Method for synchronously preparing two composite substrates, acoustic wave filter and preparation method of acoustic wave filter

Abstract

The invention discloses a method for synchronously preparing two composite substrates, an acoustic wave filter and a preparation method of the acoustic wave filter. The method comprises the steps that a first high-resistance silicon substrate and a piezoelectric substrate are prepared, and the piezoelectric substrate comprises a positive electrode face and a negative electrode face which are oppositely arranged; bonding the first high-resistance silicon substrate with the positive electrode surface of the piezoelectric substrate by adopting a first bonding method to form a first bonding body; performing ion implantation in the piezoelectric substrate of the first bonding body to form an ion implantation layer; preparing a second high-resistance silicon substrate, and preparing a silicon oxide layer on the surface of the second high-resistance silicon substrate; pre-bonding the piezoelectric substrate side of the first bonding body and the silicon oxide layer of the second high-resistance silicon by adopting a second bonding method to obtain a second bonding body; and carrying out heat treatment on the second bonding body to enhance the bonding force, and cracking the second bonding body along the ion implantation layer to obtain the first composite substrate and the second composite substrate. The preparation cost of the composite substrate can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite substrates for acoustic wave filters, in particular to a method for synchronously preparing two kinds of composite substrates, an acoustic wave filter and a preparation method thereof. BACKGROUND

[0002] Acoustic surface wave filters are widely used in the field of communication for processing signals of different frequency bands to improve communication quality. Existing acoustic surface wave filters generally adopt the preparation of interdigital transducers on POI (composite piezoelectric substrate) to form. The structure of the POI substrate determines the frequency band of the signal processed by the acoustic surface wave filter.

[0003] In terms of market demand, there is a large demand for acoustic surface wave filters for processing low and medium frequency bands (represented by kHz and MHz) and high frequency bands (represented by GHz).

[0004] However, in the prior art, only one piezoelectric wafer can be used to prepare one POI, resulting in a great waste of piezoelectric materials and high production costs. SUMMARY

[0005] The present application provides a method for synchronously preparing two kinds of composite substrates, an acoustic wave filter and a preparation method thereof, to solve the problem that only one piezoelectric wafer can be used to prepare one composite substrate in the prior art, which causes waste of piezoelectric materials and high production costs.

[0006] In a first aspect, the embodiments of the present application provide a method for synchronously preparing two kinds of composite piezoelectric substrates, characterized in that the method comprises:

[0007] preparing a first high-resistance silicon substrate and a piezoelectric substrate, wherein the piezoelectric substrate comprises a positive electrode surface and a negative electrode surface arranged oppositely;

[0008] bonding the first high-resistance silicon substrate and the positive electrode surface of the piezoelectric substrate by using a first bonding method to form a first bonding body;

[0009] forming an ion implantation layer in the piezoelectric substrate of the first bonding body by ion implantation;

[0010] preparing a second high-resistance silicon substrate and preparing a silicon oxide layer on the surface of the second high-resistance silicon substrate;

[0011] pre-bonding the piezoelectric substrate side of the first bonding body and the silicon oxide layer of the second high-resistance silicon substrate by using a second bonding method to obtain a second bonding body;

[0012] The second bonding body is subjected to heat treatment to enhance the bonding force while cracking the second bonding body along the ion implantation layer to obtain a first composite substrate and a second composite substrate; wherein the first composite substrate comprises a first high-resistance silicon substrate and a first piezoelectric layer, and a negative electrode surface of the first piezoelectric layer is exposed outside; the second composite substrate comprises a second high-resistance silicon substrate, the silicon oxide layer and a second piezoelectric layer, and a positive electrode surface of the second piezoelectric layer is exposed outside; a thickness of the first piezoelectric layer of the first composite substrate is greater than a thickness of the second piezoelectric layer of the second composite substrate.

[0013] Optionally, the first high-resistance silicon substrate is bonded to the positive electrode surface of the piezoelectric substrate by using a first bonding method, comprising:

[0014] The first high-resistance silicon substrate is bonded to the positive electrode surface of the piezoelectric substrate by using a room-temperature activated bonding method.

[0015] Optionally, the thickness of the first piezoelectric layer of the first composite substrate ranges from 2 microns to 35 microns.

[0016] The thickness of the second piezoelectric layer of the second composite substrate ranges from 100 nanometers to 950 nanometers.

[0017] Optionally, after the first bonding body is formed, the method further comprises:

[0018] The piezoelectric substrate side of the first bonding body is subjected to thinning treatment.

[0019] A silicon oxide layer is prepared on the surface of the second high-resistance silicon substrate, comprising:

[0020] Polysilicon is deposited on the surface of the second high-resistance silicon substrate to form the polysilicon layer.

[0021] The second high-resistance silicon substrate on which the polysilicon layer is formed is subjected to thermal oxygen oxidation treatment to form the silicon oxide layer on a side of the polysilicon layer away from the second high-resistance silicon substrate.

[0022] Optionally, the piezoelectric substrate side of the first bonding body is pre-bonded to the silicon oxide layer of the second high-resistance silicon by using a second bonding method, comprising:

[0023] The piezoelectric substrate side of the first bonding body is pre-bonded to the silicon oxide layer of the second high-resistance silicon by using a hydrophilic pre-bonding method.

[0024] In a second aspect, an embodiment of the present application provides a preparation method of a first acoustic wave filter, comprising:

[0025] The first composite substrate is prepared by using the preparation method of the first aspect.

[0026] The thickness of the first piezoelectric layer of the first composite substrate is controlled to be between 2 micrometers and 35 micrometers. A first interdigital transducer is fabricated on the side of the first piezoelectric layer away from the first high-resistivity silicon substrate to obtain the first acoustic filter.

[0027] Thirdly, embodiments of the present invention provide a first acoustic filter, which is prepared by the preparation method described in the second aspect.

[0028] Fourthly, embodiments of the present invention provide a method for preparing a second acoustic filter, comprising:

[0029] The second composite substrate is prepared using the preparation method described in the first aspect;

[0030] The thickness of the second piezoelectric layer on the second composite substrate is controlled to be between 100 nm and 950 nm. A second interdigital transducer is fabricated on the side of the second piezoelectric layer away from the second high-resistivity silicon substrate to obtain the second acoustic filter.

[0031] Fifthly, embodiments of the present invention provide a second acoustic filter, which is prepared by the preparation method described in the fourth aspect.

[0032] The technical solution of this invention employs two different bonding technologies in a single process, using only one piezoelectric substrate and two silicon substrates to simultaneously fabricate a first composite substrate with a thickness of micrometers for fabricating low- and mid-frequency acoustic wave filters and a second composite substrate with a thickness of nanometers for fabricating high-frequency second acoustic wave filters. Compared to technical solutions where only one piezoelectric substrate can fabricate one composite substrate or only one type of composite substrate, this not only reduces the fabrication cost of the composite substrate but also improves the applicability of the fabricated composite substrate, making it more in line with market demands and possessing high economic and industrial application value.

[0033] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A flowchart illustrating a method for simultaneously preparing two composite substrates according to an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of a fabrication process for simultaneously preparing two composite substrates, provided as an embodiment of the present invention. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0038] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices. The terms "upper," "lower," "left," "right," etc., indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings and are only used to describe the relative positional relationships between components or constituent parts, and do not specifically limit the specific installation orientation of each component or constituent part.

[0039] Figure 1 A flowchart illustrating a method for simultaneously preparing two composite substrates according to an embodiment of the present invention is provided, referencing... Figure 1 The method for simultaneously preparing two composite substrates in this invention includes:

[0040] S110. Prepare a first high-resistivity silicon substrate 10 and a piezoelectric substrate 30, wherein the piezoelectric substrate 30 includes a positive electrode surface 31 and a negative electrode surface 32 disposed opposite to each other.

[0041] Figure 2 This is a schematic diagram of a fabrication process for simultaneously preparing two composite substrates according to an embodiment of the present invention. (Refer to...) Figure 2 For details of the first high-resistivity silicon substrate 10 and piezoelectric substrate 30 prepared in step S110, please refer to [link to relevant documentation]. Figure 2In Figure (a1), the piezoelectric substrate 30 includes a positive electrode surface 31 and a negative electrode surface 32 disposed opposite to each other. It should be noted that the first high-resistivity silicon substrate 10 in the embodiments of the present invention can be a high-resistivity silicon substrate, and the material of the piezoelectric substrate 30 can be lithium niobate or lithium tantalate.

[0042] As one possible implementation, preparing the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30 includes: preparing the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30 with a surface roughness of less than 0.3 nm.

[0043] In this embodiment of the invention, by setting the surface roughness of the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30 to be less than 0.3 nm, it is beneficial to improve the bonding quality and yield of the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30.

[0044] Optionally, after preparing the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30, the method for simultaneously preparing the two composite substrates in this embodiment of the invention may further include cleaning the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30. Specifically, an RCA cleaning process can be used to clean the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30. For example, a standard RCA solution can be used to clean the piezoelectric substrate 30 and the first high-resistivity silicon substrate 10.

[0045] It should be noted that the number of defects (e.g., particles larger than 0.3 μm, scratches, protrusions, and depressions) on the surface of the first high-resistivity silicon substrate 10 after cleaning is less than 20, and the number of defects (e.g., particles larger than 0.3 μm, scratches, protrusions, and depressions) on the surface of the piezoelectric substrate 30 after cleaning is less than 20.

[0046] In this embodiment of the invention, the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30 are cleaned before bonding the positive electrode surface 31 of the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30, which can further improve the bonding quality and yield of the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30.

[0047] S120. The first high-resistivity silicon substrate 10 is bonded to the positive electrode surface 31 of the piezoelectric substrate 30 using a first bonding method to form a first bonded body.

[0048] For example, bonding between a silicon substrate and a piezoelectric substrate 30 can be achieved by bonding the positive electrode surface 31 of the piezoelectric substrate 30 to a first high-resistivity silicon substrate 10. The first bond formed by the bonding is as follows: Figure 2 As shown in Figure (a1).

[0049] As a feasible implementation, a first bonding method is used to bond the first high-resistivity silicon substrate 10 to the positive electrode surface 31 of the piezoelectric substrate 30, including: bonding the first high-resistivity silicon substrate 10 to the positive electrode surface 31 of the piezoelectric substrate 30 using a room-temperature activated bonding method. Furthermore, to reduce the influence of the difference in thermal expansion coefficients between the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30 on their bonding, the bonding temperature T1 of the room-temperature activated bonding method in this embodiment of the invention satisfies: T1 < 30°C.

[0050] For details, please refer to Figure 2 First, the bonding surface of the first high-resistivity silicon substrate 10 and the positive electrode surface 31 of the piezoelectric substrate 30 are ion-activated. Then, the bonding surface of the first high-resistivity silicon substrate 10 is brought into contact with the positive electrode surface 31 of the piezoelectric substrate 30. Finally, pressure is applied at room temperature to make the bonding strength between the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30 greater than 1.2 J / m. 2 This ensures that the piezoelectric substrate 30 is free from the risk of falling off during subsequent operations.

[0051] It is understandable that room temperature bonding strength is high and no thermal annealing process is required. By setting room temperature activation bonding to bond the first high-resistivity silicon substrate 10 and the positive electrode surface 31, the present invention can avoid the situation where the two heterogeneous wafers (i.e., the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30) break due to the difference in thermal expansion during the thermal process.

[0052] It should be noted that during the ion activation process of the bonding surface of the first high-resistivity silicon substrate 10, amorphous silicon will be generated on the surface of the first high-resistivity silicon substrate 10. The generation of amorphous silicon is unfavorable. However, since the first composite substrate including the first high-resistivity silicon substrate 10 is used to prepare the first filter in the mid-to-low frequency band, the influence of amorphous silicon on the first composite substrate can be ignored. Therefore, it is possible to use room temperature activation bonding to bond the first high-resistivity silicon substrate 10 and the piezoelectric substrate 30 in this embodiment of the invention.

[0053] Optionally, after forming the first bond, the method for simultaneously preparing two composite substrates in this embodiment of the invention further includes: thinning the piezoelectric substrate 30 side of the first bond.

[0054] For example, the thinned piezoelectric substrate 30 is as follows Figure 2As shown in Figure (a2), it should be noted that the thickness W1 of the thinned piezoelectric substrate 30 satisfies: 10μm≤W1≤50μm. To ensure that the thickness of the thinned piezoelectric substrate 30 meets the required thickness of the two composite substrates, this embodiment of the invention sets the thickness of the thinned piezoelectric substrate 30 to be at least 10μm; to avoid the piezoelectric substrate 30 from being too thick and breaking during subsequent heat treatment, this embodiment of the invention sets the maximum thickness of the thinned piezoelectric substrate 30 to be 50μm.

[0055] Optionally, after thinning the piezoelectric substrate 30 from one side of the negative electrode surface 32, the negative electrode surface 32 of the piezoelectric substrate 30 can be polished and cleaned sequentially. Specifically, during the polishing process, a 1-2 μm thick layer of the piezoelectric substrate 30 is removed, the roughness of the polished negative electrode surface 32 is less than 0.3 nm, and the number of defects (such as particles larger than 0.3 μm, scratches, protrusions, and depressions) on the negative electrode surface 32 after cleaning using the standard RCA cleaning method is less than 20.

[0056] In this embodiment of the invention, after the piezoelectric substrate 30 is thinned, the negative electrode surface 32 of the piezoelectric substrate 30 is polished and cleaned in sequence. This helps to improve the accuracy and yield of subsequent ion implantation and avoids the situation of uneven thickness of the ion implantation layer 40.

[0057] S130, Ion implantation is performed on the piezoelectric substrate 30 of the first bond to form an ion implantation layer 40.

[0058] For example, the ion-implanted layer 40 formed after ion implantation of the piezoelectric substrate 30 is as follows: Figure 2 As shown in Figure (a3). It should be noted that the ion implantation in the embodiments of the present invention should be carried out at room temperature, and the implanted element is H+ or He+. There are no restrictions on the implantation conditions, as long as the film thickness requirement is met and it matches the cleavage conditions.

[0059] In a feasible implementation, the ion implantation depth is preferably 1 μm - 2 μm, and the distance D1 between the ion implantation layer 40 and the negative electrode surface 32 satisfies: 1 μm ≤ D1 ≤ 2 μm.

[0060] S140. Prepare a second high-resistivity silicon substrate 20 and prepare a silicon oxide layer 60 on the surface of the second high-resistivity silicon substrate 20.

[0061] The second high-resistivity silicon substrate 20 prepared in step S140 is detailed in [link to details]. Figure 2In Figure (a4), the second high-resistivity silicon substrate 20 in this embodiment of the invention can be a high-resistivity silicon substrate. As a feasible implementation, a silicon oxide layer 60 is prepared on the surface of the second high-resistivity silicon substrate 20, comprising: depositing polysilicon on one side of the second high-resistivity silicon substrate 20 to form a polysilicon layer 50; and performing a thermal oxidation treatment on the second high-resistivity silicon substrate 20 on which the polysilicon layer 50 is formed, so as to form a silicon oxide layer 60 on the side of the polysilicon layer 50 away from the second high-resistivity silicon substrate 20.

[0062] For example, refer to Figure 2 First, a polycrystalline silicon layer 50 is prepared on the two opposite surfaces of the second high-resistivity silicon substrate 20 using a low-pressure chemical vapor deposition (LPCVD) process, as shown below. Figure 2 The first polysilicon layer 51 and the second polysilicon layer 52 shown in Figure (a4) are then subjected to thermal oxidation treatment on the second high-resistivity silicon substrate 20 on which the polysilicon layer 50 is deposited. This allows the formation of a polysilicon layer 50 on the side of the polysilicon layer 50 away from the piezoelectric substrate 30. Figure 2 The first silicon oxide layer 61 and the second silicon oxide layer 62 are shown in Figure (a5).

[0063] Optionally, preparing the second high-resistivity silicon substrate 20 includes: preparing a second high-resistivity silicon substrate 20 with a surface roughness of less than 0.3 nm. Before sequentially fabricating a polysilicon layer 50 and a silicon oxide layer 60 on one side of the second high-resistivity silicon substrate 20, the second high-resistivity silicon substrate 20 may also be cleaned. Specifically, the second high-resistivity silicon substrate 20 can be cleaned using an RCA cleaning process, and the number of defects (e.g., particles larger than 0.3 μm, scratches, protrusions, and depressions) on the surface of the second high-resistivity silicon substrate 20 after cleaning using a standard RCA cleaning method is less than 20.

[0064] The present invention improves the yield of polysilicon layer 50 and silicon oxide layer 60 prepared on the second high-resistivity silicon substrate 20 before sequentially preparing polysilicon layer 50 and silicon oxide layer 60 on one side of the second high-resistivity silicon substrate 20, and cleans the second high-resistivity silicon substrate 20. This improves the bonding quality and yield of the subsequent silicon oxide layer 60 and piezoelectric substrate 30.

[0065] S150. Using a second bonding method, the piezoelectric substrate 30 side of the first bonded body is pre-bonded to the silicon oxide layer 60 on the second high-resistivity silicon substrate 20 to obtain the second bonded body.

[0066] For example, the second bond formed by bonding the piezoelectric substrate 30 and the silicon oxide layer 60 is as follows Figure 2 As shown in Figure (a6).

[0067] As a feasible implementation method, a second bonding method is used to pre-bond the piezoelectric substrate 30 side of the first bond to the silicon oxide layer 60 of the second high-resistivity silicon 20, including: using a hydrophilic pre-bonding method to pre-bond the piezoelectric substrate 30 side of the first bond to the silicon oxide layer 60 of the second high-resistivity silicon 20.

[0068] It should be noted that the bonding strength of the hydrophilic prebonding is relatively low and cannot meet the requirements for industrial applications. Annealing is required for the second bond shown in Figure (a6) to increase the bonding strength. See step S160 below for details.

[0069] S160. The second bond is heat-treated to enhance the bonding force, and at the same time, the second bond is cracked along the ion implantation layer 40 to obtain a first composite substrate and a second composite substrate; wherein, the first composite substrate includes a first high-resistivity silicon substrate 10 and a first piezoelectric layer 301, and the negative electrode surface 32 of the first piezoelectric layer 301 is exposed on the outside; the second composite substrate includes a second high-resistivity silicon substrate 20, a silicon oxide layer 60 and a second piezoelectric layer 302, and the positive electrode surface 31 of the second piezoelectric layer 302 is exposed on the outside; the thickness of the first piezoelectric layer 301 of the first composite substrate is greater than the thickness of the second piezoelectric layer 302 of the second composite substrate.

[0070] For example, refer to Figure 2 The second bond shown in Figure (a6) is subjected to annealing. Specifically, the annealing temperature is below 300℃, the heat treatment time is 1 H - 10 H, and the heating rate is 0.5-10℃ / min, which helps to ensure temperature uniformity. The above annealing not only strengthens the bonding strength of the bonding surface, but also causes the ion implantation layer 40 to crack, forming the first composite substrate and the second composite substrate. The first composite substrate shown in Figure (a71) includes a first high-resistivity silicon substrate 10 and a first piezoelectric layer 301, with the negative electrode surface 32 of the first piezoelectric layer 301 exposed on the outside. The second composite substrate in this embodiment of the invention includes at least a second high-resistivity silicon substrate 20, a silicon oxide layer 60, and a second piezoelectric layer 302. If a polysilicon layer 50 is first formed on the second high-resistivity silicon substrate 20 and then the silicon oxide layer 60 is formed on the polysilicon layer 50, then the second composite substrate in this embodiment of the invention will include a second high-resistivity silicon substrate 20, a polysilicon layer 50, a silicon oxide layer 60, and a second piezoelectric layer 302, as shown in Figure (a72).

[0071] Optionally, after obtaining the first composite substrate and the second composite substrate, the thickness of the first piezoelectric layer 301 of the first composite substrate can be controlled to be 2 micrometers-35 micrometers, and the thickness of the second piezoelectric layer 302 of the second composite substrate can be controlled to be 100 nanometers-950 nanometers.

[0072] It should be noted that the first composite substrate shown in Figure (a71) can be used to prepare a mid-to-low frequency acoustic wave filter. The reason is that the structure of the first composite substrate is a high-resistivity silicon-piezoelectric substrate 30, and the exposed surface of the piezoelectric substrate 30 (i.e. the first piezoelectric layer 301) is the negative electrode surface 32. That is, along the -c axis, the ions are arranged oppositely, and the compressive stress component on the surface is more prominent. When the sound wave propagates, the stress distribution is relatively deeper, especially for low-frequency long-wavelength sound waves. Moreover, the stress dominated by compression has less interface damage to the thick film structure, which is more suitable for alleviating the accumulated stress in the thick film composite substrate. The thickness range of the piezoelectric substrate 30 in the thick film composite substrate is 2μm-35μm. The first composite substrate (i.e., thick film composite substrate) prepared in the embodiments of the present invention is used to process mid-to-low frequency signals. Mid-to-low frequency signals are easy to excite multimodes when propagating in the first composite substrate. Since the surface of the first composite substrate is the negative electrode surface 32, the lattice characteristics of the negative electrode surface 32 can reduce signal distortion caused by mode mixing. Low frequency signals are long-wavelength. At the -c surface, although the coupling efficiency is slightly lower than that at the +c surface, the stress distribution is deeper, which can reduce energy reflection at the electrode edge and improve the signal integrity of the low frequency band.

[0073] (a72) The second composite substrate shown in the figure can be used to fabricate high-frequency acoustic wave filters because the structure of the second composite substrate is high-resistivity silicon-polycrystalline silicon-silicon oxide-piezoelectric substrate 30, and the exposed surface of the piezoelectric substrate 30 (i.e., the second piezoelectric layer 302) is the positive electrode surface 31. Along the +c axis direction, the cations in the lattice (such as Li) + ) and anions (such as TaO3) - / NbO3 - The arrangement of the piezoelectric substrate 30 on the +c surface makes the tensile stress component on the surface more significant. When sound waves (especially high-frequency short waves) propagate on the +c surface, the stress is mainly concentrated in the shallow surface layer, and the alternation of tension and compression along the propagation direction is more intense. This is suitable for thin-film composite substrates where energy is highly concentrated on the surface. The thickness of the piezoelectric substrate 30 in the thin-film composite substrate ranges from 100nm to 950nm. High-frequency signals are short waves, and because the energy is concentrated on the surface, the electric field coupling between the positive electrode surface 31 and the interdigital transducer is more direct, resulting in higher energy conversion efficiency and reduced signal loss. The lattice orientation of the +c surface makes the propagation speed of high-frequency SAW more stable, and the energy is concentrated on the surface, making it less likely to propagate into the substrate interior. This is suitable for high-frequency filters with high frequency accuracy requirements.

[0074] The technical solution of this invention employs two different bonding technologies in a single process, using only one piezoelectric substrate 30 and two silicon substrates to simultaneously fabricate a micron-thick first composite substrate for fabricating a low-to-medium frequency first acoustic wave filter and a nanometer-thick second composite substrate for fabricating a high-frequency second acoustic wave filter. Compared to technical solutions where one piezoelectric substrate 30 can only fabricate one composite substrate or only one type of composite substrate, this not only helps to reduce the fabrication cost of the composite substrate but also improves the applicability of the fabricated composite substrate, making it more in line with market demands and possessing high economic and industrial application value.

[0075] Based on the same inventive concept, this invention also provides a method for fabricating a first acoustic filter, comprising: fabricating a first composite substrate using the method provided in any of the above embodiments of this invention; controlling the thickness of the first piezoelectric layer 301 of the first composite substrate to be 2 micrometers-35 micrometers; and fabricating a first interdigital transducer on the side of the first piezoelectric layer 301 away from the first high-resistivity silicon substrate 10 to obtain the first acoustic filter. Therefore, this method for fabricating the first acoustic filter includes the technical features of the above-described method for simultaneously fabricating two composite substrates, and possesses the beneficial effects of the above-described method for simultaneously fabricating two composite substrates; similarities can be found in the description above.

[0076] It should be noted that the first acoustic filter in this embodiment of the invention can be a mid-to-low frequency acoustic filter, and the frequency f1 of the mid-to-low frequency acoustic filter satisfies: 1kHz ≤ f1 < 1000MHz. Based on the same inventive concept, this embodiment of the invention also provides a first acoustic filter, which is prepared by the preparation method of the first acoustic filter provided in the above embodiments. Therefore, the first acoustic filter includes the technical features of the preparation method of the first acoustic filter described above, and possesses the beneficial effects of the preparation method of the first acoustic filter described above. Similarities can be found in the description above.

[0077] Based on the same inventive concept, this invention also provides a method for fabricating a second acoustic filter, comprising: fabricating a second composite substrate using the method provided in any of the above embodiments of this invention; controlling the thickness of the second piezoelectric layer 302 of the second composite substrate to be 100 nm-950 nm; and fabricating a second interdigital transducer on the side of the second piezoelectric layer 302 away from the second high-resistivity silicon substrate 20 to obtain the second acoustic filter. Therefore, this method for fabricating the second acoustic filter includes the technical features of the method for simultaneously fabricating two composite substrates described above, and possesses the beneficial effects of the method for simultaneously fabricating two composite substrates described above. The similarities can be found in the description above.

[0078] It should be noted that the second acoustic filter in the embodiments of the present invention can be a high-frequency acoustic filter, and the frequency f2 of the high-frequency acoustic filter satisfies: f2≥1GHz.

[0079] Based on the same inventive concept, this embodiment of the invention also provides a second acoustic filter, which is prepared by the preparation method of the second acoustic filter provided in the above embodiments. Therefore, this second acoustic filter includes the technical features of the preparation method of the above-described second acoustic filter and possesses the beneficial effects of the preparation method of the above-described second acoustic filter; similarities can be found in the description above.

[0080] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for simultaneously preparing two composite substrates, characterized in that, include: Prepare a first high-resistivity silicon substrate and a piezoelectric substrate, wherein the piezoelectric substrate includes a positive electrode surface and a negative electrode surface disposed opposite to each other; The first high-resistivity silicon substrate is bonded to the positive electrode surface of the piezoelectric substrate using a first bonding method to form a first bonded body; Ion implantation is performed into the piezoelectric substrate of the first bond to form an ion implantation layer; Prepare a second high-resistivity silicon substrate, and fabricate a silicon oxide layer on the surface of the second high-resistivity silicon substrate; The piezoelectric substrate side of the first bonded body is pre-bonded to the silicon oxide layer of the second high-resistivity silicon substrate using a second bonding method to obtain the second bonded body; The second bond is heat-treated to enhance the bonding force, and simultaneously the second bond is cracked along the ion implantation layer to obtain a first composite substrate and a second composite substrate; wherein, the first composite substrate includes a first high-resistivity silicon substrate and a first piezoelectric layer, with the negative electrode surface of the first piezoelectric layer exposed on the outside; the second composite substrate includes a second high-resistivity silicon substrate, the silicon oxide layer and a second piezoelectric layer, with the positive electrode surface of the second piezoelectric layer exposed on the outside; the thickness of the first piezoelectric layer in the first composite substrate is greater than the thickness of the second piezoelectric layer in the second composite substrate.

2. The method according to claim 1, characterized in that, The first bonding method is used to bond the first high-resistivity silicon substrate to the positive electrode surface of the piezoelectric substrate, including: The first high-resistivity silicon substrate is bonded to the positive electrode surface of the piezoelectric substrate using a room-temperature activated bonding method.

3. The method according to claim 1, characterized in that, The thickness of the first piezoelectric layer on the first composite substrate ranges from 2 micrometers to 35 micrometers; The thickness of the second piezoelectric layer on the second composite substrate ranges from 100 nanometers to 950 nanometers.

4. The method according to claim 1, characterized in that, After forming the first bond, the method further includes: The piezoelectric substrate side of the first bond is thinned.

5. The method according to claim 1, characterized in that, A silicon oxide layer is prepared on the surface of the second high-resistivity silicon substrate, including: Polysilicon is deposited on the surface of the second high-resistivity silicon substrate to form the polysilicon layer; The second high-resistivity silicon substrate on which the polycrystalline silicon layer is formed is subjected to thermal oxidation treatment to form the silicon oxide layer on the side of the polycrystalline silicon layer away from the second high-resistivity silicon substrate.

6. The method according to claim 1, characterized in that, The second bonding method is used to pre-bond the piezoelectric substrate side of the first bond to the silicon oxide layer of the second high-resistivity silicon, including: A hydrophilic pre-bonding method is used to pre-bond the piezoelectric substrate side of the first bond to the silicon oxide layer of the second high-resistivity silicon.

7. A method for fabricating a first acoustic wave filter, characterized in that, include: The first composite substrate is prepared using the preparation method according to any one of claims 1-6; The thickness of the first piezoelectric layer of the first composite substrate is controlled to be between 2 micrometers and 35 micrometers. A first interdigital transducer is fabricated on the side of the first piezoelectric layer away from the first high-resistivity silicon substrate to obtain the first acoustic filter.

8. A first acoustic wave filter, characterized in that, Prepared by the preparation method as described in claim 7.

9. A method for fabricating a second acoustic wave filter, characterized in that, include: The second composite substrate is prepared using the preparation method according to any one of claims 1-6; The thickness of the second piezoelectric layer on the second composite substrate is controlled to be between 100 nm and 950 nm. A second interdigital transducer is fabricated on the side of the second piezoelectric layer away from the second high-resistivity silicon substrate to obtain the second acoustic filter.

10. A second acoustic wave filter, characterized in that, Prepared by the preparation method as described in claim 9.

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