A method for preparing an acoustic wave resonator and an acoustic wave resonator

Abstract

The present invention relates to the field of microelectronic devices, and in particular to a method for preparing an acoustic wave resonator and an acoustic wave resonator. Two piezoelectric structures are prepared by utilizing the same process; each piezoelectric structure includes a supporting substrate and a piezoelectric film layer arranged in sequence from bottom to top; the difference in thickness of the two piezoelectric film layers is less than or equal to 20% of the thickness of the preset piezoelectric film layer; the preset piezoelectric film layer is the thicker piezoelectric film layer of the two piezoelectric film layers; the two piezoelectric structures are bonded to obtain a bonding structure; the two piezoelectric film layers are located in the middle layer area of ​​the bonding structure; any one of the supporting substrates in the bonding structure is removed; a cavity is prepared in the area of ​​the supporting substrate close to the piezoelectric film layer in the retained piezoelectric structure, so that the piezoelectric film layer is suspended. The symmetrically complementary piezoelectric films in the heterogeneous integrated structure provided in the present application can offset the overall internal stress of the two piezoelectric film layers, thereby improving device performance.

Description

Technical Field

[0001] The invention relates to the field of microelectronic devices, and in particular to a method for preparing an acoustic wave resonator and the acoustic wave resonator. Background Art

[0002] The modern communications industry has increasingly higher requirements for signal quality and the competition for communications spectrum resources is becoming increasingly fierce. Low loss, wide bandwidth, tunability and temperature stability have become the common goals pursued by the communications industry. Acoustic resonators, including surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators, are currently widely used in the communications field due to their small size, large bandwidth and high Q value. However, thermal mismatch during the growth or transfer of piezoelectric films will lead to residual stress in the piezoelectric film. In the process of suspending the film, excessive stress will cause the film to crack, bend, deform, or even fall off, which will lead to a decrease in the performance of the resonator or even failure.

[0003] In the related art, the process parameters of low-temperature deposition are usually determined by first determining the stress value of the piezoelectric film, and then a stress compensation film layer is deposited on the piezoelectric film layer according to the process parameters of low-temperature deposition, and the stress of the piezoelectric film layer is balanced by the compensation film layer; but it has the disadvantage of complex preparation steps; another way to reduce the stress of the piezoelectric film is to design a "bowl"-shaped effective area structure to cope with and offset the "umbrella"-shaped protrusion caused by the stress that may be brought in the process, and improve the stress unevenness caused by the growth process of the piezoelectric film. This solution is suitable for film bulk acoustic resonator filters (FBARs), but for the modes propagating in the horizontal direction, it destroys the in-plane continuity, resulting in a decrease in device performance. Summary of the invention

[0004] In order to solve the above technical problems, the present application discloses, on one hand, a method for preparing an acoustic wave resonator, which comprises:

[0005] Two piezoelectric structures are prepared by the same process; each piezoelectric structure includes a supporting substrate and a piezoelectric film layer arranged in sequence from bottom to top; the difference in thickness of the two piezoelectric film layers is less than or equal to 20% of the thickness of the preset piezoelectric film layer; the preset piezoelectric film layer is the thicker piezoelectric film layer of the two piezoelectric film layers;

[0006] Bonding the two piezoelectric structures to obtain a bonded structure; the two piezoelectric film layers are located in the middle layer region of the bonded structure;

[0007] removing any supporting substrate in the bonding structure;

[0008] A cavity is prepared in a region of the support substrate close to the piezoelectric film layer in the retained piezoelectric structure, so that the piezoelectric film layer is suspended.

[0009] In a feasible embodiment, the support substrate includes a first support substrate and a second support substrate stacked together; a piezoelectric film layer is provided on the second support substrate; and a cavity is prepared in a region of the support substrate close to the piezoelectric film layer in the retained piezoelectric structure, including:

[0010] The second supporting substrate is etched by a front etching process to form a cavity in the middle below the piezoelectric film layer.

[0011] In a feasible embodiment, a cavity is prepared in a region of the support substrate close to the piezoelectric film layer in the retained piezoelectric structure, comprising:

[0012] The supporting substrate is etched by a backside etching process to form a cavity below the piezoelectric film layer.

[0013] In a feasible embodiment, the method further includes:

[0014] A metal electrode is prepared on the piezoelectric film layer away from the supporting substrate.

[0015] In a feasible embodiment, a metal electrode is disposed on a surface of the piezoelectric film layer of each piezoelectric structure close to the supporting substrate.

[0016] In a feasible embodiment, a method for preparing a piezoelectric structure includes:

[0017] Providing a piezoelectric film wafer;

[0018] Performing ion implantation on the piezoelectric film wafer from an implantation surface to form a defect layer in the piezoelectric film wafer;

[0019] providing a supporting substrate;

[0020] Bonding the support substrate to the implantation surface to obtain a first bonding structure;

[0021] The first bonding structure is subjected to annealing, stripping and polishing treatments along the defective layer to obtain a piezoelectric structure.

[0022] In a feasible embodiment, a method for preparing a piezoelectric structure includes:

[0023] Providing a piezoelectric film wafer and a supporting substrate;

[0024] Bonding the piezoelectric film wafer to the supporting substrate to obtain a second bonding structure;

[0025] The piezoelectric film wafer is thinned to obtain a piezoelectric structure.

[0026] In a feasible embodiment, a method for preparing a piezoelectric structure includes:

[0027] providing a supporting substrate;

[0028] A piezoelectric thin film layer is epitaxially grown on a supporting substrate.

[0029] In a feasible embodiment, an intermediate layer is provided on the piezoelectric film layer of each piezoelectric structure;

[0030] The middle layer is one or more of a suspension electrode, a heat dissipation layer, a temperature compensation layer and a bonding layer.

[0031] On the other hand, the present application also discloses an acoustic wave resonator, which is prepared using the above method.

[0032] By adopting the above technical solution, the method for preparing the acoustic wave resonator provided in the present application has the following beneficial effects:

[0033] Two piezoelectric structures are prepared using the same process; each piezoelectric structure includes a supporting substrate and a piezoelectric film layer arranged in sequence from bottom to top; the difference in thickness of the two piezoelectric film layers is less than or equal to 20% of the thickness of the preset piezoelectric film layer; the preset piezoelectric film layer is the thicker piezoelectric film layer of the two piezoelectric film layers; the two piezoelectric structures are bonded to obtain a bonded structure; the two piezoelectric film layers are located in the middle layer area of ​​the bonded structure; any one of the supporting substrates in the bonded structure is removed; a cavity is prepared in the area of ​​the supporting substrate close to the piezoelectric film layer in the retained piezoelectric structure, so that the piezoelectric film layer is suspended. Thus, the two prepared piezoelectric film layers have the same stress distribution, and when the two piezoelectric film layers are symmetrically bonded together, the internal stress of the piezoelectric film is offset due to the complementary stress, thereby improving the device performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 It is a schematic flow chart of a method for preparing an acoustic wave resonator provided in an embodiment of the present application;

[0036] Figure 2 It is a process schematic diagram of a first method for preparing an acoustic wave resonator provided in an embodiment of the present application;

[0037] Figure 3 is a schematic diagram of a process for preparing a piezoelectric structure provided in an embodiment of the present application;

[0038] Figure 4 is a schematic diagram of the process of preparing a second acoustic wave resonator provided in an embodiment of the present application;

[0039] Figure 5 is a schematic diagram of the process of preparing a third acoustic wave resonator provided in an embodiment of the present application;

[0040] Figure 6 is a schematic structural diagram of an acoustic wave resonator provided in an embodiment of the present application;

[0041] Figure 7 is a schematic diagram of the structure of another acoustic wave resonator provided in an embodiment of the present application;

[0042] Figure 8 It is a schematic structural diagram of an acoustic wave resonator with no stress on a piezoelectric film layer provided in an embodiment of the present application;

[0043] Fig. 9 yes Figure 8 The simulated admittance curve of the acoustic wave resonator shown;

[0044] Fig.10 It is a schematic structural diagram of a first type of acoustic wave resonator with stress in a piezoelectric film layer provided in an embodiment of the present application;

[0045] Fig.11 is a schematic structural diagram of a second acoustic wave resonator with stress in the piezoelectric film layer provided in an embodiment of the present application;

[0046] Fig.12 It is a schematic structural diagram of a third type of acoustic wave resonator with stress in the piezoelectric film layer provided in an embodiment of the present application;

[0047] Fig.13 It is a schematic structural diagram of a fourth acoustic wave resonator with stress in the piezoelectric film layer provided in an embodiment of the present application;

[0048] Fig.14 yes Fig.10 The simulated admittance curve of the acoustic wave resonator shown;

[0049] Fig.15 yes Fig.12 The simulated admittance curve of the acoustic wave resonator shown;

[0050] Fig.16 yes Fig.14 Mode shape diagram of the target mode shown;

[0051] Fig.17 yes Fig.14 The vibration mode diagram of the parasitic mode is shown;

[0052] Fig.18 yes Fig.15 Mode shape diagram of the target mode shown;

[0053] Fig.19 yes Fig.15 The vibration mode diagram of the parasitic mode is shown;

[0054] Fig. 20 is a simulated admittance curve of an acoustic wave resonator provided in an embodiment of the present application;

[0055] Fig.21 is a vibration mode diagram of an acoustic wave resonator with a different structure provided in an embodiment of the present application;

[0056] Fig. 22 is a simulated admittance curve of another acoustic wave resonator provided in an embodiment of the present application;

[0057] Fig.23 This is a vibration mode diagram of another acoustic wave resonator with a different structure provided in an embodiment of the present application.

[0058] The following is a supplementary description of the attached drawings:

[0059] 1-support substrate; 11-first support substrate; 12-second support substrate; 2-piezoelectric film layer; 21-first piezoelectric film layer; 22-second piezoelectric film layer; 3-metal electrode; 4-cavity; 5-defect layer; 6-suspended electrode; 7-bonding layer. DETAILED DESCRIPTION

[0060] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0061] The term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present application. In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", etc. is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first" and "second" are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may include one or more of the features explicitly or implicitly. Moreover, the terms "first", "second", etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here.

[0062] For the purpose of the following detailed description, it should be understood that the present invention may adopt various alternative changes and step sequences, unless expressly specified to the contrary. In addition, except in any operating examples, or otherwise indicated, all numbers representing the amount of ingredients used in the specification and claims should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters set forth in the following specification and the attached claims are approximate values ​​that vary according to the desired performance to be obtained by the present invention. At least it is not intended to limit the application of the doctrine of equivalents to the scope of the claims, and each numerical parameter should at least be interpreted according to the number of reported significant figures and by applying ordinary rounding techniques.

[0063] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0064] When a numerical range is disclosed herein, the above range is deemed to be continuous and includes the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all sub-ranges included therein. For example, a specified range from "1 to 10" should be deemed to include any and all sub-ranges between a minimum of 1 and a maximum of 10. Exemplary sub-ranges of ranges 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0065] See also Figure 1 and Figure 2 , Figure 1 is a schematic flow chart of a method for preparing an acoustic wave resonator provided in an embodiment of the present application, Figure 2 1 is a schematic diagram of the process of preparing the first acoustic wave resonator provided in an embodiment of the present application. The method for preparing the acoustic wave resonator may specifically include the following steps:

[0066] S101: Two piezoelectric structures are prepared using the same process; each piezoelectric structure includes a supporting substrate 1 and a piezoelectric film layer 2 arranged in sequence from bottom to top; the difference in thickness between the two piezoelectric film layers 2 is less than or equal to 20% of the preset thickness of the piezoelectric film layer 2; the preset piezoelectric film layer 2 is the thicker piezoelectric film layer 2 of the two piezoelectric film layers 2.

[0067] In a feasible embodiment, the method for preparing a piezoelectric structure includes: providing a piezoelectric film wafer, performing ion implantation on the piezoelectric film wafer from an implantation surface to form a defect layer 5 (such as Figure 3 Provide a supporting substrate 1 (such as Figure 3 The support substrate 1 is bonded to the implantation surface to obtain a first bonding structure (such as Figure 3 The first bonding structure is subjected to annealing, peeling and polishing along the defective layer 5 to obtain a piezoelectric structure (such as Figure 3 The structure shown in Figure (d) in the figure can be obtained to obtain a piezoelectric single crystal thin film, and the piezoelectric thin film wafer after peeling can also be recycled.

[0068] In another feasible embodiment, a method for preparing a piezoelectric structure includes: providing a piezoelectric film wafer and a supporting substrate 1; bonding the piezoelectric film wafer to the supporting substrate 1 to obtain a second bonding structure; and thinning the piezoelectric film wafer to obtain a piezoelectric structure.

[0069] In another feasible embodiment, a method for preparing a piezoelectric structure includes: providing a support substrate 1; and epitaxially growing a piezoelectric film layer 2 on the support substrate 1. The piezoelectric structure can be prepared by selecting any one of the above ion implantation and stripping processes, bonding and grinding processes, or film growth processes as needed.

[0070] In a feasible embodiment, the support substrate 1 includes a first support substrate 11 and a second support substrate 12 stacked together; the second support substrate 12 is provided with a piezoelectric film layer 2, and of course the support substrate 1 can also be a single-layer structure; the support substrate 1 includes at least one of lithium niobate, lithium tantalate, silicon, quartz, spinel, germanium, silicon carbide, diamond, diamond-like carbon, sapphire, aluminum nitride, and silicon nitride. The second support substrate 12 can also be called a sacrificial layer, which can be a structure of different materials from the first support substrate 11.

[0071] Optionally, the piezoelectric film layer 2 may be composed of a multilayer piezoelectric material, or a composite film of a piezoelectric material and other materials. It should be noted that, after the device is prepared, the multilayer materials in the first piezoelectric film layer 21 and the second piezoelectric film layer 22 are symmetrically distributed. Optionally, the piezoelectric material includes at least one of lithium niobate, lithium tantalate, potassium niobate, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate, or lead magnesium niobate-lead titanate crystals.

[0072] Optionally, the step of preparing the metal electrode 3 may be after step S107 below, and specifically, the metal electrode 3 may be prepared on the piezoelectric film layer 2; optionally, as needed, when it is necessary to prepare a resonator having both a top electrode and a bottom electrode, the metal electrode 3 may be prepared when preparing the piezoelectric structure, that is, the metal electrode 3 is prepared on the surface of the piezoelectric film layer 2 of each piezoelectric structure close to the supporting substrate 1 (that is, the bottom of the piezoelectric film layer 2). The piezoelectric structure may be as follows: Figure 4 In the structure shown in Figure (a) or Figure (b), a metal electrode 3 is provided at the bottom of the piezoelectric film layer 2. In order to better distinguish the piezoelectric film layers 2 in the two piezoelectric structures, the piezoelectric film layer 2 in one piezoelectric structure is referred to as the first piezoelectric film layer 21, and the piezoelectric film layer 2 in the other piezoelectric structure is referred to as the second piezoelectric film layer 22. The two piezoelectric structures are subsequently bonded to obtain the following: Figure 4 The structure shown in Figure (c) is then removed, and the supporting substrate 1 near the second piezoelectric film layer 22 is removed to obtain the structure shown in Figure (c). Figure 4 The structure shown in FIG. (d) can be specifically etched by using a front etching process on the first support substrate 11, so that a cavity can be formed in the middle of the first support substrate 11, that is, the support substrate 1 and the first piezoelectric film layer 21 form a cavity 4, and the structure shown in FIG. Figure 4 The structure shown in Figure (e).

[0073] In another feasible embodiment, an intermediate layer is provided on the piezoelectric film layer 2 of each piezoelectric structure; the intermediate layer is one or more of a suspension electrode 6, a heat dissipation layer, a temperature compensation layer and a bonding layer 7, wherein the role of the suspension electrode 6 is to realize the longitudinal electric field excitation of the acoustic wave mode, such as the high-order modes of the horizontal shear wave, such as SH1 and SH2 modes; the heat dissipation layer is mainly used to improve the heat dissipation of the device, the temperature compensation layer is to adapt to different working environments and ensure the stability of the device frequency, and the role of the bonding layer 7 is to improve the bonding strength to meet the actual performance requirements. This piezoelectric structure with an intermediate layer can be specifically as follows Figure 5 For each piezoelectric structure, a metal electrode 3 may be provided at the bottom of the piezoelectric film layer 2, and an intermediate layer may be provided at the top of the piezoelectric film layer 2. The two piezoelectric structures may be bonded together to obtain the following structure: Figure 5 The structure shown in Figure (c) is then removed, and the supporting substrate 1 near the second piezoelectric film layer 22 is removed to obtain the structure shown in Figure (c). Figure 5 The structure shown in FIG. (d) can be obtained by etching the first support substrate 11 using a front etching process, so that a cavity can be formed in the middle of the first support substrate 11. Figure 4 The structure shown in Figure (e) in FIG. If necessary, the support substrate can also be etched using a backside etching process to allow the piezoelectric film layer 2 to be suspended.

[0074] It is understandable that the intermediate layer may be composed of multiple functional layers, such as specifically composed of a suspension electrode 6 and a bonding layer 7, so that the structure of the resonator finally obtained may be as follows: Figure 6 The intermediate layer may also be a single functional layer, such as a suspended electrode 6, so that the structure of the resulting resonator may be as follows Figure 7 The metal electrode 3 of the present application may be an interdigitated electrode (such as Figure 4 Figure (e) in the figure); the interdigitated electrodes include a first bus bar and a second bus bar relative to each other; the first bus bar is provided with a plurality of first electrodes arranged at intervals; the second bus bar is provided with a plurality of second electrodes arranged at intervals, and the plurality of first electrodes and the plurality of second electrodes are arranged alternately and at intervals to form interdigitated electrodes; optionally, the distance between adjacent second electrodes is equal to the distance between adjacent first electrodes. Optionally, the period of the interdigitated electrodes is the spacing distance between the centers of adjacent first electrodes in the plurality of first electrodes, or the spacing distance between the centers of adjacent second electrodes in the plurality of second electrodes. It can also be a surface electrode (such as Figure 7As shown), a device similar to FBAR can be formed. Assuming that the thickness of the first piezoelectric film layer 21 is D1, and the thickness of the second piezoelectric film layer 22 is D2, when D2 is greater than D1, the difference in thickness between the two △D=D2-D1. Specifically, △D can be 20%D2, such as 0, 5%D2, 10%D2, 15%D2 and 20%D2.

[0075] S103: Bonding the two piezoelectric structures to obtain a bonded structure; the two piezoelectric film layers 2 are located in the middle layer region of the bonded structure.

[0076] In the embodiment of the present application, the bonding structure can be as follows: Figure 2 The structure shown in Figure (c) can also be Figure 4 The structure shown in Figure (c) can also be Figure 5 The structure shown in Figure (c).

[0077] S105: Remove any supporting substrate 1 in the bonding structure to obtain Figure 2 The structure shown in Figure (d) can also be obtained as Figure 4 The structure shown in Figure (d) can also be obtained as follows Figure 5 The structure shown in Figure (d).

[0078] S107: Prepare a cavity in the region of the support substrate 1 close to the piezoelectric film layer 2 in the retained piezoelectric structure so that the piezoelectric film layer 2 is suspended in the air, and the following can be obtained: Figure 4 The structure shown in Figure (e) can also be obtained as follows Figure 5 The structure shown in Figure (e).

[0079] In a feasible embodiment, after step S105, the method further includes: preparing a metal electrode 3 on the piezoelectric film layer 2 away from the supporting substrate 1. The preparation of the metal electrode 3 can be completed in the step of preparing the piezoelectric heterogeneous substrate (that is, completed in step S101), and the following is obtained: Figure 4 The structure shown in FIG. (e) can also be completed after the piezoelectric film layer 2 is exposed, that is, after step S105, to obtain Figure 2 The structure shown in Figure (e).

[0080] In a feasible embodiment, in step S107, a cavity is prepared in a region of the support substrate close to the piezoelectric film layer in the retained piezoelectric structure, including: etching the second support substrate 12 using a front etching process to form a cavity in the middle of the second support substrate 12, and finally the following can be obtained: Figure 2In the structure shown in the middle figure (e), before the second supporting substrate 12 is etched by the front etching process, an etched through hole is formed in the upper structure of the second supporting substrate 12, and the cavity finally formed in the second supporting substrate 12 is connected to the etched through hole.

[0081] In another feasible embodiment, in step S107, a cavity is prepared in an area of ​​the supporting substrate close to the piezoelectric film layer in the retained piezoelectric structure, including: etching the supporting substrate 1 using a back side etching process to form a cavity in the middle of the supporting substrate 1, so that the piezoelectric film layer 2 is suspended.

[0082] The target mode of the acoustic wave resonator prepared as described above is a horizontal shear mode, a Lamb wave mode and one of their higher-order modes.

[0083] Optionally, the acoustic wave resonator may specifically be as follows Figure 2 In the structure shown in Figure (e), the material of the supporting substrate 1 is sapphire, the first piezoelectric film layer 21 and the second piezoelectric film layer 22 are both Y36-cut lithium niobate, the metal electrode 3 is an interdigitated electrode, and the target mode of the acoustic wave resonator is the zero-order horizontal shear wave (SH0) mode; optionally, the acoustic wave resonator can also be specifically as follows Figure 4 In the structure shown in the middle figure (e), the material of the supporting substrate 1 is sapphire, the first piezoelectric film layer 21 and the second piezoelectric film layer 22 are both Y36-cut lithium niobate, the metal electrode 3 is an interdigitated electrode, and the target mode of the acoustic wave resonator is the zero-order horizontal shear wave (SH0) mode; the acoustic wave resonator can also be specifically as follows Figure 4 In the structure shown in the middle figure (e), the material of the supporting substrate 1 is sapphire, the first piezoelectric film layer 21 and the second piezoelectric film layer 22 are both Z-cut lithium niobate, the metal electrode 3 is an interdigitated electrode, and the target mode of the acoustic wave resonator is the first-order antisymmetric Lamb wave (A1) mode; the acoustic wave resonator can also be similar to Figure 7 In the structure shown, the material of the supporting substrate 1 is sapphire, the first piezoelectric film layer 21 and the second piezoelectric film layer 22 are both X-cut lithium niobate, the metal electrode 3 is an interdigitated electrode, and the middle layer is a suspended electrode 6. The target mode of the acoustic wave resonator is the high-order mode (SH1) of the first-order horizontal shear wave.

[0084] The present application also discloses an acoustic wave resonator, which is prepared by the above method. The structures of different acoustic wave resonators obtained by different preparation methods have been described in detail above, and will not be repeated here.

[0085] In order to better illustrate the beneficial effects of the present application, specific embodiments will be described below.

[0086] Embodiment 1:

[0087] Provide as Figure 8 The resonator in the prior art with no stress on the piezoelectric film layer 2 (i.e., a resonator under ideal conditions) is shown, that is, there is only a single crystal piezoelectric film layer 2 on the supporting substrate 1, the piezoelectric film layer 2 of the resonator is 300nm thick Y36-cut lithium niobate, the metal electrode 3 is a gold interdigital electrode with a thickness of 50nm, the period of the interdigital electrode is 1.5μm, the supporting substrate 1 is sapphire, and the target mode is SH0. It can be tested and the following results are obtained: Fig. 9 The admittance curve shown is Fig. 9 It can be seen that its admittance ratio is 105dB, and there is basically no parasitic mode. However, in the actual environment, since residual stress will be present inside the piezoelectric film when it is prepared, when the supporting substrate 1 is subsequently etched to form the cavity 4, the piezoelectric film layer 2 will have problems such as cracks, bending, deformation, and even falling off. In one case, when the piezoelectric film layer 2 is etched on the front side, the boundaries of the piezoelectric film layer 2 are etched away. After the second supporting substrate 12 is removed, the piezoelectric film layer 2 will bend, and the following is obtained: Fig.10 In the structure shown in FIG. 1 , when the cavity 4 of the acoustic wave resonator is large, although the deformed piezoelectric film layer 2 can be prevented from contacting the supporting substrate 1, the deformation of the film cannot be avoided (see FIG. 1 ). Fig.11 ); When the deformation degree of the piezoelectric film layer 2 is greater than the height of the cavity 4, the following is obtained: Fig.12 Another case is that the back side etching process is used to etch the support substrate 1, and the structure shown in FIG. Fig.13 In the structure shown, although the cavity 4 is larger and there is no etched boundary around the resonator, the film can be prevented from contacting the supporting substrate 1 and the deformation of the film can be reduced, but the deformation of the film cannot be completely prevented. Fig.10 and Fig.12 The resonator shown with Figure 8 The resonator has the same structure and composition. Fig.10 and Fig.12 The resonator is simulated and calculated, and the following can be obtained respectively: Fig.14 and Fig.15 The admittance curve shown in the figure shows that the admittance ratio of the admittance curve shown in the figure has dropped to 91dB and 83dB, and a parasitic mode appears on the right side of the main mode anti-resonance frequency (i.e., the target mode) (see Fig.12 and Fig.15 This indicates that the stress-induced deformation of the piezoelectric film layer 2 will cause the resonator Q value to decrease. Fig.16 and Fig.17 , Fig.16 yes Fig.14 Mode shape diagram of the target mode shown; Fig.17 yes Fig.14The vibration mode diagram of the parasitic mode shown in FIG. 1 is a diagram showing that if the piezoelectric film layer 2 is severely deformed, clutter will appear in the propagation direction (the direction perpendicular to the interdigital electrodes). In the vibration mode diagram, the parasitic mode appears as a longitudinal mode ( Fig.17 See Fig.18 and Fig.19 , Fig.18 yes Fig.15 The vibration mode diagram of the target mode shown in Fig.15 Medium solid frame, Fig.19 yes Fig.15 From the vibration mode diagram of the parasitic mode shown, it can be seen that the sudden change in the acoustic boundary causes the leakage of the acoustic wave energy into the interior of the supporting substrate 1, which is one of the important reasons for the decrease in the resonator admittance ratio.

[0088] Provide as Figure 2 The acoustic wave resonator structure of the present application shown in FIG. (e) has a thickness of 150 nanometers for each piezoelectric film layer 2, and other parameters are the same as those described above. Figure 8 The structure is the same, and by simulating and calculating the resonator structure provided in this application, the following can be obtained: Fig. 20 The admittance curve shown in Figure 8 The structure of the piezoelectric film layer 2 without stress is roughly the same, and no new parasitic modes appear; see Fig.21 , Fig.21 The corresponding figure (a) in Fig. 9 The vibration shape diagram of the target mode in Fig.21 The corresponding figure (b) in Fig. 20 From the vibration mode diagram of the target mode in FIG. 1 , it can be seen that the vibration modes of the two are also substantially the same. Therefore, it can be shown that the resonator prepared by the above preparation method provided by the present application can completely eliminate the stress inside the piezoelectric film layer 2 and improve the device performance.

[0089] Embodiment 2:

[0090] Provide as Figure 4 The acoustic wave resonator structure of the present application shown in FIG. (e) has a thickness of 300 nanometers for each piezoelectric film layer 2, and other parameters are the same as those described above. Figure 8 The structure is the same, by simulating the structure provided by the present application, the following can be obtained: Fig. 22 The admittance curve shown in Figure 8 This piezoelectric film layer 2 has a substantially unstressed structure, and no obvious parasitic modes appear; see Fig.23 , Fig.23 The corresponding figure (a) in Fig. 9 The vibration shape diagram of the target mode in Fig.23 The corresponding figure (b) in Fig. 22It can be seen from the vibration mode diagram of the target mode in the figure that the vibration modes of the two are also roughly the same. It further illustrates that the resonator prepared by the above-mentioned preparation method provided by the present application can completely eliminate the stress inside the piezoelectric film layer 2 and improve the performance of the device. In addition, the resonator prepared by the above-mentioned preparation method provided by the present application can completely eliminate the stress inside the piezoelectric film layer 2 and improve the performance of the device. Figure 2 The thickness of the piezoelectric film layer 2 of the resonator shown in Figure (e) is relative to Figure 8 This means that the resonator structure is more stable, and the heat dissipation capacity and capacitance are improved.

[0091] To sum up, the acoustic wave resonator proposed in this scheme realizes stress cancellation by combining stress-complementary piezoelectric film layers 2 into a composite film. Since the piezoelectric films used come from piezoelectric heterogeneous substrates prepared with the same process parameters, no matter how the stress in each layer of piezoelectric film is distributed, when they are symmetrically bonded together, the stress in the composite film can be just cancelled out, avoiding bending deformation, depression and cracks of the film, which is beneficial to improving the Q value and structural stability of the resonator.

[0092] When the preparation method provided by the present application is adopted, there is no need to monitor the stress of the piezoelectric film, nor is there any need to additionally design a stress compensation layer with appropriate stress and thickness, and the method is very simple. The method also does not use an additional anchoring structure or a concave-convex structure to offset the stress, thereby ensuring the continuity inside the resonator. The resonator composed of a symmetrical piezoelectric film can also achieve a doubling of the film thickness and capacitance, which is beneficial to improving the stability of the device structure, improving the heat dissipation capacity, and reducing the device area required for impedance matching.

[0093] The above are only optional embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing an acoustic wave resonator, characterized in that: include: Two piezoelectric structures are prepared by the same process; each of the piezoelectric structures comprises a supporting substrate and a piezoelectric film layer arranged in sequence from bottom to top; The difference between the thicknesses of the two piezoelectric film layers is less than or equal to 20% of the thickness of the preset piezoelectric film layer; the preset piezoelectric film layer is the thicker piezoelectric film layer of the two piezoelectric film layers; Bonding the two piezoelectric structures to obtain a bonding structure; the two piezoelectric film layers are located in the middle layer region of the bonding structure; removing any one supporting substrate in the bonding structure; A cavity is prepared in a region of the support substrate close to the piezoelectric film layer in the retained piezoelectric structure, so that the piezoelectric film layer is suspended.

2. The preparation method according to claim 1, characterized in that: The support substrate includes a first support substrate and a second support substrate stacked together; The piezoelectric film layer is provided on the second supporting substrate; The step of preparing a cavity in a region of the support substrate close to the piezoelectric film layer in the retained piezoelectric structure comprises: The second supporting substrate is etched by a front etching process to form a cavity below the piezoelectric film layer.

3. The preparation method according to claim 1, characterized in that: The step of preparing a cavity in a region of the support substrate close to the piezoelectric film layer in the retained piezoelectric structure comprises: The support substrate is etched using a backside etching process to form a cavity below the piezoelectric film layer.

4. The preparation method according to claim 1, characterized in that: The method further comprises: A metal electrode is prepared on the piezoelectric film layer away from the supporting substrate.

5. The preparation method according to claim 1, characterized in that: A metal electrode is disposed on a surface of the piezoelectric film layer of each piezoelectric structure close to the supporting substrate.

6. The preparation method according to claim 1, characterized in that: The method for preparing the piezoelectric structure comprises: Providing a piezoelectric film wafer; Performing ion implantation on the piezoelectric thin film wafer from an implantation surface to form a defect layer in the piezoelectric thin film wafer; providing a supporting substrate; Bonding the support substrate to the implantation surface to obtain a first bonding structure; The first bonding structure is subjected to annealing, stripping and polishing treatment along the defective layer to obtain the piezoelectric structure.

7. The preparation method according to claim 1, characterized in that: The method for preparing the piezoelectric structure comprises: Providing a piezoelectric film wafer and a supporting substrate; Bonding the piezoelectric film wafer to the supporting substrate to obtain a second bonding structure; The piezoelectric film wafer is thinned to obtain the piezoelectric structure.

8. The preparation method according to claim 1, characterized in that: The method for preparing the piezoelectric structure comprises: providing a supporting substrate; A piezoelectric thin film layer is epitaxially grown on the supporting substrate.

9. The preparation method according to claim 1, characterized in that: An intermediate layer is provided on the piezoelectric film layer of each piezoelectric structure; The intermediate layer is one or more of a suspension electrode, a heat dissipation layer, a temperature compensation layer and a bonding layer.

10. An acoustic wave resonator, characterized in that: It is prepared by the method according to any one of claims 1 to 9.

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