Acoustic resonator structure, filter and preparation method thereof

Abstract

The invention relates to the technical field of sound wave radio frequency filters, in particular to a sound wave resonator structure, a filter and a preparation method thereof, and the sound wave resonator structure comprises an IDT layer, a piezoelectric film substrate and a supporting layer; the piezoelectric film substrate adopts an X-cut LN film substrate capable of exciting surface longitudinal waves; the IDT layer is arranged on the first end face and comprises an interdigital electrode with a constant period or a variable period; the supporting layer is arranged on the second end face, and a cavity is formed in the supporting layer; the supporting layer enables the side, away from the IDT layer, of the piezoelectric film substrate to form a cavity, and the cavity is in an extremely low acoustic impedance state and is far lower than that of a solid material, so that acoustic waves are almost totally reflected at the interface of the piezoelectric layer and the cavity, energy is almost not leaked in the depth direction, and the quality factor Q value of the resonator is much higher. And meanwhile, the occurrence of parasitic modes can be greatly reduced by the simplified reflection interface, and in addition, the production cost can be greatly reduced due to the removal of the complex solid Bragg reflection layer.

Description

Technical Field

[0001] The present invention relates to the technical field of acoustic wave radio frequency filters, and in particular to an acoustic wave resonator structure, a filter and a preparation method thereof. Background Art

[0002] With the development of 5G technology, the demand for high-frequency (>3GHz) and large-bandwidth filters is becoming increasingly urgent, such as those in the N77 and N79 bands. However, traditional SAW filters struggle to achieve high frequencies, while the bandwidths of FBAR and SMR BAW filters are insufficient to meet these demands. While XBAR filters offer higher frequencies and wider bandwidths, their Lamb wave operation requires frequency adjustment based on the thickness of the piezoelectric film. Typically, a single filter consists of dozens of resonators, requiring XBARs to implement more than a dozen different piezoelectric layer thicknesses within the same filter chip. This makes the production process extremely difficult, and no commercially available XBAR filters have yet been mass-produced. For these reasons, high-frequency, large-bandwidth filters for consumer electronics are currently dominated by LTCC filters, which, due to their inherent principles, are larger in size and have a poor rectangular coefficient.

[0003] In recent years, another type of leaky longitudinal surface acoustic wave (LLSAW) structure has emerged. Composed primarily of a piezoelectric film, a Bragg reflector, and a support layer, it primarily operates in a surface longitudinal wave mode parallel to the substrate surface. This longitudinal wave continuously leaks energy deep into the substrate during propagation. To minimize this energy leakage, a solid Bragg reflector is added to the bottom of the piezoelectric film to reflect the acoustic waves. This structure has the advantage of utilizing the simple SAW tape-out process while offering a high acoustic velocity and a high coupling coefficient, making it potentially suitable for high-frequency and wide-bandwidth applications. However, this structure requires an extremely complex substrate, requiring multiple layers of high and low acoustic impedance materials, resulting in high production costs. Furthermore, the solid Bragg reflector is far from achieving total reflection, resulting in significant energy leakage and the generation of severe parasitic modes in the piezoelectric film. Summary of the Invention

[0004] The present invention aims to provide an acoustic wave resonator structure, a filter, and a method for manufacturing the same, in order to address the energy leakage and high cost problems of the conventional leaky longitudinal surface acoustic wave (LLSAW) structure, and further address the complex XBAR manufacturing process in the conventional art.

[0005] The technical solution of the present invention is: an acoustic wave resonator structure, comprising: A piezoelectric film substrate having a first end surface and a second end surface; An IDT layer is provided on the first end surface and includes interdigital electrodes having a constant period or a varying period; A support layer is provided on the second end surface, and the support layer has a cavity therein; The piezoelectric film substrate adopts an X-cut LN film substrate that can excite surface longitudinal waves. The propagation direction of the acoustic wave is parallel to the surface of the piezoelectric film substrate, and the frequency of the acoustic wave resonator structure is correlated with the period of the interdigital electrodes in the IDT layer. The interface between the piezoelectric film substrate and the cavity has an acoustic impedance difference, thereby forming a total reflection interface, which is used to suppress acoustic wave leakage.

[0006] Preferably, the acoustic wave propagation direction of the acoustic wave resonator structure is parallel to the surface of the piezoelectric thin film substrate, and the angle θ between the acoustic wave propagation direction and the Y axis of the crystal used in the piezoelectric thin film substrate is 40°.

[0007] Preferably, the interdigital electrodes have a constant period, and the interdigital period is set to λ; the thickness h of the piezoelectric film substrate satisfies: h<0.5λ.

[0008] Preferably, the IDT layer includes an IDT and reflective gratings arranged at both ends of the IDT, and the IDT and the reflective gratings use the same or different structural periods.

[0009] Preferably, the IDT layer is formed by combining a plurality of variable-period IDTs and reflective gratings.

[0010] Preferably, the IDT layer is covered with a first passivation layer, and the thickness of the first passivation layer is less than 100 nm.

[0011] Preferably, a second passivation layer is provided on a side of the support layer away from the piezoelectric film substrate, and the thickness of the second passivation layer is less than 100 nm.

[0012] The present application also discloses a filter comprising a plurality of the above-mentioned acoustic wave resonator structures; the IDT layers of the plurality of acoustic wave resonator structures have interdigital electrodes of the same period or different periods, and reflection gratings are provided at both ends of the IDT.

[0013] The present application further discloses a method for preparing an acoustic wave resonator structure, the preparation method being as follows: S1. forming a multilayer structure by a bonding process, where the multilayer structure includes a support layer, a piezoelectric film substrate, and a second passivation layer; S2. Based on the provision of the second passivation layer, forming a cavity on the support layer by etching, wherein the second passivation layer protects the piezoelectric film substrate from damage during etching; S3. Based on the determined resonator frequency, determine the interdigital period of the interdigital electrodes of the IDT layer, and form the IDT layer on the piezoelectric film substrate, followed by covering with a first passivation layer.

[0014] Compared with the prior art, the advantages of the present invention are: (1) A cavity structure is used under the piezoelectric film substrate. Compared with the complex solid Bragg reflector layer of the LLSAW structure, the cavity of the present application itself is in an extremely low acoustic impedance state, which is much lower than that of solid materials. Therefore, the sound wave is almost completely reflected at the interface between the piezoelectric film substrate and the cavity, and there is almost no energy leakage in the depth direction. Therefore, the quality factor Q value of the resonator will be much higher. At the same time, the simplified reflection interface can also greatly reduce the occurrence of parasitic modes. In addition, the removal of the complex solid Bragg reflector layer will greatly reduce the process difficulty and production cost.

[0015] (2) Compared with the traditional XBAR, the present invention uses a longitudinal wave mode propagating parallel to the surface instead of a Lamb wave mode. Therefore, the frequency can be adjusted by adjusting the IDT period. The structural frequency is correlated with the interdigital period of the IDT. The frequency is little affected by the thickness of the piezoelectric film substrate. Therefore, in the process of preparing a filter composed of dozens of resonators, only the interdigital period needs to be adjusted. The preparation process is simpler and the cost is low.

[0016] (3) Compared with traditional SAW filters, the acoustic wave resonator structure of the present application has a higher sound velocity and can also be applied to higher frequencies and larger bandwidths. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 is a schematic diagram of an acoustic wave resonator structure according to the present invention; Figure 2 The cut shape and crystal coordinate system X of the piezoelectric film substrate of the present invention are j Y j Z j Schematic diagram of the relative positions of Figure 3 The figure shows the comparison of the effects on parasitic modes when the angles of θ in the cut of an acoustic wave resonator structure according to the present invention are 30°, 40°, and 50° respectively. Figure 4 The distribution diagram of LLSAW energy with depth in the prior art; Figure 5 A diagram showing the distribution of energy with depth in an acoustic wave resonator structure according to the present invention; Figure 6 This is a simulation diagram of energy distribution in an acoustic wave resonator structure according to the present invention; Figure 7 The following are the corresponding admittance curves when the structural periods p of the IDT layer in the acoustic wave resonator structure of the present invention are 1 μm, 0.8 μm, and 0.6 μm respectively; Figure 8The following are the corresponding admittance curves when p is 1 μm and the thickness of the piezoelectric film substrate is 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, and 0.6 μm, respectively, in an acoustic wave resonator structure according to the present invention; Figure 9 This is an admittance curve corresponding to a piezoelectric film substrate thickness of 400nm and a structural period p of 0.8um in an acoustic wave resonator structure described in the present invention; Figure 10 This is the admittance curve corresponding to the traditional NormalSAW in the prior art when the structural period p is 0.8um.

[0018] in: 100, IDT layer, 101, interdigital electrode; 200. Piezoelectric film substrate; 300. Support layer, 301. Cavity. DETAILED DESCRIPTION

[0019] The present invention will be described in further detail below with reference to specific embodiments: To facilitate understanding, the relevant performance terms of the resonator are first explained: Elastic waves: including longitudinal waves, transverse waves, lamb waves, etc. Longitudinal waves refer to the mode in which the particle vibration direction and the wave propagation direction are the same, transverse waves refer to the mode in which the particle vibration direction and the wave propagation direction are perpendicular, and lamb waves refer to a standing wave mode unique to thin plates.

[0020] Rectangular coefficient: The two most important performance indicators of a filter are insertion loss in the passband and out-of-band rejection. The steepness of the transition band between the passband frequency and the out-of-band rejection frequency is the rectangular coefficient. The steeper the transition band, that is, the higher the rectangular coefficient, the more room the filter leaves for process deviation and temperature drift, and the better the performance.

[0021] Cut: Piezoelectric materials are generally anisotropic, meaning that the material properties are different in each direction. When making elastic wave RF filters, there are special requirements for the orientation of the piezoelectric substrate. This description of the substrate's orientation in the crystal coordinate system is generally called the cut.

[0022] Elastic wave RF filters are mainly divided into surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters.

[0023] The energy of a SAW filter is primarily concentrated on the surface of the piezoelectric substrate, with the propagation direction parallel to the substrate surface. The resonant frequency is primarily related to the structural period of the interdigital transducer (IDT). These include NormalSAW, TFSAW, TCSAW, and LLSAW. NormalSAW refers to a process for fabricating circuits directly on a single-layer piezoelectric substrate, TFSAW refers to a multi-layer thin-film substrate process, and TCSAW still uses a single-layer piezoelectric substrate, but with a thicker SiO2 layer covering the chip surface.

[0024] The particles of BAW vibrate along the normal direction of the substrate plane, and the propagation direction is also along the normal direction of the substrate. The resonant frequency is mainly related to the thickness of the piezoelectric film. According to the structural differences, it is often divided into FBAW, SMR BAW, and XBAR. Among them, FBAW and SMR BAW both use AlN as the piezoelectric layer and work in the longitudinal body wave mode, while XBAR generally uses Z-cut LN (lithium niobate) as the piezoelectric layer and works in the Lamb body wave mode in the thin plate.

[0025] like Figure 1 As shown, the present application discloses an acoustic wave resonator structure, which is a thin film longitudinal surface acoustic wave device (defined as "CFSAW") using a cavity as a reflective layer; the acoustic wave resonator structure includes an IDT layer 100, a piezoelectric film substrate 200, and a support layer 300 arranged in sequence from top to bottom.

[0026] The piezoelectric film substrate 200 has a first end face and a second end face; the IDT layer 100 is disposed on the first end face and includes interdigital electrodes 101 having a constant period or a varying period; the support layer 300 is disposed on the second end face and has a cavity 301 therein, thereby forming a cavity structure on the side of the piezoelectric film substrate 200 facing away from the IDT layer 100; the interface between the piezoelectric film substrate 200 and the cavity 301 has an acoustic impedance difference, thereby forming a total reflection interface, and the total emission interface is used to suppress acoustic wave leakage; the piezoelectric film substrate 200 uses an X-cut LN film substrate that can excite surface longitudinal waves, the propagation direction of the acoustic wave is parallel to the surface of the piezoelectric film substrate, and the frequency of the acoustic wave resonator structure is correlated with the period of the interdigital electrodes 101 of the IDT layer. Of course, in other embodiments, the piezoelectric film substrate can also use other materials that can excite surface acoustic waves.

[0027] Example 1

[0028] An acoustic wave resonator structure includes an IDT layer, a piezoelectric film substrate, and a support layer arranged in sequence from top to bottom. Figure 1 、 Figure 2 As shown, the piezoelectric film substrate, as the main body of vibration, adopts X-cut LN film substrate. j Y j Z jIn the crystal coordinate system, the angle θ is 30°. This angle θ is the angle between the direction of acoustic wave propagation and the Y axis of the crystal used for the piezoelectric thin film substrate.

[0029] In the IDT layer, the interdigitated electrodes have a constant period, such as Figure 1 As shown, the structural period is p, the electrical period (interdigital period) is λ, λ=2×p; the thickness h of the piezoelectric film substrate satisfies: h<0.5λ.

[0030] In this embodiment, the thickness h of the piezoelectric thin film substrate is 400 nm, and the interdigital period λ is 1.6 um.

[0031] The IDT layer is covered with a first passivation layer (PSV layer). This first passivation layer can be made of SiO2 and has a thickness of less than 100nm. This first passivation layer primarily protects the IDT layer. Its thickness affects the performance and parasitic modes of the structure, and it also serves to modulate the frequency within a small range.

[0032] The support layer can be made of silicon or other process materials that are easy to process by semiconductor etching. A second passivation layer (PSV layer) is provided on the side of the support layer away from the piezoelectric film substrate. The second passivation layer can be made of SiO2 to facilitate the implementation of the back-hole perforation process of the structure, that is, to facilitate etching to form a cavity. It can serve as a stop layer during the etching process. The thickness of the second passivation layer is less than 100nm.

[0033] Example 2

[0034] The piezoelectric film substrate is used as the main body of vibration, and the X-cut LN film substrate is used. j Y j Z j In the crystal coordinate system, the angle θ is 40°.

[0035] In this embodiment, the thickness h of the piezoelectric film substrate is 400 nm, and the interdigital period λ of the IDT layer is 1.6 μm, that is, the structural period p is 0.8 μm.

[0036] The IDT layer is covered with a first passivation layer (PSV layer), which can be made of SiO2 and has a thickness of less than 100nm. The support layer can be made of silicon or other materials that are easily processed by semiconductor etching. A second passivation layer (PSV layer) is provided on the side of the support layer away from the piezoelectric film substrate, with a thickness of less than 100nm.

[0037] Example 3

[0038] The piezoelectric film substrate is used as the main body of vibration, and the X-cut LN film substrate is used. j Y j Z j In the crystal coordinate system, the angle θ is 50°.

[0039] In this embodiment, the thickness h of the piezoelectric thin film substrate is 400 nm, and the interdigital period λ of the IDT layer is 1.6 μm.

[0040] The IDT layer is covered with a first passivation layer (PSV layer), which can be made of SiO2 and has a thickness of less than 100nm. The support layer can be made of silicon or other materials that are easily processed by semiconductor etching. A second passivation layer (PSV layer) is provided on the side of the support layer away from the piezoelectric film substrate, with a thickness of less than 100nm.

[0041] In the above embodiments 1-3, a CFSAW with a cavity structure is disclosed, and the main mode is a longitudinal wave mode propagating in a direction parallel to the surface of the piezoelectric film substrate. Figure 3 As shown in FIG, comparing the effect of θ on the parasitic mode in the cutting of the piezoelectric film substrate, when the angle θ is 40°, the parasitic mode can be effectively suppressed and the quality factor Q value will be much higher.

[0042] Regarding the CFSAW disclosed in this application, Figure 4 、 Figure 5 As shown, compared with the traditional LLSAW, the present application uses a cavity instead of a solid Bragg reflector to suppress the energy leakage of longitudinal waves and reduce parasitic modes; specifically, as Figure 4 As shown, in the traditional LLSAW structure, there are multiple layers of high and low acoustic impedance materials stacked together. In practical applications, due to the acoustic impedance difference of the solid material itself within an order of magnitude, there is still a lot of energy leakage. Therefore, the longitudinal wave will continue to leak energy deep into the substrate during propagation. In this application, combined with Figure 5 、 Figure 6 As shown in the figure, since the cavity itself is in an extremely low acoustic impedance state (<10e3 rayl), which is much lower than that of solid materials (>10e6 rayl), the sound waves are almost totally reflected at the interface between the piezoelectric film substrate and the cavity due to the difference in acoustic impedance, forming a totally reflective interface, and there is almost no energy leakage in the depth direction.

[0043] Example 4

[0044] An acoustic wave resonator structure includes an IDT layer, a piezoelectric film substrate, and a support layer arranged in sequence from top to bottom. The piezoelectric film substrate is used as the main body of vibration and adopts an X-cut LN film substrate. j Y j Z j In the crystal coordinate system, the angle θ is 40°.

[0045] In this embodiment, the thickness h of the piezoelectric thin film substrate is 400 nm, and the structural period p of the IDT layer is 1 um.

[0046] The IDT layer is covered with a first passivation layer, the thickness of which is less than 100 nm; a second passivation layer is provided on the side of the support layer away from the piezoelectric film substrate, the thickness of which is less than 100 nm.

[0047] Example 5

[0048] The piezoelectric film substrate is used as the main body of vibration, and the X-cut LN film substrate is used. j Y j Z j In the crystal coordinate system, the angle θ is 40°.

[0049] In this embodiment, the thickness h of the piezoelectric thin film substrate is 400 nm, and the structural period p of the IDT layer is 0.6 um.

[0050] The IDT layer is covered with a first passivation layer, the thickness of which is less than 100 nm; a second passivation layer is provided on the side of the support layer away from the piezoelectric film substrate, the thickness of which is less than 100 nm.

[0051] Combined with Example 2, Example 4 and Example 5, and referring to Figure 7 As shown, the frequency of the acoustic wave resonator structure is affected by the structural period p of the IDT layer. Mainly because this application uses a longitudinal wave mode propagating parallel to the surface instead of a Lamb wave mode, the structural frequency can be controlled by adjusting the interdigital period of the IDT layer. Then, in the same filter chip composed of dozens of resonators, it is only necessary to adjust the interdigital period to achieve frequency regulation. Compared with traditional XBAR, the production process is simpler and the cost can be controlled. This application covers the IDT layer with a PSV layer, which can protect the IDT while also playing a role in frequency modulation within a small range.

[0052] Example 6

[0053] An acoustic wave resonator structure includes an IDT layer, a piezoelectric film substrate, and a support layer arranged in sequence from top to bottom. The piezoelectric film substrate is used as the main body of vibration and adopts an X-cut LN film substrate. j Y j Z j In the crystal coordinate system, the angle θ is 40°.

[0054] In this embodiment, the thickness h of the piezoelectric film substrate is 0.25 μm, and the structural period p of the IDT layer is 1 μm.

[0055] The IDT layer is covered with a first passivation layer, and a second passivation layer is provided on the side of the support layer away from the piezoelectric film substrate, and the thickness of both layers is not less than 100 nm.

[0056] Example 7

[0057] The piezoelectric film substrate is used as the main body of vibration, and the X-cut LN film substrate is used. j Y j Z j The angle θ in the crystal coordinate system is 40°. In this embodiment, the thickness h of the piezoelectric thin film substrate is 0.3 μm, and the structural period p of the IDT layer is 1 μm.

[0058] Example 8

[0059] The piezoelectric film substrate is used as the main body of vibration, and the X-cut LN film substrate is used. j Y j Z j The angle θ in the crystal coordinate system is 40°. In this embodiment, the thickness h of the piezoelectric thin film substrate is 0.4 μm, and the structural period p of the IDT layer is 1 μm.

[0060] Example 9

[0061] The piezoelectric film substrate is used as the main body of vibration, and the X-cut LN film substrate is used. j Y j Z j The angle θ in the crystal coordinate system is 40°. In this embodiment, the thickness h of the piezoelectric thin film substrate is 0.5 μm, and the structural period p of the IDT layer is 1 μm.

[0062] Example 10

[0063] The piezoelectric film substrate is used as the main body of vibration, and the X-cut LN film substrate is used. j Y j Z j In the crystal coordinate system, the angle θ is 40°. In this embodiment, the thickness h of the piezoelectric thin film substrate is 0.6 μm, and the structural period p of the IDT layer is 1 μm.

[0064] like Figure 8 As shown, combined with Examples 6-10, it can be seen that when the structural period of the IDT layer is the same and the thickness of the piezoelectric film substrate LN changes, the frequency difference of the acoustic wave resonator structure is not large, but the parasitic mode decreases with the increase of the thickness of the piezoelectric film substrate LN. In the actual design process, it is necessary to control the parasitic mode outside the required frequency band.

[0065] In summary, in the present application, a cavity structure is formed under the piezoelectric film substrate LN, so that the interface between the piezoelectric film substrate and the cavity forms a total reflection interface, and thus there is almost no energy leakage in the depth direction; in the process, the energy leakage can also be reduced by controlling the thickness of the piezoelectric film substrate LN, so h is required to be less than 0.5λ. On the other hand, the resonant frequency of the parasitic mode can also be controlled by the thickness of the piezoelectric film substrate LN.

[0066] As a further supplement, Figure 9 As shown, referring to the simulation results of Example 2 in this application, when the angle θ is 40°, the thickness h of the piezoelectric film substrate is 400nm, and the structural period p is 0.8um, the resonant frequency fr (the frequency with the maximum admittance) is as high as 3.59GHz, the bandwidth BW is as high as 474MHz, the relative bandwidth is BW / fr, and the coupling coefficient K is 2 =π 2 BW / fr / 4, the relative bandwidth is calculated to be 13.2%, and the coupling coefficient K 2 As high as 32.6%.

[0067] Comparative Example 1 This comparative example provides a traditional NormalSAW. NormalSAW is a periodic device with a circuit fabricated directly on a single-layer piezoelectric substrate. Its resonant frequency is related to the structural period and has the following characteristics: The interdigital period λ of the interdigital transducer (IDT) is 1.6 μm, that is, the structural period p is 0.8 μm.

[0068] Based on simulation analysis, such as Figure 10 As shown in the figure, the NormalSAW with the same interdigital period as the CFSAW has a resonant frequency fr of only 2.248 GHz, a bandwidth of only 79 MHz, a relative bandwidth of 3.5%, and a coupling coefficient of 8.6%.

[0069] Based on the above, the CFSAW of this application is compared with LLSAW, XBAR and traditional SAW filters (Normal SAW, TFSAW, TCSAW). See Table 1 for details: Table 1. Performance comparison of CFSAW, LLSAW, XBAR and traditional SAW

[0070] In summary, with the demand for high frequency and wide bandwidth, although the traditional XBAR has a higher frequency and wider bandwidth, it can only use the thickness of the piezoelectric film to adjust the frequency. For a filter composed of dozens of resonators, it is extremely difficult and costly to achieve different thicknesses of the piezoelectric film substrate in a filter chip. The traditional LLSAW uses finger periodicity to adjust the frequency and has the potential to be used for high frequency and large bandwidth, but the substrate required for the structure is extremely complex and requires multiple layers of high and low acoustic impedance materials to be stacked, resulting in energy leakage and high production costs. The traditional SAW filter has a sound velocity of about 4000m / s, the frequency is generally below 3GHz, and it cannot be applied to the demand for large bandwidth. The CFSAW of the present application, by forming a cavity structure, achieves almost total reflection at the interface between the piezoelectric film substrate and the cavity, and there is almost no energy leakage in the depth direction; through the selection of the cutting type of the piezoelectric film substrate, unlike XBAR, the structural frequency is correlated with the interdigital period of the IDT, thereby simplifying the manufacturing process and achieving effective cost control; at the same time, the sound speed of CFSAW is much higher, about 6000m / s, so it can be applied to frequencies greater than 3GHz.

[0071] In the above embodiment, the interdigital electrodes in the IDT layer have a constant period. Generally, an impedance element resonator (IE) is used. The IE is a resonator composed of an IDT and a reflector at both ends. In one embodiment, the IDT and the reflector can use the same structural period. For details, refer to Figure 1 As shown; in other embodiments, the IDT and the reflector can also use different structural periods. The frequency of the acoustic wave resonator structure involved in this application is correlated with the period of the interdigital electrodes in the IDT layer, wherein the structural period of the reflector has little effect on the frequency of the acoustic wave resonator structure.

[0072] The present application may also use an acoustically coupled filter (CRF), which is also often referred to as a dual-mode filter (DMS), and is a filter composed of a plurality of variable-period IDTs and a reflection grating.

[0073] In practical applications, parasitic Lamb waves can also be suppressed by changing the shape of the cavity, such as using an irregular polygonal cavity structure.

[0074] This application also discloses a filter comprising multiple acoustic wave resonator structures described above; the IDT layers of the multiple acoustic wave resonator structures have interdigitated electrodes with the same or different periods. In this case, frequency control can be achieved within a single filter chip simply by adjusting the interdigitated frequency of the IDTs, simplifying the manufacturing process.

[0075] The present application further discloses a method for preparing an acoustic wave resonator structure, the preparation method is as follows: S1. forming a multilayer structure by a bonding process, where the multilayer structure includes a support layer, a piezoelectric film substrate, and a second passivation layer; S2. Based on the second passivation layer, a cavity is formed on the support layer by etching. In this case, the second passivation layer can serve as a stop layer during the etching process to protect the piezoelectric film substrate from damage. S3. Based on the determined resonator frequency, determine the interdigital period of the interdigital electrodes of the IDT layer, and form the IDT layer on the piezoelectric film substrate, followed by covering with a first passivation layer.

[0076] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they are not intended to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention.

Claims

1. An acoustic wave resonator structure, characterized in that: include: A piezoelectric film substrate having a first end surface and a second end surface; An IDT layer is provided on the first end surface and includes interdigital electrodes having a constant period or a varying period; A support layer is provided on the second end surface, and the support layer has a cavity therein; The piezoelectric film substrate adopts an X-cut LN film substrate that can excite surface longitudinal waves. The propagation direction of the acoustic wave is parallel to the surface of the piezoelectric film substrate, and the frequency of the acoustic wave resonator structure is correlated with the period of the interdigital electrodes of the IDT layer. There is an acoustic impedance difference at the interface between the piezoelectric film substrate and the cavity, thereby forming a total reflection interface, and the total reflection interface is used to suppress acoustic wave leakage.

2. The acoustic wave resonator structure according to claim 1, characterized in that: The angle θ between the propagation direction of the acoustic wave and the Y axis of the crystal used in the piezoelectric film substrate is 40°.

3. The acoustic wave resonator structure according to claim 2, characterized in that: The interdigital electrodes have a constant period, and the interdigital period is set to λ; the thickness h of the piezoelectric film substrate satisfies: h<0.5λ.

4. The acoustic wave resonator structure according to claim 1, wherein: The IDT layer includes an IDT and reflection gratings arranged at both ends of the IDT. The IDT and the reflection gratings use the same or different structural periods.

5. The acoustic wave resonator structure according to claim 1, characterized in that: The IDT layer is formed by combining a plurality of variable-period IDTs and reflective gratings.

6. The acoustic wave resonator structure according to claim 1, characterized in that: The IDT layer is covered with a first passivation layer, and the thickness of the first passivation layer is less than 100 nm.

7. The acoustic wave resonator structure according to claim 1, characterized in that: A second passivation layer is provided on a side of the support layer away from the piezoelectric film substrate, and the thickness of the second passivation layer is less than 100 nm.

8. A filter, characterized in that: An acoustic wave resonator structure comprising a plurality of structures according to any one of claims 1 to 7; The IDT layers of the multiple acoustic wave resonator structures have interdigital electrodes with the same period or different periods, and reflection gratings are provided at both ends of the IDT.

9. A method for preparing an acoustic wave resonator structure, characterized in that: Used to prepare an acoustic wave resonator structure according to any one of claims 1 to 7; The preparation method is as follows: S1. forming a multilayer structure by a bonding process, where the multilayer structure includes a support layer, a piezoelectric film substrate, and a second passivation layer; S2. forming a cavity on the support layer by etching, wherein the second passivation layer protects the piezoelectric film substrate from damage during etching; S3. Based on the determined resonator frequency, determine the interdigital period of the interdigital electrodes of the IDT layer, and form the IDT layer on the piezoelectric film substrate, followed by covering with a first passivation layer.

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