Surface acoustic wave resonator and manufacturing method thereof

Abstract

The invention relates to a surface acoustic wave resonator and a manufacturing method thereof. The surface acoustic wave resonator comprises a substrate, a piezoelectric composite layer and an electrode layer. Wherein the piezoelectric composite layer is located between the substrate and the electrode layer. The piezoelectric composite layer comprises a first piezoelectric film and a second piezoelectric film. The second piezoelectric film is located between the first piezoelectric film and the substrate. The piezoelectric composite layer is excited to generate a first mode wave under the excitation of an electric field applied by the electrode layer, and a second mode wave is generated in the propagation process of the first mode wave in the piezoelectric composite layer. Wherein the first piezoelectric film is configured to limit the energy of the first mode wave in the first piezoelectric film for propagation. The second piezoelectric film is configured to guide the second mode wave to leak toward the direction of the substrate. According to the surface acoustic wave resonator, effective suppression of a stray mode in the working process of the resonator is realized, and the overall working performance of the resonator is improved. The process steps of the manufacturing method are simple and easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a surface acoustic wave resonator and a manufacturing method thereof. Background Art

[0002] Surface acoustic wave resonators are widely used in various acoustic devices such as RF filters, duplexers, delay lines, discriminators, and modulators due to their resonant properties. These devices play a vital role in wireless communications, especially in the input / output RF filters of receivers and transmitters, which allow efficient wireless communications over multiple frequency bands.

[0003] Piezoelectric surface acoustic wave resonators are based on piezoelectric films and interdigital transducers formed on their surfaces. Based on the piezoelectric effect, under the excitation of the electric field applied by the interdigital transducer, the main mode surface acoustic wave is generated in the piezoelectric film and propagates along the propagation area formed by the interdigital electrodes in the interdigital transducer. While the main mode surface acoustic wave is generated, multiple spurious mode waves are also generated in the piezoelectric film. The spurious mode is an unwanted acoustic resonance that appears at the same time as the main mode. The spurious mode waves usually have different propagation characteristics (for example, speed, direction, and frequency, etc.) from the main mode waves. These spurious mode waves will affect the output performance of the resonator. For example, these spurious modes will not only affect the passband performance of the filter, but also affect the performance of the out-of-band and high-frequency range, reducing power durability and linearity (including harmonic distortion and intermodulation distortion).

[0004] Therefore, how to provide a surface acoustic wave resonator and a method for manufacturing the same to effectively suppress stray mode waves and improve the working performance of the resonator has become an important technical problem that needs to be solved urgently by those skilled in the art.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present invention and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology section of the present invention. Summary of the invention

[0006] Based on this, an object of the present invention is to provide a surface acoustic wave resonator and a method for manufacturing the same, so as to solve the problem in the prior art that stray modal waves need to be suppressed during the operation of the surface acoustic wave resonator.

[0007] To achieve the above-mentioned object and other related objects, in a first aspect, a surface acoustic wave resonator is provided, the surface acoustic wave resonator comprising: a substrate, a piezoelectric composite layer and an electrode layer;

[0008] The piezoelectric composite layer is located between the substrate and the electrode layer; the piezoelectric composite layer includes a first piezoelectric film and a second piezoelectric film, and the second piezoelectric film is located between the first piezoelectric film and the substrate;

[0009] The piezoelectric composite layer is excited to generate a first mode wave under the excitation of the electric field applied by the electrode layer, and a second mode wave is generated during the propagation of the first mode wave in the piezoelectric composite layer. The first piezoelectric film is configured to confine the energy of the first mode wave to propagate within the first piezoelectric film, and the second piezoelectric film is configured to guide the second mode wave to leak toward the substrate.

[0010] In one embodiment, the first mode wave comprises a horizontal shear acoustic wave, and the second mode wave comprises a bulk acoustic wave.

[0011] In one embodiment, the acoustic impedance of the second mode wave propagating in the first piezoelectric film is smaller than the acoustic impedance of the second mode wave propagating in the second piezoelectric film.

[0012] In one embodiment, the material of the first piezoelectric film includes YX rotary cut lithium tantalate, and the material of the second piezoelectric film includes YX rotary cut lithium niobate; the thickness of the first piezoelectric film ranges from 1 μm to 30 μm; the thickness of the second piezoelectric film ranges from 5 μm to 20 μm.

[0013] In one embodiment, the thickness of the first piezoelectric film is in the range of 2 μm to 10 μm, the material of the first piezoelectric film is 42° YX rotary cut lithium tantalate, and the material of the second piezoelectric film is 70° YX rotary cut lithium niobate.

[0014] In one embodiment, the surface acoustic wave resonator further includes an intermediate layer, wherein the intermediate layer is located between the first piezoelectric film and the second piezoelectric film, and / or the intermediate layer is located between the substrate and the second piezoelectric film.

[0015] In one embodiment, the material of the intermediate layer includes at least one of an acoustic insulating material and an electrical insulating material; the material of the substrate includes at least one of silicon, low-temperature co-fired ceramics, high-temperature co-fired ceramics, silicon carbide, alumina, glass, quartz and metal.

[0016] In one embodiment, the piezoelectric composite layer is directly bonded to the substrate.

[0017] In a second aspect, a method for manufacturing a surface acoustic wave resonator is provided, comprising the following steps:

[0018] providing a substrate;

[0019] forming a piezoelectric composite layer on the substrate, and forming an electrode layer on the piezoelectric composite layer, wherein the piezoelectric composite layer includes a first piezoelectric film and a second piezoelectric film, and the second piezoelectric film is located between the first piezoelectric film and the substrate;

[0020] The piezoelectric composite layer is excited to generate a first mode wave under the excitation of the electric field applied by the electrode layer, and a second mode wave is generated during the propagation of the first mode wave in the piezoelectric composite layer. The first mode wave and the second mode wave are different at least in the propagation mode. The first piezoelectric film is configured to confine the energy of the first mode wave to propagate within the first piezoelectric film, and the second piezoelectric film is configured to guide the second mode wave to leak toward the substrate.

[0021] In one embodiment, the method of forming the piezoelectric film on the substrate includes a direct bonding method.

[0022] The above-mentioned surface acoustic wave resonator is achieved by adjusting the traditional single-layer piezoelectric layer to a piezoelectric composite layer, wherein the piezoelectric composite layer includes a first piezoelectric film and a second piezoelectric film, wherein the first piezoelectric film is configured to limit the energy of the first mode wave generated in the piezoelectric composite layer to propagate within the first piezoelectric film, and the second piezoelectric film is configured to guide the second mode wave generated during the propagation of the first mode wave to leak toward the substrate, thereby preventing the second mode wave from propagating as a stray mode within the first piezoelectric film and affecting the propagation characteristics of the first mode wave, thereby achieving effective suppression of stray modes during the operation of the resonator, and helping to improve the overall working performance of the resonator. Further, by optimizing the materials and thicknesses of the first piezoelectric film and the second piezoelectric film, it is possible to achieve complete suppression of stray modes in some frequency ranges while achieving good limitation of the energy of the first mode wave and suppressing the PSC effect, thereby improving the working performance and competitiveness of the resonator and expanding the application scenarios of the resonator.

[0023] The method for manufacturing the surface acoustic wave resonator has simple process steps and is easy to implement, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of a surface acoustic wave resonator provided in an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of the amplitude of a displacement component of a first mode wave when propagating in a first piezoelectric film provided by an embodiment of the present invention;

[0026] Figure 3 A curve diagram showing the relationship between the phase velocity and the electromechanical coupling coefficient of a first mode wave propagating in a first piezoelectric film and the thickness of the first piezoelectric film provided by an embodiment of the present invention;

[0027] Figure 4 An admittance curve diagram of a resonator using a first piezoelectric film as a piezoelectric layer provided by an embodiment of the present invention;

[0028] Figure 5 A curve diagram showing the relationship between the admittance of a resonator provided by an embodiment of the present invention and the thickness of a first piezoelectric film;

[0029] Figure 6 A graph showing a change in the admittance curve of the resonator provided by an embodiment of the present invention as a function of the tangential angle of the second piezoelectric film;

[0030] Figure 7 A comparison diagram of the conductivity curves of the resonators provided by the embodiment of the present invention and the comparative example;

[0031] Figure 8 A comparison diagram of the susceptance curves of the resonator provided by the embodiment of the present invention and the comparative example.

[0032] Description of reference numerals:

[0033] 10 - substrate 10; 20 - piezoelectric composite layer; 21 - first piezoelectric film; 22 - second piezoelectric film; 30 - electrode layer. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0035] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0036] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0037] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0039] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0040] The present invention provides a surface acoustic wave resonator. Figure 1 , Figure 1 The schematic diagram of the structure of the surface acoustic wave resonator is shown. The surface acoustic wave resonator comprises a substrate 10 , a piezoelectric composite layer 20 and an electrode layer 30 .

[0041] Specifically, the piezoelectric composite layer 20 is located between the substrate 10 and the electrode layer 30. The piezoelectric composite layer 20 includes a first piezoelectric film 21 and a second piezoelectric film 22. The second piezoelectric film 22 is located between the first piezoelectric film 21 and the substrate 10. The piezoelectric composite layer 20 is excited to generate a first mode wave under the excitation of the electric field applied by the electrode layer 30, and a second mode wave is generated during the propagation of the first mode wave in the piezoelectric composite layer. The first piezoelectric film 21 is configured to confine the energy of the first mode wave to propagate in the first piezoelectric film 21, and the second piezoelectric film 22 is configured to guide the second mode wave to leak toward the substrate 10.

[0042] In some embodiments, the first mode wave includes a horizontal shear acoustic wave, and the second mode wave includes a bulk acoustic wave. That is, the resonator structure provided in the embodiment of the present invention suppresses the stray modes caused by the propagation of the bulk acoustic wave through the second piezoelectric film 22 to ensure the good propagation characteristics of the horizontal shear acoustic wave and the working performance of the resonator with the horizontal shear wave as the main mode. Of course, in other embodiments, the first mode wave and the second mode wave can also be other modes of acoustic waves.

[0043] In some embodiments, the acoustic impedance Z1 of the second mode wave propagating in the first piezoelectric film 21 is less than the acoustic impedance Z2 of the second mode wave propagating in the second piezoelectric film 22. Under the condition that Z1<Z2, the energy of the second mode wave will encounter resistance when penetrating from the first piezoelectric film 21 to the second piezoelectric film 22, so that the energy of the second mode wave leaks from the first piezoelectric film 21 to the second piezoelectric film 22 and gradually decays, thereby preventing the energy of the second mode wave from propagating in the first piezoelectric film 21 and affecting the propagation characteristics of the first mode wave restricted by the first piezoelectric film 21. If Z1>Z2, in the process of the second mode wave leaking from the first piezoelectric film 21 to the substrate 10, a strong reflection will be generated at the contact interface between the first piezoelectric film 21 and the second piezoelectric film 22, or even at the contact interface between the second piezoelectric film 22 and the substrate 10, which will enhance the signal of the stray mode and be detrimental to the propagation characteristics of the first mode wave.

[0044] In the embodiment of the present invention, by configuring the first piezoelectric film 21 to confine the energy of the first mode wave to propagate within the first piezoelectric film 21, the first mode wave can be directly bounded, that is, a directly bounded SAW resonator structure is formed. Among them, since the first mode wave as the main working mode propagates within a specific area (that is, the first piezoelectric film 21), the energy loss of the first mode wave during the propagation process can be reduced, the transmission efficiency of the first mode wave can be improved, and the working performance of the resonator can be improved. In order to avoid the adverse effect of the radiation of the second mode wave on the propagation of the first mode wave, based on the acoustic perspective, by selecting and optimizing parameters such as the crystal material type, cutting direction and thickness of the first piezoelectric film 21 and the second piezoelectric film 22, on the one hand, the propagation direction of the second mode wave in the piezoelectric composite layer 20 is changed, so that the second piezoelectric film 22 guides the second mode wave to selectively leak in the direction of the substrate 10; on the other hand, by controlling the acoustic impedance characteristics of the second mode wave propagating in the first piezoelectric film 21 and the second piezoelectric film 22, the second mode wave is further avoided from being reflected at the interface between different structural layers to aggravate the stray, thereby effectively suppressing the stray mode, while meeting the effects of device miniaturization and high output characteristics.

[0045] In some embodiments, the material of the first piezoelectric film 21 includes YX spin-cut lithium tantalate. The thickness of the first piezoelectric film 21 ranges from 1 μm to 30 μm (including end values), and can be 6 μm, 10 μm, 15 μm, 20 μm or 25 μm.

[0046] See also Figure 2 , Figure 2 FIG. 2 shows a schematic diagram of the displacement component amplitude when the first mode wave propagates in the first piezoelectric film. Since the surface acoustic wave (e.g., the first mode wave) causes a small displacement of the medium (e.g., the first piezoelectric film 21) when propagating in the medium, the small displacement can be decomposed into components along three orthogonal directions: x, y, and z. Figure 2 The u, v and w shown in are the components of the total displacement caused by the first mode wave propagating in the first piezoelectric film 21. The three components are equally displaced in the x, y and z three-dimensional coordinate systems. However, due to the anisotropy of the crystal of the first piezoelectric film 21, the three components are different in the coordinate system in the crystal direction. Figure 2It can be seen that when the distance from the upper surface of the first piezoelectric film 21 downwardly extending into the first piezoelectric film 21 exceeds 5 μm, the three components u, v and w are all 0, that is, at any position in the first piezoelectric film 21 that is more than 5 μm away from the upper surface of the first piezoelectric film 21, the first mode wave has no sound field (that is, there is no intensity distribution of the first mode wave), and the displacement amplitude is almost zero, which means that using the first piezoelectric film 21 with a thickness greater than 5 μm can ensure that the energy of the first mode wave is confined within the first piezoelectric film 21, and the thickness of the first mode wave leaking into the substrate 10 can be ignored.

[0047] In addition, for the directly bounded surface acoustic wave resonator, the parasitic surface conductance (PSC) effect will also occur during its operation, and the PSC effect may cause unnecessary current leakage to the substrate 10. For example, the reasons for the PSC effect include that when the piezoelectric film is bonded to the substrate 10, the direct bonding process at the interface of the highly anisotropic crystal material (for example, the contact interface between the silicon substrate and the piezoelectric film) may cause the degradation of the crystal structure (the degradation may be caused by thermal stress, mechanical stress or other physical and chemical effects during the bonding process), thereby generating free charges in the interface region. The source of the free charges may be due to chemical changes during the bonding process or material defects (such as vacancies, impurities, etc.). These free charges will form a conductive layer on the surface of the silicon substrate 10, thereby causing the PSC effect. The PSC effect will reduce the effective resistivity of the substrate 10 and increase the high-frequency loss of the transmitted signal, thereby affecting the performance of the resonator (especially the RF performance). In short, the existence of the PSC effect will lead to power consumption and performance loss of the resonator.

[0048] See also Figure 3 , Figure 3 The graph shows the relationship between the phase velocity and the electromechanical coupling coefficient k2 when the first mode wave propagates in the first piezoelectric film and the thickness of the first piezoelectric film. Figure 3 It can be seen that the phase velocity and electromechanical coupling coefficient of the first mode wave tend to be stable when the thickness of the first piezoelectric film 21 is greater than 2μm (especially 3μm). Due to the existence of the PSC effect, part of the acoustic wave energy will not propagate through the piezoelectric film, but through the substrate or other materials, which reduces the electromechanical coupling of the piezoelectric material and thus reduces the electromechanical coupling coefficient. If the PSC effect is effectively suppressed, the acoustic wave will mainly propagate through the piezoelectric material, which will increase the phase velocity and electromechanical coupling coefficient. Therefore, when the thickness of the piezoelectric film increases to a certain value (for example, Figure 3The phase velocity and electromechanical coupling coefficient no longer change with increasing thickness, which indicates that the PSC effect is effectively suppressed because a piezoelectric film with a certain thickness can effectively prevent the transmission of acoustic wave energy through a non-piezoelectric path. In summary, the relatively thick first piezoelectric film 21 can achieve good energy confinement of the first mode wave, while suppressing the PSC effect to prevent the first mode wave from leaking through the second piezoelectric film 22 or even the substrate 10, thereby ensuring the working performance of the resonator.

[0049] Although when the first piezoelectric film 21 is relatively thick (for example, greater than 2μm, 3μm, 5μm, etc.), the displacement amplitude of the first mode wave in the portion of the first piezoelectric film 21 away from the electrode layer 30 is substantially zero. However, other modes of waves can propagate at any position of the above-mentioned portion, and then a strong stray mode appears inside the entire first piezoelectric film 21. For example, the second mode wave generated by the first mode wave propagates in the first piezoelectric film 21 at the same time as the first mode wave to form a stray mode. Please refer to Figure 4 , Figure 4 The figure shows the admittance curve of the resonator with the first piezoelectric film as the piezoelectric layer, wherein the red curve is the real part of the admittance curve and the black curve is the imaginary part of the admittance curve. Figure 4 It can be seen that strong broadband spurious signals appear in the out-of-band (OOB) and high-frequency (HF) frequency ranges. The spurious signals appear as significant peaks on the curve. For example, at frequencies below the resonant frequency ( Figure 4 1965MHz), resonant frequency and anti-resonant frequency ( Figure 4 Strong spurious peaks are shown in the range between 2040 MHz and 2040 MHz, as well as in the range greater than the anti-resonance frequency, especially the bulk acoustic wave spurious in the area shown by the dotted box.

[0050] Furthermore, in order to achieve good acoustic wave propagation performance, the first piezoelectric film 21 itself usually has good waveguide characteristics. Therefore, under normal circumstances, the propagation loss of the second mode wave in the first piezoelectric film 21 during propagation is low, and it is difficult to suppress the propagation of the second mode wave by adjusting only the first piezoelectric film 21 itself. In addition, due to the difference in acoustic properties of materials, the acoustic impedances between different materials are not matched, and high reflection of acoustic waves is prone to occur. For example, there is a reflection boundary at the contact interface between the first piezoelectric film 21 and the substrate 10, which will further aggravate the stray adverse effects generated by the second mode wave. For example, please refer to Figure 5 , Figure 5The curve of the admittance of the resonator changing with the thickness of the first piezoelectric film 21 is shown. When the thickness of the first piezoelectric film 21 changes in the range of 0.6λ to 1.2λ (λ is the wavelength of the resonator), the admittance curve of the resonator does not change substantially, that is, the adjustment of the thickness of the first piezoelectric film 21 has little effect on the suppression of the stray mode. Therefore, it is impossible to achieve the suppression of the stray mode from the perspective of adjusting the thickness of the first piezoelectric film 21. That is, although the thickness of the first piezoelectric film 21 is relatively large and can well limit the energy of the first mode wave, it cannot well suppress the adverse effects of the stray mode wave on the output characteristics of the resonator. Therefore, the thickness range of the first piezoelectric film 21 provided in the embodiment of the present invention is a numerical range summarized to obtain a good limit on the energy of the first mode wave and the suppression of the PSC effect. The thickness of the first piezoelectric film 21 can be adjusted within the above range based on the desired surface acoustic wave propagation characteristics and resonator parameters (for example, phase velocity, electromechanical coupling coefficient k2 and quality factor Q, etc.).

[0051] In some embodiments, the material of the second piezoelectric film 22 includes YX spin-cut lithium niobate. The thickness of the second piezoelectric film 22 ranges from 5 μm to 20 μm (including end values), and can be 10 μm, 15 μm or 18 μm.

[0052] Based on the above content, it can be known that the relatively thick first piezoelectric film 21 can achieve good restriction of the energy of the first mode wave and at the same time achieve the effect of suppressing the PSC effect, thereby ensuring the working performance of the resonator to a certain extent. However, the relatively thick piezoelectric layer is not conducive to meeting the performance requirements of the miniaturization of the resonator, and weakens the original advantages of the directly bounded resonator, and still faces the problem of greater influence of stray modes. Therefore, a relatively thin first piezoelectric film 21 can be used to basically meet the good restriction of the first mode wave and the suppression of the PSC effect, and adjust the piezoelectric layer structure of the resonator. However, the relatively thin first piezoelectric film 21 faces the problem of higher stray modes. Therefore, in the embodiment of the present invention, the second piezoelectric film 22 is added, and the material and structure of the second piezoelectric film 22 are optimized to suppress the propagation of the second mode wave in the first piezoelectric film 21, thereby further improving the working performance of the resonator. The second piezoelectric film 22 provided in the embodiment of the present invention is particularly suitable for suppressing the stray mode of the resonator with a thinned YX rotary cut lithium tantalate piezoelectric film.

[0053] In some embodiments, the thickness of the first piezoelectric film 21 ranges from 2 μm to 10 μm (including endpoint values), and can be 3 μm, 5 μm, or 8 μm. The material of the first piezoelectric film 21 is 42° YX rotary cut lithium tantalate, and the material of the second piezoelectric film 22 is 70° YX rotary cut lithium niobate.

[0054] See also Figure 6 , which is a graph showing the variation of the admittance curve of the resonator according to the embodiment of the present invention with the tangential angle of the second piezoelectric film. Figure 6 It can be seen that when the tangential angle range of the second piezoelectric film 22 is 60° to 80°, the spurious mode is suppressed compared with other tangential angles, which is manifested by the reduction of the height of the stray peak and the number of stray peaks. In particular, when the tangential angle is 70°, the suppression effect of the stray mode is the best, and no stray peaks appear in the range of 1800MHz to 2100MHz. This shows that while the first mode wave is well confined to propagate in the first piezoelectric film 21, the second mode wave in the resonator can be effectively suppressed by optimizing the material and tangential angle of the second piezoelectric film 22, thereby reducing the stray effect caused by the second mode wave propagating in the first piezoelectric film 21 along with the first mode wave.

[0055] See also Figure 7 and Figure 8 ,in, Figure 7 A comparison diagram of the conductance curves of the resonators provided by the embodiment of the present invention and the comparative example is shown, Figure 8 The susceptance curves of the resonators provided by the embodiment of the present invention and the comparative example are shown. The dotted lines in the two figures correspond to the curves of the embodiment of the present invention, and the solid lines correspond to the curves of the comparative example. The difference between the embodiment of the present invention and the comparative example is only that the first piezoelectric film 21 and the second piezoelectric film 22 constitute the piezoelectric composite layer 20 in the embodiment of the present invention, while the first piezoelectric film 21 is used as the piezoelectric layer in the comparative example. The material, thickness and overall structure of the first piezoelectric film 21 in the embodiment of the present invention and the first piezoelectric film 21 in the comparative example are consistent (including the substrate 10 and the electrode layer 30). Figure 7 and Figure 8 It can be seen that in the conductance curve and the susceptance curve of the resonator provided by the embodiment of the present invention, the number and height of stray peaks are significantly reduced, and there are no stray peaks between the resonant frequency and the anti-resonant frequency, which shows that the piezoelectric composite layer 20 structure in the embodiment of the present invention has an outstanding effect on suppressing stray modes, and the stopband performance of the resonator is not reduced, which means that the resonator structure provided by the embodiment of the present invention can be applied to a variety of filters.

[0056] In some embodiments, the piezoelectric composite layer 20 is directly bonded to the substrate 10. Direct bonding is a technology that connects two surfaces together at a molecular interface without the use of an adhesive or an intermediate layer, and relies on van der Waals forces or chemical reactions to form structural bonds between materials. That is, there are no other structural layers between the piezoelectric composite layer 20 and the substrate 10, and the piezoelectric composite layer 20 is in direct contact and connection with the substrate 10, allowing the piezoelectric composite layer 20 and the substrate 10 to match in thermal expansion coefficient, thereby reducing the internal stress and strain caused by temperature changes. The residual stress and strain between the piezoelectric composite layer 20 and the substrate 10 do not require additional compensation, which can reduce the impact of temperature changes on the resonator frequency, thereby improving the temperature coefficient of frequency (TCF) of the resonator, so that the resonator maintains a stable frequency at different temperatures without causing temperature drift of the frequency. If the conventional bonding technology requiring an adhesive layer is used, the presence of the adhesive layer may introduce additional interface stress and strain, which needs to be compensated for in the overall structural design of the resonator, increasing the complexity of the device structure. At the same time, the use of a material with good thermal conductivity to make the substrate 10 helps to quickly disperse the heat generated by the resonator during operation, prevent the resonator from overheating, and thus improve the stability and durability of the resonator under high power conditions.

[0057] In some embodiments, the surface acoustic wave resonator further includes an intermediate layer (not shown), the intermediate layer is located between the first piezoelectric film 21 and the second piezoelectric film 22 , and / or the intermediate layer is located between the substrate 10 and the second piezoelectric film 22 .

[0058] In some embodiments, the intermediate layer is located between the first piezoelectric film 21 and the second piezoelectric film 22. The thickness and material of the intermediate layer are selected to match the acoustic impedance and phase matching between the first piezoelectric film 21 and the second piezoelectric film 22, which is conducive to the effective excitation of the first mode wave. At the same time, when the first piezoelectric film 21 and the second piezoelectric film 22 are connected by bonding, the intermediate layer can also improve the connection strength between the two and improve the mechanical stability of the resonator.

[0059] In some embodiments, the intermediate layer is located between the substrate 10 and the second piezoelectric film 22, and the thickness of the intermediate layer is at the atomic level (the specific thickness depends on the material of the intermediate layer). At this time, the piezoelectric composite layer 20 and the substrate 10 are no longer strictly combined with the definition of "direct bonding". The intermediate layer is introduced between the two interfaces to be bonded as a seed layer of the piezoelectric composite layer 20. When the materials of both the substrate 10 and the second piezoelectric film 22 are highly anisotropic, it can avoid the difficulty of good matching of the crystal structure when the two are in direct contact, resulting in residual stress and strain at the bonding interface (even delamination and accumulation may occur), thereby improving the bonding quality between the two and increasing the bonding strength. At the same time, since the thickness of the intermediate layer is at the atomic level, it will not affect the acoustic propagation effect of the first mode wave in the first piezoelectric film 21 (or the impact can be ignored).

[0060] In some embodiments, the material of the intermediate layer includes at least one of an acoustic insulating material and an electrical insulating material. The electrical insulating material can reduce charge scattering at the bonding contact and improve the bonding quality, and the electrical insulating material includes at least one of semi-insulating polysilicon, aluminum nitride, aluminum boron nitride, and silicon dioxide.

[0061] In some embodiments, the material of the substrate 10 includes at least one of silicon Si (e.g.,

[111] Si), low temperature co-fired ceramic (LTCC), high temperature co-fired ceramic (HTCC), silicon carbide SiC, aluminum oxide Al2O3, glass, quartz and metal. The substrate 10 is mainly used as a supporting structure in the resonator. The material selection of the substrate 10 has an important influence on the power handling capacity and TCF of the resonator. Therefore, it is necessary to select a suitable material to make the substrate 10 based on the actual application scenario of the resonator. Among them, the thermal expansion coefficient of the substrate material directly affects the TCF of the resonator, and a higher TCF of the resonator will reduce the available effective bandwidth of the resonator. At the same time, the thermal conductivity and thermal stability of the substrate material will also directly affect the power handling capacity of the resonator. For example, SiC material has excellent thermal conductivity, so that the resonator based on the SiC substrate has relatively good power handling capacity. Therefore, the material of the substrate 10 is reasonably selected based on the actual application scenario of the resonator.

[0062] In some embodiments, the material of the electrode layer includes at least one of aluminum, copper, platinum, gold, silver, titanium, nickel, chromium, molybdenum and tungsten, or an alloy with any of the foregoing metals as the main body. Optionally, the thickness of the electrode layer ranges from 0.1 μm to 0.5 μm (including the end value), and can be 0.2 μm or 0.4 μm.

[0063] The surface acoustic wave resonator of the embodiment of the present invention is obtained by adjusting the traditional single-layer piezoelectric layer to a piezoelectric composite layer, wherein the piezoelectric composite layer includes a first piezoelectric film and a second piezoelectric film, wherein the first piezoelectric film is configured to limit the energy of the first mode wave generated in the piezoelectric composite layer to propagate within the first piezoelectric film, and the second piezoelectric film is configured to guide the second mode wave generated during the propagation of the first mode wave to leak toward the substrate, thereby preventing the second mode wave from propagating as a stray mode in the first piezoelectric film and affecting the propagation characteristics of the first mode wave, thereby achieving effective suppression of stray modes during the operation of the resonator, and helping to improve the overall working performance of the resonator. Further, by optimizing the materials and thicknesses of the first piezoelectric film and the second piezoelectric film, it is possible to achieve complete suppression of stray modes in a certain frequency range while achieving good limitation of the energy of the first mode wave and suppressing the PSC effect, thereby improving the working performance and competitiveness of the resonator and expanding the application scenarios of the resonator.

[0064] The present invention also provides a method for manufacturing a surface acoustic wave resonator. The method can be used to manufacture the surface acoustic wave resonator as described above or other suitable resonator structures. Figure 1 , the preparation method comprises the following steps:

[0065] Providing a substrate 10;

[0066] A piezoelectric composite layer 20 is formed on the substrate 10, and an electrode layer 30 is formed on the piezoelectric composite layer 20, wherein the piezoelectric composite layer 20 includes a first piezoelectric film 21 and a second piezoelectric film 22, and the second piezoelectric film 22 is located between the first piezoelectric film 21 and the substrate 10;

[0067] The piezoelectric composite layer 20 is excited to generate a first mode wave under the excitation of the electric field applied by the electrode layer 30, and a second mode wave is generated during the propagation of the first mode wave in the piezoelectric composite layer 20. The first piezoelectric film 21 is configured to confine the energy of the first mode wave to propagate within the first piezoelectric film 21, and the second piezoelectric film 22 is configured to guide the second mode wave to leak toward the substrate 10.

[0068] In some embodiments, the method of forming the piezoelectric composite layer 20 on the substrate 10 includes a direct bonding method.

[0069] The method for manufacturing the surface acoustic wave resonator of this embodiment has simple process steps and is easy to implement, and is suitable for large-scale production.

[0070] In summary, the surface acoustic wave resonator of the present invention is obtained by adjusting the traditional single-layer piezoelectric layer to a piezoelectric composite layer, wherein the piezoelectric composite layer includes a first piezoelectric film and a second piezoelectric film, wherein the first piezoelectric film is configured to limit the energy of the first mode wave generated in the piezoelectric composite layer to propagate within the first piezoelectric film, and the second piezoelectric film is configured to guide the second mode wave generated during the propagation of the first mode wave to leak toward the substrate, thereby preventing the second mode wave from propagating as a stray mode in the first piezoelectric film and affecting the propagation characteristics of the first mode wave, thereby achieving effective suppression of stray modes during the operation of the resonator, and helping to improve the overall working performance of the resonator. Further, by optimizing the materials and thicknesses of the first piezoelectric film and the second piezoelectric film, it is possible to achieve complete suppression of stray modes in a partial frequency range while achieving good limitation of the energy of the first mode wave and suppressing the PSC effect, thereby improving the working performance and competitiveness of the resonator and expanding the application scenarios of the resonator. The method for making the surface acoustic wave resonator of the present invention has simple process steps and is easy to implement, and is suitable for large-scale production. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0071] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A surface acoustic wave resonator, characterized in that: include: Substrate, piezoelectric composite layer and electrode layer; The piezoelectric composite layer is located between the substrate and the electrode layer; The piezoelectric composite layer includes a first piezoelectric film and a second piezoelectric film, wherein the second piezoelectric film is located between the first piezoelectric film and the substrate; The piezoelectric composite layer is excited to generate a first mode wave under the excitation of the electric field applied by the electrode layer, and a second mode wave is generated during the propagation of the first mode wave in the piezoelectric composite layer. The first piezoelectric film is configured to confine the energy of the first mode wave to propagate within the first piezoelectric film, and the second piezoelectric film is configured to guide the second mode wave to leak toward the substrate.

2. The surface acoustic wave resonator according to claim 1, characterized in that: The first mode wave comprises a horizontal shear acoustic wave, and the second mode wave comprises a bulk acoustic wave.

3. The surface acoustic wave resonator according to claim 2, characterized in that: An acoustic impedance of the second mode wave propagating in the first piezoelectric film is smaller than an acoustic impedance of the second mode wave propagating in the second piezoelectric film.

4. The surface acoustic wave resonator according to claim 2, characterized in that: The material of the first piezoelectric film includes YX rotary cut lithium tantalate, and the material of the second piezoelectric film includes YX rotary cut lithium niobate; the thickness of the first piezoelectric film ranges from 1 μm to 30 μm; the thickness of the second piezoelectric film ranges from 5 μm to 20 μm.

5. The surface acoustic wave resonator according to claim 4, characterized in that: The thickness of the first piezoelectric film is in the range of 2 μm to 10 μm. The material of the first piezoelectric film is 42° YX rotary cut lithium tantalate. The material of the second piezoelectric film is 70° YX rotary cut lithium niobate.

6. The surface acoustic wave resonator according to claim 1, characterized in that: The surface acoustic wave resonator further includes an intermediate layer, wherein the intermediate layer is located between the first piezoelectric film and the second piezoelectric film, and / or the intermediate layer is located between the substrate and the second piezoelectric film.

7. The surface acoustic wave resonator according to claim 6, characterized in that: The material of the intermediate layer includes at least one of an acoustic insulating material and an electrical insulating material; the material of the substrate includes at least one of silicon, low temperature co-fired ceramics, high temperature co-fired ceramics, silicon carbide, alumina, glass, quartz and metal.

8. The surface acoustic wave resonator according to any one of claims 1 to 7, characterized in that: The piezoelectric composite layer is directly bonded to the substrate.

9. A method for manufacturing a surface acoustic wave resonator, characterized in that: The following steps are involved: providing a substrate; forming a piezoelectric composite layer on the substrate, and forming an electrode layer on the piezoelectric composite layer, wherein the piezoelectric composite layer includes a first piezoelectric film and a second piezoelectric film, and the second piezoelectric film is located between the first piezoelectric film and the substrate; The piezoelectric composite layer is excited to generate a first mode wave under the excitation of the electric field applied by the electrode layer, and a second mode wave is generated during the propagation of the first mode wave in the piezoelectric composite layer. The first piezoelectric film is configured to confine the energy of the first mode wave to propagate within the first piezoelectric film, and the second piezoelectric film is configured to guide the second mode wave to leak toward the substrate.

10. The method for manufacturing a surface acoustic wave resonator according to claim 9, characterized in that: The method of forming the piezoelectric film on the substrate includes a direct bonding method.

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