Surface acoustic wave device and preparation method thereof

Abstract

The invention discloses a surface acoustic wave device and a preparation method thereof. The surface acoustic wave device comprises a supporting substrate, a piezoelectric layer and an electrode, the piezoelectric layer is arranged on one side of the supporting substrate; the electrode is arranged on one side of the piezoelectric layer away from the supporting substrate; the supporting substrate comprises a base and a reflecting layer; the piezoelectric layer is arranged on one side of the reflecting layer away from the substrate; the sound velocity of the substrate is smaller than that of the reflecting layer and larger than that of the piezoelectric layer, and the sound velocity of the reflecting layer is larger than that of the piezoelectric layer. According to the technical scheme, the supporting substrate, the piezoelectric layer and the electrode are arranged in the surface acoustic wave device, the base and the reflecting layer are arranged in the supporting substrate, the sound velocity of longitudinal waves or quasi longitudinal waves propagated in the reflecting layer of the surface acoustic wave device is larger than that of the base, and therefore the effect of limiting sound wave energy to the piezoelectric layer can be achieved; leakage of longitudinal wave energy is suppressed, and the performance of the high-frequency surface acoustic wave filter is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a surface acoustic wave device and a preparation method thereof. Background Art

[0002] With the continuous iteration and update of mobile communication technology, wireless communication spectrum resources are becoming increasingly scarce, and people are increasingly in need of using higher frequency bands to achieve more diverse, faster, and higher throughput wireless communications. RF filters are one of the core components of wireless communications. In order to meet the needs of mobile communications in the new era, the development of high-frequency RF filters is very important.

[0003] However, the development and preparation of high-performance, small-size, low-cost high-frequency RF filters is still a technical challenge. In conventional surface acoustic wave devices, longitudinal waves in the prior art usually leak a large amount of energy to the substrate, so they cannot be used as the main mode of surface acoustic wave devices, making it difficult to achieve a higher passband frequency, reducing the performance of high-frequency surface acoustic wave filters. Summary of the invention

[0004] The present invention provides a surface acoustic wave device and a preparation method thereof, so as to solve the problem in the prior art that the longitudinal wave leaks in the surface acoustic wave device, resulting in poor performance of a high-frequency surface acoustic wave filter.

[0005] According to one aspect of the present invention, there is provided a surface acoustic wave device, comprising: a supporting substrate, a piezoelectric layer and an electrode;

[0006] The piezoelectric layer is arranged on one side of the supporting substrate; the electrode is arranged on the side of the piezoelectric layer away from the supporting substrate;

[0007] The supporting substrate comprises a base and a reflective layer; the piezoelectric layer is arranged on the side of the reflective layer away from the base; the sound velocity of the base is smaller than the sound velocity of the reflective layer and larger than the sound velocity of the piezoelectric layer, and the sound velocity of the reflective layer is larger than the sound velocity of the piezoelectric layer.

[0008] Optionally, the reflective layer includes a diamond film.

[0009] Optionally, the heat dissipation efficiency of the reflective layer is greater than the heat dissipation efficiency of the piezoelectric layer.

[0010] Optionally, a transition layer is further included between the substrate and the reflective layer;

[0011] The sound velocity of the transition layer is lower than that of the reflection layer.

[0012] Optionally, the thickness x1 of the piezoelectric layer and the wavelength λ of the surface acoustic wave device satisfy x1≤0.5λ;

[0013] The thickness x2 of the reflective layer and the wavelength λ of the surface acoustic wave device satisfy x2>0.3λ.

[0014] Optionally, the thickness x3 of the electrode and the wavelength λ of the surface acoustic wave device satisfy 0.05λ≤x3≤0.12λ.

[0015] Optionally, the resistivity of the supporting substrate is greater than 1000 Ω·cm.

[0016] Optionally, the cutting direction of the piezoelectric layer is Y, and the cutting edge direction is Z;

[0017] Alternatively, the cutting direction of the piezoelectric layer is X, and the cutting edge direction is 36°Y.

[0018] According to another aspect of the present invention, a method for preparing a surface acoustic wave device is provided, which is used for preparing a surface acoustic wave device;

[0019] The preparation method comprises:

[0020] providing a substrate and a piezoelectric layer;

[0021] Growing a reflective layer on one side of the substrate to form a supporting substrate; wherein the acoustic velocity of the reflective layer is greater than the acoustic velocity of the substrate;

[0022] Bonding the support substrate and the piezoelectric layer; wherein the piezoelectric layer is arranged on a side of the reflective layer away from the substrate;

[0023] An electrode is grown on the side of the piezoelectric layer away from the supporting substrate.

[0024] Optionally, bonding the support substrate and the piezoelectric layer comprises:

[0025] Polishing the reflective layer on a side away from the substrate, and polishing the first side of the piezoelectric layer;

[0026] The reflective layer is aligned and bonded to the first surface of the piezoelectric layer on a surface away from the substrate.

[0027] The technical solution of the present invention is to set a supporting substrate, a piezoelectric layer and an electrode in a surface acoustic wave device, and set a base and a reflective layer in the supporting substrate. The sound velocity of longitudinal waves or quasi-longitudinal waves propagating in the reflective layer of the surface acoustic wave device is greater than the sound velocity of the base, so the sound wave energy can be limited to the piezoelectric layer, the leakage of longitudinal wave energy is suppressed, and the performance of the high-frequency surface acoustic wave filter is improved; at the same time, since the cost of ultra-high sound velocity materials is relatively high, the sound velocity of the base set in the supporting substrate is also greater than the sound velocity of the piezoelectric layer but less than the sound velocity of the reflective layer, which reduces the cost while ensuring the performance of the surface acoustic wave device and improves the flexibility of adjustment of the surface acoustic wave device.

[0028] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 is a schematic structural diagram of a first surface acoustic wave device provided according to an embodiment of the present invention;

[0031] Figure 2 is a schematic structural diagram of a second surface acoustic wave device provided according to an embodiment of the present invention;

[0032] Figure 3 is a schematic diagram of an admittance curve of a first surface acoustic wave device provided according to an embodiment of the present invention;

[0033] Figure 4 is a schematic diagram of the main wave vibration shape of an acoustic wave of a first surface acoustic wave device provided according to an embodiment of the present invention;

[0034] Figure 5 is a schematic diagram of an admittance curve of a third surface acoustic wave device provided according to an embodiment of the present invention;

[0035] Figure 6 is a schematic diagram of the main wave vibration shape of an acoustic wave of a third surface acoustic wave device provided according to an embodiment of the present invention;

[0036] Figure 7 is a schematic diagram of an admittance curve of a fourth surface acoustic wave device provided according to an embodiment of the present invention;

[0037] Figure 8 is a schematic diagram of the main wave vibration shape of an acoustic wave of a fourth surface acoustic wave device provided according to an embodiment of the present invention;

[0038] Fig. 9 is a flow chart for preparing a first surface acoustic wave device provided according to an embodiment of the present invention;

[0039] Fig.10 is a structural diagram corresponding to the preparation process of the first surface acoustic wave device provided by an embodiment of the present invention;

[0040] Fig.11 It is a flow chart of preparing a second surface acoustic wave device provided according to an embodiment of the present invention.

[0041] Figure numerals: 1. supporting substrate; 2. piezoelectric layer; 3. electrode; 11. base; 12. reflective layer; 4. transition layer. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein.

[0044] Surface acoustic wave devices are solid devices that utilize the characteristics of acoustic-electric transducers to perform various processes on acoustic signals propagating on the surface of a piezoelectric material substrate and perform various functions. Surface acoustic wave devices include electrodes, which may be interdigitated electrodes. When an alternating voltage is applied to the interdigitated electrodes, surface acoustic waves can be stimulated on the surface of the piezoelectric layer. Different electrode parameters and piezoelectric layer parameters will stimulate different surface acoustic waves. In conventional surface acoustic wave devices, longitudinal waves usually leak a large amount of energy to the substrate, so they cannot be used as the main mode of the surface acoustic wave device, and thus a higher passband efficiency of the surface acoustic wave device cannot be achieved. Therefore, an embodiment of the present invention provides a surface acoustic wave device, Figure 1 Schematic diagram of the structure of a first surface acoustic wave device provided according to an embodiment of the present invention. Figure 1 As shown, the surface acoustic wave device includes: a supporting substrate 1, a piezoelectric layer 2 and an electrode 3;

[0045] The piezoelectric layer 2 is arranged on one side of the supporting substrate 1; the electrode 3 is arranged on the side of the piezoelectric layer 2 away from the supporting substrate 1;

[0046] The supporting substrate 1 includes a base 11 and a reflective layer 12; the piezoelectric layer 2 is arranged on the side of the reflective layer 12 away from the base 11; the sound velocity of the base 11 is smaller than the sound velocity of the reflective layer 12 and larger than the sound velocity of the piezoelectric layer 2, and the sound velocity of the reflective layer 12 is larger than the sound velocity of the piezoelectric layer 2.

[0047] Among them, the supporting substrate 1 includes a base 11 and a reflective layer 12. The base 11 can be used to prepare the reflective layer 12. The material of the base 11 can be silicon or silicon carbide. In order to use the longitudinal wave or quasi-longitudinal wave with a higher sound speed as the main mode in the surface acoustic wave device and ensure the high passband frequency, the reflective layer 12 is set in the supporting substrate 1. Since the propagation of longitudinal waves is greatly affected by the material, a better longitudinal wave surface acoustic wave device should be one in which most of the sound wave energy is propagated in the piezoelectric layer 2. The reflective layer 12 is set, and the sound speed of the reflective layer 12 is greater than the sound speed of the base 11 and the sound speed of the piezoelectric layer 2, so that the reflective layer 12 limits the sound wave energy in the piezoelectric layer 2 in the piezoelectric layer 2, ensures the quality of the longitudinal wave, and improves the quality factor of the surface acoustic wave.

[0048] Among them, since sound waves tend to propagate more in materials with low sound speed, setting the sound speed of the substrate 11 to be greater than the sound speed of the piezoelectric layer 2 can further limit or reflect the sound waves to the piezoelectric layer 2. Setting the sound speed of the substrate 11 to be less than the reflection layer 12 is to set a high sound speed film layer adjacent to the piezoelectric layer 2 to thereby improve the sound speed limiting effect in the piezoelectric layer 2.

[0049] It is understandable that in the prior art, a low acoustic velocity layer is set between the piezoelectric layer 2 and the substrate 11, which causes the low acoustic velocity layer adjacent to the piezoelectric layer 2 and the piezoelectric layer 2 to propagate a large amount of longitudinal wave energy. The parameters of the low acoustic velocity layer will reduce the quality of the longitudinal wave, thereby affecting the performance of the device. When the longitudinal wave is concentrated in the piezoelectric layer 2, the electromechanical coupling coefficient of the surface acoustic wave is high, so that the bandwidth of the surface acoustic wave device is large. However, since the low acoustic velocity layer has no piezoelectricity, the electromechanical coupling coefficient of the surface acoustic wave device is greatly reduced, so that the bandwidth of the surface acoustic wave device becomes smaller. Therefore, in the embodiment of the present invention, a high acoustic velocity reflection layer 12 is set between the piezoelectric layer 2 and the substrate 11, which can limit the acoustic wave energy in the piezoelectric layer 2, improve the electromechanical coupling coefficient of the surface acoustic wave, and ensure the bandwidth of the surface acoustic wave device.

[0050] It can be understood that in the embodiment of the present invention, an ultra-high acoustic velocity reflection layer 12 is provided close to the piezoelectric layer 2, and a substrate 11 is provided on the side of the ultra-high acoustic velocity reflection layer 12 away from the piezoelectric layer 2, because in the actual process, the ultra-high speed material is usually more expensive, so considering the cost and the limiting effect of the acoustic wave energy, the substrate 11 is provided on the side of the reflection layer 12, thereby reducing the cost while ensuring the performance of the surface acoustic wave device. In addition, the parameters of the supporting substrate 1 can be changed by adjusting the thickness of the substrate 11 and other parameters according to the needs of the surface acoustic wave device, thereby completing the adjustment of the performance of the surface acoustic wave device, which also reduces the preparation cost of the surface acoustic wave.

[0051] Exemplarily, in the process of preparing a surface acoustic wave device, a substrate 11 with a thickness of 525 μm is first obtained, and a reflective layer 12 is grown on the surface of the wafer, and the thickness of the reflective layer 12 is slightly thicker than 1.2 μm; then the reflective layer 12 is surface treated by a polishing process to ensure that the surface is smooth and the thickness of the reflective layer 12 is 1.2 μm. Then a piezoelectric layer 2 with a cutting direction of Y and a cutting edge direction of Z is obtained, and the surface of the piezoelectric layer 2 is cleaned and polished. The piezoelectric layer 2 and the reflective layer 12 are aligned and bonded along the polished surface to obtain a bonding structure. The bonded piezoelectric layer 2 is ground and thinned to a thickness of about 1 μm. Then the surface of the thinned piezoelectric layer 2 is polished and other processes are performed to make the surface smooth and the thickness of the piezoelectric layer 2 is 0.6 microns, and the preparation of the bonded wafer is completed, and then an electrode 3 is prepared on the side of the piezoelectric layer 2 away from the substrate to complete the preparation of the surface acoustic wave device.

[0052] The technical solution of the embodiment of the present invention is to set a supporting substrate, a piezoelectric layer and an electrode in a surface acoustic wave device, and set a base and a reflective layer in the supporting substrate. The sound speed of longitudinal waves or quasi-longitudinal waves propagating in the reflective layer of the surface acoustic wave device is greater than the sound speed of the base, so the sound wave energy can be limited to the piezoelectric layer, the leakage of longitudinal wave energy is suppressed, and the performance of the high-frequency surface acoustic wave filter is improved; at the same time, since the cost of ultra-high sound speed materials is relatively high, the sound speed of the base set in the supporting substrate is also greater than the sound speed of the piezoelectric layer but less than the sound speed of the reflective layer, which reduces the cost while ensuring the performance of the surface acoustic wave device and improves the flexibility of adjustment of the surface acoustic wave device.

[0053] Optional, continue to refer to Figure 1 As shown, the heat dissipation efficiency of the reflective layer 12 is greater than the heat dissipation efficiency of the piezoelectric layer 2 .

[0054] Among them, a reflective layer 12 with both ultra-high sound speed and high heat dissipation efficiency can be set, so that the reflective layer 12 can not only suppress the leakage of longitudinal wave energy, but also quickly export the heat of the piezoelectric layer 2, thereby increasing the internal heat diffusion efficiency of the surface acoustic wave device, alleviating the problem of uneven heat distribution inside the surface acoustic wave device, and improving the power tolerance of the surface acoustic wave device.

[0055] In some embodiments, the reflective layer 12 includes a diamond film. Since the diamond film has an ultra-high sound velocity, the diamond film is provided as the reflective layer 12 to limit the energy of the sound wave. At the same time, the diamond film also has extremely high thermal conductivity and is close to the piezoelectric layer 2, which increases the heat diffusion efficiency inside the surface acoustic wave device, effectively alleviates the uneven in-plane heat distribution between the various parts inside the surface acoustic wave device, and thus improves the power tolerance of the surface acoustic wave device.

[0056] It is understandable that, due to the high cost of the diamond film, it is provided in the supporting substrate 1 with a relatively thin thickness, which not only suppresses the leakage of longitudinal wave energy but also ensures the cost of the surface acoustic wave device.

[0057] Optional, Figure 2 is a schematic diagram of the structure of a second surface acoustic wave device provided according to an embodiment of the present invention, such as Figure 2 As shown, a transition layer 4 is further included between the substrate 11 and the reflective layer 12;

[0058] The sound velocity of the transition layer 4 is lower than the sound velocity of the reflection layer 12 .

[0059] The transition layer 4 can play a role in adjusting the bandwidth of the surface acoustic wave device, and the material of the transition layer 4 can include silicon dioxide or silicon nitride, etc. The thickness of the transition layer 4 can be determined according to the needs of the surface acoustic wave device. In order not to affect the suppression of longitudinal waves, the transition layer 4 is arranged between the substrate 11 and the reflection layer 12, and the sound velocity of the transition layer 4 is less than the sound velocity of the reflection layer 12, which suppresses the leakage of longitudinal wave energy while satisfying the regulation of the bandwidth of the surface acoustic wave device.

[0060] It can be understood that when preparing the transition layer 4 , the transition layer 4 is first grown on the substrate 11 , and then the reflective layer 12 is grown on the side of the transition layer 4 away from the substrate 11 .

[0061] The technical solution of the embodiment of the present invention, by setting a transition layer between the substrate and the reflective layer and setting the sound velocity of the transition layer to be smaller than the sound velocity of the reflective layer, suppresses the leakage of longitudinal wave energy while satisfying the regulation function of the bandwidth of the surface acoustic wave device.

[0062] Optional, continue to refer to Figure 1 As shown, the thickness x1 of the piezoelectric layer 2 and the wavelength λ of the surface acoustic wave device satisfy x1≤0.5λ;

[0063] The thickness x2 of the reflective layer 12 and the wavelength λ of the surface acoustic wave device satisfy x2>0.3λ.

[0064] The thickness of the piezoelectric layer 2 should not be too thick, because when the piezoelectric layer 2 is too thick, the supporting substrate 1 disposed below the piezoelectric layer 2 becomes relatively small, and the regulating effect on the acoustic wave in the piezoelectric layer 2 will also become smaller. At this time, the effect of the supporting substrate 1 is relatively weak and cannot play a good inhibitory role. Therefore, the thickness x1 of the piezoelectric layer 2 is set to satisfy x1≤0.5λ with the wavelength λ of the surface acoustic wave device. Preferably, the thickness of the piezoelectric layer 2 is set to 0.6μm.

[0065] The thickness of the reflective layer 12 should not be too thick or too thin, because the cost of ultra-high acoustic velocity materials is relatively high; when the thickness of the reflective layer 12 is too thin, it will not have a good inhibitory effect. In order to reduce the cost of the surface acoustic wave device and ensure the function of the reflective layer 12, a suitable thickness of the reflective layer 12 is set, so the thickness x2 of the reflective layer 12 and the wavelength λ of the surface acoustic wave device are set to satisfy x2>0.3λ. Preferably, the thickness of the reflective layer 12 is set to 1.2μm.

[0066] For example, Figure 3 is a schematic diagram of an admittance curve of a first surface acoustic wave device provided according to an embodiment of the present invention, Figure 4 is a schematic diagram of the main wave vibration shape of the acoustic wave of the first surface acoustic wave device provided according to an embodiment of the present invention, combined with Figure 1 , Figure 3 and Figure 4 As shown, the thickness of the piezoelectric layer 2 is 0.6 microns, and the thickness of the diamond film is 1.2 microns. In the operation process of the surface acoustic wave device, the frequency and intensity of the main mode response of the acoustic wave are high. In a large frequency range, the clutter response is small and weak, and the main mode of the acoustic wave does not leak downward. Therefore, the surface acoustic wave device has the characteristics of high frequency and high performance. Figure 5 is a schematic diagram of an admittance curve of a third surface acoustic wave device provided according to an embodiment of the present invention, Figure 6 is a schematic diagram of the main wave vibration shape of the acoustic wave of the third surface acoustic wave device provided according to an embodiment of the present invention, and combined with Figure 5 and Figure 6 As shown in FIG. 1 , for comparison, when the thickness of the piezoelectric layer 2 is increased to 2 μm and other settings remain unchanged, the simulated admittance curve of an unreasonable designed surface acoustic wave device is obtained as shown in FIG. Figure 6 Obviously, in this case, the clutter responses are more numerous and stronger, and the quality of the resonator is poor. Figure 7 is a schematic diagram of an admittance curve of a fourth surface acoustic wave device provided according to an embodiment of the present invention, Figure 8 is a schematic diagram of the main wave vibration shape of the acoustic wave of the fourth surface acoustic wave device provided according to an embodiment of the present invention, combined with Figure 7 and Figure 8 As shown in FIG. 1 , for comparison, when the thickness of the reflective layer 12, i.e., the diamond film, is thinned to 0.4 μm and other settings remain unchanged, the main mode vibration shape diagram of another unreasonable designed surface acoustic wave device is obtained as shown in FIG. Figure 7 Obviously, in this case, the main mode of the acoustic wave leaks downward, and the quality of the resonator is poor.

[0067] The technical solution of the embodiment of the present invention ensures that the reflection layer suppresses longitudinal waves or quasi-longitudinal waves, improves the downward leakage of longitudinal waves or quasi-longitudinal waves, improves the performance of the surface acoustic wave device, and controls the cost by setting the thickness x1 of the piezoelectric layer and the wavelength λ of the surface acoustic wave device to satisfy x1≤0.5λ; and setting the thickness x2 of the reflection layer and the wavelength λ of the surface acoustic wave device to satisfy x2>0.3λ.

[0068] Optional, continue to refer to Figure 1 As shown, the thickness x3 of the electrode 3 and the wavelength λ of the surface acoustic wave device satisfy 0.05λ≤x3≤0.12λ.

[0069] The electrode 3 may include an interdigital transducer, a reflective grid, a bus bar and an electrode 3 pad, each interdigital transducer alternately connecting two electrical ends; the reflective grid is arranged on both sides of the interdigital transducer, and the reflective grids on each side are interconnected. The thickness x3 of the electrode 3 and the wavelength λ of the surface acoustic wave device are set to satisfy 0.05λ≤x3≤0.12λ, because the coupling coefficient between the electrode 3 and the piezoelectric layer 2 must be satisfied to achieve coupling to generate stable sound waves, so the thickness of the electrode 3 should not be too thin or too thick, for example, 160nm, to ensure the stability of the generation of longitudinal waves or quasi-longitudinal waves.

[0070] In some embodiments, the IDT may include one or more layers, and at least one layer is a main layer; the main layer is made of aluminum or an alloy with aluminum as the main element; the thickness of the main layer may account for more than 80% of the total thickness of the IDT. In some embodiments, in order to ensure the bonding reliability of the IDT, a layer of titanium underlayer and a layer of aluminum underlayer are provided on the IDT, the thickness of titanium is 5 nanometers, and the thickness of aluminum is 155 nanometers. The titanium underlayer plays a bonding role, ensuring that the main layer aluminum and the piezoelectric layer 2 have poor adhesion, which leads to the problem of motor falling off, and improves reliability.

[0071] The technical solution of the embodiment of the present invention ensures the coupling between the electrode and the voltage layer and the stability of the generation of longitudinal waves or quasi-longitudinal waves by limiting the thickness x3 of the electrode and the wavelength λ of the surface acoustic wave device to satisfy 0.05λ≤x3≤0.12λ.

[0072] Optional, continue to refer to Figure 1 As shown, the resistivity of the support substrate 1 is greater than 1000 Ω·cm.

[0073] Among them, since the surface acoustic wave device is an electrical device, if the resistivity of the supporting substrate 1 is poor, it will easily cause the surface acoustic wave device to generate induced capacitance, thereby affecting the performance of the filter. Therefore, the resistivity of the supporting substrate 1 is set to be greater than 1000Ω·cm to avoid affecting the filter performance.

[0074] In some embodiments, the resistivity of the support substrate 1 may be set to be equal to 3000 Ω·cm.

[0075] The technical solution of the embodiment of the present invention further improves the performance of the surface acoustic wave device and ensures the normal operation of the surface acoustic wave device by setting the resistivity of the supporting substrate to be greater than 1000Ω·cm.

[0076] Optional, continue to refer to Figure 1 As shown, the cutting direction of the piezoelectric layer 2 is Y, and the cutting edge direction is Z;

[0077] Alternatively, the cutting direction of the piezoelectric layer 2 is X, and the cutting edge direction is 36°Y.

[0078] Among them, the piezoelectric layer 2 may include lithium niobate material. Since the density, elastic modulus and other parameters of the piezoelectric layer 2 will affect the sound waves formed by the piezoelectric layer 2, and the elastic modulus of the piezoelectric layer 2 in different cutting directions and cutting edge directions is different, the cutting direction of the piezoelectric layer 2 is set to Y, and the cutting edge direction is set to Z, or the cutting direction of the piezoelectric layer 2 is set to X, and the cutting edge direction is 36°Y, to ensure the formation of stable and fixed frequency band sound waves.

[0079] In some embodiments, the acoustic wave wavelength of the surface acoustic wave device can be between 500nm and 3μm by setting parameters such as the width and spacing of the electrode 3 and parameters such as the density and elastic modulus of the piezoelectric layer 2 to ensure the performance of the surface acoustic wave device.

[0080] The technical solution of the present invention is to set a supporting substrate, a piezoelectric layer and an electrode in a surface acoustic wave device, and set a base and a reflective layer in the supporting substrate. The sound velocity of longitudinal waves or quasi-longitudinal waves propagating in the reflective layer of the surface acoustic wave device is greater than the sound velocity of the base, so the sound wave energy can be limited to the piezoelectric layer, the leakage of longitudinal wave energy is suppressed, and the performance of the high-frequency surface acoustic wave filter is improved; at the same time, since the cost of ultra-high sound velocity materials is relatively high, the sound velocity of the base set in the supporting substrate is also greater than the sound velocity of the piezoelectric layer but less than the sound velocity of the reflective layer, which reduces the cost while ensuring the performance of the surface acoustic wave device and improves the flexibility of adjustment of the surface acoustic wave device.

[0081] Based on the same inventive concept, Fig. 9 is a flow chart of preparing a first surface acoustic wave device according to an embodiment of the present invention, Fig.10 is a structural diagram corresponding to the preparation process of the first surface acoustic wave device provided in an embodiment of the present invention, combined with Fig. 9 and Fig.10 As shown, a method for preparing a surface acoustic wave device is provided, which is used to prepare a surface acoustic wave device;

[0082] The preparation method comprises:

[0083] S10, providing a substrate and a piezoelectric layer. Fig.10 As shown in step (a).

[0084] The substrate 11 may be used to prepare the reflective layer 12, and the substrate 11 may be made of silicon or silicon carbide. The material of the piezoelectric layer 2 may include lithium niobate.

[0085] S11, growing a reflective layer on one side of the substrate to form a supporting substrate. The acoustic velocity of the reflective layer is greater than the acoustic velocity of the substrate. Fig.10 As shown in step (b).

[0086] In order to use the longitudinal wave or quasi-longitudinal wave with a higher sound speed as the main mode in the surface acoustic wave device and ensure the high passband frequency, a reflective layer 12 is provided in the supporting substrate 1. Since the propagation of longitudinal waves is greatly affected by the material, a more optimal longitudinal wave surface acoustic wave device should be one in which most of the sound wave energy propagates in the piezoelectric layer 2, and a reflective layer 12 is provided, and the sound speed of the reflective layer 12 is greater than the sound speed of the substrate 11 and the sound speed of the piezoelectric layer 2, so that the reflective layer 12 limits the sound wave energy in the piezoelectric layer 2 in the piezoelectric layer 2, ensures the quality of the longitudinal wave, and improves the quality factor of the surface acoustic wave.

[0087] S12, bonding the support substrate and the piezoelectric layer. The piezoelectric layer is arranged on the side of the reflective layer away from the substrate. Fig.10 As shown in step (c).

[0088] The supporting substrate 1 and the piezoelectric layer 2 are bonded so that the reflective layer 12 is disposed between the base 11 and the piezoelectric layer 2. Since sound waves tend to propagate in materials with low sound speed, setting the sound speed of the base 11 to be greater than the sound speed of the piezoelectric layer 2 can further limit or reflect the sound waves to the piezoelectric layer 2. Setting the sound speed of the base 11 to be less than the reflective layer 12 is to set a high sound speed film layer adjacent to the piezoelectric layer 2, thereby improving the sound speed limiting effect in the piezoelectric layer 2.

[0089] S13, growing an electrode on the side of the piezoelectric layer away from the supporting substrate. Fig.10 As shown in step (d).

[0090] The electrode 3 can be prepared on the side of the piezoelectric layer 2 away from the substrate 11 by using a photolithography process, a coating process, a stripping process, and the like.

[0091] Exemplarily, in the process of preparing the surface acoustic wave device, a substrate 11 with a thickness of 525 μm is first obtained, and a reflective layer 12 is grown on the surface of the wafer, and the thickness of the reflective layer 12 is slightly thicker than 1.2 μm; then the reflective layer 12 is surface treated by a polishing process to ensure a smooth surface and a thickness of 1.2 μm. Then, a piezoelectric layer 2 with a cutting direction of Y and a cutting edge direction of Z is obtained, and the surface of the piezoelectric layer 2 is cleaned and polished. The piezoelectric layer 2 and the reflective layer 12 are aligned and bonded along the polished surface to obtain a bonding structure. The bonded piezoelectric layer 2 is ground and thinned to a thickness of about 1 μm. The surface of the thinned piezoelectric layer 2 is then polished and other treatments are performed to make the surface smooth and the thickness of the piezoelectric layer 2 is 0.6 microns, completing the preparation of the bonded wafer; the surface of the bonded wafer is then cleaned, and the pattern of the designed electrode 3 of the surface acoustic wave device is transferred to the photoresist above the lithium niobate layer of the bonded wafer using a photolithography process; 5 nanometers of titanium and 155 nanometers of aluminum are plated on the piezoelectric layer 2 and the photoresist in sequence using a coating process; the photoresist and excess electrode 3 material above it are removed using a stripping process, and the electrode 3 material left above the piezoelectric layer 2 forms the designed electrode 3 pattern, i.e., forms the electrode 3; overlay and other treatments are then performed, and after subsequent processes such as packaging, the preparation of the high-frequency surface acoustic wave device is completed.

[0092] The technical solution of the embodiment of the present invention is to prepare a supporting substrate, a piezoelectric layer and an electrode in a surface acoustic wave device, and prepare a reflecting layer on the base of the supporting substrate. The sound velocity of longitudinal waves or quasi-longitudinal waves propagating in the reflecting layer of the surface acoustic wave device is greater than the sound velocity of the base, so the sound wave energy can be limited to the piezoelectric layer, the leakage of longitudinal wave energy is suppressed, and the performance of the high-frequency surface acoustic wave filter is improved; at the same time, since the cost of ultra-high sound velocity materials is relatively high, the sound velocity of the base in the supporting substrate is also set to be greater than the sound velocity of the piezoelectric layer but less than the sound velocity of the reflecting layer, which reduces the cost while ensuring the performance of the surface acoustic wave device and improves the flexibility of adjustment of the surface acoustic wave device.

[0093] Based on the above embodiments, Fig.11 is a flow chart of preparing a second surface acoustic wave device according to an embodiment of the present invention, combined with Figure 1 and Fig.11 As shown, the preparation method comprises:

[0094] S20. Provide a substrate and a piezoelectric layer.

[0095] S21, growing a reflective layer on one side of the substrate to form a supporting substrate, wherein the acoustic velocity of the reflective layer is greater than the acoustic velocity of the substrate.

[0096] S22, polishing the side of the reflective layer away from the substrate, and polishing the first side of the piezoelectric layer.

[0097] After the reflective layer 12 is prepared, the reflective layer 12 is polished; at the same time, the piezoelectric layer 2 is polished to facilitate subsequent bonding.

[0098] It is understandable that, since both the reflective layer 12 and the piezoelectric layer 2 need to be polished, the thickness of the grown reflective layer 12 needs to be greater than the target thickness. Similarly, the thickness of the piezoelectric layer 2 needs to be greater than the target thickness.

[0099] S23, aligning and bonding the surface of the reflective layer away from the substrate to the first surface of the piezoelectric layer.

[0100] After the reflective layer 12 and the piezoelectric layer 2 are polished, the polished surfaces of the reflective layer 12 and the piezoelectric layer 2 are aligned and bonded to complete the preparation of the bonded wafer.

[0101] S24. Growing an electrode on the side of the piezoelectric layer away from the supporting substrate.

[0102] The technical solution of the embodiment of the present invention ensures the reliability of the bonded wafer by polishing the reflective layer and the piezoelectric layer before bonding, improves the process flow of the surface acoustic wave device, and improves the performance of the high-frequency surface acoustic wave filter.

[0103] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0104] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A surface acoustic wave device, characterized in that: include: supporting substrate, piezoelectric layer and electrodes; The piezoelectric layer is arranged on one side of the supporting substrate; The electrode is arranged on a side of the piezoelectric layer away from the supporting substrate; The supporting substrate comprises a base and a reflective layer; the piezoelectric layer is arranged on a side of the reflective layer away from the base; the sound velocity of the base is smaller than the sound velocity of the reflective layer and larger than the sound velocity of the piezoelectric layer, and the sound velocity of the reflective layer is larger than the sound velocity of the piezoelectric layer.

2. The surface acoustic wave device according to claim 1, characterized in that: The reflective layer includes a diamond thin film.

3. The surface acoustic wave device according to claim 1, characterized in that: The heat dissipation efficiency of the reflective layer is greater than the heat dissipation efficiency of the piezoelectric layer.

4. The surface acoustic wave device according to claim 1, characterized in that: A transition layer is also included between the substrate and the reflective layer; The sound velocity of the transition layer is lower than the sound velocity of the reflection layer.

5. The surface acoustic wave device according to claim 1, characterized in that: The thickness x1 of the piezoelectric layer and the wavelength λ of the surface acoustic wave device satisfy x1≤0.5λ; The thickness x2 of the reflective layer and the wavelength λ of the surface acoustic wave device satisfy x2>0.3λ.

6. The surface acoustic wave device according to claim 5, characterized in that: The thickness x3 of the electrode and the wavelength λ of the surface acoustic wave device satisfy 0.05λ≤x3≤0.12λ.

7. The surface acoustic wave device according to claim 1, characterized in that: The resistivity of the support substrate is greater than 1000Ω·cm.

8. The surface acoustic wave device according to claim 1, characterized in that: The cutting direction of the piezoelectric layer is Y, and the cutting edge direction is Z; Alternatively, the cutting direction of the piezoelectric layer is X, and the cutting edge direction is 36°Y.

9. A method for preparing a surface acoustic wave device, characterized in that: Used for preparing a surface acoustic wave device according to any one of claims 1 to 8; The preparation method comprises: providing a substrate and a piezoelectric layer; Growing a reflective layer on one side of the substrate to form a supporting substrate; wherein the acoustic velocity of the reflective layer is greater than the acoustic velocity of the substrate; Bonding the support substrate and the piezoelectric layer; wherein the piezoelectric layer is arranged on a side of the reflective layer away from the substrate; An electrode is grown on a side of the piezoelectric layer away from the supporting substrate.

10. The method for preparing a surface acoustic wave device according to claim 9, characterized in that: Bonding the support substrate and the piezoelectric layer, comprising: Polishing the reflective layer on a side away from the substrate, and polishing the first side of the piezoelectric layer; The reflective layer is aligned and bonded to a surface away from the substrate and the first surface of the piezoelectric layer.

Images