Surface acoustic wave resonator and preparation method therefor, filter, and electronic device

Abstract

Provided in the embodiments of the present application are a surface acoustic wave resonator and a preparation method therefor, a filter, and an electronic device, which relate to the technical field of semiconductors and are used for ameliorating the problem of lateral energy leakage in surface acoustic wave resonators. The surface acoustic wave resonator comprises a piezoelectric layer, an interdigital transducer, and a cover layer. The interdigital transducer comprises a first bus bar, a second bus bar, a plurality of first electrode strips and a plurality of second electrode strips, wherein the plurality of first electrode strips are connected to the first bus bar, and the plurality of second electrode strips are connected to the second bus bar. The cover layer is located on the first bus bar and the second bus bar, and the shear wave velocity of the cover layer is higher than the shear wave velocity of the piezoelectric layer. The described surface acoustic wave resonator is applied to an electronic device, thereby improving the performance of the electronic device.

Description

Surface acoustic wave resonator, preparation method thereof, filter and electronic device

[0001] The present application claims priority to the Chinese patent application No. 202411358360.9, filed on September 26, 2024, and entitled "Surface acoustic wave resonator, preparation method thereof, filter and electronic device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of semiconductor, and in particular to a surface acoustic wave resonator, a preparation method thereof, a filter and an electronic device. BACKGROUND

[0003] A surface acoustic wave (SAW) resonator utilizes the piezoelectric property of a piezoelectric material to convert an electrical signal into an acoustic signal, and then convert the acoustic signal into an electrical signal, so as to filter the signal and improve the signal quality. The surface acoustic wave resonator has the advantages of small structure size and good performance, and is widely used in various fields, such as the radio frequency field. However, there is a problem of transverse energy leakage in the surface acoustic wave resonator, which has a bad influence on the performance of the surface acoustic wave resonator. SUMMARY

[0004] Embodiments of the present application provide a surface acoustic wave resonator, a preparation method thereof, a filter and an electronic device, which are used to improve the problem of transverse energy leakage in the surface acoustic wave resonator and improve the performance of the surface acoustic wave resonator.

[0005] To achieve the above-mentioned purpose, embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, a surface acoustic wave resonator is provided. The surface acoustic wave resonator includes a piezoelectric layer, an interdigital transducer and a cover layer. The interdigital transducer is located on the piezoelectric layer, and the interdigital transducer includes a first bus bar, a second bus bar, a plurality of first electrode strips and a plurality of second electrode strips; the first bus bar and the second bus bar are both extended along a first direction and oppositely arranged, and the plurality of first electrode strips and the plurality of second electrode strips are both located between the first bus bar and the second bus bar; the plurality of first electrode strips and the plurality of second electrode strips are both extended along a second direction, and in the first direction, the plurality of first electrode strips and the plurality of second electrode strips are alternately arranged; the plurality of first electrode strips are connected with the first bus bar, and the plurality of second electrode strips are connected with the second bus bar; the first direction and the second direction intersect, and are both parallel to a surface of the piezoelectric layer close to the interdigital transducer; the cover layer is located on the first bus bar and the second bus bar, and a transverse wave speed of the cover layer is higher than a transverse wave speed of the piezoelectric layer.

[0007] The surface acoustic wave resonator provided by the embodiments of the present application comprises a piezoelectric layer, an interdigital transducer and a cover layer. The interdigital transducer is located on the piezoelectric layer. The transverse wave speed of the cover layer is higher than that of the piezoelectric layer. In this way, when the cover layer is arranged on the first bus bar and the second bus bar, the cover layer can increase the propagation speed of the surface acoustic wave in the area where the first bus bar and the second bus bar are located, and increase the cutoff frequency of the area where the first bus bar and the second bus bar are located. The surface acoustic wave with a frequency lower than the cutoff frequency will rapidly attenuate. Therefore, the higher the cutoff frequency of the area where the first bus bar and the second bus bar are located, the more low-frequency spurious modes can be filtered out by the surface acoustic wave resonator, and the less the transverse energy is prone to leak, so that the transverse energy leakage can be suppressed. The higher the cutoff frequency of the area where the first bus bar and the second bus bar are located, the higher the transverse energy barrier of the area where the first bus bar and the second bus bar are located, so that the transverse energy leakage to the outside of the interdigital transducer can be blocked, and the problem of transverse energy leakage can be improved.

[0008] The surface acoustic wave resonator provided by the embodiments of the present application can effectively suppress the transverse energy leakage, so that the quality factor of the surface acoustic wave resonator can be improved, and the performance of the surface acoustic wave resonator can be improved. Meanwhile, when the cover layer is arranged on the first bus bar and the second bus bar, the diffraction loss of the surface acoustic wave resonator can also be suppressed, so that the quality factor of the surface acoustic wave resonator can be further improved, and the performance of the surface acoustic wave resonator can be improved.

[0009] In some embodiments, the first bus bar and the second bus bar each comprise a first extension, a second extension and a plurality of connecting portions; the first extension and the second extension each extend along the first direction and are oppositely arranged, and the plurality of connecting portions are located between the first extension and the second extension and connect the first extension and the second extension. The second extension of the first bus bar is connected with the plurality of first electrode strips, and the second extension of the second bus bar is connected with the plurality of second electrode strips; the number of the plurality of first electrode strips is greater than the number of the connecting portions in the first bus bar; and the number of the plurality of second electrode strips is greater than the number of the connecting portions in the second bus bar.

[0010] In this way, the speed of the surface acoustic wave propagating in the area where the connecting portions in the first bus bar and the connecting portions in the second bus bar are located can be obviously greater than the speed of the surface acoustic wave propagating in the area where the plurality of first electrode strips and the plurality of second electrode strips are arranged, the area between the plurality of first electrode strips and the second bus bar, and the area between the plurality of second electrode strips and the first bus bar, so that the transverse energy barrier of the area where the connecting portions in the first bus bar and the connecting portions in the second bus bar are located is higher, and most of the transverse energy leakage in the surface acoustic wave resonator can be suppressed.

[0011] In some embodiments, in the second direction, the cover layer is located between the first extension and the second extension, and the cover layer is located on a side of the plurality of connecting portions away from the piezoelectric layer.

[0012] In this way, the propagation speed of the surface acoustic wave in the region between the first extension and the second extension, i.e., the region where the connecting portions are located, can be higher, the corresponding cutoff frequency of the region where the connecting portions are located can be higher, and the transverse energy potential barrier of the region where the connecting portions are located can be higher, thereby facilitating further suppression of transverse energy leakage in the surface acoustic wave resonator and improving the Q value of the surface acoustic wave resonator.

[0013] The embodiments of the present application provide the cover layer between the first extension and the second extension, i.e., the cover layer is provided in the region where the plurality of connecting portions are located, which can improve the working frequency corresponding to the gap mode without affecting the main mode of the surface acoustic wave, so that the working frequency corresponding to the gap mode approaches or even exceeds the anti-resonance frequency of the surface acoustic wave resonator, thereby suppressing or even eliminating the gap mode and improving the Q value of the surface acoustic wave resonator near the anti-resonance frequency point. In this way, when the surface acoustic wave resonator provided by the embodiments of the present application is applied to a filter, the in-band flatness of the filter can also be ensured.

[0014] In some embodiments, the cover layer is also located on a side of the first extension and / or the second extension away from the piezoelectric layer.

[0015] In this way, not only can the cover layer suppress the gap mode, improve the cutoff frequency corresponding to the region where the first bus bar and the second bus bar are located, and improve the problem of transverse energy leakage of the surface acoustic wave resonator, but also the preparation difficulty of the cover layer can be reduced, the alignment accuracy requirement of the cover layer in the preparation process of the surface acoustic wave resonator can be relaxed, and mass production of the surface acoustic wave resonator can be facilitated.

[0016] In some embodiments, the projections of the first bus bar and the second bus bar on the piezoelectric layer are in the form of strips. In this way, the structure of the first bus bar and the second bus bar can be relatively simple, which facilitates simplification of the preparation process of the first bus bar and the second bus bar, improvement of the preparation efficiency of the first bus bar and the second bus bar, and reduction of the preparation cost.

[0017] In some embodiments, the plurality of first electrode strips and the plurality of second electrode strips each comprise a first portion, a second portion, a third portion and a fourth portion connected in sequence; the second portion and the fourth portion each have a width greater than that of the first portion and the third portion; the width is a dimension of the first portion, the second portion, the third portion or the fourth portion in the first direction. The first portions of the plurality of first electrode strips are connected to the first bus bar, and the first portions of the plurality of second electrode strips are connected to the second bus bar. In this way, a piston mode can be formed, effectively suppressing the transverse mode and improving the performance of the surface acoustic wave resonator.

[0018] In some embodiments, the interdigital transducer further comprises a plurality of first dummy fingers and a plurality of second dummy fingers, the plurality of first dummy fingers are each connected to the first bus bar and are respectively located between the first bus bar and the plurality of second electrode strips, and the plurality of second dummy fingers are each connected to the second bus bar and are respectively located between the second bus bar and the plurality of first electrode strips. The projection of the cover layer on the piezoelectric layer is spaced apart from the projection of the plurality of first dummy fingers on the piezoelectric layer, and the projection of the cover layer on the piezoelectric layer is spaced apart from the projection of the plurality of second dummy fingers on the piezoelectric layer.

[0019] In this way, the influence of the cover layer on the propagation speed of the surface acoustic wave in the area where the first dummy finger is located can be avoided, the influence of the cover layer on the propagation speed of the surface acoustic wave in the area where the second dummy finger is located can be avoided, and the influence of the cover layer on the scattering of the surface acoustic wave in the areas where the first dummy finger and the second dummy finger are located can be prevented, thereby ensuring the performance of the surface acoustic wave resonator.

[0020] In some embodiments, the first bus bar and the plurality of second electrode strips have a plurality of first gaps therebetween, and the second bus bar and the plurality of second electrode strips have a plurality of second gaps therebetween. The cover layer comprises a first cover portion, a second cover portion, a third cover portion and a fourth cover portion; the first cover portion is located on a side of the first bus bar away from the piezoelectric layer, the second cover portion is located on a side of the second bus bar away from the piezoelectric layer, the projection of the third cover portion on the piezoelectric layer partially overlaps the projection of the first gap on the piezoelectric layer, and the projection of the fourth cover portion on the piezoelectric layer partially overlaps the projection of the second gap on the piezoelectric layer.

[0021] In the embodiments of the present application, the cover layer includes a first cover portion, a second cover portion, a third cover portion and a fourth cover portion, wherein the first cover portion and the second cover portion can improve the energy barrier of the area where the first bus bar and the second bus bar are located, and the third cover portion and the fourth cover portion can improve the energy barrier of the area where the first gap and the second gap are located. In this way, the problem of transverse energy leakage of the surface acoustic wave resonator can be further improved, the quality factor of the surface acoustic wave resonator can be improved, and the performance of the surface acoustic wave resonator can be improved.

[0022] Meanwhile, the projection of the third cover portion on the piezoelectric layer partially overlaps the projection of the first gap on the piezoelectric layer, and the projection of the fourth cover portion on the piezoelectric layer partially overlaps the projection of the second gap on the piezoelectric layer. In addition, the problem that the projection of the third cover layer on the piezoelectric layer completely overlaps the projection of the first gap on the piezoelectric layer, and the projection of the fourth cover portion on the piezoelectric layer completely overlaps the projection of the second gap on the piezoelectric layer, so that the surface acoustic wave appears transverse mode, can be avoided, and the performance of the surface acoustic wave resonator can be ensured.

[0023] In some embodiments, the surface acoustic wave resonator is a thin film surface acoustic wave resonator, and the surface acoustic wave resonator further includes a substrate and an intermediate layer. The substrate is located on the side of the piezoelectric layer away from the interdigital transducer. The intermediate layer is located between the piezoelectric layer and the substrate, and the transverse wave speed of the intermediate layer is less than the transverse wave speed of the piezoelectric layer. In this way, the acoustic waveguide can be established in the sagittal plane and the acoustic energy can be limited on the surface of the surface acoustic wave resonator.

[0024] In some embodiments, the surface acoustic wave resonator is a temperature-compensated surface acoustic wave resonator, and the surface acoustic wave resonator further includes a temperature compensation layer located between the piezoelectric layer and the cover layer; and the material of the temperature compensation layer includes a positive temperature coefficient material.

[0025] In the case where the temperature compensation layer is not provided, the frequency temperature coefficient of the surface acoustic wave resonator is mainly determined by the piezoelectric layer. The material of the piezoelectric layer is generally lithium niobate or lithium tantalate. The frequency temperature coefficient of the surface acoustic wave resonator is negative, and the frequency decreases with the increase of temperature, which affects the performance of the surface acoustic wave resonator. In the embodiments of the present application, the temperature compensation layer using a positive temperature coefficient material is provided, which can improve the frequency temperature coefficient of the surface acoustic wave resonator, so that the frequency of the surface acoustic wave resonator is not easily changed with temperature change, and the working stability of the surface acoustic wave resonator is improved.

[0026] In some embodiments, the surface acoustic wave resonator further comprises a first weight-increasing portion and a second weight-increasing portion, the first weight-increasing portion and the second weight-increasing portion are located on a side of the temperature compensation layer away from the piezoelectric layer. A projection of the first weight-increasing portion on the piezoelectric layer overlaps with a projection of an end portion of the plurality of second electrode strips close to the first bus bar on the piezoelectric layer; a projection of the second weight-increasing portion on the piezoelectric layer overlaps with a projection of an end portion of the plurality of first electrode strips close to the second bus bar on the piezoelectric layer; wherein the first weight-increasing portion and the cover layer are spaced apart, and the second weight-increasing portion and the cover layer are spaced apart.

[0027] In the surface acoustic wave resonator provided by the embodiments of the present application, the first weight-increasing portion is located on a side of an end portion of the plurality of second electrode strips away from the piezoelectric layer, and the second weight-increasing portion is located on a side of an end portion of the plurality of first electrode strips away from the piezoelectric layer, so that the mass loading effect can be used to reduce the propagation speed of the surface acoustic wave in the region where the end portion of the plurality of second electrode strips close to the first bus bar and the end portion of the plurality of first electrode strips close to the second bus bar are located, so that the propagation speed of the surface acoustic wave in this region can be less than the propagation speed of the surface acoustic wave in the region between the first weight-increasing portion and the second weight-increasing portion, thereby facilitating the formation of a piston mode and reducing the transverse mode.

[0028] In some embodiments, the material of the piezoelectric layer comprises lithium niobate or lithium tantalate, and the material of the cover layer comprises at least one of silicon nitride, silicon carbide and diamond.

[0029] In a second aspect, a preparation method of a surface acoustic wave resonator is provided. The preparation method comprises: forming an interdigital transducer on a piezoelectric layer; and forming a cover layer on the first bus bar and the second bus bar. The interdigital transducer comprises a first bus bar, a second bus bar, a plurality of first electrode strips and a plurality of second electrode strips; the first bus bar and the second bus bar both extend along a first direction and are oppositely arranged, and the plurality of first electrode strips and the plurality of second electrode strips are both located between the first bus bar and the second bus bar; the plurality of first electrode strips and the plurality of second electrode strips both extend along a second direction, and in the first direction, the plurality of first electrode strips and the plurality of second electrode strips are alternately arranged; the plurality of first electrode strips are connected to the first bus bar, and the plurality of second electrode strips are connected to the second bus bar; the first direction and the second direction intersect and are both parallel to a surface of the piezoelectric layer close to the interdigital transducer. The shear wave speed of the cover layer is higher than the shear wave speed of the piezoelectric layer.

[0030] In a third aspect, a filter is provided. The filter comprises a plurality of surface acoustic wave resonators, and the plurality of surface acoustic wave resonators are the surface acoustic wave resonators provided in any of the above embodiments.

[0031] In a fourth aspect, an electronic device is provided. The electronic device includes a circuit board and a filter, the filter being located on and connected to the circuit board. The filter is the filter provided in any of the embodiments of the filter.

[0032] The technical effects brought by any of the designs in the second aspect to the fourth aspect can be referred to the technical effects brought by the different designs in the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the present application, the following will briefly introduce the drawings needed to be used in some embodiments of the present application. Obviously, the drawings described in the following description are only some drawings of the embodiments of the present application, and other drawings can also be obtained by those skilled in the art according to these drawings. In addition, the drawings in the following description can be regarded as schematic diagrams, and are not limited to the actual size, actual process, actual time sequence, etc. of the products involved in the embodiments of the present application.

[0034] Fig. 1 is a structural schematic diagram of an electronic device provided in an embodiment of the present application;

[0035] Fig. 2 is a structural schematic diagram of a filter provided in an embodiment of the present application;

[0036] Fig. 3 is a structural schematic diagram of a surface acoustic wave resonator provided in an embodiment of the present application;

[0037] Fig. 4 is a top view schematic diagram of the surface acoustic wave resonator shown in Fig. 3;

[0038] Fig. 5 is a sectional view schematic diagram of the surface acoustic wave resonator shown in Fig. 3 at A-A';

[0039] Fig. 6 is a top view schematic diagram of another surface acoustic wave resonator provided in an embodiment of the present application;

[0040] Fig. 7 is a structural schematic diagram of another surface acoustic wave resonator provided in an embodiment of the present application;

[0041] Fig. 8 is a top view schematic diagram of the surface acoustic wave resonator shown in Fig. 7;

[0042] Fig. 9 is a sectional view schematic diagram of the surface acoustic wave resonator shown in Fig. 7 at B-B';

[0043] Fig. 10 is a structural schematic diagram of still another surface acoustic wave resonator provided in an embodiment of the present application;

[0044] Fig. 11 is a top view schematic diagram of the surface acoustic wave resonator shown in Fig. 10;

[0045] Fig. 12 is a sectional view schematic diagram of the surface acoustic wave resonator shown in Fig. 10 at C-C'.

[0046] FIG. 13 is a preparation flowchart of a surface acoustic wave resonator according to an embodiment of the present application;

[0047] FIGS. 14 to 23 are performance curve diagrams of the surface acoustic wave resonator according to an embodiment of the present application. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application.

[0049] In the embodiments of the present application, the terms “first”, “second”, and the like are only used for convenience, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with “first”, “second”, and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of “a plurality of” is two or more.

[0050] In the embodiments of the present application, “up”, “down”, “left”, and “right” are not limited to the relative positions of the components shown in the drawings, and it should be understood that these directional terms can be relative concepts, which are used for relative description and clarification, and can change accordingly according to the change of the position of the components shown in the drawings.

[0051] In the embodiments of the present application, unless otherwise required by the context, the term “comprising” is interpreted as open, inclusive meaning, i.e. “including, but not limited to”. In the description of the specification, the terms “one embodiment”, “some embodiments”, “exemplary embodiments”, “exemplarily” or “some examples” and the like are intended to indicate that the specific features, structures, materials or characteristics related to the embodiment or example are included in at least one embodiment or example of the present disclosure. The exemplary representation of the above terms does not necessarily mean the same embodiment or example. In addition, the specific features, structures, materials or characteristics described can be included in any one or more embodiments or examples in any appropriate manner.

[0052] Exemplary embodiments are described herein with reference to cross-sectional illustrations and / or plan illustrations and / or equivalent circuit diagrams that are depicted as idealized exemplary illustrations. In the drawings, the thickness of layers and regions are exaggerated for clarity. Accordingly, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are to be expected. Thus, the exemplary embodiments should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an etched region illustrated as a rectangle will typically have rounded or curved features. Thus, the regions illustrated in the drawings are schematic and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the exemplary embodiments.

[0053] Embodiments of the present application provide an electronic device. The electronic device is, for example, a consumer electronic product, a home electronic product, a vehicle-mounted electronic product, a financial terminal product, a communication electronic product. The consumer electronic product is, for example, a mobile phone, a pad, a notebook computer, an e-book reader, a personal computer (PC), a personal digital assistant (PDA), a desktop display, a smart wearable product (for example, a smart watch, a smart bracelet), a virtual reality (VR) terminal device, an augmented reality (AR) terminal device, a drone, and the like. The home electronic product is, for example, a smart door lock, a television, a remote controller, a refrigerator, a charging household small appliance (for example, a soybean milk machine, a sweeping robot), and the like. The vehicle-mounted electronic product is, for example, a vehicle-mounted navigation, a vehicle-mounted high-density digital video disc (DVD), and the like. The financial terminal product is, for example, an automated teller machine (ATM), a self-service terminal, and the like.

[0054] For the convenience of description, the electronic device is taken as a mobile phone as an example. As shown in FIG. 1, the electronic device 100 mainly includes a cover plate 11, a display screen 12, a middle frame 13, and a back shell 14. The back shell 14 and the display screen 12 are respectively located on two sides of the middle frame 13, and the middle frame 13 and the display screen 12 are arranged in the back shell 14. The cover plate 11 is arranged on a side of the display screen 12 away from the middle frame 13, and a display surface of the display screen 12 faces the cover plate 11.

[0055] The display screen 12 can be a liquid crystal display (LCD) or an organic light emitting diode (OLED) display. The middle frame 13 includes a bearing plate 131 and a frame 132 surrounding the bearing plate 131. The electronic device 100 can further include electronic components such as a printed circuit board (PCB), a battery, and a camera, which can be disposed on the bearing plate 131.

[0056] The electronic device 100 can further include a system on chip (SOC) and a radio frequency chip disposed on the PCB, which is configured to carry and electrically connect the SOC and the radio frequency chip. The radio frequency chip can include a filter and a processor. The processor is configured to process various signals, and the filter is an important part of radio frequency signal processing and is configured to pass signals of a specific frequency and block signals of other frequencies.

[0057] Embodiments of the present application provide a filter, which can be applied to the electronic device 100 described above, for example, to a radio frequency chip in the electronic device 100, and disposed on and connected to a circuit board (e.g., a printed circuit board).

[0058] The filter provided by embodiments of the present application can be, for example, a low-pass surface acoustic wave filter, a high-pass surface acoustic wave filter, a band-pass surface acoustic wave filter, a band-stop surface acoustic wave filter, or an active surface acoustic wave filter.

[0059] Of course, the filter provided by embodiments of the present application is not limited to being integrated in the electronic device 100. The filter can also be a separate component, or the filter can be integrated with a power amplifier or the like into a device (e.g., a radio frequency device, a radio frequency module, a filter module, or the like).

[0060] As shown in FIG. 2, the filter 200 provided by embodiments of the present application can include a plurality of surface acoustic wave resonators 300. The plurality of surface acoustic wave resonators 300 can be cascaded in series and / or in parallel. FIG. 2 also shows a signal input end Vi, a signal output end Vo, and a ground end GND of the filter 200.

[0061] In some examples, the plurality of resonators 300 can have different resonant frequencies, and the performance of the filter 200 is closely related to the performance of the surface acoustic wave resonators 300.

[0062] The surface acoustic wave resonator has the advantages of small volume, light weight, good performance, high reliability, good consistency, flexible design, and can be manufactured by microelectronic processing technology, suitable for mass production, etc., and is applied to many fields such as mobile communication, broadcast television, nondestructive testing, identification and positioning, navigation and telemetry.

[0063] The main working principle of the surface acoustic wave resonator is that an interdigital transducer (IDT) is formed on the surface of a piezoelectric material. A radio frequency electrical signal receives an electrical signal through the input end of the interdigital transducer, excites a sound wave through the inverse piezoelectric effect of the piezoelectric material, and the sound wave propagates on the surface of the device to the output end, and then converts the acoustic vibration into an electrical output through the piezoelectric effect of the piezoelectric material. There is a correlation between the interdigital transducer finger spacing and the wavelength of the sound wave, so that other frequency signals can be blocked by a signal of a specific frequency (wavelength).

[0064] FIG. 3 is a structural schematic diagram of a surface acoustic wave resonator 300 provided by an embodiment of the present application. FIG. 4 is a top view schematic diagram of the surface acoustic wave resonator 300 shown in FIG. 3. As shown in FIG. 3 and FIG. 4, some embodiments of the present application provide a surface acoustic wave resonator 300. The surface acoustic wave resonator 300 can include a piezoelectric layer 10, an interdigital transducer (IDT) 20, and a cover layer 30.

[0065] The interdigital transducer 20 is located on the piezoelectric layer 10, and the interdigital transducer 20 includes a first bus bar 21, a second bus bar 22, a plurality of first electrode strips 23, and a plurality of second electrode strips 24. The first bus bar 21 and the second bus bar 22 are both extended along a first direction X and oppositely arranged, and the plurality of first electrode strips 23 and the plurality of second electrode strips 24 are both located between the first bus bar 21 and the second bus bar 22. The plurality of first electrode strips 23 and the plurality of second electrode strips 24 are both extended along a second direction Y, and in the first direction X, the plurality of first electrode strips 23 and the plurality of second electrode strips 24 are alternately arranged. The plurality of first electrode strips 23 are connected with the first bus bar 21, and the plurality of second electrode strips 24 are connected with the second bus bar 22. The first direction X and the second direction Y intersect, and are both parallel to a surface Q of the piezoelectric layer 10 close to the interdigital transducer 20. The cover layer 30 is located on the first bus bar 21 and the second bus bar 22. The transverse wave speed of the cover layer 30 is higher than the transverse wave speed of the piezoelectric layer 10.

[0066] In some examples, the material of the piezoelectric layer 10 can include lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and other piezoelectric materials. The size (such as length, width, and thickness, etc.) and shape of the piezoelectric layer 10 are not limited by the embodiments of the present application, and can be designed according to actual needs.

[0067] In some examples, the material of the interdigital transducer 20 can include a metal, such as aluminum, gold, silver, copper, molybdenum, tungsten, or the like.

[0068] It can be understood that, in the second direction Y, the plurality of first electrode strips are arranged spaced apart from the second bus bar, and the plurality of second electrode strips are arranged spaced apart from the first bus bar.

[0069] In some examples, the first bus bar 21 and the second bus bar 22 can have the same shape and size. The first electrode strips 23 and the second electrode strips 24 can have the same shape, size, and number. The number of the first electrode strips 23 and the number of the second electrode strips 24 are not limited in the embodiments of the present application, and can be designed according to the specific requirements of the surface acoustic wave resonator 300.

[0070] For simplicity of description, hereinafter, the region provided with the plurality of first electrode strips 23 and the plurality of second electrode strips 24 is referred to as an aperture region M0, and the region between the plurality of first electrode strips 23 and the second bus bar 22 and the region between the plurality of second electrode strips 24 and the first bus bar 21 are both referred to as a first gap region M1.

[0071] The cover layer 30 is located on the first bus bar 21 and the second bus bar 22, that is, a portion of the cover layer 30 is located on the first bus bar 21, and another portion of the cover layer 30 is located on the second bus bar 22. As shown in FIGS. 3 and 4, the cover layer 30 can include a first cover portion 31 and a second cover portion 32, the first cover portion 31 is located on the first bus bar 21, and the second cover portion 32 is located on the second bus bar 22.

[0072] In order to improve the structural symmetry of the surface acoustic wave resonator 300 and simplify the preparation process of the surface acoustic wave resonator 300, the material, shape, and size of the first cover portion 31 and the second cover portion 32 can be kept consistent. Of course, the material, shape, and size of the first cover portion 31 and the second cover portion 32 can also be different.

[0073] The transverse wave speed of the cover layer 30 is higher than the transverse wave speed of the piezoelectric layer 10. For example, in the case where the material of the piezoelectric layer 10 includes lithium niobate or lithium tantalate, the material of the cover layer 30 can include at least one of silicon nitride (Si3N4), silicon carbide (SiC), and diamond.

[0074] The transverse wave speed of lithium tantalate is 3551 m / s (meters per second), the transverse wave speed of lithium niobate is 3980 m / s, the transverse wave speed of silicon nitride is 6426 m / s, the transverse wave speed of silicon carbide is 7126 m / s, and the transverse wave speed of diamond is 12823 m / s. The transverse wave speeds of silicon nitride, silicon carbide and diamond are all greater than the transverse wave speeds of lithium niobate or lithium tantalate. Silicon carbide is a semiconductor material and has multiple crystal forms. When the material of the cover layer 30 is silicon carbide, the material of the cover layer 30 can be 6H-SiC. That is, the hexagonal crystal form of SiC is selected. It can be understood that the cover layer 30 provided in the embodiments of the present application can be a single-layer structure or a multi-layer structure.

[0075] The surface acoustic wave resonator 300 provided in the embodiments of the present application includes the piezoelectric layer 10, the interdigital transducer 20 and the cover layer 30. The interdigital transducer 20 is located on the piezoelectric layer 10. The transverse wave speed of the cover layer 30 is higher than the transverse wave speed of the piezoelectric layer 10, and the transverse wave speed of the cover layer 30 is relatively high. In this way, when the cover layer 30 is arranged on the first bus bar 21 and the second bus bar 22, the cover layer 30 can improve the propagation speed of the surface acoustic wave in the area where the first bus bar 21 and the second bus bar 22 are located, and improve the cutoff frequency of the area where the first bus bar 21 and the second bus bar 22 are located. The surface acoustic wave with a frequency lower than the cutoff frequency will be rapidly attenuated. Therefore, the higher the cutoff frequency of the area where the first bus bar 21 and the second bus bar 22 are located, the more low-frequency spurious modes can be filtered out by the surface acoustic wave resonator, and the less the low-frequency spurious modes, the less the transverse energy is likely to leak, so that the transverse energy leakage can be suppressed. The higher the cutoff frequency of the area where the first bus bar 21 and the second bus bar 22 are located, the higher the transverse energy potential barrier of the area where the first bus bar 21 and the second bus bar 22 are located, so that the transverse energy leakage to the outside of the interdigital transducer can be blocked, and the problem of transverse energy leakage can be improved.

[0076] The surface acoustic wave resonator 300 provided in the embodiments of the present application can effectively suppress the transverse energy leakage, so that the quality factor (i.e., Q value) of the surface acoustic wave resonator 300 can be improved, and the performance of the surface acoustic wave resonator 300 can be improved. At the same time, when the cover layer 30 is arranged on the first bus bar 21 and the second bus bar 22, the diffraction loss of the surface acoustic wave resonator can also be suppressed, so that the quality factor of the surface acoustic wave resonator 300 can be further improved, and the performance of the surface acoustic wave resonator 300 can be improved.

[0077] In some embodiments, as shown in FIG. 4, the first bus bar 21 and the second bus bar 22 each include a first extension 211, a second extension 212, and a plurality of connecting portions 213. The first extension 211 and the second extension 212 each extend along the first direction X and are oppositely arranged, and the plurality of connecting portions 213 are located between the first extension 211 and the second extension 212 and connect the first extension 211 and the second extension 212.

[0078] In the first bus bar 21, the second extension 212 is connected with the plurality of first electrode strips 23, and in the second bus bar 22, the second extension 212 is connected with the plurality of second electrode strips 24. The number of the plurality of first electrode strips 23 is greater than the number of the connecting portions 213 in the first bus bar 21, and the number of the plurality of second electrode strips 24 is greater than the number of the connecting portions 213 in the second bus bar 22.

[0079] In some examples, the first extension 211 and the second extension 212 can have the same shape and size. In other examples, the first extension 211 and the second extension 212 can have different shapes and sizes. In FIG. 4, the width of the first extension 211 is greater than the width of the second extension 212 as an example. The "width" refers to the dimension of the first extension 211 or the second extension 212 along the second direction Y.

[0080] In this way, the speed of the surface acoustic wave propagating in the region where the connecting portions 213 in the first bus bar 21 and the connecting portions 213 in the second bus bar 22 are located can be significantly greater than the speed of the surface acoustic wave propagating in the aperture region M0 and the first gap region M1. The transverse energy potential barrier of the region where the connecting portions 213 in the first bus bar 21 and the connecting portions 213 in the second bus bar 22 are located is high, so that the region where the connecting portions 213 in the first bus bar 21 and the connecting portions 213 in the second bus bar 22 are located can suppress most of the transverse energy leakage in the surface acoustic wave resonator 300.

[0081] For simplicity of description, hereinafter, the region where the connecting portions 213 in the first bus bar 21 and the connecting portions 213 in the second bus bar 22 are located, and the region between the first extension and the second extension are collectively referred to as the second gap region M2.

[0082] In some examples, the number of the connection portions 213 in the first bus bar 21 can be the same as the number of the connection portions 213 in the second bus bar 22. In this way, on the one hand, the symmetry of the surface acoustic wave resonator 300 can be improved, and the structural stability of the surface acoustic wave resonator 300 can be improved. On the other hand, the energy barrier of the area where the connection portions 213 in the first bus bar 21 are located and the energy barrier of the area where the connection portions 213 in the second bus bar 22 are located can be the same, so that the area where the connection portions 213 in the first bus bar 21 are located and the area where the connection portions 213 in the second bus bar 22 are located can effectively suppress the transverse energy leakage, and the Q value of the surface acoustic wave resonator 300 can be further improved.

[0083] In some examples, the number of the connection portions 213 in the first bus bar 21 can be half of the number of the first electrode strips 23, and the number of the connection portions 213 in the second bus bar 22 can be half of the number of the second electrode strips 24. In this way, the arrangement period of the connection portions 213 in the first bus bar 21 is greatly different from the arrangement period of the first electrode strips 23, and the arrangement period of the connection portions 213 in the second bus bar 22 is greatly different from the arrangement period of the second electrode strips 24. The speed of the surface acoustic wave propagating in the second gap area M2 can be greatly different from the speed of the surface acoustic wave propagating in the aperture area M0 and the first gap area M1, and the second gap area M2 can more effectively suppress the transverse energy leakage.

[0084] The number of the connection portions 213 in the first bus bar 21 and the number of the connection portions 213 in the second bus bar 22 are not limited in the embodiments of the present application, and can be designed according to requirements. It can be understood that the number of the first electrode strips 23, the second electrode strips 24 and the connection portions 213 shown in FIGS. 3 and 4 does not limit the number of the first electrode strips 23, the second electrode strips 24 and the connection portions 213 in the surface acoustic wave resonator 300 provided by the embodiments of the present application.

[0085] In some embodiments, as shown in FIG. 6, in the second direction Y, the cover layer 30 can be located between the first extension portion 211 and the second extension portion 212, and the cover layer 30 is located on the side of the plurality of connection portions 213 away from the piezoelectric layer 10.

[0086] In this way, the speed of the surface acoustic wave propagating in the area between the first extension portion 211 and the second extension portion 212, that is, in the second gap area M2, can be higher, the corresponding cutoff frequency of the second gap area M2 can be higher, and the transverse energy barrier of the second gap area M2 can be higher, thereby facilitating further suppression of the transverse energy leakage in the surface acoustic wave resonator 300 and improving the Q value of the surface acoustic wave resonator.

[0087] The inventors of the present application have found that, because the number of the plurality of connecting portions 213 in the first bus bar 21 is less than the number of the plurality of first electrode strips 23, and the number of the plurality of connecting portions 213 in the second bus bar 22 is less than the number of the plurality of second electrode strips 24, during the operation of the surface acoustic wave resonator 300, the area where the connecting portions 213 are located (i.e., the second gap region M2) introduces a new spurious mode (also referred to as a gap mode), which causes the Q value near the anti-resonance frequency point of the surface acoustic wave resonator 300 to decrease.

[0088] The embodiment of the present application provides the cover layer 30 between the first extension portion 211 and the second extension portion 212, i.e., the cover layer 30 is provided in the area where the plurality of connecting portions 213 are located, which not only improves the cutoff frequency of the second gap region M2, but also improves the operating frequency corresponding to the gap mode without affecting the main mode of the surface acoustic wave, so that the operating frequency corresponding to the gap mode is close to, or even exceeds, the anti-resonance frequency of the surface acoustic wave resonator 300, thereby suppressing or even eliminating the gap mode and improving the Q value of the surface acoustic wave resonator 300 near the anti-resonance frequency point. In this way, when the surface acoustic wave resonator provided by the embodiment of the present application is applied to a filter, the in-band flatness of the filter can also be ensured.

[0089] In other examples, as shown in FIGS. 4 and 5, the cover layer 30 can be located not only between the first extension portion 211 and the second extension portion 212, but also on the side of the first extension portion 211 and / or the second extension portion 212 away from the piezoelectric layer 10.

[0090] That is, the cover layer 30 can also be located on the side of the first extension portion 211 away from the piezoelectric layer 10. Alternatively, the cover layer 30 can also be located on the side of the second extension portion 212 away from the piezoelectric layer 10. Alternatively, the cover layer 30 can also be located on the side of the first extension portion 211 and the second extension portion 212 away from the piezoelectric layer 10.

[0091] In this way, not only can the cover layer 30 suppress the gap mode and improve the cutoff frequency of the area where the first bus bar 21 and the second bus bar 22 are located, thereby improving the problem of transverse energy leakage of the surface acoustic wave resonator 300, but also the preparation difficulty of the cover layer 30 can be reduced, and the alignment accuracy requirement of the cover layer 30 in the preparation process of the surface acoustic wave resonator 300 can be relaxed, which is conducive to the mass production of the surface acoustic wave resonator 300.

[0092] FIG. 7 is a three-dimensional structural schematic diagram of another surface acoustic wave resonator provided by an embodiment of the present application, and FIG. 8 is a top view of the surface acoustic wave resonator shown in FIG. 7. FIG. 9 is a cross-sectional schematic diagram of the surface acoustic wave resonator shown in FIG. 7 at B-B'.

[0093] In some embodiments, as shown in FIGS. 7 and 8, the projections of the first bus bar 21 and the second bus bar 22 on the piezoelectric layer 10 are both strip-shaped. In this way, the structures of the first bus bar 21 and the second bus bar 22 can be relatively simple, which is conducive to simplifying the manufacturing process of the first bus bar 21 and the second bus bar 22, improving the manufacturing efficiency of the first bus bar 21 and the second bus bar 22, and reducing the manufacturing cost.

[0094] At this time, in some examples, as shown in FIG. 8, the projections of the first bus bar 21 and the second bus bar 22 on the piezoelectric layer 10 can both be rectangular. In other examples, the projection of the first bus bar 21 and / or the second bus bar 22 on the piezoelectric layer 10 can be zigzag-shaped. In yet other examples, the projection of the first bus bar 21 and / or the second bus bar 22 on the piezoelectric layer 10 can be curved. Of course, the shape of the projection of the first bus bar 21 and / or the second bus bar 22 on the piezoelectric layer 10 in the embodiments of the present application is not limited to this.

[0095] As shown in FIG. 8, the first covering part 31 of the covering layer 30 can be located on the first bus bar 21, and the second covering part 32 of the covering layer 30 can be located on the second bus bar 22. The width w1 of the first covering part 31 can be less than or equal to the width w3 of the first bus bar 21, and the width w2 of the second covering part 32 can be less than or equal to the width w4 of the second bus bar 22.

[0096] The above width is the dimension of the first covering part 31, the first bus bar 21, the second covering part 32, or the second bus bar 22 in the second direction Y.

[0097] As shown in FIG. 8, in some embodiments, the plurality of first electrode strips 23 and the plurality of second electrode strips 24 each include a first part 231, a second part 232, a third part 233, and a fourth part 234 connected in sequence. The width d2 of the second part 232 and the width d4 of the fourth part 234 are both greater than the width d1 of the first part 231 and the width d3 of the third part 233. The above width is the dimension of the first part 231, the second part 232, the third part 233, or the fourth part 234 in the first direction X. The first part 231 of the plurality of first electrode strips 23 is connected to the first bus bar 21, and the first part 231 of the plurality of second electrode strips 24 is connected to the second bus bar 22.

[0098] In this way, referring to FIG. 9, in the second direction Y, the region where the first portions 231 of the plurality of first electrode strips 23 are located can form a first sound velocity region C1, the region where the second portions 232 of the first electrode strips 23 and the fourth portions 234 of the second electrode strips 24 are located can form a second sound velocity region C2, the region where the third portions 233 of the first electrode strips 23 and the second electrode strips 24 are located can form a third sound velocity region C3, the region where the fourth portions 234 of the first electrode strips 23 and the second portions 232 of the second electrode strips 24 are located can form a fourth sound velocity region C4, and the region where the first portions 231 of the plurality of second electrode strips 24 are located can form a fifth sound velocity region C5.

[0099] In this way, the propagation speed of the surface acoustic wave in the first sound velocity region C1 and the fifth sound velocity region C5 is greater than the propagation speed of the surface acoustic wave in the third sound velocity region C3, and the propagation speed of the surface acoustic wave in the second sound velocity region C2 and the fourth sound velocity region C4 is less than the propagation speed of the surface acoustic wave in the third sound velocity region C3, so that a piston mode can be formed, the transverse mode can be effectively suppressed, and the performance of the surface acoustic wave resonator 300 can be improved.

[0100] In some examples, the width d2 of the second portion 232 and the width d4 of the fourth portion 234 can be the same. The width d1 of the first portion 231 and the width d3 of the third portion 233 can be the same. The lengths of the first portion 231, the second portion 232, the third portion 233, and the fourth portion 234 are not limited in the embodiments of the present application, and can be limited according to actual needs. The "length" is the dimension of the first portion 231, the second portion 232, the third portion 233, or the fourth portion 234 in the second direction Y.

[0101] In some embodiments, as shown in FIGS. 3 to 9, the interdigital transducer 20 can further include a plurality of first dummy fingers 25 and a plurality of second dummy fingers 26. The plurality of first dummy fingers 25 are each connected to the first bus bar 21 and are respectively located between the first bus bar 21 and the plurality of second electrode strips 24. The plurality of second dummy fingers 26 are each connected to the second bus bar 22 and are respectively located between the second bus bar 22 and the plurality of first electrode strips 23.

[0102] In this way, the propagation speed of the surface acoustic wave in the first sound velocity region C1 and the fifth sound velocity region C5 is greater than the propagation speed of the surface acoustic wave in the third sound velocity region C3, and the propagation speed of the surface acoustic wave in the second sound velocity region C2 and the fourth sound velocity region C4 is less than the propagation speed of the surface acoustic wave in the third sound velocity region C3, so that a piston mode can be formed, the transverse mode can be effectively suppressed, and the performance of the surface acoustic wave resonator 300 can be improved.

[0103] It can be understood that, in the case that the interdigital transducer 20 includes the plurality of first dummy fingers 25 and the plurality of second dummy fingers 26, in the first direction X, the plurality of first dummy fingers 25 are arranged alternately with the plurality of first electrode strips 23, and the plurality of second dummy fingers 26 are arranged alternately with the plurality of second electrode strips 24. In the second direction Y, the plurality of first dummy fingers 25 are arranged spaced apart from the plurality of second electrode strips 24, and the plurality of second dummy fingers 26 are arranged spaced apart from the plurality of first electrode strips 23.

[0104] In the embodiments of the present application, the size and shape of the first dummy finger 25 and the second dummy finger 26 are not limited, and can be designed according to actual needs. In the embodiments of the present application, the spacing of the first dummy finger 25 and the first electrode strip 23 in the first direction X, the spacing of the first dummy finger 25 and the second electrode strip 24 in the second direction Y, the spacing of the second dummy finger 26 and the second electrode strip 24 in the first direction X, and the spacing of the second dummy finger 26 and the first electrode strip 23 in the second direction Y are not limited, and can be designed according to actual needs.

[0105] In some examples, the material of the plurality of first dummy fingers 25 can be the same as the material of the first bus bar 21, and the material of the plurality of second dummy fingers 26 can be the same as the material of the second bus bar 22. At this time, the plurality of first dummy fingers 25 and the first bus bar 21 can be of an integrated structure, and the plurality of second dummy fingers 26 and the second bus bar 22 can be of an integrated structure. The first dummy finger 25 can be prepared synchronously with the first bus bar 21, and the second dummy finger 26 can be prepared synchronously with the second bus bar 22, thereby facilitating the preparation process of the surface acoustic wave resonator 300.

[0106] In the surface acoustic wave resonator 300 provided in the embodiments of the present application, the first dummy finger 25 and the second dummy finger 26 do not participate in the transmission of signals, but the first dummy finger 25 and the second dummy finger 26 can effectively reduce the scattering of the surface acoustic wave in the propagation process, thereby improving the transmission efficiency of the surface acoustic wave and the signal quality. By setting the first dummy finger 25 and the second dummy finger 26, not only the performance of the surface acoustic wave resonator can be improved, but also more possibilities can be provided for the application of the surface acoustic wave resonator in the fields of wireless communication, filter design, etc.

[0107] As shown in FIG. 4 and FIG. 8, in the case that the interdigital transducer 20 includes the plurality of first dummy fingers 25 and the plurality of second dummy fingers 26, the projection of the cover layer 30 on the piezoelectric layer 10 is arranged spaced apart from the projection of the plurality of first dummy fingers 25 on the piezoelectric layer 10, and the projection of the cover layer 30 on the piezoelectric layer 10 is arranged spaced apart from the projection of the plurality of second dummy fingers 26 on the piezoelectric layer 10.

[0108] The cover layer 30 includes a first cover portion 31 located on the side of the first bus bar 21 away from the piezoelectric layer 10 and a second cover portion 32 located on the side of the second bus bar 22 away from the piezoelectric layer 10. In this case, the projection of the cover layer 30 on the piezoelectric layer 10 can be spaced apart from the projections of the plurality of first dummy fingers 25 on the piezoelectric layer 10, and the projection of the cover layer 30 on the piezoelectric layer 10 can be spaced apart from the projections of the plurality of second dummy fingers 26 on the piezoelectric layer 10. Alternatively, the projection of the first cover portion 31 on the piezoelectric layer 10 can be spaced apart from the projections of the plurality of first dummy fingers 25 on the piezoelectric layer 10, and the projection of the second cover portion 32 on the piezoelectric layer 10 can be spaced apart from the projections of the plurality of second dummy fingers 26 on the piezoelectric layer 10.

[0109] It can be understood that, when the projection of the first cover portion 31 on the piezoelectric layer 10 is spaced apart from the projections of the plurality of first dummy fingers 25 on the piezoelectric layer 10, in the second direction Y, the boundary of the projection of the first cover portion 31 on the piezoelectric layer 10 close to the first dummy fingers 25 can coincide with the boundary of the projections of the plurality of first dummy fingers 25 on the piezoelectric layer 10 close to the first cover portion 31. When the projection of the second cover portion 32 on the piezoelectric layer 10 is spaced apart from the projections of the plurality of second dummy fingers 26 on the piezoelectric layer 10, in the second direction Y, the boundary of the projection of the second cover portion 32 on the piezoelectric layer 10 close to the second dummy fingers 26 can coincide with the boundary of the projections of the plurality of second dummy fingers 26 on the piezoelectric layer 10 close to the second cover portion 32.

[0110] In this way, the cover layer 30 (the first cover portion 31) can avoid affecting the propagation speed of the surface acoustic wave in the region of the first dummy fingers 25, the cover layer 30 (the second cover portion 32) can avoid affecting the propagation speed of the surface acoustic wave in the region of the second dummy fingers 26, and the cover layer 30 can avoid affecting the scattering of the surface acoustic wave in the regions of the first dummy fingers 25 and the second dummy fingers 26, thereby ensuring the performance of the surface acoustic wave resonator 300.

[0111] The above describes an embodiment in which the interdigital transducer 20 includes the plurality of first dummy fingers 25 and the plurality of second dummy fingers 26 with reference to FIGS. 3 to 9. An embodiment in which the interdigital transducer 20 does not include the plurality of first dummy fingers 25 and the plurality of second dummy fingers 26 is described below with reference to FIGS. 10 to 12. FIG. 10 is a structural schematic diagram of another surface acoustic wave resonator 300 provided by an embodiment of the present application, and FIG. 11 is a top view of the surface acoustic wave resonator 300 shown in FIG. 10. FIG. 12 is a sectional view of the surface acoustic wave resonator 300 shown in FIG. 10 at C-C'. FIG. 10 takes the projections of the first bus bar and the second bus bar on the piezoelectric layer as strips for example.

[0112] As shown in FIGS. 11 and 12, in some embodiments, the first bus bar 21 and the plurality of second electrode strips 24 have a plurality of first gaps 201 therebetween, and the second bus bar 22 and the plurality of second electrode strips 24 have a plurality of second gaps 202 therebetween. It can be understood that at this time, the plurality of first dummy fingers 25 described above are not arranged between the first bus bar 21 and the plurality of second electrode strips 24, and the plurality of second dummy fingers 26 described above are not arranged between the second bus bar 22 and the plurality of first electrode strips 23.

[0113] Based on this, the cover layer 30 can not only include the first cover portion 31 located on the side of the first bus bar 21 away from the piezoelectric layer 10, and the second cover portion 32 located on the side of the second bus bar 22 away from the piezoelectric layer 10, but also include a third cover portion 33 and a fourth cover portion 34. The projection of the third cover portion 33 on the piezoelectric layer 10 partially overlaps the projection of the first gap 201 on the piezoelectric layer 10, and the projection of the fourth cover portion 34 on the piezoelectric layer 10 partially overlaps the projection of the second gap 202 on the piezoelectric layer 10.

[0114] In some examples, the third cover portion 33 can be located in the first gap 201, and the fourth cover portion 34 can be located in the second gap 202. In other examples, as shown in FIGS. 11 and 12, the third cover portion 33 can be located on the side of the first gap 201 away from the piezoelectric layer 10, and the fourth cover portion 34 can be located on the side of the second gap 202 away from the piezoelectric layer 10.

[0115] In some examples, as shown in FIG. 12, the third cover portion 33 can be connected to the first cover portion 31, and the fourth cover portion 34 can be connected to the second cover portion 32. In other examples, the third cover portion 33 can be arranged apart from the first cover portion 31, and the fourth cover portion 34 can be arranged apart from the second cover portion 32.

[0116] In some examples, the material of the third cover portion 33 can be the same as the material of the first cover portion 31, and the material of the fourth cover portion 34 can be the same as the material of the second cover portion 32. At this time, the first cover portion 31 and the third cover portion 33 can be prepared synchronously, and the second cover portion 32 and the fourth cover portion 34 can be prepared synchronously, thereby facilitating the simplification of the preparation process and the reduction of the preparation cost.

[0117] In other examples, the material of the first cover portion 31, the material of the second cover portion 32, the material of the third cover portion 33, and the material of the fourth cover portion 34 can be the same. In this way, the first cover portion 31, the second cover portion 32, the third cover portion 33, and the fourth cover portion 34 can be prepared synchronously, thereby facilitating the further simplification of the preparation process and the reduction of the preparation cost.

[0118] In the embodiments of the present application, the cover layer 30 includes a first cover portion 31, a second cover portion 32, a third cover portion 33, and a fourth cover portion 34. The first cover portion 31 and the second cover portion 32 can improve the energy barrier of the area where the first bus bar 21 and the second bus bar 22 are located, and the third cover portion 33 and the fourth cover portion 34 can improve the energy barrier of the area where the first gap 201 and the second gap 202 are located. In this way, the problem of transverse energy leakage of the surface acoustic wave resonator 300 can be further improved, the quality factor of the surface acoustic wave resonator 300 can be improved, and the performance of the surface acoustic wave resonator 300 can be improved.

[0119] Meanwhile, the projection of the third cover portion 33 on the piezoelectric layer 10 partially overlaps the projection of the first gap 201 on the piezoelectric layer 10, and the projection of the fourth cover portion 34 on the piezoelectric layer 10 partially overlaps the projection of the second gap 202 on the piezoelectric layer 10. This can also avoid the problem that the projection of the third cover layer on the piezoelectric layer 10 completely overlaps the projection of the first gap 201 on the piezoelectric layer 10, and the projection of the fourth cover portion 34 on the piezoelectric layer 10 completely overlaps the projection of the second gap 202 on the piezoelectric layer 10, resulting in the problem of transverse mode of the surface acoustic wave, and ensuring the performance of the surface acoustic wave resonator.

[0120] In some embodiments, as shown in FIGS. 3 to 9, the surface acoustic wave resonator 300 is a thin film surface acoustic wave resonator. At this time, the surface acoustic wave resonator 300 further includes a substrate 40 and an intermediate layer 50. The substrate 40 is located on the side of the piezoelectric layer 10 away from the interdigital transducer 20. The intermediate layer 50 is located between the piezoelectric layer 10 and the substrate 40, and the transverse wave speed of the intermediate layer 50 is less than the transverse wave speed of the piezoelectric layer 10. In this way, it is helpful to establish an acoustic waveguide in the sagittal plane and limit the acoustic energy on the surface of the surface acoustic wave resonator 300.

[0121] In some examples, the material of the substrate 40 can include silicon, and the material of the intermediate layer 50 can include silicon dioxide. It can be understood that the material of the substrate 40 and the material of the intermediate layer 50 in the embodiments of the present application are not limited to this. When the surface acoustic wave resonator 300 is a thin film surface acoustic wave resonator, the material of the piezoelectric layer can be lithium tantalate.

[0122] In other embodiments, as shown in FIGS. 10 to 12, the surface acoustic wave resonator 300 can be a temperature compensated surface acoustic wave (TC SAW) resonator, and the surface acoustic wave resonator 300 further includes a temperature compensation layer 60 located between the piezoelectric layer 10 and the cover layer 30. The material of the temperature compensation layer 60 includes a positive temperature coefficient material.

[0123] In the case where the surface acoustic wave resonator 300 is a temperature-compensated surface acoustic wave resonator, the material of the piezoelectric layer can be lithium niobate.

[0124] In the case where the temperature compensation layer 60 is not provided, the temperature coefficient of frequency of the surface acoustic wave resonator 300 is mainly determined by the material of the piezoelectric layer 10, which is generally lithium niobate or lithium tantalate. The temperature coefficient of frequency (TCF) of the surface acoustic wave resonator 300 is negative, and the frequency of the surface acoustic wave resonator 300 decreases with the increase of temperature, which affects the performance of the surface acoustic wave resonator 300. In the embodiment of the present application, the temperature compensation layer 60 made of a material with a positive temperature coefficient is provided, which can improve the temperature coefficient of frequency of the surface acoustic wave resonator 300, so that the frequency of the surface acoustic wave resonator 300 is not easily changed with the change of temperature, and the working stability of the surface acoustic wave resonator 300 is improved.

[0125] In some examples, as shown in FIGS. 10 to 12, the surface acoustic wave resonator 300 further includes a first weight-increasing portion 71 and a second weight-increasing portion 72, and the first weight-increasing portion 71 and the second weight-increasing portion 72 are both located on the side of the temperature compensation layer 60 away from the piezoelectric layer 10. The projection of the first weight-increasing portion 71 on the piezoelectric layer 10 overlaps with the projection of the end of the plurality of second electrode strips 24 close to the first bus bar 21 on the piezoelectric layer 10. The projection of the second weight-increasing portion 72 on the piezoelectric layer 10 overlaps with the projection of the end of the plurality of first electrode strips 23 close to the second bus bar 22 on the piezoelectric layer 10. The first weight-increasing portion 71 is spaced apart from the cover layer 30, and the second weight-increasing portion 72 is spaced apart from the cover layer 30.

[0126] In the surface acoustic wave resonator 300 provided by the embodiment of the present application, the first weight-increasing portion 71 is located on the side of the end of the plurality of second electrode strips 24 close to the first bus bar 21 away from the piezoelectric layer 10, and the second weight-increasing portion 72 is located on the side of the end of the plurality of first electrode strips 23 close to the second bus bar 22 away from the piezoelectric layer 10, so that the mass loading effect can be used to reduce the propagation speed of the surface acoustic wave in the region where the end of the plurality of second electrode strips 24 close to the first bus bar 21 and the end of the plurality of first electrode strips 23 close to the second bus bar 22 are located, so that the propagation speed of the surface acoustic wave in this region can be less than the propagation speed of the surface acoustic wave in the region between the first weight-increasing portion 71 and the second weight-increasing portion 72, thereby facilitating the formation of piston mode and reducing the transverse mode.

[0127] In the embodiment of the present application, the size (for example, length, width, height, etc.), shape and material of the first weight-increasing portion 71 and the second weight-increasing portion 72 are not limited as long as the transverse mode of the surface acoustic wave resonator can be suppressed.

[0128] In some embodiments, as shown in FIGS. 3-12, to absorb the reflection interference and reduce the model size, the surface acoustic wave resonator 300 can further include a perfect matched layer 80.

[0129] In the case that the surface acoustic wave resonator 300 is a thin film surface acoustic wave resonator, as shown in FIGS. 3 and 7, the perfect matched layer 80 can include a first sub-portion 81 and a second sub-portion 82 connected. The first sub-portion 81 can be located on the side of the substrate 40 away from the piezoelectric layer 10, and the second sub-portion 82 can cover the side wall of the piezoelectric layer 10, the intermediate layer 50 and the substrate 40, and contact the side of the first bus bar 21 away from the second bus bar 22, and the side of the second bus bar 22 away from the first bus bar 21.

[0130] As shown in FIG. 3, in some examples, the second sub-portion 82 can also contact the cover layer 30. It can be understood that the cover layer 30 includes a first cover portion 31 and a second cover portion 32, both of which contact the second sub-portion 82.

[0131] In the case that the surface acoustic wave resonator 300 can be a temperature compensated surface acoustic wave resonator, as shown in FIG. 10, the perfect matched layer 80 can include a third sub-portion 83 and a fourth sub-portion 84 connected. The third sub-portion 83 can be located on the side of the piezoelectric layer 10 away from the interdigital transducer 20, and the fourth sub-portion 84 can cover the side wall of the piezoelectric layer 10, and contact the side of the first bus bar 21 away from the second bus bar 22, and the side of the second bus bar 22 away from the first bus bar 21.

[0132] As shown in FIG. 10, in some examples, the fourth sub-portion 84 can also contact the cover layer 30. It can be understood that the cover layer 30 includes a first cover portion 31 and a second cover portion 32, both of which contact the fourth sub-portion 84.

[0133] Some embodiments of the present application provide a method for manufacturing a surface acoustic wave resonator 300, as shown in FIG. 13, which includes steps S100 and S200.

[0134] S100, referring to FIG. 3, FIG. 7 and FIG. 10, the interdigital transducer 20 is formed on the piezoelectric layer 10. The interdigital transducer 20 includes a first bus bar 21, a second bus bar 22, a plurality of first electrode strips 23 and a plurality of second electrode strips 24. The first bus bar 21 and the second bus bar 22 are oppositely arranged and extend along a first direction X. The plurality of first electrode strips 23 and the plurality of second electrode strips 24 are located between the first bus bar 21 and the second bus bar 22. The plurality of first electrode strips 23 and the plurality of second electrode strips 24 extend along a second direction Y, and in the first direction X, the plurality of first electrode strips 23 and the plurality of second electrode strips 24 are arranged alternately. The plurality of first electrode strips 23 are connected to the first bus bar 21, and the plurality of second electrode strips 24 are connected to the second bus bar 22. The first direction X and the second direction Y intersect and are both parallel to the surface of the piezoelectric layer 10 close to the interdigital transducer 20.

[0135] S200, referring to FIG. 3, FIG. 7 and FIG. 10, the cover layer 30 is formed on the first bus bar 21 and the second bus bar 22. The cover layer 30 has a higher transverse wave speed than the piezoelectric layer 10.

[0136] It can be understood that the preparation method of the surface acoustic wave resonator 300 provided by the embodiments of the present application can achieve the same beneficial effects as the surface acoustic wave resonator 300 provided by any of the above embodiments, which will not be repeated here.

[0137] The above describes the surface acoustic wave resonator and the preparation method of the surface acoustic wave resonator provided by some embodiments of the present application. The performance of the surface acoustic wave resonator provided by the embodiments of the present application is analyzed below in combination with FIG. 14 to FIG. 23.

[0138] As shown in FIG. 14, in order to verify that the cover layer selects a material with a higher transverse wave speed than the piezoelectric layer, which can improve the performance of the surface acoustic wave resonator provided by the embodiments of the present application, the embodiments of the present application test the admittance characteristic curve, the conductance characteristic curve and the quality factor-frequency relationship curve of the surface acoustic wave resonator, and the dispersion curve at the second gap region M2 (referring to FIG. 4) when the material of the cover layer 30 is selected as silicon dioxide (SiO2), silicon nitride (Si3N4), silicon carbide (SiC) and diamond respectively, based on the structure shown in FIG. 3, the piezoelectric layer is lithium tantalate, and the thickness of the cover layer is 240 nanometers (nm). Meanwhile, as a control, the embodiments of the present application also test the admittance characteristic curve, the conductance characteristic curve and the quality factor-frequency relationship curve of the structure shown in FIG. 3 after removing the cover layer, and the dispersion curve of the second gap region M2.

[0139] The transverse wave speed of lithium tantalate is 3551 m / s, the transverse wave speed of silicon dioxide is 3198 m / s, the transverse wave speed of silicon nitride is 6426 m / s, the transverse wave speed of silicon carbide is 7126 m / s, and the transverse wave speed of diamond is 12823 m / s. That is, the transverse wave speed of silicon dioxide is less than the transverse wave speed of lithium tantalate, and the transverse wave speeds of silicon nitride, silicon carbide and diamond are all greater than the transverse wave speed of lithium tantalate.

[0140] Hereinafter, for the convenience of description, the surface acoustic wave resonator with the cover layer 30 made of silicon dioxide is referred to as Test Example 1, the surface acoustic wave resonator with the cover layer 30 made of silicon nitride is referred to as Test Example 2, the surface acoustic wave resonator with the cover layer 30 made of silicon carbide is referred to as Test Example 3, the surface acoustic wave resonator with the cover layer 30 made of diamond is referred to as Test Example 4, and the surface acoustic wave resonator without the cover layer is referred to as a Comparative Example.

[0141] Fig. 14(a) shows the admittance characteristic curves of Test Example 1, Test Example 2, Test Example 3, Test Example 4 and the Comparative Example. The horizontal axis is frequency, in units of gigahertz (GHz), and the vertical axis is admittance, in units of decibels (dB). In the five curves of Fig. 14(a), the frequency corresponding to the highest point is the resonance frequency, and the frequency corresponding to the lowest point is the anti-resonance frequency.

[0142] As can be seen from Fig. 14(a), the admittance characteristic curve of the Comparative Example has a resonance peak corresponding to the gap mode in the interval from the resonance frequency to the anti-resonance frequency; the resonance peak corresponding to the gap mode still exists on the admittance characteristic curve of Test Example 1 in the interval from the resonance frequency to the anti-resonance frequency, and is steeper; and the resonance peak corresponding to the gap mode can be moved out of the interval from the resonance frequency to the anti-resonance frequency on the admittance characteristic curves of Test Example 2, Test Example 3 and Test Example 4, and the admittance characteristic of the surface acoustic wave resonator can be improved. Thus, it can be proved that, in the embodiments of the present application, the cover layer is arranged between the first extension and the second extension, and the transverse wave speed of the cover layer is greater than the transverse wave speed of the piezoelectric layer, which can suppress or even eliminate the gap mode.

[0143] Figure 14 (b) shows the conductance characteristic curves of the test example 1, the test example 2, the test example 3, the test example 4 and the control example. The horizontal coordinate is frequency, unit: GHz, and the vertical coordinate is conductance, unit: dB. By comparing the five curves in Figure 14 (b), it can be found that: compared with the control example, the resonant peak positions corresponding to the main modes in the conductance characteristic curves of the test example 1, the test example 2, the test example 3 and the test example 4 are basically unchanged; compared with the control example, the resonant peaks corresponding to some spurious modes in the conductance characteristic curve of the test example 1 move to the left; compared with the control example, the resonant peaks corresponding to some spurious modes in the conductance characteristic curves of the test example 2, the test example 3 and the test example 4 move to the right. Among them, compared with the control example, the moving range of the resonant peaks corresponding to the spurious modes in the conductance characteristic curve of the test example 4 is the largest, followed by the test example 3, and the test example 2 is the smallest. The size order of the moving range of the resonant peaks corresponding to the spurious modes is the same as the size order of the transverse wave speed of the covering layer.

[0144] Therefore, it can also be proved that, in the embodiment of the present application, the covering layer is arranged between the first extension part and the second extension part, and the transverse wave speed of the covering layer is greater than the transverse wave speed of the piezoelectric layer, which can improve the operating frequency of the gap mode, so that the operating frequency corresponding to the gap mode is close to the anti-resonance frequency of the surface acoustic wave resonator, or even exceeds the anti-resonance frequency of the surface acoustic wave resonator.

[0145] At the same time, by comparing the five curves in Figure 14 (b), it can also be found that: the resonant peaks in the conductance characteristic curves of the test example 2, the test example 3 and the test example 4 are steeper than the resonant peaks in the conductance characteristic curve of the control example. This also shows that, by using the structure shown in Figure 3 and the transverse wave speed of the covering layer being greater than the transverse wave speed of the piezoelectric layer, the quality factor of the surface acoustic wave resonator can be improved.

[0146] Figure 14 (c) shows the dispersion curves of the test example 1, the test example 2, the test example 3, the test example 4 and the control example at the second gap region M2. The horizontal coordinate of Figure 14 (c) is wave number, unit: rad / μm, and the vertical coordinate is frequency, unit: GHz. The lowest point of each curve in the dispersion curve represents the cut-off frequency.

[0147] It can be seen from Figure 14 (c) that the cut-off frequency of the second gap region M2 can be improved by arranging the covering layer. Moreover, the cut-off frequency corresponding to the test example 4 is greater than the cut-off frequency corresponding to the test example 3, the cut-off frequency corresponding to the test example 3 is greater than the cut-off frequency corresponding to the test example 2, and the cut-off frequency corresponding to the test example 4 is greater than the cut-off frequency corresponding to the test example 1.

[0148] Therefore, the higher the transverse wave speed of the cover layer is, the higher the cutoff frequency of the second gap region M2 is. The higher the cutoff frequency of the second gap region M2 is, the stronger the transverse energy confinement capability of the second gap region M2 is, and the higher the quality factor of the surface acoustic wave resonator is.

[0149] Fig. 14(d) shows the quality factor-frequency curves of the test example 1, the test example 2, the test example 3, the test example 4 and the control example. The abscissa of Fig. 14(d) is frequency, in GHz, and the ordinate is quality factor. It can be seen from Fig. 14(d) that the quality factor near the anti-resonance frequency of the test example 4 is greater than that of the test example 3; the quality factor near the anti-resonance frequency of the test example 3 is greater than that of the test example 2; the quality factor near the anti-resonance frequency of the test example 2 is greater than that of the test example 1; and the quality factor near the anti-resonance frequency of the test example 1 is greater than that of the control example. The greater the transverse wave speed of the cover layer is, the greater the quality factor near the anti-resonance frequency of the surface acoustic wave resonator can be.

[0150] In summary, in the embodiments of the present application, the cover layer is selected to be a material with a transverse wave speed higher than that of the piezoelectric layer, which can improve the performance of the surface acoustic wave resonator provided by the embodiments of the present application.

[0151] Based on the structures of the three different surface acoustic wave resonators shown in Figs. 3, 7 and 10, the present application further analyzes the influence of the thickness and width of the cover layer on the performance of the surface acoustic wave resonator. As shown in Figs. 15, 16, 17 and 18, for the structure of the surface acoustic wave resonator shown in Fig. 3, the present application respectively tests the admittance characteristic curves, the conductance characteristic curves and the quality factor-frequency curves of the surface acoustic wave resonators with cover layers of different thicknesses, and the dispersion curves at the second gap region M2, when the material of the piezoelectric layer is lithium tantalate and the material of the cover layer is selected to be silicon dioxide, silicon nitride, silicon carbide and diamond.

[0152] Figure 15 shows the performance of the SAW resonator when the material of the cover layer is silicon dioxide and the thickness of the cover layer is 0 nm, 20 nm, 80 nm, 140 nm, 180 nm, 200 nm, 240 nm and 280 nm respectively. (a), (b), (c) and (d) of Figure 15 are respectively the admittance characteristic diagram, the conductance characteristic diagram, the dispersion diagram and the quality factor-frequency relationship diagram. The abscissa and the ordinate of (a), (b), (c) and (d) of Figure 15 refer to the above description of Figure 14, and are not repeated here. It can be understood that, since the change trend of the quality factor-frequency relationship diagram is relatively complex, in order to avoid too many curves interfering with the analysis and comparison, only the quality factor-frequency characteristic curves of the SAW resonator with the thickness of the cover layer being 0 nm, 20 nm, 140 nm and 240 nm are shown in (c) of Figure 15.

[0153] As can be seen from (a) of Figure 15, when the material of the cover layer is silicon dioxide, even if the thickness of the cover layer is increased, the resonance peak corresponding to the gap mode still exists in the admittance characteristic curve of the SAW resonator, and the cover layer has little effect on the gap mode. As can be seen from (b) of Figure 15, when the material of the cover layer is silicon dioxide, as the thickness of the cover layer increases, the operating frequency corresponding to other spurious modes in the conductance characteristic curve decreases, and the resonance peak corresponding to the spurious mode moves to the left. As can be seen from (c) of Figure 15, when the material of the cover layer is silicon dioxide, as the thickness of the cover layer increases, the cutoff frequency of the second gap region M2 first increases and then decreases. As can be seen from (d) of Figure 15, when the material of the cover layer is silicon dioxide, as the thickness of the cover layer increases, the quality factor of the SAW resonator is not obviously improved.

[0154] Figure 16 shows the performance of the SAW resonator when the material of the cover layer is silicon nitride and the thickness of the cover layer is 0 nm, 20 nm, 80 nm, 140 nm, 180 nm, 200 nm, 240 nm and 280 nm respectively. (a), (b), (c) and (d) of Figure 16 are respectively the admittance characteristic diagram, the conductance characteristic diagram, the dispersion diagram and the quality factor-frequency relationship diagram. The abscissa and the ordinate of (a), (b), (c) and (d) of Figure 16 refer to the above description of Figure 14, and are not repeated here. Among them, the quality factor-frequency characteristic curves of the SAW resonator when the thickness of the cover layer is 0 nm, 20 nm, 140 nm and 240 nm are also shown in (c) of Figure 16.

[0155] As can be seen from (a) of FIG. 16, when the material of the cover layer is silicon nitride, with the increase of the thickness of the cover layer, the resonance peak corresponding to the gap mode in the admittance characteristic curve of the surface acoustic wave resonator gradually moves to the right, and when the thickness of the cover layer is 80 nm, 140 nm, 180 nm, 200 nm, 240 nm and 280 nm, there is even no resonance peak corresponding to the gap mode in the admittance characteristic curve. As can be seen from (b) of FIG. 16, when the material of the cover layer is silicon nitride, with the increase of the thickness of the cover layer, the operating frequency corresponding to other spurious modes in the conductance characteristic curve increases, and the resonance peak corresponding to other spurious modes moves to the right. And when the thickness of the cover layer is small (for example, less than 240 nm), the resonance peak corresponding to other spurious modes also becomes steeper with the increase of the thickness of the cover layer. When the thickness of the cover layer is large (for example, greater than or equal to 240 nm), due to the existence of bulk wave radiation towards the direction of the substrate, the peak value of some spurious peaks becomes small. As can be seen from (c) of FIG. 16, when the material of the cover layer is silicon nitride, with the increase of the thickness of the cover layer, the cutoff frequency of the second gap region M2 gradually increases, and the transverse energy confinement ability of the region is enhanced. As can be seen from (d) of FIG. 16, when the material of the cover layer is silicon nitride, with the increase of the thickness of the cover layer, the quality factor of the surface acoustic wave resonator is obviously improved.

[0156] FIG. 17 shows the performance diagram of the surface acoustic wave resonator when the material of the cover layer is silicon carbide and the thickness of the cover layer is 0 nm, 20 nm, 80 nm, 140 nm, 180 nm, 200 nm, 240 nm and 280 nm, respectively. (a), (b), (c) and (d) of FIG. 17 are admittance characteristic curve, conductance characteristic curve, dispersion curve and quality factor-frequency relationship curve, respectively. The horizontal and vertical coordinates of (a), (b), (c) and (d) of FIG. 17 are as described above with reference to FIG. 14, and will not be described here. In (c) of FIG. 17, the quality factor-frequency characteristic curves of the surface acoustic wave resonator with the thickness of the cover layer being 0 nm, 20 nm, 140 nm and 240 nm are also shown.

[0157] As can be seen from (a) of FIG. 17, when the material of the cover layer is silicon carbide, with the increase of the thickness of the cover layer, the resonance peak corresponding to the gap mode in the admittance characteristic curve of the surface acoustic wave resonator gradually moves to the right, and when the thickness of the cover layer is greater than 20 nm, there is even no resonance peak corresponding to the gap mode in the admittance characteristic curve. However, when the thickness of the cover layer is greater than 180 nm, resonance peaks corresponding to other spurious modes appear in the interval between the resonance frequency and the anti-resonance frequency in the admittance characteristic curve.

[0158] As can be seen from (b) in FIG. 17, when the material of the cover layer is silicon carbide, as the thickness of the cover layer increases, the operating frequency corresponding to other spurious modes in the conductance characteristic curve increases, and the resonance peaks corresponding to other spurious modes move to the right. Moreover, the resonance peaks corresponding to other spurious modes also become steeper as the thickness of the cover layer increases. As can be seen from (c) in FIG. 17, when the material of the cover layer is silicon carbide, as the thickness of the cover layer increases, the cutoff frequency of the second gap region M2 gradually increases, and the transverse energy confinement capability of the region is enhanced. As can be seen from (d) in FIG. 17, when the material of the cover layer is silicon carbide, as the thickness of the cover layer increases, the quality factor of the surface acoustic wave resonator is obviously improved.

[0159] FIG. 18 shows the performance diagrams of the surface acoustic wave resonator when the material of the cover layer is diamond and the thickness of the cover layer is 0 nm, 20 nm, 80 nm, 140 nm, 180 nm, 200 nm, 240 nm and 280 nm, respectively. (a), (b), (c) and (d) in FIG. 18 are the admittance characteristic curve, the conductance characteristic curve, the dispersion curve and the relationship curve of the quality factor and the frequency, respectively. The horizontal and vertical coordinates of (a), (b), (c) and (d) in FIG. 18 are as described above with reference to FIG. 14, and will not be described here again. In (c) of FIG. 18, the quality factor and frequency characteristic curves of the surface acoustic wave resonator when the thickness of the cover layer is 0 nm, 20 nm, 140 nm and 240 nm are also shown.

[0160] As can be seen from (a) in FIG. 18, when the material of the cover layer is diamond, as the thickness of the cover layer increases, the resonance peak corresponding to the gap mode in the admittance characteristic curve of the surface acoustic wave resonator gradually moves to the right. As can be seen from (b) in FIG. 18, when the material of the cover layer is diamond, as the thickness of the cover layer increases, the operating frequency corresponding to other spurious modes in the conductance characteristic curve increases, and the resonance peaks corresponding to other spurious modes move to the right. Moreover, the resonance peaks corresponding to other spurious modes also become steeper as the thickness of the cover layer increases. As can be seen from (c) in FIG. 18, when the material of the cover layer is diamond, as the thickness of the cover layer increases, the cutoff frequency of the second gap region M2 gradually increases, and the transverse energy confinement capability of the region is enhanced. As can be seen from (d) in FIG. 18, when the material of the cover layer is diamond, as the thickness of the cover layer increases, the quality factor of the surface acoustic wave resonator is obviously improved.

[0161] In summary, when the transverse wave speed of the cover layer is higher than the transverse wave speed of the piezoelectric layer, increasing the thickness of the cover layer can also increase the propagation speed of the surface acoustic wave in the region where the first bus bar and the second bus bar are located, the cut-off frequency of the region where the first bus bar and the second bus bar are located, and the transverse energy barrier of the region where the first bus bar and the second bus bar are located, thereby improving the problem of transverse energy leakage of the surface acoustic wave resonator. Increasing the transverse wave speed of the cover layer and / or increasing the thickness of the cover layer can improve the performance of the surface acoustic wave resonator, thereby relaxing the cost requirement and size requirement of the cover layer in the embodiments of the present application.

[0162] As shown in FIG. 19, based on the structure of the surface acoustic wave resonator shown in FIG. 3, when the material of the piezoelectric layer is lithium tantalate, the material of the cover layer is selected to be silicon nitride, and the thickness of the cover layer is 240 nm, the present application embodiment tests the admittance characteristic curve and the conductance characteristic curve of the surface acoustic wave resonator in four cases, i.e., removing the cover layer (control example), the cover layer being located in the second gap region M2 (test example 1), the cover layer covering the first extension part and being located in the second gap region M2 (test example 2), and the cover layer covering the first extension part and the second extension part and being located in the second gap region M2 (test example 3). In FIG. 19, (a) is the admittance characteristic curve, and (b) is the conductance characteristic curve.

[0163] As can be seen from FIG. 19, compared with the control example, test examples 1, 2 and 3 can effectively improve the admittance characteristic and the conductance characteristic of the surface acoustic wave resonator, suppress the gap mode of the surface acoustic wave, and improve the quality factor of the surface acoustic wave resonator. Therefore, as long as the cover layer is located in the second gap region M2, the performance of the surface acoustic wave resonator can be high, and the cover area of the cover layer almost does not affect the performance of the surface acoustic wave resonator. In this way, in the preparation process of the surface acoustic wave resonator, the alignment accuracy requirement of the cover layer can be low, which is conducive to the mass production of the surface acoustic wave resonator.

[0164] As shown in FIG. 20, for the structure of the surface acoustic wave resonator shown in FIG. 7, the present application embodiment tests the admittance characteristic curve, the conductance characteristic curve, and the quality factor and frequency characteristic curve of the surface acoustic wave resonator when the material of the piezoelectric layer is lithium tantalate, the material of the cover layer is selected to be silicon nitride, and the thickness of the cover layer is 0 nm, 20 nm, 60 nm, 100 nm, 140 nm and 180 nm, respectively. The present application embodiment also tests the dispersion curve of the region where the cover layer is located when the thickness of the cover layer is 20 nm, 60 nm and 100 nm, respectively. As a control example, the present application embodiment also tests the dispersion curve of the region where the first bus bar or the second bus bar is located (i.e., the thickness of the cover layer is 0 nm), the dispersion curve of the aperture region (control example 2), and the dispersion curve of the first gap region (control example 3) when the cover layer is removed (control example 1).

[0165] Fig. 20(a), (b), (c) and (d) are respectively a plot of admittance characteristic, a plot of conductance characteristic, a plot of dispersion characteristic and a plot of quality factor versus frequency. The abscissa and ordinate of Fig. 20(a), (b), (c) and (d) refer to the above description of Fig. 14, and are not repeated here.

[0166] As can be seen from Fig. 20(a), when the material of the cover layer is silicon nitride, the admittance characteristics of the surface acoustic wave resonators with different thicknesses of the cover layer are good. As can be seen from Fig. 20(b), when the material of the cover layer is silicon nitride, as the thickness of the cover layer increases, the operating frequencies corresponding to some spurious modes in the conductance characteristic curve increase greatly, and the range of the rightward movement of the resonance peaks corresponding to the spurious modes increases. Moreover, as the thickness of the cover layer increases, the resonance peaks corresponding to the spurious modes become steeper, which also confirms the improvement of the quality factor of the surface acoustic wave resonator.

[0167] As can be seen from Fig. 20(c), the cutoff frequencies of Test Example 1, Test Example 2 and Test Example 3 are all greater than that of Control Example 1. Moreover, as the thickness of the cover layer increases, the cutoff frequencies also increase accordingly. As the thickness of the cover layer increases, the cutoff frequency of the region where the first bus bar and the second bus bar are located can be greater than the cutoff frequency of the first gap region. The increase of the thickness of the cover layer causes the increase of the cutoff frequency of the region where the first bus bar and the second bus bar are located, and improves the transverse energy barrier. As can be seen from Fig. 20(d), when the material of the cover layer is silicon nitride, as the thickness of the cover layer increases, the quality factor of the surface acoustic wave resonator improves obviously.

[0168] Therefore, for the structure of the surface acoustic wave resonator shown in Fig. 7, increasing the transverse wave speed of the cover layer and / or increasing the thickness of the cover layer can improve the performance of the surface acoustic wave resonator.

[0169] The present application also analyzes the performance of the surface acoustic wave resonator with the change of the width of the cover layer when the material of the piezoelectric layer is lithium tantalate, the material of the cover layer is silicon nitride, and the thickness of the cover layer is 100 nm. As shown in Fig. 21, the present application simulates and tests the admittance characteristic curve, the conductance characteristic curve and the quality factor versus frequency characteristic curve of the surface acoustic wave resonator when the width of the cover layer is 0.4 μm, 1.2 μm, 2 μm and 2.8 μm. Fig. 21(a) is a plot of admittance characteristic, Fig. 21(b) is a plot of conductance characteristic, and Fig. 21(c) is a plot of quality factor versus frequency.

[0170] As shown in (a) of FIG. 21, when the cover layer has different widths, the difference of the admittance characteristic curves of the surface acoustic wave resonator at the interval from the resonance frequency to the anti-resonance frequency is small. However, as the width of the cover layer increases, at the same resonance frequency, the wider the width of the cover layer, the smaller the admittance of the surface acoustic wave resonator, and the higher the filtering and frequency selection capability of the surface acoustic wave resonator. As shown in (b) of FIG. 21, as the width of the cover layer increases, the resonance peaks corresponding to some spurious modes in the conductance characteristic curve become steeper, which indicates that the quality factor of the surface acoustic wave resonator is increasing.

[0171] As shown in (c) of FIG. 21, as the thickness of the cover layer increases, the quality factor of the surface acoustic wave resonator can also be improved in a wider frequency range. Meanwhile, as shown in (c) of FIG. 21, when the width of the cover layer is 0.4 μm, 1.2 μm and 2 μm, the quality factor of the surface acoustic wave resonator at the anti-resonance frequency is small, and when the width of the cover layer is 2.8 μm, the quality factor of the surface acoustic wave resonator at the vicinity of the anti-resonance frequency is high. Thus, when the material of the cover layer is silicon nitride and the thickness is 100 nm, a surface acoustic wave resonator with high quality factor can be realized by making the width of the cover layer greater than 2.8 μm.

[0172] As shown in FIG. 22, for the structure of the surface acoustic wave resonator shown in FIG. 10, the present embodiment tests the admittance characteristic curves, the quality factor and frequency characteristic curves and the dispersion curves of the surface acoustic wave resonator when the material of the piezoelectric layer is lithium niobate, the material of the cover layer is silicon nitride, and the thickness of the cover layer is 0 nm, 10 nm, 30 nm, 50 nm, 90 nm, 100 nm and 200 nm respectively, and the conductance characteristic curves of the surface acoustic wave resonator when the thickness of the cover layer is 0 nm, 10 nm, 30 nm, 100 nm and 200 nm respectively. (a), (b), (c) and (d) of FIG. 22 are admittance characteristic curve graphs, conductance characteristic curve graphs, dispersion curve graphs and quality factor and frequency relationship curve graphs respectively. In (d) of FIG. 22, the dispersion curves of the aperture region (comparative example 1) and the first gap region (comparative example 2) are also shown. The horizontal and vertical coordinates of (a), (b), (c) and (d) of FIG. 22 refer to the above description of FIG. 14, which will not be repeated here.

[0173] As can be seen from (a) and (b) in FIG. 22, as the thickness of the cover layer increases, the resonance peaks corresponding to some spurious modes in the admittance characteristic curve and the conductance characteristic curve become steeper, indicating that as the thickness of the cover layer increases, the quality factor of the surface acoustic wave resonator also increases accordingly. As can be seen from (c) in FIG. 22, as the thickness of the cover layer increases, the cutoff frequency of the region where the first bus bar and the second bus bar are located also increases, so that the transverse energy barrier corresponding to the region where the first bus bar and the second bus bar are located can be increased accordingly, thereby improving the quality factor of the surface acoustic wave resonator.

[0174] As can be seen from (c) in FIG. 22, when the thickness of the cover layer is 0 nm (i.e., no cover layer is provided), the cutoff frequency of the region where the first bus bar and the second bus bar are located is less than the cutoff frequency of the aperture region, and the cutoff frequency of the aperture region is less than the cutoff frequency of the first gap region. By providing a cover layer, increasing the thickness of the cover layer can make the cutoff frequency of the region where the first bus bar and the second bus bar are located greater than the cutoff frequency of the aperture region. However, when the thickness of the cover layer is less than or equal to 200 nm, the cutoff frequency of the region where the first bus bar and the second bus bar are located is still less than the cutoff frequency of the first gap region.

[0175] As can be seen from (d) in FIG. 22, as the thickness of the cover layer increases, the Q value of the surface acoustic wave resonator at the anti-resonance frequency point is improved.

[0176] As shown in FIG. 23, the performance of the surface acoustic wave resonator with a cover layer made of silicon nitride and having a thickness of 30 nm is analyzed as the width of the cover layer changes. The admittance characteristic curve and the quality factor-frequency curve of the surface acoustic wave resonator are tested for four cases: no cover layer (control example), the cover layer covering the first bus bar and the second bus bar (test example 1), the cover layer covering not only the first bus bar and the second bus bar but also half of the first gap region (test example 2), and the cover layer covering not only the first bus bar and the second bus bar but also the entire first gap region (test example 3). (a) in FIG. 23 is an admittance characteristic curve, and (b) in FIG. 23 is a quality factor-frequency curve.

[0177] As can be seen from (a) in FIG. 23, the admittance characteristics of test example 1 and test example 2 are better than those of the control example. The resonance peak corresponding to the transverse mode appears in the admittance characteristic curve of test example 3. As can be seen from (b) in FIG. 23, as the width of the cover layer increases, the improvement of the quality factor of the resonator remains basically unchanged.

[0178] In summary, for the surface acoustic wave resonator shown in Fig. 10, as long as the cover layer does not cover the entire first gap region, the quality factor of the surface acoustic wave resonator can be improved. In this way, the width requirement of the cover layer in the preparation process of the surface acoustic wave resonator can be lower, which is conducive to the large-scale production of the surface acoustic wave resonator.

[0179] In the description of the present specification, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner. The above is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A surface acoustic wave resonator, characterized by, The surface acoustic wave resonator comprises: a piezoelectric layer, an interdigital transducer on the piezoelectric layer, the interdigital transducer comprising a first bus bar, a second bus bar, a plurality of first electrode strips and a plurality of second electrode strips; the first bus bar and the second bus bar are arranged opposite to each other and extend along a first direction, the plurality of first electrode strips and the plurality of second electrode strips are arranged between the first bus bar and the second bus bar, the plurality of first electrode strips and the plurality of second electrode strips extend along a second direction, and in the first direction, the plurality of first electrode strips and the plurality of second electrode strips are arranged alternately, the plurality of first electrode strips are connected to the first bus bar, and the plurality of second electrode strips are connected to the second bus bar, the first direction and the second direction intersect each other and are parallel to a surface of the piezoelectric layer close to the interdigital transducer; a cover layer on the first bus bar and the second bus bar, the cover layer has a transverse wave speed higher than that of the piezoelectric layer.

2. The surface acoustic wave resonator according to claim 1, wherein the first bus bar and the second bus bar each comprise a first extension, a second extension and a plurality of connecting portions, the first extension and the second extension are arranged opposite to each other and extend along the first direction, and the plurality of connecting portions are arranged between the first extension and the second extension and connect the first extension and the second extension; wherein the second extension of the first bus bar is connected to the plurality of first electrode strips, the second extension of the second bus bar is connected to the plurality of second electrode strips, the number of the plurality of first electrode strips is greater than the number of the connecting portions in the first bus bar, and the number of the plurality of second electrode strips is greater than the number of the connecting portions in the second bus bar.

3. The surface acoustic wave resonator according to claim 2, wherein In the second direction, the cover layer is arranged between the first extension and the second extension, and the cover layer is arranged on a side of the plurality of connecting portions away from the piezoelectric layer.

4. The surface acoustic wave resonator according to claim 3, wherein The cover layer is further arranged on a side of the first extension and / or the second extension away from the piezoelectric layer.

5. The surface acoustic wave resonator of claim 1, wherein, The projection of the first bus bar and the second bus bar on the piezoelectric layer is in the shape of a strip.

6. The SAW resonator according to any one of claims 1 to 5, characterized in that, The plurality of first electrode strips and the plurality of second electrode strips each comprise a first portion, a second portion, a third portion and a fourth portion connected in sequence, the width of the second portion and the fourth portion is greater than the width of the first portion and the third portion; the width is the size of the first portion, the second portion, the third portion or the fourth portion in the first direction; wherein the first portion of the plurality of first electrode strips is connected to the first bus bar, and the first portion of the plurality of second electrode strips is connected to the second bus bar.

7. The SAW resonator according to any one of claims 1 to 6, characterized in that, The interdigital transducer further comprises a plurality of first dummy fingers and a plurality of second dummy fingers, the plurality of first dummy fingers are connected to the first bus bar and are arranged between the first bus bar and the plurality of second electrode strips respectively, and the plurality of second dummy fingers are connected to the second bus bar and are arranged between the second bus bar and the plurality of first electrode strips respectively. A projection of the cover layer on the piezoelectric layer is spaced apart from projections of the plurality of first dummy fingers on the piezoelectric layer, and a projection of the cover layer on the piezoelectric layer is spaced apart from projections of the plurality of second dummy fingers on the piezoelectric layer.

8. The SAW resonator according to any one of claims 1 to 6, characterized in that, The first bus bar and the plurality of second electrode strips have a plurality of first gaps therebetween, and the second bus bar and the plurality of second electrode strips have a plurality of second gaps therebetween. The cover layer includes a first cover portion, a second cover portion, a third cover portion, and a fourth cover portion; the first cover portion is located on a side of the first bus bar away from the piezoelectric layer, the second cover portion is located on a side of the second bus bar away from the piezoelectric layer, a projection of the third cover portion on the piezoelectric layer partially overlaps a projection of the first gap on the piezoelectric layer, and a projection of the fourth cover portion on the piezoelectric layer partially overlaps a projection of the second gap on the piezoelectric layer.

9. The SAW resonator according to any one of claims 1 to 8, characterized in that, The surface acoustic wave resonator is a thin film surface acoustic wave resonator, and the surface acoustic wave resonator further includes: a substrate located on a side of the piezoelectric layer away from the interdigital transducer; an intermediate layer located between the piezoelectric layer and the substrate, and the intermediate layer has a transverse wave speed less than that of the piezoelectric layer.

10. The SAW resonator according to any one of claims 1 to 8, characterized in that, The surface acoustic wave resonator is a temperature-compensated surface acoustic wave resonator, and the surface acoustic wave resonator further includes: a temperature compensation layer located between the piezoelectric layer and the cover layer; the material of the temperature compensation layer includes a positive temperature coefficient material.

11. The surface acoustic wave resonator according to claim 10, wherein, Further comprising: a first weight-increasing portion and a second weight-increasing portion located on a side of the temperature compensation layer away from the piezoelectric layer; a projection of the first weight-increasing portion on the piezoelectric layer partially overlaps a projection of an end of the plurality of second electrode strips close to the first bus bar on the piezoelectric layer, and a projection of the second weight-increasing portion on the piezoelectric layer partially overlaps a projection of an end of the plurality of first electrode strips close to the second bus bar on the piezoelectric layer; wherein the first weight-increasing portion and the cover layer are spaced apart, and the second weight-increasing portion and the cover layer are spaced apart.

12. The SAW resonator according to any one of claims 1 to 11, characterized in that, The material of the piezoelectric layer includes lithium niobate or lithium tantalate, and the material of the cover layer includes at least one of silicon nitride, silicon carbide, and diamond.

13. A method of fabricating a surface acoustic wave resonator, characterized by, Comprising: forming an interdigital transducer on a piezoelectric layer, the interdigital transducer including a first bus bar, a second bus bar, a plurality of first electrode strips, and a plurality of second electrode strips; the first bus bar and the second bus bar are both extended along a first direction and oppositely arranged, the plurality of first electrode strips and the plurality of second electrode strips are both located between the first bus bar and the second bus bar; the plurality of first electrode strips and the plurality of second electrode strips are both extended along a second direction, and in the first direction, the plurality of first electrode strips and the plurality of second electrode strips are alternately arranged; the plurality of first electrode strips are connected to the first bus bar, and the plurality of second electrode strips are connected to the second bus bar; the first direction and the second direction intersect, and both are parallel to a surface of the piezoelectric layer close to the interdigital transducer; A cover layer is formed on the first bus bar and the second bus bar; the transverse wave sound speed of the cover layer is higher than the transverse wave sound speed of the piezoelectric layer.

14. A filter, characterized by Comprise: A plurality of surface acoustic wave resonators, the plurality of surface acoustic wave resonators being the surface acoustic wave resonator of any one of claims 1-12.

15. An electronic device, comprising: Comprise: A circuit board, A filter is located on the circuit board and connected with the circuit board; the filter is the filter of claim 14.

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