CN117155333A

CN117155333A - Surface acoustic wave resonator, filter, multiplexer and radio frequency front end module

Info

Publication number: CN117155333A
Application number: CN202310788166.3A
Authority: CN
Inventors: 李阳; 杜波; 王华磊; 倪建兴
Original assignee: Ruishi Chuangxin Chongqing Technology Co ltd
Current assignee: Ruishi Chuangxin Chongqing Technology Co ltd
Priority date: 2023-06-29
Filing date: 2023-06-29
Publication date: 2023-12-01
Anticipated expiration: 2043-06-29

Abstract

The application relates to a surface acoustic wave resonator, a filter, a multiplexer and a radio frequency front end module. The surface acoustic wave resonator comprises a piezoelectric substrate and at least one interdigital transducer arranged on the piezoelectric substrate, wherein the interdigital transducer comprises two bus bars which are arranged in parallel at intervals and a plurality of electrode fingers which are arranged in parallel at intervals, the electrode fingers are positioned between the two bus bars, the electrode fingers are respectively connected with one bus bar, and the electrode fingers connected with different bus bars are alternately arranged along the length direction of the bus bars; the outer surfaces of the electrode fingers exposed out of the piezoelectric substrate are provided with passivation layers so as to cover and protect the electrode fingers, and a part of the surface of the piezoelectric substrate between at least one pair of adjacent two electrode fingers is not covered with the passivation layers. According to the surface acoustic wave resonator, the passivation layer is not covered on the surface of the piezoelectric substrate between the adjacent electrode fingers, so that the flatness of the exposed surface between the adjacent electrode fingers is ensured.

Description

Surface acoustic wave resonator, filter, multiplexer and radio frequency front end module

Technical Field

The application relates to the technical field of radio frequency filtering, in particular to a surface acoustic wave resonator, a filter comprising the surface acoustic wave resonator, a multiplexer comprising the filter and a radio frequency front end module comprising the filter.

Background

In the technical field of radio frequency filtering, a surface acoustic wave resonator is generally provided with at least one interdigital transducer on a piezoelectric substrate, and mutual conversion of an electric signal and an acoustic wave signal is realized through matching of a plurality of electrode fingers on the interdigital transducer with the piezoelectric substrate.

In the related art, in order to avoid oxidation or the like caused by contact of each electrode finger with the environment, a passivation layer is generally provided on the surface of the electrode finger. However, in the related art, the surface flatness of the passivation layer is relatively poor. When the surface acoustic wave propagates to the adjacent electrode finger through the passivation layer, the surface acoustic wave may be lost due to the surface flatness problem of the passivation layer, thereby deteriorating the performance of the surface acoustic wave resonator.

Disclosure of Invention

In view of the above-mentioned drawbacks of the related art, an object of the present application is to provide a solution for improving performance of a surface acoustic wave resonator, which specifically includes the following technical solutions:

in a first aspect, an embodiment of the present application provides a surface acoustic wave resonator, including a piezoelectric substrate, and at least one interdigital transducer disposed on the piezoelectric substrate, where the interdigital transducer includes two bus bars arranged in parallel and at intervals, and a plurality of electrode fingers arranged in parallel and at intervals, the plurality of electrode fingers are located between the two bus bars, a part of the electrode fingers are connected with one bus bar, another part of the electrode fingers are connected with another bus bar, and the electrode fingers connected to different bus bars are alternately arranged along a length direction of the bus bars;

The outer surfaces of the electrode fingers exposed out of the piezoelectric substrate are provided with passivation layers, the passivation layers are used for covering and protecting the electrode fingers, and a part of the surface of the piezoelectric substrate between at least one pair of adjacent two electrode fingers is not covered with the passivation layers.

According to the surface acoustic wave resonator, the interdigital transducer is arranged on the piezoelectric substrate, so that after the bus bar receives an external electric signal, the electric signal can be transmitted to the electrode fingers, and the electric signal is converted into the surface acoustic wave based on the piezoelectric effect of the piezoelectric substrate. After receiving the acoustic surface, the electrode finger connected with the other bus bar converts the acoustic signal into an electric signal and outputs the electric signal outwards, so that the acoustic-electric conversion function of the acoustic surface wave resonator is realized.

The surface acoustic wave resonator also has the advantage that the passivation layer is arranged on the surface of the electrode finger so as to prevent external water and oxygen from entering the electrode finger, thereby protecting the electrode finger. And then, the passivation layer is not covered on the surface of the piezoelectric substrate between the adjacent electrode fingers, so that the surface evenness of the piezoelectric substrate is better, and the loss caused by the surface evenness to the propagation of the surface acoustic waves is reduced.

In one embodiment, the material of the electrode fingers includes at least one of copper, titanium, chromium, silver, or aluminum.

In one embodiment, the material of the portion of the electrode finger attached to the passivation layer comprises at least one elemental material, and the material of the passivation layer is an oxide of the at least one elemental material.

In this embodiment, the passivation layer is made of the oxide material attached to a portion of the electrode finger material, so that the passivation layer can be directly oxidized on the outer surface of the electrode finger to form the passivation layer when the passivation layer is prepared, so that the attachment of the passivation layer and the electrode finger is ensured, and the protection effect of the passivation layer on the electrode finger is further improved.

In one embodiment, the material of the passivation layer is aluminum oxide; the electrode finger is of a single-layer structure, the material of the electrode finger is aluminum, or the electrode finger is of a multi-layer structure, the electrode finger comprises an aluminum-containing metal layer, and the aluminum-containing metal layer is attached to the inner side of the passivation layer.

In this embodiment, the material of the passivation layer is set to aluminum by setting the material of the electrode finger to aluminum, so that the electrode finger can be directly oxidized in the process of preparing the passivation layer. On the other hand, by arranging the aluminum-containing metal layer on the inner side of the passivation layer, the oxidation process can be prevented from being advanced to the other structures of the electrode fingers while the aluminum-containing metal layer is oxidized to prepare the passivation layer in the process of preparing the passivation layer, so that the conductive function of the electrode fingers is ensured.

In one embodiment, the passivation layer includes a stacked protection layer and an element layer, the element layer covers and is attached to the electrode finger, the protection layer is made of silicon oxide or silicon nitride, and the element layer is made of silicon.

In this embodiment, by providing the elemental layer of silicon as a material, in the process of preparing the passivation layer, the preparation of the passivation layer may be achieved by oxidizing the elemental layer. Meanwhile, the simple substance layer covers and is attached to the electrode fingers, so that the oxidation process is prevented from advancing to the electrode fingers, and the conductive function of the electrode fingers is ensured.

In one embodiment, the electrode fingers are of a multi-layer structure, the bottom structure of the electrode fingers attached to the surface of the piezoelectric substrate is a titanium-containing metal layer, and the surface of one side of the titanium-containing metal layer, which is away from the piezoelectric substrate, is partially attached to the passivation layer.

In the embodiment, the titanium-containing metal layer attached to the surface of the piezoelectric substrate is arranged, and the surface of the titanium-containing metal layer, which is away from the piezoelectric substrate, is attached to the passivation layer, so that the better attaching performance of the titanium metal and the piezoelectric substrate is utilized, and water and oxygen are prevented from entering the electrode finger through the hole between the passivation layer and the piezoelectric substrate, so that the conductivity of the electrode finger is ensured.

In one embodiment, the electrode finger includes a first surface facing away from the piezoelectric substrate, and a sidewall connected between the first surface and the piezoelectric substrate surface, the sidewall having an angle between 60 ° -90 ° with the piezoelectric substrate surface.

In the embodiment, the included angle between the side wall and the surface of the piezoelectric substrate is set to be 60-90 degrees, so that the influence on the attaching effect of the side wall and the passivation layer due to the overlarge included angle is avoided, and the influence on the distance between adjacent electrode fingers due to the overlarge included angle is also avoided, and the filtering function of the surface acoustic wave resonator is ensured while the protection effect of the passivation layer on the electrode fingers is ensured.

In one embodiment, the thickness of the passivation layer constituting the first surface is less than or equal to the thickness of the passivation layer constituting the sidewall.

In this embodiment, the passivation layer thickness forming the sidewall is set to be greater than or equal to the passivation layer thickness forming the first surface, so that the possibility that water and oxygen enter the electrode finger from the sidewall is reduced, and the protection effect of the passivation layer on the electrode finger is further improved.

In one embodiment, the passivation layer has a thickness between 2nm and 100 nm.

In this embodiment, the thickness of the passivation layer is set between 2nm and 100nm, so that the effect of the passivation layer on protecting the electrode fingers is prevented from being influenced due to the weak structural strength of the passivation layer caused by the excessively thin passivation layer, and the distance between adjacent electrode fingers is also prevented from being influenced due to the excessively thick passivation layer, thereby ensuring the structural strength of the passivation layer and the filtering function of the surface acoustic wave resonator.

In a second aspect, an embodiment of the present application provides a surface acoustic wave resonator, including a piezoelectric substrate, and at least one interdigital transducer disposed on the piezoelectric substrate, where the interdigital transducer includes two bus bars arranged in parallel and at intervals, and a plurality of electrode fingers arranged in parallel and at intervals, the plurality of electrode fingers are located between the two bus bars, an extending direction of each electrode finger is parallel to an arrangement direction of the two bus bars, a part of the electrode fingers are connected with one bus bar, another part of the electrode fingers are connected with the other bus bar, and the electrode fingers connected to the different bus bars are alternately arranged along a length direction of the bus bars;

the outer surfaces of the electrode fingers are provided with passivation layers, the passivation layers are used for covering and protecting the electrode fingers, and the material of the passivation layers is oxide of the material of the joint part of the electrode fingers and the passivation layers; a portion of the surface of the piezoelectric substrate between at least one pair of adjacent two electrode fingers is not covered by a passivation layer.

In one embodiment, the passivation layer is made of aluminum oxide, and the main body material of the portion, which is attached to the passivation layer, of the corresponding electrode finger is aluminum.

In a third aspect, an embodiment of the present application provides a filter, including a signal input end, a signal output end, and at least two resonators electrically connected between the signal input end and the signal output end, where the at least two resonators include a surface acoustic wave resonator.

In a fourth aspect, an embodiment of the present application provides a multiplexer including an antenna, and a transmit filter and a receive filter communicatively coupled to the antenna, respectively, at least one of the transmit filter and the receive filter including a filter.

In a fifth aspect, an embodiment of the present application provides a radio frequency front end module, including a filter.

It will be appreciated that the rf front-end module provided in the fifth aspect of the present application, the multiplexer provided in the fourth aspect, and the filter provided in the third aspect of the present application are adopted in the surface acoustic wave resonator provided in the first and second aspects of the present application. The radio frequency front end module, the multiplexer and the filter also have better performance.

Drawings

Fig. 1 is a schematic structural diagram of an electronic device according to an embodiment of the present application;

FIG. 2 is a schematic structural diagram of a RF front-end module according to an embodiment of the present application;

FIG. 3 is a schematic diagram of a multiplexer according to an embodiment of the present application;

FIG. 4 is a schematic diagram of a filter according to an embodiment of the present application;

FIG. 5 is a schematic diagram of a SAW resonator in an embodiment of the present application;

FIG. 6 is a schematic diagram of another structure of a SAW resonator provided in an embodiment of the present application;

FIG. 7 is a schematic cross-sectional view of a SAW resonator in accordance with an embodiment of the present application;

fig. 8 is a front view of a surface acoustic wave resonator provided in an embodiment of the present application;

FIG. 9 is a schematic diagram showing another cross-sectional structure of a SAW resonator provided in an embodiment of the present application;

fig. 10 is a schematic structural view of a surface acoustic wave resonator in the related art;

fig. 11 is a schematic cross-sectional structure of a surface acoustic wave resonator in the related art;

fig. 12 is a schematic view showing another cross-sectional structure of a surface acoustic wave resonator in the related art;

FIG. 13 is a schematic cross-sectional view of a SAW resonator provided in an embodiment of the present application;

FIG. 14 is a schematic cross-sectional view of a SAW resonator provided in an embodiment of the present application;

fig. 15 is a schematic cross-sectional view of a surface acoustic wave resonator according to an embodiment of the present application.

Detailed Description

In order that the application may be readily understood, a more complete description of the application will be rendered by reference to the appended drawings. The drawings illustrate preferred embodiments of the application. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

The following description of the embodiments refers to the accompanying drawings, which illustrate specific embodiments in which the application may be practiced. The numbering of the components itself, e.g. "first", "second", etc., is used herein merely to distinguish between the described objects and does not have any sequential or technical meaning. The term "coupled" as used herein includes both direct and indirect coupling (coupling), unless otherwise indicated. Directional terms, such as "upper", "lower", "front", "rear", "left", "right", "inner", "outer", "side", etc., in the present application are merely referring to the directions of the attached drawings, and thus, directional terms are used for better, more clear explanation and understanding of the present application, rather than indicating or implying that the apparatus or element being referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present application.

In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; may be a mechanical connection; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application will be understood in specific cases by those of ordinary skill in the art. It should be noted that the terms "first," "second," and the like in the description and the claims of the present application and in the drawings are used for distinguishing between different objects and not for describing a particular sequential order. Furthermore, the terms "comprises," "comprising," "includes," "including," or "having," when used in this specification, are intended to specify the presence of stated features, operations, elements, etc., but do not limit the presence of one or more other features, operations, elements, etc., but are not limited to other features, operations, elements, etc. Furthermore, the terms "comprises" or "comprising" mean that there is a corresponding feature, number, step, operation, element, component, or combination thereof disclosed in the specification, and that there is no intention to exclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

Referring to fig. 1, a schematic structure of an electronic device 500 according to an embodiment of the application is shown.

As shown in fig. 1, the electronic device 500 of the present application includes a substrate 501 and a rf front-end module 400, wherein the rf front-end module 400 is mounted on the substrate 501. The substrate 501 is electrically connected to the rf front-end module 400 to control the rf front-end module 400 to operate.

Specifically, in one embodiment, the substrate 501 may be configured as a printed circuit board to implement operation control of the rf front-end module 400. Correspondingly, the electronic device 500 of the present application may be any electronic device 500 having a structure of the rf front-end module 400, such as a computer, a mobile phone, a navigator, etc., which is not limited in particular by the applicant.

Referring to fig. 2, a schematic structure of a rf front-end module 400 according to an embodiment of the application is shown.

As shown in fig. 2, the rf front-end module 400 includes a signal terminal 401, a switch 402, an amplifier 403, and a filter 200. The signal terminal 401 is used for receiving and transmitting external signals. The switch 402 is communicatively coupled between the signal terminal 401 and the filter 200 to control signal transmission between the signal terminal 401 and the filter 200. The filter 200 is used for transmitting a signal to the filter 200 and outputting a signal having a preset frequency. The amplifier 403 is electrically connected to the filter 200, so as to amplify the signal processed by the filter 200 and output the signal to a subsequent structure. Wherein the signal terminal 401 may be provided as an antenna.

It will be appreciated that in another embodiment, the filter 200 may also be provided as a multiplexer 300. The applicant does not particularly limit this.

Referring to fig. 3, a schematic structure of a multiplexer 300 according to an embodiment of the application is shown.

As shown in fig. 3, the multiplexer 300 of the present application includes an antenna 301, a transmit filter 200a, and a receive filter 200b. Wherein, the transmitting filter 200a and the receiving filter 200b each comprise a receiving end 302 for receiving signals and a transmitting end 303 for transmitting signals, and the receiving ends 302 of the transmitting filter 200a and the receiving filter 200b are each communicatively connected with the antenna 301.

When signals having different frequencies are input from the receiving end 302, the transmitting filter 200a and the receiving filter 200b process the signals of the corresponding frequencies, respectively, and are transmitted outward from the transmitting end 303. Due to the mutual spacing between the transmit filter 200a and the receive filter 200b. It will be appreciated that the multiplexer 300 of the present application allows the transmit filter 200a and the receive filter 200b to operate simultaneously. That is, the multiplexer 300 of the present application can receive signals and transmit signals at the same time.

It will be appreciated that in another embodiment, the number of filters 200 may also be plural, and that the plurality of filters 200 are each communicatively coupled to the antenna 301.

Referring to fig. 4, a schematic structure of a filter 200 according to an embodiment of the application is shown.

As shown in fig. 4, the filter 200 of the present application includes a signal input terminal 201, a signal output terminal 202, a ground port 203, a piezoelectric substrate 204, and a plurality of surface acoustic wave resonators 100. The surface acoustic wave resonators 100 are each provided on the piezoelectric substrate 204. One part of the surface acoustic wave resonator 100 is connected in series between the signal input terminal 201 and the signal output terminal 202, and the other part of the surface acoustic wave resonator 100 has one end connected to the ground port 203 and the other end connected to a series circuit between the signal input terminal 201 and the signal output terminal 202. It will be appreciated that the series connection and parallel connection of the plurality of saw resonators 100 can realize the filtering function of the filter 200 of the present application for a signal of a predetermined frequency.

It can be appreciated that in the present embodiment, the piezoelectric substrate 204 has a single-layer structure. In another embodiment, a stacked piezoelectric layer, functional layer, and base (not shown) may also be disposed on the piezoelectric substrate 204, with the piezoelectric layer between the functional layer and the saw resonator 100. The material of the functional layer may be silicon dioxide.

Specifically, for two saw resonators 100 connected in series with each other, one saw resonator 100 is electrically connected to the signal input terminal 201, and the other saw resonator 100 is electrically connected to the signal output terminal 202.

When a signal enters the surface acoustic wave resonator 100 from the signal input terminal 201, the interdigital transducer 20 within the surface acoustic wave resonator 100 receives the electrical signal. Due to the piezoelectric properties of the piezoelectric substrate 204, the interdigital transducer 20 can convert an electrical signal into an acoustic wave signal that acts on the surface of the piezoelectric substrate 204, and propagate the acoustic wave signal toward the other surface acoustic wave resonator 100.

When an acoustic wave signal propagates to another surface acoustic wave resonator 100, the piezoelectric substrate 204 converts the acoustic wave signal into an electrical signal in cooperation with the interdigital transducer 20, and is output from the signal output terminal 202 via the interdigital transducer 20. Thereby realizing the acousto-electric conversion function of the filter 200 of the present application.

Referring to fig. 5, a schematic structure of a saw resonator 100 according to an embodiment of the application is shown.

As shown in fig. 5, the surface acoustic wave resonator 100 of the present application includes a piezoelectric substrate 10 and an interdigital transducer 20, the interdigital transducer 20 being provided on the piezoelectric substrate 10. The interdigital transducer 20 includes two bus bars 21 arranged in parallel and at a spacing, and a plurality of electrode fingers 22 arranged in parallel and at a spacing. Among them, the bus bar 21 includes a first bus bar 21a for receiving an external signal and a second bus bar 21b for outputting a signal.

The electrode fingers 22 include a plurality of first electrode fingers 22a and a plurality of second electrode fingers 22b, and the first electrode fingers 22a and the second electrode fingers 22b each extend toward opposite sides of the piezoelectric substrate 10 in a first direction 001. In the second direction 002, the first electrode fingers 22a and the second electrode fingers 22b are alternately arranged.

The first bus bar 21a and the second bus bar 21b each extend toward opposite sides of the piezoelectric substrate 10 in a second direction 002, wherein the first direction 001 and the second direction 002 are perpendicular to each other. The electrode fingers 22 are each located between the first bus bar 21a and the second bus bar 21b, and the first electrode fingers 22a are each connected to the first bus bar 21a, and the second electrode fingers 22b are each connected to the second bus bar 21 b.

In one embodiment, reflective gratings (not shown) are disposed on each side of the interdigital transducer 20 in the second direction 002, for confining the generated surface acoustic wave to propagate within the interdigital transducer 20.

Due to the inverse piezoelectric effect of the piezoelectric substrate 10. When an electrical signal is transmitted to each first electrode finger 22a via the first bus bar 21a, the electrical signal on each first electrode finger 22a releases an electrostatic force to the piezoelectric substrate 10, which causes deformation of the surface of the piezoelectric substrate 10. And because the electrical signal is an alternating signal. It will be appreciated that the electrostatic force applied to the surface of the piezoelectric substrate 10 by each of the first electrode fingers 22a exhibits a periodic variation, and correspondingly, the amount of deformation of the surface of the piezoelectric substrate 10 also varies with the periodic variation of the electrical signal, thereby forming an outwardly released surface acoustic wave.

Due to the piezoelectric effect of the piezoelectric substrate 10. When the surface acoustic wave is transmitted to the second electrode fingers 22b, the surface of the piezoelectric substrate 10 that is deformed due to the contact of the second electrode fingers 22b is deformed, and polarized charges are generated on the surface of the deformed piezoelectric substrate 10, and the charges are partially charged so that each second electrode finger 22b is charged with electric energy and outputs a signal via the second bus bar 21 b.

In the surface acoustic wave propagation process, the main propagation direction of the surface acoustic wave is the second direction 002. However, in a practical process, since the electric signal may have interference of other frequency signals, the direction of the corresponding surface acoustic wave formed on the surface of the piezoelectric substrate 10 may be other directions. It will be appreciated that the surface acoustic wave propagating in the remaining direction will be absorbed by a sound absorbing material (not shown) to realize the filtering function of the surface acoustic wave resonator 100 of the present application.

It will be appreciated that in another embodiment, as shown in fig. 6, the surface acoustic wave resonator 100 of the present application may further provide two interdigital transducers 20 on the surface of the piezoelectric substrate 10, wherein the first bus bar 21a and the second bus bar 21b of one interdigital transducer are each used for receiving an external signal, and the first bus bar 21a and the second bus bar 21b of the other interdigital transducer are each used for outputting a signal outwards. In other embodiments, the number of interdigital transducers 20 provided on the surface of the piezoelectric substrate 10 may be other, and the applicant is not particularly limited thereto.

It will be appreciated that the present application may be applied to surface acoustic wave resonators, longitudinally coupled surface acoustic wave resonators, dual mode surface acoustic wave (DMS) resonators (DMS), laterally excited thin film bulk acoustic resonators (X-Film Bulk Acoustic Resonator, X-BAR), and the like, including interdigital transducers, as the present application is not limited in this regard.

Referring to fig. 7, a schematic cross-sectional structure of a saw resonator 100 according to an embodiment of the application is shown. Fig. 7 is a schematic cross-sectional structure of the surface acoustic wave resonator 100 shown in fig. 5.

As shown in fig. 7, the surface of the electrode finger 22 exposed on the piezoelectric substrate 10 is provided with a passivation layer 23, and the passivation layer 23 covers the surface of the piezoelectric substrate 10 to protect the electrode finger 22. It can be appreciated that the passivation layer 23 prevents the water and oxygen in the external environment from reacting with the electrode fingers 22, so that the electrode fingers 22 oxidize and absorb moisture. Thereby ensuring the structural integrity of the electrode finger 22, ensuring the conductive function of the electrode finger 22, and ensuring the acoustic-electric conversion function of the surface acoustic wave resonator 100 of the present application.

As shown in fig. 7, the electrode finger 22 includes a passivation material layer 221, and the passivation material layer 221 is attached to the inner side of the passivation layer 23. Wherein the material of the passivation layer 23 is an oxide of the material of the passivation material layer 221. In the process of preparing the passivation layer 23, the passivation material layer 221 may be prepared on the surface of the electrode finger 22, and the electrode finger 22 may be placed in a certain high temperature environment and in a certain oxygen plasma environment, so that the passivation material layer 221 may chemically react with oxygen element, thereby generating the passivation layer 23.

The passivation material layer 221 is bonded to the rest of the electrode finger 22. It will be appreciated that the passivation layer 23 is fabricated to be in contact with the passivation material layer 221. That is, the passivation layer 23 and the electrode finger 22 are bonded to each other.

Thus, the passivation layer 23 is prepared by oxidizing the passivation material layer 221, so that the generation of pores between the passivation layer 23 and the electrode finger 22 can be avoided, and the protection effect of the passivation layer 23 on the electrode finger 22 is improved.

Meanwhile, the passivation layer 23 is prepared by oxidizing the passivation material layer 221, so that the thickness of the passivation layer 23 is relatively uniform, and the protection effect of the passivation layer 23 on the electrode finger 22 can be improved. On the other hand, the improvement of the surface flatness of the passivation layer 23 also reduces the influence of the surface flatness of the passivation layer 23 on the surface acoustic wave resonator 100 of the present application.

On the other hand, the piezoelectric substrate 10 between the adjacent one of the first electrode fingers 22a and one of the second electrode fingers 22b has an outer surface 11 that is not covered with the passivation layer 23. Since the surface flatness of the piezoelectric substrate 10 is superior to that of the passivation layer 23, it can be understood that exposing the outer surface 11 of the piezoelectric substrate 10 between the first electrode finger 22a and the second electrode finger 22b can reduce the loss caused by the surface flatness to the propagation of the surface acoustic wave.

It will be appreciated that in another embodiment, the material of the remaining structure of the electrode finger 22 may also be the same as the material of the passivation material layer 221. The applicant does not particularly limit this.

In one embodiment, the material of passivation layer 23 is aluminum oxide and the bulk material of passivation material layer 221 is aluminum.

Referring to fig. 8, a front view of a saw resonator 100 according to an embodiment of the present application is shown.

As shown in fig. 8, the surface acoustic wave resonator 100 of the present application includes a piezoelectric substrate 10 and an interdigital transducer 20, the interdigital transducer 20 being provided on the piezoelectric substrate 10. The interdigital transducer 20 includes two bus bars 21 arranged in parallel and at a spacing, and a plurality of electrode fingers 22 arranged in parallel and at a spacing. Among them, the bus bar 21 includes a first bus bar 21a for receiving an external signal and a second bus bar 21b for outputting a signal.

Due to the inverse piezoelectric effect and the positive piezoelectric effect of the piezoelectric substrate 10. When an electrical signal is transmitted to each first electrode finger 22a via the first bus bar 21a, the electrical signal on each first electrode finger 22a acts on the piezoelectric substrate 10 and causes the piezoelectric substrate 10 to release surface acoustic waves outwards. When the surface acoustic wave is transmitted to the second electrode finger 22b, the second electrode finger 22b converts the surface acoustic wave on the piezoelectric substrate 10 into an electrical signal, and outputs the signal via the second bus bar 21 b.

It will be appreciated that in another embodiment, the surface acoustic wave resonator 100 of the present application may further include two interdigital transducers 20 disposed on the surface of the piezoelectric substrate 10. In other embodiments, the number of interdigital transducers 20 provided on the surface of the piezoelectric substrate 10 may be other, and the applicant is not particularly limited thereto.

Referring to fig. 9, another cross-sectional structure of a saw resonator 100 according to an embodiment of the application is shown. Fig. 9 is a schematic cross-sectional structure of the surface acoustic wave resonator 100 shown in fig. 8.

As shown in fig. 9, the surface of the electrode finger 22 exposed on the piezoelectric substrate 10 is provided with a passivation layer 23, and the passivation layer 23 covers the surface of the piezoelectric substrate 10 to protect the electrode finger 22. It can be appreciated that the passivation layer 23 prevents the water and oxygen in the external environment from reacting with the electrode fingers 22, so that the electrode fingers 22 oxidize and absorb moisture. Thereby ensuring the structural integrity of the electrode finger 22, ensuring the conductive function of the electrode finger 22, and ensuring the acoustic-electric conversion function of the surface acoustic wave resonator 100 of the present application.

During the propagation process of the surface acoustic wave, the surface acoustic wave is limited by the flatness of the propagation surface, and loss can occur in the surface acoustic wave. When the flatness of the propagation surface is relatively poor, the loss of the surface acoustic wave increases, possibly affecting the acoustic-electric conversion function of the surface acoustic wave resonator 100.

The piezoelectric substrate 10 between adjacent ones of the first electrode fingers 22a and the second electrode fingers 22b has an outer surface 11 that is not covered by the passivation layer 23. Since the surface flatness of the piezoelectric substrate 10 is superior to that of the passivation layer 23, it can be understood that exposing the outer surface 11 of the piezoelectric substrate 10 between the first electrode finger 22a and the second electrode finger 22b can reduce the loss caused by the surface flatness to the propagation of the surface acoustic wave.

In another embodiment, in the preparation of the surface acoustic wave resonator 100 of the present application, the passivation layer 23 may be further disposed on the outer surface 11 of the piezoelectric substrate 10 and the surfaces of the electrode fingers 22, and then the outer surface 11 of the piezoelectric substrate 10 between the two electrode fingers 22 may be etched and exposed by etching. So that the adjacent two electrode fingers 22 have a surface with better flatness, thereby reducing the loss in the process of acoustic surface wave propagation.

Referring to fig. 10, a schematic structural diagram of a related art surface acoustic wave resonator 100' is shown, fig. 11 is a schematic sectional structural diagram of the related art surface acoustic wave resonator 100', and fig. 12 is a schematic sectional structural diagram of another related art surface acoustic wave resonator 100 '.

As shown in fig. 10, 11 and 12, in the related art, a surface acoustic wave resonator 100' includes a piezoelectric substrate 10', and at least one interdigital transducer 20' provided on the piezoelectric substrate 10', the interdigital transducer 20' including two bus bars 21' arranged in parallel and at a spacing, and a plurality of electrode fingers 22' arranged in parallel and at a spacing.

In the first direction 001, a plurality of electrode fingers 22 'are located between two bus bars 21', a part of the electrode fingers 22 'are connected to one bus bar 21', another part of the electrode fingers 22 'are connected to the other bus bar 21', and the electrode fingers 22 'connected to the different bus bars 21' are alternately arranged in the second direction 002. In the related art, the passivation layer 23' is provided on the outer surface of the electrode finger 22' exposed to the piezoelectric substrate 10', and covers all of the electrode finger 22' and the piezoelectric substrate 10'.

In the related art, the passivation layer 23' is generally prepared by sputtering, evaporation, or the like. As shown in fig. 11, the passivation layer 23 'prepared by sputtering, evaporation, or the like has relatively poor surface flatness, and loss of the surface acoustic wave is aggravated when the surface acoustic wave propagates between the adjacent two electrode fingers 22'.

On the other hand, as shown in fig. 12, when the passivation layer 23 'is prepared by sputtering, evaporation, or the like, a cavity 30' may be formed between the passivation layer 23 'and the electrode finger 22' due to the influence of the actual process. It will be appreciated that the cavity 30' may have adsorbed therein water, oxygen, and other foreign substances that may corrode the electrode finger 22' and thereby affect the acoustic-electric conversion function of the saw resonator 100 '. At the same time, the existence of the cavity 30 'also distorts the surface acoustic wave, thereby affecting the acoustic-to-electrical conversion function of the surface acoustic wave resonator 100'.

Therefore, the surface acoustic wave resonator 100 of the present application ensures the flatness of the exposed surface between the adjacent electrode fingers 22 by not covering the passivation layer 23 on the surface of the piezoelectric substrate 10 between the adjacent electrode fingers 22, thereby reducing the loss of the surface acoustic wave due to the surface flatness during the propagation process.

Meanwhile, in the surface acoustic wave resonator 100 of the present application, the passivation layer 23 is formed by disposing the passivation material layer 221 on the surface of the electrode finger 22 and oxidizing the passivation material layer 221, so that the effect of the passivation layer 23 on the flatness of the exposed surface between the adjacent electrode fingers 22 is reduced, and meanwhile, the bonding effect of the passivation layer 23 and the electrode finger 22 is ensured, and the surface flatness of the passivation layer 23 is improved, so that the protection effect of the passivation layer 23 on the electrode finger 22 is improved.

In one embodiment, the material of the electrode finger 22 includes at least one of copper, titanium, chromium, silver, or aluminum.

In one embodiment, the material of the portion of the electrode finger 22 attached to the passivation layer 23 includes at least one elemental material, and the material of the passivation layer 23 is an oxide of the at least one elemental material. As shown in fig. 9, the electrode finger 22 has a single-layer structure, and the material of the electrode finger 22 is aluminum, and the material of the passivation layer 23 is aluminum oxide. It will be appreciated that in other embodiments, the material of the electrode finger 22 may be other than aluminum, and the material of the corresponding passivation layer 23 may be a corresponding oxide.

It can be appreciated that in the process of preparing the passivation layer 23, the electrode finger 22 can be directly oxidized to be exposed on the surface of the piezoelectric substrate 10, so that the adhesion between the passivation layer 23 and the electrode finger 22 is ensured, and the influence of the pores formed in the preparation process of the passivation layer 23 and the electrode finger 22 on the electrode finger 22 is avoided. The protective effect of the passivation layer 23 on the electrode finger 22 is further improved.

Specifically, please refer to fig. 13, which is a schematic cross-sectional structure diagram of a saw resonator 100 according to an embodiment of the present application.

As shown in fig. 13, the electrode finger 22 has a multi-layer structure, wherein the electrode finger 22 further includes a metal layer 222, and the metal layer 222 is attached to the inner side of the passivation layer 23. Since the passivation layer 23 is formed by oxidizing the metal layer 222, the remaining structure of the electrode finger 22 within the metal layer 222 is oxidized.

Further, the material of the rest of the electrode finger 22 in the metal layer 222 may be a conductive material that is not easily oxidized, which is not limited by the present application.

It can be appreciated that the metal layer 222 is attached to the inner side of the passivation layer 23, so that the passivation layer 23 and the rest of the electrode finger 22 can be spaced apart, and oxidation process is avoided to oxidize the rest of the electrode finger 22, thereby ensuring the conductivity of the electrode finger 22. Illustratively, the metal layer 222 may be an aluminum-containing metal layer 222, and the material of the passivation layer 23 is aluminum oxide. In other embodiments, the material in the metal layer 222 may be other than aluminum, and the material of the corresponding passivation layer 23 may be a corresponding oxide.

In another embodiment, the body material of the electrode finger 22 is aluminum, or the material of the electrode finger 22 is aluminum copper alloy. The material of the metal layer 222 is aluminum. During the preparation of the passivation layer 23, the passivation layer 23 may completely oxidize the metal layer 222, so that the passivation layer 23 is attached to the electrode finger 22 whose host material is aluminum or aluminum copper alloy.

Referring to fig. 14, another cross-sectional structure of a saw resonator 100 according to an embodiment of the present application is shown.

As shown in fig. 14, the passivation layer 23 includes a protective layer 231 and an elemental layer 232 stacked, and the elemental layer 232 covers and adheres to the electrode finger 22.

Non-metallic fabrication may also be used in the fabrication of passivation layer 23. It can be understood that the surface of the electrode finger 22 is provided with an element layer 232 attached to the electrode finger 22, and a protective layer 231 of a corresponding material is formed on the basis of the element layer 232, so as to avoid the process of forming the protective layer 231 from affecting the electrode finger 22.

Illustratively, the material of the protective layer 231 is silicon oxide or silicon nitride, and the material of the simple substance layer 232 is silicon. In other embodiments, the material of the simple substance layer 232 may be other, and the material of the corresponding protection layer 231 may be a compound containing the simple substance material of the corresponding simple substance layer 232, which is not limited by the applicant.

Referring to fig. 15, a schematic cross-sectional view of a saw resonator 100 according to an embodiment of the present application is shown.

As shown in fig. 15. The electrode finger 22 is a multi-layered structure, and the electrode finger 22 further includes a titanium-containing metal layer 223. The titanium-containing metal layer 223 is attached to the surface of the piezoelectric substrate 10, and the titanium-containing metal layer 223 extends toward two opposite sides of the piezoelectric substrate 10 along the second direction 002, so that the surface of the titanium-containing metal layer 223 facing away from the piezoelectric substrate 10 is partially attached to the passivation layer 23.

In one embodiment, the passivation layer 23 conforms to the surface of the titanium-containing metal layer 223 facing away from the piezoelectric substrate 10 and the side of the titanium-containing metal layer 223. Further, the passivation layer 23 extends to the surface of the piezoelectric substrate 10.

Since the adhesion of the titanium-containing metal layer 223 to the piezoelectric substrate 10 is relatively good, there may be a case where the passivation layer 23 is not tightly adhered to the piezoelectric substrate 10. It can be appreciated that the titanium-containing metal layer 223 attached to the piezoelectric substrate 10 is disposed on the bottom structure of the electrode finger 22, so as to prevent water and oxygen from entering the rest of the electrode finger 22 between the passivation layer 23 and the piezoelectric substrate 10, and avoid oxidizing the rest of the electrode finger 22 by the water and oxygen. Thereby ensuring the conductivity of the electrode finger 22 and ensuring the acoustic-electric conversion function of the surface acoustic wave resonator 100 of the present application.

In one embodiment, referring back to fig. 7 and 9, the electrode finger 22 includes a first surface 224 and a sidewall 225, the first surface 224 being the surface of the electrode finger 22 facing away from the piezoelectric substrate 10, the sidewall 225 being connected between the first surface 224 and the outer surface 11 of the piezoelectric substrate 10. Wherein the angle a between the sidewall 225 and the outer surface 11 of the piezoelectric substrate 10 is between 60 ° and 90 °.

In one embodiment, the angle A between the sidewall 225 and the outer surface 11 of the piezoelectric substrate 10 is between 70-80.

In the range of 60 ° -90 °, if the included angle a is too large, the elemental layer 232 formed on the surface of the electrode finger 22 by electron beam evaporation or magnetron sputtering may be too thin at the sidewall 225 of the electrode finger 22, and the passivation layer 23 finally formed by oxidation or nitridation may be too thin at the sidewall 225, thereby deteriorating the passivation effect in the diagrams shown in fig. 13 and 14. Or the material containing aluminum or silicon formed on the surface of the electrode finger 22 by electron beam evaporation or magnetron sputtering may be too thin at the side wall 225 of the electrode finger 22, so that in the oxidation or nitridation process of the simple substance layer 232 on the surface of the electrode finger 22, excessive oxidation or nitridation of the side wall of the electrode finger 22 is easily caused, thereby changing the formation of the electrode finger 22 and affecting the performance of the surface acoustic wave resonator 100.

When the included angle a is smaller than 60 °, in the case that the resonant frequency of the surface acoustic wave resonator 100 of the present application is fixed, in the second direction 002, the bonding length between the electrode fingers 22 and the piezoelectric substrate 10 increases, so that the distance between two adjacent electrode fingers 22 decreases, and the risk of short-circuiting of the surface acoustic wave resonator 100 increases. On the other hand, the film thickness of the electrode finger 22 may be reduced, which may affect the performance of the surface acoustic wave resonator 100.

Thereby, the included angle a between the sidewall 225 and the outer surface 11 of the piezoelectric substrate 10 is 60 ° -90 °, and the filtering function of the surface acoustic wave resonator 100 can be ensured while the attaching effect of the passivation layer 23 to the sidewall 225 of the electrode finger 22 is ensured.

In one embodiment, as shown in fig. 7 and 9, the passivation layer 23 constituting the first surface 224 has a first thickness D1, and the passivation layer 23 constituting the sidewall 225 has a second thickness D2, wherein the first thickness D1 is less than or equal to the second thickness D2.

When the electrode finger 22 is fabricated in a multi-layered structure, the layered structures having different materials within the electrode finger 22 may be stacked on each other in the thickness direction of the piezoelectric substrate 10 (as shown in fig. 13). And when water and oxygen enter between two material layers (not shown) stacked on each other from the sidewall 225, the water and oxygen more easily react with the stacked material layers. That is, when the electrode finger 22 is fabricated in a multi-layer structure, water and oxygen enter the electrode finger 22 from the sidewall 225 and cause greater damage to the electrode finger 22 than the first surface 224.

It can be appreciated that in the related art, the passivation layer 23' formed on the surface of the interdigital transducer 20' may have a smaller thickness on the side surfaces of the electrode fingers 20' than on the upper surface, so that the passivation layer 23' has a poor protection effect on the side surfaces and the reliability of the passivation layer 23' is reduced. The second thickness D2 which is larger than or equal to the first thickness D1 is arranged, so that the possibility that water and oxygen enter the electrode finger 22 from the side wall 225 can be reduced, and the protection effect of the passivation layer 23 on the electrode finger 22 is further improved.

Specifically, the thickness of the passivation layer 23 of the sidewall 225 of the electrode finger 22 is greater than the thickness of the passivation layer 23 of the first surface 224, and may be formed by coating the sidewall of the electrode finger 22 multiple times or increasing the oxidation or nitridation time of the sidewall of the electrode finger 22. In other embodiments, the magnitude relation between the first thickness D1 and the second thickness D2 may also be implemented by other implementations, which is not specifically limited in the present application.

In one embodiment, as shown in fig. 7 and 9, the passivation layer 23 has a thickness D between 2nm and 100 nm. When the thickness D of the passivation layer 23 is less than 2nm, the structural strength of the passivation layer 23 is relatively weak. During the operation of the surface acoustic wave resonator 100 of the present application, the passivation layer 23 is easily damaged by external force, thereby affecting the protection effect of the passivation layer 23 on the electrode finger 22. Meanwhile, the passivation layer 23 is too thin, so that the protection effect of the passivation layer 23 on the electrode finger 22 is relatively weak.

When the thickness D of the passivation layer 23 is greater than 100nm, the distance between two adjacent electrode fingers 22 may be affected, so that the distance between two adjacent electrode fingers 22 becomes smaller, thereby affecting the filtering function of the surface acoustic wave resonator 100 of the present application.

Therefore, the thickness of the passivation layer 23 is set to be between 2nm and 100nm, so that the filtering function of the surface acoustic wave resonator 100 can be ensured, and meanwhile, the structural strength of the passivation layer 23 can be ensured, and the protection effect of the passivation layer 23 on the electrode fingers 22 can be ensured.

In one embodiment, as shown in fig. 7 and 9, the piezoelectric substrate 10 includes a laminated substrate 12 and piezoelectric substrate 13, with the piezoelectric substrate 13 being located between the substrate 12 and electrode fingers 22. In another embodiment, the piezoelectric substrate 10 may also be a single layer piezoelectric substrate 13.

The material of the piezoelectric substrate 13 may be aluminum nitride, zinc oxide, lead zirconate titanate, or rare earth doped material with a certain atomic ratio. In another embodiment, the material of the piezoelectric substrate 13 may also be a single crystal piezoelectric material, illustratively, single crystal aluminum nitride, lithium niobate, lithium tantalate, quartz, or the like. The present application is not particularly limited thereto.

In one embodiment, the material of the substrate 12 is silicon.

In one embodiment, the material of the interdigital transducer 20 is one of molybdenum, tungsten, ruthenium, gold, magnesium, aluminum, copper, chromium, titanium, osmium, iridium, or a composite of the above metals, or alloys thereof, or the like.

In one embodiment, the passivation layer 23 may also be disposed on the bus bar 21. The passivation layer 23 is prepared by the same method as the passivation layer 23 disposed on the electrode finger 22. In another embodiment, the passivation layer 23 may be disposed on the bus bar 21 by plating, which is not particularly limited by the applicant.

It should be appreciated that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more features. In the description of the embodiments of the present application, the meaning of "plurality" is two or more, unless explicitly defined otherwise.

In the description of the present specification, reference is made to the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., meaning that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

It is to be understood that the application is not limited in its application to the examples described above, but is capable of modification and variation in light of the above teachings by those skilled in the art, and that all such modifications and variations are intended to be included within the scope of the appended claims. Those skilled in the art will recognize that the full or partial flow of the embodiments described above can be practiced and equivalent variations of the embodiments of the present application are within the scope of the appended claims.

Claims

1. A surface acoustic wave resonator, comprising a piezoelectric substrate, and at least one interdigital transducer provided on the piezoelectric substrate, wherein the interdigital transducer comprises two bus bars which are arranged in parallel and at intervals, and a plurality of electrode fingers which are arranged in parallel and at intervals, the plurality of electrode fingers are positioned between the two bus bars, part of the electrode fingers are connected with one bus bar, the other part of the electrode fingers are connected with the other bus bar, and the electrode fingers connected with different bus bars are alternately arranged along the length direction of the bus bars;

the electrode fingers are exposed out of the outer surface of the piezoelectric substrate, a passivation layer is arranged on the outer surface of the piezoelectric substrate, the passivation layer is used for covering and protecting the electrode fingers, and a part of the surface of the piezoelectric substrate between at least one pair of adjacent two electrode fingers is not covered by the passivation layer.

2. The surface acoustic wave resonator of claim 1, wherein the material of the electrode fingers comprises at least one of copper, titanium, chromium, silver, or aluminum.

3. The surface acoustic wave resonator according to claim 1, wherein the material of the portion of the electrode finger attached to the passivation layer comprises at least one elemental material, and the material of the passivation layer is an oxide of the at least one elemental material.

4. A saw resonator as claimed in claim 3, wherein the passivation layer is alumina; the electrode finger is of a single-layer structure, the material of the electrode finger is aluminum, or the electrode finger is of a multi-layer structure, the electrode finger comprises an aluminum-containing metal layer, and the aluminum-containing metal layer is attached to the inner side of the passivation layer.

5. The surface acoustic wave resonator according to claim 3, wherein the passivation layer comprises a stacked protective layer and an elemental layer, the elemental layer covers and is attached to the electrode finger, the material of the protective layer is silicon oxide or silicon nitride, and the material of the elemental layer is silicon.

6. The surface acoustic wave resonator according to claim 1, wherein the electrode finger has a multilayer structure, the underlying structure of the electrode finger attached to the surface of the piezoelectric substrate is a titanium-containing metal layer, and the surface of the side of the titanium-containing metal layer facing away from the piezoelectric substrate is partially attached to the passivation layer.

7. The surface acoustic wave resonator of any of claims 1-6, wherein the electrode fingers comprise a first surface facing away from the piezoelectric substrate, and a sidewall connected between the first surface and the piezoelectric substrate surface, the sidewall having an angle with the piezoelectric substrate surface of between 60 ° -90 °.

8. The surface acoustic wave resonator according to claim 7, characterized in that the thickness of the passivation layer constituting the first surface is smaller than or equal to the thickness of the passivation layer constituting the side wall.

9. The surface acoustic wave resonator according to any of claims 1-6, characterized in that the passivation layer has a thickness between 2nm and 100 nm.

10. A surface acoustic wave resonator, comprising a piezoelectric substrate, and at least one interdigital transducer arranged on the piezoelectric substrate, wherein the interdigital transducer comprises two bus bars which are arranged in parallel and at intervals, and a plurality of electrode fingers which are arranged in parallel and at intervals, the electrode fingers are positioned between the two bus bars, the extending direction of each electrode finger is parallel to the arrangement direction of the two bus bars, part of the electrode fingers are connected with one bus bar, the other part of the electrode fingers are connected with the other bus bar, and the electrode fingers connected with different bus bars are alternately arranged along the length direction of the bus bars;

The outer surfaces of the electrode fingers are provided with passivation layers, the passivation layers are used for covering and protecting the electrode fingers, and the material of the passivation layers is oxide of the material of the joint part of the electrode fingers and the passivation layers; a portion of the surface of the piezoelectric substrate between at least one pair of adjacent two of the electrode fingers does not cover the passivation layer.

11. The surface acoustic wave resonator according to claim 10, wherein the passivation layer is made of aluminum oxide, and the main body material corresponding to the portion of the electrode finger bonded to the passivation layer is made of aluminum.

12. A filter comprising a signal input, a signal output, and at least two resonators electrically connected between the signal input and the signal output, the at least two resonators comprising the surface acoustic wave resonator of any one of claims 1-11.

13. A multiplexer comprising an antenna and a transmit filter and a receive filter communicatively coupled to the antenna, respectively, at least one of the transmit filter and the receive filter comprising the filter of claim 12.

14. A radio frequency front end module comprising the filter of claim 12.