes: and bonding the first bonding layer and the second bonding layer at normal temperature to form a third intermediate layer, wherein the third intermediate layer is positioned between the second substrate and the piezoelectric layer and is at least used for bonding the second substrate and the piezoelectric layer, and the normal temperature is 25-250 ℃.

14. A method for forming a surface acoustic wave resonator device as claimed in claim 13, wherein the material of said third intermediate layer includes at least one of: polymer, insulating dielectric, polysilicon.

15. A method of forming a surface acoustic wave resonator device as set forth in claim 1, wherein removing the first substrate includes: and polishing the first substrate or etching the first substrate.

16. A method for forming a surface acoustic wave resonator device as set forth in claim 3, further comprising: and removing the first intermediate layer after removing the first substrate.

17. A method of forming a surface acoustic wave resonator device, as set forth in claim 1, wherein said forming the first portion further comprises: and before the piezoelectric pretreatment layer and the first substrate are jointed, an isolation layer is formed, is positioned on one side of the first substrate, covers the first substrate and is at least used for shielding an etching agent to protect the piezoelectric layer.

18. A method for forming a surface acoustic wave resonator device as claimed in claim 17, wherein a material of said spacer layer includes at least one of: silicon oxide, silicon nitride, aluminum oxide, metal.

19. A method of forming a surface acoustic wave resonator device as set forth in claim 17, wherein bonding the piezoelectric pretreatment layer and the first substrate includes: forming a fourth intermediate layer between the piezoelectric pretreatment layer and the isolation layer for at least bonding the isolation layer and the piezoelectric pretreatment layer, the fourth intermediate layer and the first substrate being respectively located on both sides of the isolation layer.

20. A method for forming a surface acoustic wave resonator device as claimed in claim 19, wherein a material of said fourth intermediate layer includes at least one of: polymer, insulating dielectric, polysilicon, metal.

21. A method for forming a surface acoustic wave resonator device as claimed in claim 19, wherein the thickness of said fourth intermediate layer includes: 0.2 to 1 micron.

22. A method for forming a surface acoustic wave resonator device as set forth in claim 19, further comprising: removing the isolation layer after removing the first substrate; and removing the fourth intermediate layer after removing the isolation layer.

23. A method of forming a surface acoustic wave resonator device, as set forth in claim 1, wherein the material of the first substrate includes at least one of: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

24. A method of forming a surface acoustic wave resonator device as set forth in claim 1, wherein a material of said first substrate is the same as a material of said piezoelectric pretreatment layer.