CN117728790A

CN117728790A - Surface acoustic wave resonator, preparation method thereof and electronic equipment

Info

Publication number: CN117728790A
Application number: CN202311756974.8A
Authority: CN
Inventors: 高安明; 路晓明; 姜伟
Original assignee: Zhejiang Xingyao Semiconductor Co ltd
Current assignee: Zhejiang Xingyao Semiconductor Co ltd
Priority date: 2023-12-19
Filing date: 2023-12-19
Publication date: 2024-03-19

Abstract

The utility model discloses a surface acoustic wave resonator and preparation method, electronic equipment thereof, through increasing two low sound velocity structures between substrate and interdigital transducer, these two low sound velocity structures are between two busbar respectively near a busbar relative setting, the orthographic projection of low sound velocity structure in the plane of substrate place runs through the orthographic projection of all electrode fingers in the plane of substrate place, the sound velocity of low sound velocity structure propagation surface acoustic wave is less than the sound velocity of the common non-overlapping area propagation surface acoustic wave of all electrode fingers and low sound velocity structure in the direction of perpendicular to the plane of substrate place, the maximum distance x between the end that low sound velocity structure is close to nearest one busbar and the end of electrode finger that connects another busbar is less than or equal to 0.3λ, and the minimum width y of low sound velocity structure along the extending direction of electrode finger is more than or equal to λ, λ is the wavelength of surface acoustic wave, effectively restrain the horizontal spurious mode in the surface acoustic wave resonator, and do not bring other negative effects to the performance of surface acoustic wave resonator.

Description

Surface acoustic wave resonator, preparation method thereof and electronic equipment

Technical Field

The present disclosure relates to the field of radio frequency technology, and in particular, to a surface acoustic wave resonator, a method for manufacturing the same, and an electronic device including the same.

Background

A Surface Acoustic Wave (SAW) resonator and a filter are Acoustic devices widely applied to the radio frequency field, electric energy and mechanical energy are mutually converted mainly by utilizing a piezoelectric effect, the low insertion loss and good inhibition performance are integrated, and meanwhile, the volume is small. TC-SAW (Temperature Compensated SAW) resonators and thin film TF-SAW (Thin FilmSAW) resonators with temperature compensation are also used for a large number of product designs.

However, during operation of the saw resonator, many other transverse spurious modes (i.e., transverse modes) are generated in addition to the primary acoustic mode, thereby affecting the performance of the saw resonator and increasing energy dissipation. Therefore, how to effectively suppress the transverse spurious mode in the surface acoustic wave resonator without causing other negative effects on the performance of the surface acoustic wave resonator is a technical problem to be solved by those skilled in the art.

Disclosure of Invention

In order to solve the technical problems, the embodiment of the application provides a surface acoustic wave resonator, so as to effectively inhibit a transverse stray mode in the surface acoustic wave resonator, and not bring other negative effects on the performance of the surface acoustic wave resonator.

In order to achieve the above purpose, the embodiment of the present application provides the following technical solutions:

a surface acoustic wave resonator comprising:

a substrate;

an interdigital transducer positioned on one side of the substrate, wherein the interdigital transducer comprises two bus bars which are oppositely arranged, and a plurality of electrode fingers which are positioned between the two bus bars and are parallel and arranged at intervals, each electrode finger is connected with one bus bar, and the electrode fingers connected with different bus bars are alternately arranged along the extending direction of the bus bars;

the two low-sound-velocity structures are arranged between the substrate and the interdigital transducer, are respectively close to one bus bar and are oppositely arranged between the two bus bars, the orthographic projection of the low-sound-velocity structures on the plane of the substrate penetrates through the orthographic projection of all the electrode fingers on the plane of the substrate, and the sound velocity of the surface acoustic wave propagated by the low-sound-velocity structures is smaller than that of the surface acoustic wave propagated by the common non-overlapping area of all the electrode fingers and the low-sound-velocity structures in the direction perpendicular to the plane of the substrate;

and the maximum distance x between one end of the low-sound-speed structure close to the nearest bus bar and the tail end of the electrode finger connected with the other bus bar is less than or equal to 0.3λ, and the minimum width y of the low-sound-speed structure along the extending direction of the electrode finger is more than or equal to λ, wherein λ is the wavelength of the surface acoustic wave.

Optionally, an end of the low acoustic velocity structure near the nearest one of the bus bars is flush with an end of the electrode finger connected to the other bus bar.

Optionally, the electrode fingers connected to one of the bus bars cover a sidewall of the low acoustic speed structure adjacent to the other bus bar toward the other bus bar.

Optionally, the low acoustic velocity structure is different from the width of the overlapping area of at least two electrode fingers in the direction perpendicular to the plane of the substrate along the extending direction of the electrode fingers.

Optionally, the distance between the end of the low sound speed structure facing away from the nearest bus bar and the nearest bus bar increases and decreases along the extending direction of the bus bar.

Optionally, the distance between the end of the low sound speed structure facing away from the nearest bus bar and the nearest bus bar changes linearly along the extending direction of the bus bar or changes stepwise.

Optionally, the two low-sound-speed structures are axisymmetrically arranged along the extending direction of the bus bar, or are non-axisymmetrically arranged.

Optionally, the material of the low-sound-speed structure is silicon dioxide, and the thickness z of the low-sound-speed structure along the direction perpendicular to the plane of the substrate meets the following conditions: z is more than or equal to 0.025 lambda and less than or equal to 0.035 lambda.

Optionally, along the extending direction of the electrode finger, the section of the low sound speed structure is rectangular or trapezoidal.

Optionally, the substrate comprises a non-piezoelectric base, and at least one piezoelectric layer and at least one dielectric layer positioned on the non-piezoelectric base;

alternatively, the substrate is a piezoelectric base.

Optionally, the material of the low acoustic velocity structure is at least one of silicon dioxide, silicon oxynitride, lithium oxide, tantalum pentoxide, fluorine, carbon or boron doped silicon oxide.

Optionally, the surface acoustic wave resonator further includes reflective grating structures located at two opposite sides of the interdigital transducer along the extension direction of the bus bar;

the orthographic projection of the low sound speed structure on the plane of the substrate also penetrates through the orthographic projection of the reflecting grating structure on the plane of the substrate.

A preparation method of a surface acoustic wave resonator comprises the following steps:

providing a substrate;

forming a low acoustic velocity layer on the substrate;

removing part of the low sound velocity layer, and reserving the low sound velocity layer at a preset position to form two low sound velocity structures;

forming an interdigital transducer on one side of the low sound speed structure away from the substrate;

the interdigital transducer comprises two bus bars which are oppositely arranged, and a plurality of electrode fingers which are arranged in parallel and at intervals between the two bus bars, wherein each electrode finger is connected with one bus bar, and the electrode fingers connected with different bus bars are alternately arranged along the extending direction of the bus bars;

The two low-sound-speed structures are respectively arranged close to one bus bar in an opposite mode, orthographic projection of the low-sound-speed structures on the plane of the substrate penetrates through orthographic projections of all the electrode fingers on the plane of the substrate, and sound speed of the surface acoustic waves propagated by the low-sound-speed structures is smaller than sound speed of the surface acoustic waves propagated by the common non-overlapping areas of all the electrode fingers and the low-sound-speed structures in the direction perpendicular to the plane of the substrate;

An electronic device comprising the surface acoustic wave resonator of any one of the above claims.

Compared with the prior art, the technical scheme has the following advantages:

the surface acoustic wave resonator provided by the embodiment of the application comprises a substrate and an interdigital transducer positioned on one side of the substrate, wherein the interdigital transducer comprises two bus bars which are oppositely arranged, and a plurality of electrode fingers which are positioned between the two bus bars and are parallel and are arranged at intervals, the electrode fingers are respectively connected with one bus bar, and the electrode fingers connected with different bus bars are alternately arranged along the extending direction of the bus bars; by adding two low-sound-velocity structures between the substrate and the interdigital transducer, the two low-sound-velocity structures are respectively arranged between the two bus bars and are close to one bus bar, the orthographic projection of the low-sound-velocity structures on the plane of the substrate penetrates through the orthographic projection of all electrode fingers on the plane of the substrate, the sound velocity of the surface acoustic wave propagated by the low-sound-velocity structures is smaller than that of the surface acoustic wave propagated by the common non-overlapping area of all electrode fingers and the low-sound-velocity structures in the direction perpendicular to the plane of the substrate, therefore, the sound velocity of the surface acoustic wave propagated by the low-sound-velocity structures in the corresponding area perpendicular to the plane of the substrate is reduced, the two ends of the low-sound-velocity structures along the extending direction of the electrode fingers respectively form larger sound velocity difference interfaces with the adjacent areas, so that the reflection of the transverse stray modes on the sound velocity difference interfaces is increased, the transverse stray modes in the surface acoustic wave resonator are effectively inhibited, meanwhile, the main acoustic modes are not influenced by the low-sound-velocity structures due to the fact that the propagation directions of the main acoustic modes are perpendicular to the extending directions of the electrode fingers and are parallel to the extending directions of the bus bars, and the main acoustic modes are not influenced by the transverse stray modes in the surface acoustic wave resonator, and the other resonance performance are not influenced.

In addition, considering that the gap area between the electrode finger and the opposite bus bar is the area with the highest sound velocity of the propagating surface acoustic wave, in the surface acoustic wave resonator provided by the embodiment of the application, by setting the maximum distance x between one end of the low sound velocity structure close to the nearest bus bar and the end of the electrode finger connected with the other bus bar to be less than or equal to 0.3λ, and the minimum width y of the low sound velocity structure along the extending direction of the electrode finger to be more than or equal to λ, λ is the wavelength of the surface acoustic wave, the end of the low sound velocity structure close to the nearest bus bar is flush with the end of the electrode finger connected with the other bus bar as much as possible, so that a larger sound velocity difference interface is formed between the end of the low sound velocity structure close to the nearest bus bar and the end of the electrode finger connected with the other bus bar, the reflection effect on the transverse stray mode is further enhanced, the energy dissipation caused by resonance formed by the transverse stray mode is avoided, and the performance of the resonator is improved.

It will be appreciated that the low acoustic speed structure is flush with the end of the electrode finger connected to the other bus bar near the end of the nearest bus bar, and has the best effect of suppressing the transverse stray mode; however, in view of the actual process, it is more likely that the electrode fingers connected to one bus bar will cover the low acoustic speed structure near the other bus bar toward the side wall of the other bus bar.

Under the condition that the minimum width y of the low sound velocity structure along the extending direction of the electrode fingers is more than or equal to lambda, and the sound velocity difference interface formed by the two ends of the low sound velocity structure along the extending direction of the electrode fingers and the adjacent area has a good reflection effect on the transverse stray mode, the low sound velocity structure and at least two electrode fingers can be arranged to be different in width along the extending direction of the electrode fingers in the overlapping area in the direction perpendicular to the plane of the substrate, so that more discontinuous interfaces with abrupt acoustic impedance changes are formed, meanwhile, the transverse stray mode can not form resonance after reflection in a mode of reflecting towards different directions, the inhibiting effect on the transverse stray mode is further improved, extra dissipation of energy is avoided, and the performance of the resonator is improved.

Further optionally, one end of the low sound speed structure, which is away from the nearest bus bar, may be in a gradual change shape along an extending direction of the bus bar, for example, a distance between one end of the low sound speed structure, which is away from the nearest bus bar, and the nearest bus bar is increased and then reduced along the extending direction of the bus bar, so that more discontinuous interfaces with abrupt acoustic impedance are formed, and meanwhile, a transverse stray mode cannot form resonance after reflection in a manner of reflecting to different directions, so that an inhibiting effect on the transverse stray mode is further improved, extra dissipation of energy is avoided, and performance of the resonator is improved.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1a is a schematic top view of a conventional SAW resonator;

FIG. 1b is a schematic cross-sectional view of the SAW resonator of FIG. 1a along the extending direction of the electrode finger;

FIG. 2 is a schematic cross-sectional view of a conventional TC-SAW resonator with temperature compensation along the extension direction of an electrode finger;

FIG. 3 is a schematic cross-sectional view of a conventional thin film TF-SAW resonator along the extension direction of electrode fingers;

FIG. 4 is a schematic top view of a prior art SAW resonator with a false finger;

FIG. 5 is a schematic top view of a conventional SAW resonator having a reflective grating structure;

FIG. 6 is a schematic cross-sectional view of a conventional SAW resonator suppressing lateral spurious modes along the extension direction of an electrode finger;

FIG. 7 is a schematic cross-sectional view of another conventional SAW resonator suppressing lateral spurious modes along the extension direction of the electrode finger;

FIG. 8 is an admittance-frequency curve and a conductance-frequency curve simulated for a SAW resonator employing a prior art design for suppressing transverse spurious modes;

fig. 9 is a schematic top view of a surface acoustic wave resonator according to an embodiment of the present disclosure;

fig. 10 is a schematic cross-sectional view of a surface acoustic wave resonator along an extending direction of an electrode finger according to an embodiment of the present disclosure;

fig. 11 is a schematic cross-sectional view of another surface acoustic wave resonator according to an embodiment of the present disclosure along an extending direction of an electrode finger, and a schematic sound velocity diagram of a surface acoustic wave propagating in different areas of the cross-section;

fig. 12 is a schematic cross-sectional view of still another surface acoustic wave resonator according to an embodiment of the present disclosure along an extending direction of an electrode finger;

FIG. 13a is a schematic top view of another SAW resonator provided in an embodiment of the present application;

FIG. 13b is a schematic cross-sectional view of the SAW resonator shown in FIG. 13a along the extension direction of the electrode finger;

FIG. 14a is a schematic top view of yet another SAW resonator provided in an embodiment of the present application;

FIG. 14b is a schematic cross-sectional view of the SAW resonator shown in FIG. 14a along the finger of the reflective grating structure;

FIG. 15 is a schematic top view of yet another SAW resonator provided in an embodiment of the present application;

FIG. 16 is a schematic top view of yet another SAW resonator provided in an embodiment of the present application;

FIG. 17 is a schematic top view of a surface acoustic wave resonator according to an embodiment of the present disclosure;

FIG. 18 is a schematic top view of yet another SAW resonator provided in an embodiment of the present application;

FIGS. 19-24 are graphs of admittance versus frequency and conductance versus frequency for a surface acoustic wave resonator provided by embodiments of the present application when the thickness z of the low acoustic velocity structure in a direction perpendicular to the plane of the substrate is 30nm, 40nm, 50nm, 60nm, 70nm, and 80nm, respectively;

fig. 25 is a schematic cross-sectional view of still another surface acoustic wave resonator according to an embodiment of the present disclosure along an extending direction of an electrode finger;

fig. 26a to 26f are schematic structural diagrams corresponding to each process step in the method for manufacturing a surface acoustic wave resonator according to the embodiment of the present application.

Detailed Description

The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, but the present application may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present application is not limited to the specific embodiments disclosed below.

Next, the present application will be described in detail with reference to the schematic drawings, wherein the cross-sectional views of the device structure are not to scale for the sake of illustration, and the schematic drawings are merely examples, which should not limit the scope of protection of the present application. In addition, the three-dimensional dimensions of length, width and depth should be included in actual fabrication.

For the convenience of understanding the present application, the structure of the surface acoustic wave resonator and the conventional mode of suppressing the transverse spurious mode will be described first.

Fig. 1a shows a schematic top view of a conventional surface acoustic wave resonator, as shown in fig. 1a, the surface acoustic wave resonator generally includes a piezoelectric substrate 01 and an interdigital transducer 02, the interdigital transducer 02 further includes a bus bar 021 and an electrode finger 022 led out from the bus bar 021, and fig. 1b further shows a schematic cross-sectional view of the surface acoustic wave resonator shown in fig. 1a along an extending direction of the electrode finger 022.

FIG. 2 shows a schematic cross-sectional view of a TC-SAW resonator with temperature compensation along the extension direction of electrode finger 022, the TC-SAW resonator shown in FIG. 2 further comprises a temperature compensation layer 03 covering over interdigital transducer 02, compared with the SAW resonator shown in FIG. 1a, the temperature compensation layer 03 typically being made of SiO ₂ A material.

Fig. 3 shows a schematic cross-sectional view of a thin film TF-SAW resonator along the extending direction of the electrode finger 022, unlike the SAW resonator structure shown in fig. 1a, the interdigital transducer 02 of the thin film TF-SAW resonator is located on a POI multilayer substrate 04, specifically, the POI multilayer substrate 04 often comprises a Si base 041, a piezoelectric thin film layer 042, a temperature compensation layer 043, and other dielectric layers 044, etc.

Sometimes, as shown in fig. 4, the interdigital transducer 02 further includes a dummy finger (dummy fingers) 023 provided opposite to the electrode finger 022 in the extending direction of the electrode finger 022. Sometimes, as shown in fig. 5, the surface acoustic wave resonator further includes reflection grating structures 05 disposed at opposite sides of the interdigital transducer 02 along the extending direction of the bus bar 021.

The foregoing describes some prior art saw resonator structures, and as described in the background section, during operation of the saw resonator, there are many other transverse spurious modes (i.e., transverse modes) generated in addition to the primary acoustic mode, thereby affecting the performance of the saw resonator and increasing the energy dissipation.

Taking fig. 6 as an example, in the prior art, a groove 06 with a specific shape is formed in a piezoelectric material region corresponding to the lower part of the interdigital transducer 02, and a low sound speed material is filled in the groove 06, so that the sound speed of the acoustic surface wave propagating in the corresponding region of the groove 06 is changed by using the low sound speed material in the groove 06, and the suppression effect on the transverse stray mode is enhanced. However, on the one hand, for a thin film TF-SAW resonator (see fig. 3), the process thickness of the piezoelectric thin film layer 042 does not allow for the provision of grooves 06; on the other hand, providing the grooves 06 in the corresponding piezoelectric material areas below the interdigital transducer 02 and filling with a low acoustic velocity material also affects the piezoelectric effect in normal operation of the resonator, and therefore this way of suppressing the lateral spurious modes is not practical.

Taking fig. 7 as an example, it is also taught in the prior art to place an interposer 08 in the dielectric layer 07 above the interdigital transducer 02, and the interposer 08 is a low acoustic velocity material, and in combination with the TC-SAW resonator with temperature compensation as shown in fig. 2, this way of suppressing the lateral spurious modes is particularly applicable to TC-SAW resonators with temperature compensation. However, this method of suppressing the lateral spurious mode causes the manufacturing process to become more complicated, increases the manufacturing cost, and affects the thickness and volume of the resonator, which is not practical in many cases.

Also, it can be seen that the two above existing approaches to suppressing the lateral spurious modes are not applicable to thin film TF-SAW resonators.

Fig. 8 shows an admittance-frequency curve and a conductance-frequency curve simulated for a surface acoustic wave resonator employing a design for suppressing a transverse spurious mode, where the abscissa is frequency (units/MHz), the ordinate is dB, the dark curve is the Y parameter (i.e., admittance-frequency curve), the light curve is the real part of the Y parameter (i.e., conductance-frequency curve), and it can be seen from fig. 8 that the conventional design for suppressing a transverse spurious mode has poor suppression effect on the transverse spurious mode, specifically, the resonance peak is relatively not sharp, and the curve is relatively unsmooth, and the resonator performance is not ideal.

In view of this, the embodiments of the present application provide a surface acoustic wave resonator that has a better suppression effect on the lateral spurious modes, and that does not have other adverse effects on the performance of the surface acoustic wave resonator. Fig. 9 is a schematic top view of a surface acoustic wave resonator according to an embodiment of the present application, and as shown in fig. 9, the surface acoustic wave resonator includes a substrate 10 and an interdigital transducer 20 located on one side of the substrate 10, the interdigital transducer 20 includes two bus bars 21 and 22 disposed opposite to each other, and a plurality of electrode fingers 23 disposed between the two bus bars 21 and 22 in parallel and spaced apart relation, the electrode fingers 23 are each connected to one bus bar 21 or 22, and the electrode fingers 23 connected to different bus bars 21 and 22 are alternately arranged along the extending direction of the bus bars 21/22, that is, the electrode fingers 23 (labeled 231) connected to the bus bar 21 and the electrode fingers 23 (labeled 232) connected to the bus bar 22 are alternately arranged along the extending direction of the bus bars 21/22.

It will be appreciated that the direction of extension of the electrode fingers 23 intersects the direction of extension of the bus bars 21/22 in a generally perpendicular relationship, with the electrode fingers 23 (labeled 231) of the connecting bus bar 21 and the electrode fingers 23 (labeled 232) of the connecting bus bar 22 together forming an interdigitated shape.

Fig. 10 further illustrates a schematic cross-sectional view of a saw resonator along the extending direction of the electrode fingers 23 according to the embodiment of the present application, and, in conjunction with fig. 9 and fig. 10, the saw resonator further includes two low-sound-velocity structures 30 located between the substrate 10 and the interdigital transducer 20, where the two low-sound-velocity structures 30 are disposed between the two bus bars 21 and 22 and are respectively adjacent to one bus bar, and an orthographic projection of the low-sound-velocity structures 30 on the plane of the substrate 10 penetrates through an orthographic projection of all the electrode fingers 23 on the plane of the substrate, and a sound velocity of a surface acoustic wave propagating by the low-sound-velocity structures 30 is smaller than a sound velocity of a surface acoustic wave propagating by a common non-overlapping area CC of all the electrode fingers 23 and the low-sound-velocity structures 30 in a direction perpendicular to the plane of the substrate 10. Also, as can be seen from fig. 10, the interdigital transducer 20 is convex in a direction away from the substrate 10 at a location corresponding to the low acoustic velocity structure 30.

In the surface acoustic wave resonator, as shown in fig. 9, the main acoustic mode of the surface acoustic wave propagates in a direction perpendicular to the extending direction of the electrode finger 23, that is, in the extending direction of the bus bar 21/22, and the gap area AA between the end of the electrode finger 23 connected to one bus bar and the other bus bar is the area where the acoustic velocity of the propagating surface acoustic wave is highest, and the acoustic velocity of the propagating surface acoustic wave of the overlapping area BB of all the electrode fingers 23 in the extending direction of the bus bar 21/22 is smaller than the acoustic velocity of the propagating surface acoustic wave of the above-mentioned gap area AA. If the low acoustic velocity structure 30 is not provided, although the interface between the area AA and the area BB may also form an acoustic velocity difference interface, the acoustic velocity difference interface cannot effectively suppress the transverse spurious mode, thereby affecting the resonator performance and increasing the energy dissipation.

In the surface acoustic wave resonator provided in this embodiment, as shown in fig. 9 and 10, two low-sound-velocity structures 30 are disposed between the substrate 10 and the interdigital transducer 20, and the two low-sound-velocity structures 30 are disposed between the two bus bars 21 and 22 and are respectively close to one bus bar, so that the forward projection of the low-sound-velocity structure 30 on the plane of the substrate 10 penetrates through the forward projection of all the electrode fingers 23 on the plane of the substrate 10, the sound velocity of the surface acoustic wave propagated by the low-sound-velocity structure 30 is smaller than the sound velocity of the surface acoustic wave propagated by the common non-overlapping region CC of all the electrode fingers 23 and the low-sound-velocity structure 30 in the direction perpendicular to the plane of the substrate 10, and therefore, the sound velocity of the surface acoustic wave propagated by the corresponding region DD of the low-sound-velocity structure 30 in the direction perpendicular to the plane of the substrate 10 is reduced, and the two ends of the low-sound-velocity structure 30 along the extending direction of the electrode fingers 23 form larger sound velocity difference interfaces with the adjacent regions (i.e., regions AA and regions CC) respectively, so as to increase the reflection of the transverse spurious modes on the surface acoustic wave interface, effectively inhibit the transverse spurious modes in the surface acoustic wave resonator, and simultaneously, the main acoustic spurious modes in the surface acoustic wave resonator are inhibited, and the main acoustic wave mode is not affected by the spurious modes in the direction parallel to the direction of the electrode fingers 23, and the main acoustic mode is not affected by the direction of the main acoustic mode and the spurious mode.

Specifically, fig. 11 shows a schematic cross-sectional view of another surface acoustic wave resonator along the extending direction of the electrode finger 23 and a schematic sound velocity view of a surface acoustic wave propagating in a different area of the cross-section, and as can be seen in connection with fig. 9 and 11, the low sound velocity structure 30 can reduce the sound velocity of the surface acoustic wave propagating in a corresponding area DD perpendicular to the plane direction of the substrate 10, and the sound velocity of the surface acoustic wave propagating in the area DD is smaller than the sound velocity of the surface acoustic wave propagating in the area AA and smaller than the sound velocity of the surface acoustic wave propagating in the area CC, so that a larger sound velocity difference interface is formed between the area DD and the area AA and between the area DD and the area CC, and in particular, the sound velocity difference between the area DD and the area AA is smaller than the sound velocity difference between the area BB and the area AA when the low sound velocity structure 30 is not provided, so that the reflection of the transverse spurious mode at the sound velocity difference interface is increased, and the transverse spurious mode in the surface acoustic wave resonator is effectively suppressed.

In the embodiment of the present application, the end of the electrode finger 23 refers to the end of the electrode finger 23 facing away from the bus bar 21/22 to which it is connected, specifically, the end of the electrode finger 231 of the connecting bus bar 21 refers to the end of the electrode finger 231 facing away from the bus bar 21, and the end of the electrode finger 232 of the connecting bus bar 22 refers to the end of the electrode finger 232 facing away from the bus bar 22.

Considering that the gap area AA between the end of the electrode finger 23 and the opposite bus bar 21/22 (i.e., the bus bar not connected to the electrode finger 23) is the area where the acoustic velocity of the propagating surface acoustic wave is highest, it can be understood that, in the surface acoustic wave resonator provided in the embodiment of the present application, the arrangement of the low acoustic velocity structure 30 flush with the end of the electrode finger 23 forms a reflection interface with a larger acoustic velocity difference between the area DD and the area AA, so that the suppression effect on the lateral stray mode is best. However, in consideration of the actual process, it is sufficient to provide the low acoustic velocity structure 30 so as to be flush with the tip of the electrode finger 23 as much as possible.

As shown in fig. 9 and 11, in the surface acoustic wave resonator provided in this embodiment of the present application, by setting the maximum distance x between the end of the low sound speed structure 30 near the nearest one of the bus bars and the end of the electrode finger 23 connected to the other bus bar to be less than or equal to 0.3λ, and the minimum width y of the low sound speed structure 30 along the extending direction of the electrode finger 23 to be greater than or equal to λ, λ is the wavelength of the surface acoustic wave, the end of the low sound speed structure 30 near the nearest one of the bus bars is as flush as possible with the end of the electrode finger 23 connected to the other bus bar, so that a larger sound speed difference interface is formed between the end of the low sound speed structure 30 near the nearest one of the bus bars and the end of the electrode finger 23 connected to the other bus bar, the reflection effect on the transverse stray mode is further enhanced, and the energy dissipation caused by the resonance formed by the transverse stray mode is avoided, and the performance of the resonator is improved.

From the above analysis, it is preferable that the end of the low sound speed structure 30 near the nearest one of the bus bars is flush with the end of the electrode finger 23 connected to the other bus bar, which has the best effect of suppressing the lateral stray mode, specifically, the end of the low sound speed structure 30 near the bus bar 21 toward the bus bar 21 is flush with the end of the electrode finger 232 connected to the bus bar 22, and at the same time, the end of the low sound speed structure 30 near the bus bar 22 toward the bus bar 22 is flush with the end of the electrode finger 231 connected to the bus bar 21. In the present embodiment, as shown in fig. 9, the cross section of the low acoustic velocity structure 30 is rectangular along the extending direction of the electrode finger 23.

In the embodiment of the present application, the maximum distance x between the end of the low sound speed structure 30 near the nearest one bus bar and the end of the electrode finger 23 connected to the other bus bar is less than or equal to 0.3λ, that is, the redundant distance that the end of the low sound speed structure 30 near the nearest one bus bar is not flush with the end of the electrode finger 23 connected to the other bus bar is less than or equal to 0.3λ, specifically, the end of the low sound speed structure 30 near the nearest one bus bar may be located within or outside the range of 0.3λ from the end of the electrode finger 23 connected to the other bus bar.

In the embodiment of the application, the minimum width y of the low-sound-speed structure 30 along the extending direction of the electrode finger 23 is larger than or equal to lambda, so as to ensure that the sound speed difference interface formed by two ends of the low-sound-speed structure 30 along the extending direction of the electrode finger 23 and adjacent areas has better reflection effect on the transverse stray mode.

However, considering the actual process, it is more difficult for the end position metal of the electrode finger 23 to be perfectly flush with the low acoustic velocity structure 30 in the direction perpendicular to the plane of the substrate, and it is more likely that the electrode finger 23 connected to one bus bar covers the low acoustic velocity structure 30 close to the other bus bar toward the side wall of the other bus bar as shown in fig. 12. Specifically, as shown in fig. 9 and 12, the electrode finger 231 connected to the bus bar 21 covers the side wall of the low acoustic velocity structure 30 near the bus bar 22 toward the bus bar 22, while the electrode finger 232 connected to the bus bar 22 covers the side wall of the low acoustic velocity structure 30 near the bus bar 21 toward the bus bar 21. In the present embodiment, the cross section of the low acoustic velocity structure 30 is more likely to be trapezoidal along the extending direction of the electrode finger 23.

Alternatively, in some embodiments, as shown in the schematic top view of fig. 13a and the schematic cross-sectional view along the extension direction of the electrode fingers 23 of fig. 13b, the interdigital transducer 20 further comprises dummy fingers 24, wherein the dummy fingers 24 are disposed opposite to the electrode fingers 23 in the extension direction of the electrode fingers 23 and are connected to opposite bus bars of the electrode fingers 23. In this embodiment, the low sound speed structure 30 is arranged in a manner fully referring to the foregoing embodiment without any change.

Optionally, in some embodiments, as shown in a schematic top view shown in fig. 14a and a schematic cross-sectional view along the extending direction of the electrode finger 23 shown in fig. 14b, the saw resonator further includes reflective grating structures 40 disposed on opposite sides of the interdigital transducer 20 along the extending direction of the bus bar 21/22, where, optionally, an orthographic projection of the low-sound-speed structure 30 on the plane of the substrate 10 may further intersect an orthographic projection of the reflective grating structure 40 on the plane of the substrate 10, and the low-sound-speed structure 30 may also reduce a sound speed of a surface acoustic wave propagating in a direction perpendicular to the plane of the substrate 10 corresponding to a corresponding region of the reflective grating structure 40, so as to form a sound speed difference interface, and play a role of suppressing a lateral stray mode. Of course, alternatively, the orthographic projection of the low acoustic velocity structure 30 on the plane of the substrate 10 may not intersect the orthographic projection of the reflective grating structure 40 on the plane of the substrate 10, as the case may be. It should be noted that, as shown in fig. 13a, the reflective grating structure 40 includes a finger strip extending in the same direction as the electrode finger 23, and fig. 13b is a schematic cross-sectional view along the finger strip of the reflective grating structure 40 when the orthographic projection of the low acoustic velocity structure 30 on the plane of the substrate 10 passes through the orthographic projection of the reflective grating structure 40 on the plane of the substrate 10.

In the case that the minimum width y of the low sound speed structure 30 along the extending direction of the electrode finger 23 is equal to or greater than λ, so that the reflection effect of the sound speed difference interface formed by the two ends of the low sound speed structure 30 along the extending direction of the electrode finger 23 and the adjacent region on the transverse stray mode is better, further optionally, the width of the interface formed by the overlapping region of the low sound speed structure 30 along the extending direction of the electrode finger 23 in the direction perpendicular to the plane of the substrate 10 is different from the width of the overlapping region of the at least two electrode fingers 23 along the extending direction of the electrode finger 23, for example, as shown in fig. 15, the width of the overlapping region of one low sound speed structure 30 and one electrode finger 23 along the extending direction of the electrode finger 23 in the direction perpendicular to the plane of the substrate 10 is y1, the width of the overlapping region of the other electrode finger 23 along the extending direction of the electrode finger 23 is y2, y1 is not equal to y2, then the impedance of the interface formed by the low sound speed structure 30 and the two electrode fingers 23 in the direction perpendicular to the plane of the substrate 10 is not connected, for further enhancing the reflection effect of the non-parallel spurious mode in the opposite direction, and further enhancing the transverse stray mode can not be formed by the different from the transversal spurious mode.

In view of simplicity and easiness in the manufacturing process, one end of the low sound speed structure 30 facing away from the nearest bus bar may be set to a gradual shape along the extending direction of the bus bar 21/22, alternatively, as shown in fig. 15, the distance between one end of the low sound speed structure 30 facing away from the nearest bus bar and the nearest bus bar increases and decreases along the extending direction of the bus bar 21/22, or in other words, one end of the low sound speed structure 30 facing away from the nearest bus bar moves away from the nearest bus bar along the extending direction of the bus bar 21/22 and approaches the nearest bus bar. In the present embodiment, when the end of the low sound speed structure 30 near the nearest bus bar is parallel to the extending direction of the bus bar 21/22, the width of the low sound speed structure 30 in the extending direction of the electrode finger 23 increases and then decreases in the extending direction of the bus bar 21/22.

Alternatively, as shown in fig. 15 and 16, the two low sound speed structures 30 may be disposed axisymmetrically along the extending direction of the bus bar 21/22, that is, the two low sound speed structures 30 may have one-to-one correspondence with the change in the extending direction of the bus bar 21/22 at the end facing away from the nearest bus bar. In this embodiment, alternatively, as shown in fig. 15, the position where the two low sound speed structures 30 are away from the end of the nearest bus bar and the maximum distance between the nearest bus bars may correspond to the center position of the interdigital transducer 20 along the extending direction of the bus bars 21/22; alternatively, as shown in fig. 16, the end of the two low acoustic velocity structures 30 facing away from the nearest bus bar and the maximum distance between the nearest bus bars may not correspond to the center position of the interdigital transducer 20 in the extending direction of the bus bars 21/22, as the case may be. When the end of the low sound speed structure 30 near the nearest bus bar is parallel to the extending direction of the bus bar 21/22, the position where the maximum distance between the end of the low sound speed structure 30 away from the nearest bus bar and the nearest bus bar corresponds to the position where the maximum width of the low sound speed structure 30 along the extending direction of the electrode finger 23 is located, at this time, the positions where the maximum widths of the two low sound speed structures 30 along the extending direction of the electrode finger 23 may correspond to the central position of the interdigital transducer 20 along the extending direction of the bus bar 21/22, or may not correspond to the central position of the interdigital transducer 20 along the extending direction of the bus bar 21/22, as the case may be.

Alternatively, as shown in fig. 17, the two low-sound-speed structures 30 may be disposed in a non-axisymmetric manner along the extending direction of the bus bar 21/22, that is, the two low-sound-speed structures 30 may not have one-to-one correspondence with each other in the extending direction of the bus bar 21/22 at the end facing away from the nearest bus bar.

Alternatively, as shown in fig. 15, 16 and 17, the distance between the end of the low sound speed structure 30 facing away from the nearest bus bar and the nearest bus bar varies linearly along the extending direction of the bus bar 21/22, that is, the end of the low sound speed structure 30 facing away from the nearest bus bar varies linearly along the extending direction of the bus bar 21/22.

Alternatively, as shown in fig. 18, the distance between the end of the low sound speed structure 30 facing away from the nearest bus bar and the nearest bus bar is changed stepwise in the extending direction of the bus bar 21/22, that is, the end of the low sound speed structure 30 facing away from the nearest bus bar is changed stepwise in the extending direction of the bus bar 21/22.

It will be appreciated that in other embodiments of the present application, the gradual change of the shape of the end of the low acoustic velocity structure 30 facing away from the nearest bus bar along the extending direction of the bus bar 21/22 is not limited to those shown in fig. 15-18, and more discontinuous interfaces with abrupt acoustic impedance can be formed, and meanwhile, the transverse spurious mode cannot form resonance after reflection by reflecting in different directions, so that the suppression effect on the transverse spurious mode is further improved, extra dissipation of energy is avoided, and the performance of the resonator is improved.

The inventors have further studied and found that when the material of the low acoustic velocity structure is silicon dioxide, and the thickness z of the low acoustic velocity structure 30 in the direction perpendicular to the plane of the substrate 10 satisfies: when z is more than or equal to 0.025 lambda and less than or equal to 0.035 lambda, the performance of the surface acoustic wave resonator is better.

The thickness of the electrode finger 23 in the direction perpendicular to the plane of the substrate 10 is 124nm, the wavelength lambda of the surface acoustic wave is 2 μm, and the low acoustic velocity structure 30 is SiO ₂ The performance of a saw resonator using a low acoustic speed structure 30 having different thicknesses z in a direction perpendicular to the plane of the substrate 10 was simulated by the arrangement of the materials, and specifically, fig. 19 to 24 sequentially show admittance-frequency curves and conductivity-frequency curves of the saw resonator when the low acoustic speed structure 30 has thicknesses z in the direction perpendicular to the plane of the substrate 10 of 30nm, 40nm, 50nm, 60nm, 70nm and 80nm, respectively, wherein the abscissa is frequency (unit/MHz), the ordinate is dB, the dark curve is the Y parameter (i.e., admittance-frequency curve), the light curve is the real part of the Y parameter (i.e., conductivity-frequency curve), as is apparent from fig. 19 to 24, in the mid-frequency range, when the thickness z of the low acoustic velocity structure 30 in the direction perpendicular to the plane of the substrate 10 is in the range of 50nm to 70nm (inclusive), i.e., in the range of 0.025 λ to 0.035 λ, or in other words, in consideration of the relationship between the thickness of the electrode finger 23 of the interdigital transducer 20 in the direction perpendicular to the plane of the substrate 10 and the surface acoustic wave wavelength λ, the suppression of the lateral spurious mode is performed when the thickness z of the low acoustic velocity structure 30 in the direction perpendicular to the plane of the substrate 10 is in the range of 40% -56% (inclusive) relative to the thickness of the electrode finger 23 of the interdigital transducer 20 in the direction perpendicular to the plane of the substrate 10 The effect is best, the resonance peak is sharp, the transmission curve between the resonance point and the anti-resonance point is smoother, the interference is less, and the performance of the resonator is better.

It should be noted that, in the case where the material of the low acoustic velocity structure 30 is certain, as the frequency band range is reduced, the optimal thickness of the low acoustic velocity structure 30 in the direction perpendicular to the plane of the substrate 10 is increased, for example, for the lower frequency band range, and the low acoustic velocity structure is SiO ₂ The optimal thickness of the low acoustic velocity structure 30 in the direction perpendicular to the plane of the substrate 10 may be on the order of hundreds of nm, greater than the 50nm-70nm range described above, but still in the range of 0.025 lambda-0.035 lambda, and in the range of 40% -56% of the thickness of the electrode fingers 23 of the interdigital transducer 20 in the direction perpendicular to the plane of the substrate 10. Obviously, when materials of different acoustic impedance are used for the low acoustic velocity structure 30, the optimal thickness of the low acoustic velocity structure 30 in the direction perpendicular to the plane of the substrate 10 should be different and may be obtained experimentally, as the case may be.

Alternatively, the substrate 10 may be a piezoelectric substrate, based on any of the embodiments described above. Alternatively, as shown in fig. 25, the substrate 10 may also include a non-piezoelectric substrate 11, and at least one piezoelectric layer 12 and at least one dielectric layer 13 disposed on the non-piezoelectric substrate 11, that is, the substrate 10 may be a POI multilayer substrate, and the manner of setting the low acoustic velocity structure 30 between the substrate 10 and the interdigital transducer 20 to suppress the transverse spurious mode in the embodiment of the present application is suitable for a thin film TF-SAW resonator, and a better effect of suppressing the transverse spurious mode in the thin film TF-SAW resonator can be obtained, however, the manner of setting the low acoustic velocity structure 30 between the substrate 10 and the interdigital transducer 20 to suppress the transverse spurious mode in the embodiment of the present application is also suitable for a common surface acoustic wave resonator and a TC-SAW resonator with a temperature compensation function, which is not described herein.

Alternatively to any of the above embodiments, the material of the low acoustic velocity structure 30 may be at least one of silicon dioxide, silicon oxynitride, lithium oxide, tantalum pentoxide, fluorine, carbon or boron doped silicon oxide.

The embodiment of the application also provides a preparation method of the surface acoustic wave resonator, and the preparation method is described below by taking a film TF-SAW resonator as an example, and comprises the following steps:

s10: a substrate 10 is provided.

Specifically, first, as shown in fig. 26a, a non-piezoelectric substrate 11 is provided, and Si material is commonly used for the non-piezoelectric substrate 11, and various ceramics such as alumina, sapphire, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, dielectrics such as diamond and glass, and semiconductors such as gallium nitride, resins, and the like may be used;

next, as shown in fig. 26b, at least one piezoelectric layer 12 and at least one dielectric layer 13 are formed on the non-piezoelectric substrate 11 to form the POI multilayer substrate 10, wherein the piezoelectric layer 12 may be a 30 ° -60 ° cut lithium tantalate or lithium niobate piezoelectric film; the dielectric layer may comprise SiO for achieving temperature compensation effect ₂ The layer may be a tuning layer for realizing a sound velocity change.

S20: as shown in fig. 26c, a low acoustic velocity layer 301 is formed on the substrate 10.

Alternatively, the material of the low acoustic velocity layer 201 may be silicon dioxide, silicon oxynitride, lithium oxide, tantalum pentoxide, fluorine-, carbon-, or boron-doped silicon oxide, or the like.

S30: as shown in fig. 26d, a part of the low acoustic velocity layer 301 is removed, and the low acoustic velocity layer 301 at a predetermined position is left, forming two low acoustic velocity structures 30.

S40: as shown in fig. 26e, the interdigital transducer 20 is formed on the side of the low acoustic velocity structure 30 facing away from the substrate 10.

Specifically, a metal electrode is formed at a designated position on one side of the low acoustic velocity structure 30 facing away from the substrate 10, so as to form an interdigital transducer, wherein the metal electrode formed in the position region of the low acoustic velocity structure 30 protrudes in a direction facing away from the substrate 10.

In the embodiment of the present application, referring to fig. 9, the interdigital transducer 20 includes two bus bars 21, 22 disposed opposite to each other, and a plurality of electrode fingers 23 disposed in parallel and spaced between the two bus bars 21 and 22, the electrode fingers 23 being each connected to one bus bar 21 or 22, and the electrode fingers 23 connected to the different bus bars 21 and 22 being alternately arranged along the extending direction of the bus bars 21/22.

As shown in connection with fig. 9 and 10, two low acoustic velocity structures 30 located between the substrate 10 and the interdigital transducer 20 are disposed between the two bus bars 21 and 22, respectively, in opposition to one bus bar, and the orthographic projection of the low acoustic velocity structures 30 on the plane of the substrate 10 penetrates through the orthographic projection of all the electrode fingers 23 on the plane of the substrate, and the acoustic velocity of the surface acoustic wave propagated by the low acoustic velocity structures 30 is smaller than the acoustic velocity of the surface acoustic wave propagated by the common non-overlapping region CC of all the electrode fingers 23 and the low acoustic velocity structures 30 in the direction perpendicular to the plane of the substrate 10.

As shown in fig. 9 and 11, the maximum distance x between the end of the low sound speed structure 30 near the nearest one of the bus bars and the end of the electrode finger 23 connected to the other bus bar is 0.3λ or less, and the minimum width y of the low sound speed structure 30 along the extending direction of the electrode finger 23 is λ or more, λ being the wavelength of the surface acoustic wave.

Further optionally, the preparation method may further include:

s50: a passivation protection layer or conditioning layer 50 is coated on the side of the interdigital transducer 20 facing away from the substrate 10 for use in a trimming process or the like.

The surface acoustic wave resonator manufactured by the method provided by the embodiment of the present application is described in detail in the foregoing embodiments, and will not be described in detail herein.

The embodiment of the application also provides electronic equipment, which comprises the surface acoustic wave resonator provided by any embodiment. Since the surface acoustic wave resonator has been described in detail in the foregoing embodiments, a detailed description thereof is omitted.

In the description, each part is described in a parallel and progressive mode, and each part is mainly described as a difference with other parts, and all parts are identical and similar to each other.

The features described in the various embodiments of the present disclosure may be interchanged or combined with one another in the description to enable those skilled in the art to make or use the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A surface acoustic wave resonator, comprising:

a substrate;

2. The surface acoustic wave resonator according to claim 1, characterized in that an end of the low sound speed structure near the nearest one of the bus bars is flush with an end of the electrode finger connected to the other bus bar.

3. The surface acoustic wave resonator according to claim 1, characterized in that the electrode finger connected to one of the bus bars covers the side wall of the low acoustic velocity structure close to the other bus bar toward the other bus bar.

4. The surface acoustic wave resonator according to claim 1, characterized in that the low acoustic velocity structure is different from the width of an overlapping area of at least two of the electrode fingers in a direction perpendicular to the plane of the substrate along the extending direction of the electrode fingers.

5. The surface acoustic wave resonator according to claim 4, characterized in that a distance between an end of the low sound velocity structure facing away from the nearest bus bar and the nearest bus bar increases and decreases in the extending direction of the bus bar.

6. The surface acoustic wave resonator according to claim 5, characterized in that a distance between an end of the low sound velocity structure facing away from the nearest bus bar and the nearest bus bar varies linearly or stepwise along an extending direction of the bus bar.

7. The surface acoustic wave resonator according to claim 5, characterized in that two of the low acoustic velocity structures are arranged axisymmetrically or non-axisymmetrically along the extending direction of the bus bar.

8. The surface acoustic wave resonator according to any of claims 1-7, characterized in that the material of the low acoustic velocity structure is silicon dioxide, and the thickness z of the low acoustic velocity structure in a direction perpendicular to the plane of the substrate is such that: z is more than or equal to 0.025 lambda and less than or equal to 0.035 lambda.

9. The surface acoustic wave resonator according to any of claims 1-7, characterized in that the cross section of the low acoustic velocity structure is rectangular or trapezoidal along the extension direction of the electrode fingers.

10. The surface acoustic wave resonator according to any of claims 1-7, characterized in that the substrate comprises a non-piezoelectric base, and at least one piezoelectric layer and at least one dielectric layer on the non-piezoelectric base;

alternatively, the substrate is a piezoelectric base.

11. The surface acoustic wave resonator according to any of claims 1-7, characterized in that the material of the low acoustic velocity structure is at least one of silicon dioxide, silicon oxynitride, lithium oxide, tantalum pentoxide, fluorine-, carbon-, or boron-doped silicon oxide.

12. The surface acoustic wave resonator according to any of claims 1-7, characterized in that it further comprises reflecting grating structures disposed on opposite sides of the interdigital transducer along the bus bar extension direction;

13. A method of manufacturing a surface acoustic wave resonator, comprising:

providing a substrate;

forming a low acoustic velocity layer on the substrate;

14. An electronic device comprising the surface acoustic wave resonator of any one of claims 1-12.