CN113273080A

CN113273080A - Surface acoustic wave filter, preparation method thereof, radio frequency front-end chip and mobile terminal

Info

Publication number: CN113273080A
Application number: CN201980088165.XA
Authority: CN
Inventors: 刘鹏; 徐向明
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2019-01-14
Filing date: 2019-01-14
Publication date: 2021-08-17
Also published as: WO2020146973A1

Abstract

A surface acoustic wave filter and a method of manufacturing the same, the filter comprising a substrate (10) and a piezoelectric material layer (20) which are disposed opposite to each other, wherein a cavity (30) is provided between the substrate (10) and the piezoelectric material layer (20); an interdigital transducer (202) is arranged on the surface of the piezoelectric material layer (20) facing the substrate (10); an interdigital transducer (202) is located within the cavity (30). The inside of the cavity (30) may be a vacuum environment or a gas environment. The acoustic wave can not be propagated in vacuum, and compared with a solid medium, the propagation capacity of the acoustic wave in a gas medium is lower, so that the acoustic wave energy is not easy to leak out of the substrate (10) through the cavity (30), and therefore, the cavity (30) formed between the substrate (10) and the piezoelectric material layer (20) can reduce the existence of the acoustic wave in a stray mode, reduce the possibility of the acoustic wave energy leaking out of the substrate (10), and further improve the Q value and the insertion loss of the SAW filter. In addition, a radio frequency front-end chip and a mobile terminal comprising the surface acoustic wave filter are also disclosed.

Description

Surface acoustic wave filter, preparation method thereof, radio frequency front-end chip and mobile terminal

Technical Field

The application relates to the technical field of semiconductor equipment, in particular to a surface acoustic wave filter and a manufacturing method thereof, and further relates to a radio frequency front-end chip and a mobile terminal comprising the surface acoustic wave filter.

Background

With the requirement of miniaturization of mobile terminals, in the field of radio frequency front ends, Surface Acoustic Wave (SAW) or Bulk Acoustic Wave (BAW) technology is generally adopted for filters smaller than 6 GHz. Compared with a BAW filter, the SAW filter has the advantages of relatively simple process and relatively low cost, and is widely applied to a frequency band less than 2 GHz.

A conventional SAW filter structure is formed by directly forming an Interdigital Transducer (IDT) on a substrate. The SAW filter structure causes acoustic energy to leak from the substrate, resulting in low Quality Factor (Q) and Insertion Loss (IL) of the SAW filter.

Disclosure of Invention

In view of the above, the present application provides a surface acoustic wave filter and a method of manufacturing the same. In addition, the application also provides a radio frequency front-end chip and a mobile terminal comprising the surface acoustic wave filter.

In order to solve the technical problem, the following technical scheme is adopted in the application:

a first aspect of the present application provides a surface acoustic wave filter including: the piezoelectric transducer comprises a substrate and a piezoelectric material layer which are oppositely arranged, wherein a cavity is arranged between the substrate and the piezoelectric material layer; a welding pad used for bonding the substrate and the piezoelectric material layer is arranged on the side wall of the cavity; an interdigital transducer is arranged on the surface, facing the substrate, of the piezoelectric material layer; the interdigital transducer is located within the cavity.

The surface acoustic wave filter provided by the first aspect comprises a substrate and a piezoelectric material layer which are oppositely arranged, wherein a cavity is arranged between the substrate and the piezoelectric material layer; an interdigital transducer is arranged on the surface of the piezoelectric material layer facing the substrate; an interdigital transducer is located within the cavity. The interior of the cavity can be a vacuum environment or a gas environment. The acoustic wave cannot be propagated in vacuum, and compared with a solid medium, the acoustic wave has lower propagation capacity in a gas medium, so that acoustic wave energy is not easy to leak out of the substrate through the cavity, and therefore, the cavity formed between the substrate and the piezoelectric material layer can reduce the existence of the acoustic wave in a stray mode, reduce the possibility of the acoustic wave energy leaking out of the substrate, and further improve the Q value and the insertion loss of the SAW filter.

In a possible implementation manner, the welding pads include a first welding pad located on the surface of the substrate facing the piezoelectric material layer, and/or a second welding pad located on the surface of the piezoelectric material layer facing the substrate; the first welding pad and the second welding pad are arranged in a stacked mode. This possible implementation facilitates bonding of the substrate and the piezoelectric material layer more easily.

In one possible implementation, the filter further includes: the temperature compensation layer is positioned on the surface of the piezoelectric material layer, which faces away from the substrate. The possible implementation mode can relieve the problem that the passband frequency of the SAW filter drifts along with the temperature change to a certain extent.

In one possible implementation, the filter further includes: a sound speed increasing layer covering at least a surface region of the temperature compensation layer facing away from the interdigital transducer. The sound velocity increasing layer can improve the equivalent sound velocity of the surface acoustic wave.

In one possible implementation, the filter further includes: and the heat dissipation layer at least covers the surface area of the temperature compensation layer back to the interdigital transducer. The heat dissipation layer can improve the heat dissipation performance of the device.

In one possible implementation, the filter further includes: and the packaging protection layer covers the sound velocity increasing layer and the surface, opposite to the substrate, of the temperature compensation layer which is not covered by the sound velocity increasing layer. The packaging protective layer can prevent water vapor or external environment from influencing the internal structure of the SAW filter, and the reliability of the SAW filter is improved.

In one possible implementation, the filter further includes: and the packaging protective layer covers the heat dissipation layer and the surface, back to the substrate, of the temperature compensation layer which is not covered by the heat dissipation layer. The packaging protective layer can prevent water vapor or external environment from influencing the internal structure of the SAW filter, and the reliability of the SAW filter is improved.

In one possible implementation, the interdigital transducer is in contact with the substrate.

In one possible implementation, a buffer layer is disposed on a surface of the substrate facing the piezoelectric material layer. The buffer layer can relieve stress between the interdigital transducer and the substrate and prevent the piezoelectric material layer and the interdigital transducer from being damaged due to overlarge stress.

In one possible implementation, the thickness of the temperature compensation layer is between 1000 and

in the meantime. The possible implementation mode can reduce the preparation process while ensuring better temperature compensation effect.

In one possible implementation, passive devices are disposed on a surface of the substrate facing the piezoelectric material layer.

In a possible implementation manner, a third pad is further disposed on a surface of the temperature compensation layer opposite to the substrate, and the third pad is electrically connected to the second pad.

In a possible implementation manner, a surface of the third pad facing away from the substrate is further provided with a metal solder ball, and the metal solder ball is used for electrical connection with an external circuit.

In a possible implementation manner, a conductive plunger penetrating through the substrate is arranged on the substrate, and the third welding pad is led out through the second welding pad, the first welding pad and the conductive plunger.

A second aspect of the present application provides a method of manufacturing a surface acoustic wave filter, including: forming a first bonding pad on a surface of a first substrate; performing ion implantation on the first surface of the second substrate to form a piezoelectric material layer on one side close to the first surface of the second substrate; forming a second pad and an interdigital transducer on the piezoelectric material layer; when the first substrate and the second substrate are stacked and the surface of the first substrate, on which the first welding pads are formed, faces the piezoelectric material layer, the first welding pads and the second welding pads correspond to each other one by one; bonding the first bonding pad and the second bonding pad which are in one-to-one correspondence, so that the interdigital transducer is positioned in a cavity formed by the first bonding pad and the second bonding pad; and carrying out heat treatment on the second substrate to separate the piezoelectric material layer from the second substrate.

In the method for manufacturing a SAW filter according to the second aspect of the present application, the interdigital transducer may be placed in a cavity, and the inside of the cavity may be a vacuum environment or a gas environment. The acoustic wave cannot be propagated in vacuum, and compared with a solid medium, the acoustic wave has lower propagation capacity in a gas medium, so that the acoustic wave energy is not easy to leak out from the substrate side through the cavity, and therefore, the cavity formed between the substrate and the piezoelectric material layer can reduce the existence of the acoustic wave in a stray mode, reduce the possibility of the acoustic wave energy leaking from the substrate, and further improve the Q value and the insertion loss of the SAW filter.

In one possible implementation, after the heat-treating the second substrate to separate the piezoelectric material layer from the second substrate, the method further includes: and carrying out heat treatment on the piezoelectric material layer so as to improve the piezoelectric property of the piezoelectric material layer.

In a possible implementation manner, the performing heat treatment on the piezoelectric material layer specifically includes: the piezoelectric material layer is heat-treated at a temperature ranging from 400 to 500 ℃.

In one possible implementation, after the heat-treating the second substrate to separate the piezoelectric material layer from the second substrate, the method further includes: and forming a temperature compensation layer on the surface of the piezoelectric material layer opposite to the first substrate.

In one possible implementation manner, after forming the temperature compensation layer on the surface of the piezoelectric material layer opposite to the first substrate, the method further includes: and trimming the thickness of the temperature compensation layer according to design requirements.

In one possible implementation, after forming the temperature compensation layer on the surface of the piezoelectric material layer opposite to the first substrate, the method further includes: and forming a sound velocity increasing layer or a heat dissipation layer on the surface of the temperature compensation layer, which is opposite to the first substrate, wherein the sound velocity increasing layer or the heat dissipation layer only covers part of the surface area of the temperature compensation layer, which is opposite to the substrate.

In one possible implementation manner, after forming the sound speed increasing layer or the heat dissipation layer on the surface of the temperature compensation layer opposite to the first substrate, the method further includes: the thickness of the sound velocity increasing layer and/or the heat dissipation layer is trimmed according to design requirements. This possible implementation improves the product yield and performance of the SAW filter.

In a possible implementation manner, after forming the sound speed increasing layer and/or the heat dissipation layer on the surface of the temperature compensation layer opposite to the first substrate, the method further includes: and annealing the sound velocity increasing layer and/or the heat dissipation layer to eliminate stress in the layer.

In one possible implementation, after the heat-treating the second substrate to separate the piezoelectric material layer from the second substrate, the method further includes: and forming an encapsulation protection layer on the surface of the piezoelectric material layer opposite to the first substrate. The packaging protective layer can prevent water vapor or external environment from influencing the internal structure of the SAW filter, and the reliability of the SAW filter is improved.

In a possible implementation manner, before the bonding of the first pad and the second pad, the method further includes: a buffer layer is formed on a surface of the first substrate on which the first pad is formed. The buffer layer can relieve stress between the interdigital transducer and the substrate and prevent the piezoelectric material layer and the interdigital transducer from being damaged due to overlarge stress.

In a possible implementation manner, after forming the temperature compensation layer, the method further includes: and forming a third welding pad on the surface of the temperature compensation layer, which is opposite to the first substrate, wherein the third welding pad is connected with the second welding pad.

In a possible implementation manner, after forming the third pad, the method further includes: and a metal solder ball is formed on the surface of the third bonding pad opposite to the first substrate and is used for electrically connecting with an external circuit.

A third aspect of the present application provides a radio frequency front-end chip, including a surface acoustic wave filter, a low noise amplifier, a power amplifier, and a data transmission interface; the surface acoustic wave filter is the surface acoustic wave filter described in the first aspect and any possible implementation manner, and the low noise amplifier, the power amplifier, and the data transmission interface are located inside the cavity and on a surface of the substrate facing the piezoelectric material layer.

Because the rf front-end chip provided by the third aspect of the present application includes the surface acoustic wave filter described in the first aspect of the present application and any possible implementation manner, accordingly, the rf front-end chip has the beneficial effects of the surface acoustic wave filter described in the first aspect of the present application and any possible implementation manner.

A fourth aspect of the present application provides a mobile terminal, comprising: a communication module, wherein the communication module includes a surface acoustic wave filter, and the surface acoustic wave filter is the surface acoustic wave filter described in the first aspect and any possible implementation manner thereof.

Because the mobile terminal provided by the fourth aspect of the present application includes the surface acoustic wave filter described in the first aspect of the present application and any possible implementation manner thereof, accordingly, the mobile terminal has the beneficial effects of the surface acoustic wave filter described in the first aspect of the present application and any possible implementation manner thereof.

Compared with the prior art, the method has the following beneficial effects:

based on the technical scheme, the surface acoustic wave filter provided by the application comprises a substrate and a piezoelectric material layer which are oppositely arranged, wherein a cavity is arranged between the substrate and the piezoelectric material layer; an interdigital transducer is arranged on the surface of the piezoelectric material layer facing the substrate; an interdigital transducer is located within the cavity. The interior of the cavity can be a vacuum environment or a gas environment. And the sound wave can not propagate in vacuum, and compared with a solid medium, the transmission capability of the sound wave in a gas medium is lower, so that compared with the prior art, due to the existence of the cavity, the surface acoustic wave filter provided by the application reduces the capability of the sound wave energy leaking out from the substrate. Also, the acoustic wave of the spurious mode of the surface acoustic wave filter is caused by the leaked acoustic wave energy, so the acoustic wave energy whose leakage capability is reduced reduces the existence of the acoustic wave of the spurious mode of the surface acoustic wave filter, thereby enabling more acoustic wave energy to be transmitted through a desired transmission path (surface transmission path), thereby improving the Q value and insertion loss of the SAW filter.

Drawings

In order that the detailed description of the present application may be clearly understood, a brief description of the drawings that will be used when describing the detailed description of the present application will be provided.

Fig. 1 is a schematic structural diagram of a SAW filter according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of an interdigital transducer provided by an embodiment of the present application;

FIG. 3 is a schematic structural diagram of another SAW filter provided in the embodiments of the present application;

fig. 4 is a schematic structural diagram of another SAW filter provided in an embodiment of the present application;

fig. 5 is a schematic structural diagram of another SAW filter provided in an embodiment of the present application;

fig. 6 is a schematic structural diagram of another SAW filter provided in an embodiment of the present application;

FIG. 7 is a flow chart illustrating a method for manufacturing a SAW filter according to an embodiment of the present application;

fig. 8(1) to 8(7) are schematic structural diagrams corresponding to a series of processes of a method for manufacturing a SAW filter according to an embodiment of the present disclosure;

FIG. 9 is a flow chart illustrating another method for manufacturing a SAW filter according to an embodiment of the present application;

fig. 10(1) to 10(4) are schematic structural diagrams corresponding to a series of processes of another SAW filter manufacturing method according to an embodiment of the present application;

fig. 11 is a schematic structural diagram of a radio frequency front end chip provided in an embodiment of the present application;

fig. 12 is a schematic structural diagram of a mobile terminal according to an embodiment of the present application.

Detailed Description

In order to solve the problem that the SAW filter in the background art has the problem that the acoustic wave energy leaks from the substrate, and further causes the problem that the quality factor and the insertion loss of the SAW filter are low, the SAW filter is provided based on the characteristic that the propagation capacity of the acoustic wave in a vacuum or air medium is low. The SAW filter comprises a substrate and a piezoelectric material layer which are oppositely arranged, wherein a cavity is arranged between the substrate and the piezoelectric material layer; a welding pad used for bonding the substrate and the piezoelectric material layer is arranged on the side wall of the cavity; an interdigital transducer is arranged on the surface, facing the substrate, of the piezoelectric material layer; the interdigital transducer is located within the cavity. The inside of the cavity can be a vacuum environment or a gas environment. And the sound wave can not propagate in vacuum, and compared with a solid medium, the transmission capability of the sound wave in a gas medium is lower, so that compared with the prior art, due to the existence of the cavity, the surface acoustic wave filter provided by the application reduces the capability of the sound wave energy leaking out from the substrate. Also, the acoustic wave of the spurious mode of the surface acoustic wave filter is caused by the leaked acoustic wave energy, so the acoustic wave energy whose leakage capability is reduced reduces the existence of the acoustic wave of the spurious mode of the surface acoustic wave filter, thereby enabling more acoustic wave energy to be transmitted through a desired transmission path (surface transmission path), thereby improving the Q value and insertion loss of the SAW filter.

In order to make the technical problems, technical solutions and technical effects solved by the present application clearer and more complete, specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

Referring to fig. 1, an embodiment of the present application provides a SAW filter including:

the piezoelectric element comprises a substrate 10 and a piezoelectric material layer 20 which are oppositely arranged, wherein a cavity 30 is arranged between the substrate 10 and the piezoelectric material layer 20;

a first pad 101 is disposed on a surface of the substrate 10 facing the piezoelectric material layer 20; the first pad 101 is located on a sidewall of the cavity 30;

a second pad 201 and an interdigital transducer 202 are arranged on the surface of the piezoelectric material layer 20 facing the substrate 10; interdigital transducer 202 is located within cavity 30; the second pad 201 is located on the sidewall of the cavity 30;

wherein, the first pad 101 and the second pad 201 are laminated and bonded together.

In addition, a third pad 203 may be further disposed on a surface of the piezoelectric material layer 20 opposite to the substrate 10, wherein the third pad 203 is electrically connected to the second pad 201. As an example, the second pad 201 and the third pad 203 are disposed opposite to each other, and a conductive via 204 is disposed in a region of the piezoelectric material layer 20 where the second pad 201 and the third pad 203 are opposite to each other, and the third pad 203 and the second pad 201 are electrically connected through the conductive via 204. In the embodiment of the present application, the third pad 203 can also be used as a test pad for testing the performance of the SAW filter in the process of manufacturing the SAW filter, so as to perform fine tuning on the passband frequency of the SAW filter according to the test result, thereby improving the yield of the device.

In addition, a metal pad 205 is further disposed on a surface of the third pad 203 opposite to the piezoelectric material layer 20 to implement connection of the SAW filter with an external circuit, and the metal pad 205 may be a metal solder ball, for example.

It should be noted that, in the embodiment of the present application, the cavity is a closed cavity structure, the sidewall of the cavity may be composed of a closed interlayer dielectric layer or a metal interconnection layer, and the first pad 101 may be disposed on the sidewall of the cavity 30. As an example, the first pad 101 may be a metal bump or a metal solder ball. Accordingly, the second pads 201 may be metal bumps or metal solder balls.

In the structure of the SAW filter described above, the substrate 10 is a supporting substrate, which may be a silicon substrate, a glass substrate, or a sapphire substrate.

As an example, passive devices (not shown in fig. 1) may be further disposed on the surface of the substrate 10 facing the piezoelectric material layer 20 according to the design requirements of the SAW filter structure, and the passive devices may be matched with the SAW filter. By way of example, the passive device may be a capacitive or inductive device.

As an example, the piezoelectric material layer 20 may be obtained by implanting ions to a certain depth into the surface of the piezoelectric material substrate and then separating the ions from the interface where the concentration of the implanted ions is the highest. As an example, the material of the piezoelectric material substrate may be lithium niobate (LiNbO)₃) Or lithium tantalate (LiTaO)₃). The type of the implanted ions may be hydrogen ions, and the depth of implantation may be determined according to the thickness of the designed piezoelectric material layer. And the implantation energy is selected according to the depth of implantation.

The interdigital transducer 202 is a metal pattern formed on the surface of the piezoelectric material layer 20 in a shape like a finger cross of two hands, and functions to realize acoustic-electric transduction. In addition, the interdigital transducer 202 can also perform a filtering function. By way of example, FIG. 2 illustrates a top view of an interdigital transducer 202. In the embodiment of the present application, the metal material and the processing method used for the interdigital transducer 202 are not particularly limited. By way of example, the preparation of interdigital transducer 202 can be accomplished by a lift-off process. As another example, in order to suppress the spurious mode, the metal material used in the interdigital transducer 202 may be a metal material with a relatively large density, such as Au, Ta, W, or Cu.

As yet another example, the thickness of interdigital transducer 202 may be in the range of 1000A to

In the meantime.

Note that, in the embodiment of the present application, both the first pad 101 and the second pad 201 may be used as a bonding pad. In this way, the piezoelectric material layer 20 and the substrate 10 are bonded together through the first bonding pads 101 and the second bonding pads 201, wherein the first bonding pads 101 correspond to the second bonding pads 201 one to one, and when the piezoelectric material layer 20 is placed opposite to the substrate 10, the first bonding pads 101 and the second bonding pads 201 are respectively aligned one to one, so that the piezoelectric material layer 20 and the substrate 10 are bonded together through a bonding process.

As an implementation, the second pad 201 can be used to realize electrical connection between electrodes in the interdigital transducer 202 in addition to being used as a bonding pad. As another alternative implementation of the present application, the pads used to make the electrical connection between the electrodes in the interdigital transducer 202 may be separated from the pads used as the bond, subject to the limitations of the bonding process.

As an example, the first pad 101 may be a pad formed by growing polysilicon by a Low Pressure Chemical Vapor Deposition (LPCVD) method and etching. As another example, the first pad 101 may also be a metal pad formed through an electroplating process or an electron beam evaporation deposition process.

As another example, the second pad 201 may be a metal pad formed by an electroplating process or an electron beam evaporation deposition process. The metal pad can be made of gold and has a thickness of 2000 to 2000A

In the meantime.

As another implementation manner of the present application, in order to improve the bonding force between the first pad 101 and the second pad 201, an adhesion layer (not shown in fig. 1) may be further disposed between the first pad 101 and the second pad 201, and the material of the adhesion layer may be Ti or Cr.

The foregoing is a specific implementation manner of the SAW filter provided in the embodiments of the present application. In a specific implementation of the SAW filter provided in the above embodiment, pads for bonding the substrate 10 and the piezoelectric material layer 20 are provided on both of the surfaces of the substrate 10 and the piezoelectric material layer 20 that are opposite to each other. In fact, as an extended embodiment of the present application, a pad may be provided only on the surface of the substrate 10 facing the piezoelectric material layer 20, and the pad may be directly bonded on the surface of the piezoelectric material layer 20 facing the substrate 10. As another extended embodiment of the present application, a pad may be provided only on the surface of the piezoelectric material layer 20 facing the substrate 10, and the pad is directly bonded on the surface of the substrate 10 facing the piezoelectric material layer 20.

In the specific implementation of the SAW filter provided in the embodiment of the present application, the substrate 10 is disposed opposite to the piezoelectric material layer 20, and the cavity 30 is located between the substrate 10 and the piezoelectric material layer 20; and an interdigital transducer 202 disposed on the surface of the piezoelectric material layer 20 is located within the cavity 30. The inside of the cavity can be a vacuum environment or a gas environment. And the sound wave can not propagate in vacuum, and compared with a solid medium, the transmission capability of the sound wave in a gas medium is lower, so that compared with the prior art, due to the existence of the cavity, the surface acoustic wave filter provided by the application reduces the capability of the sound wave energy leaking out from the substrate. Also, the acoustic wave of the spurious mode of the surface acoustic wave filter is caused by the leaked acoustic wave energy, so the acoustic wave energy whose leakage capability is reduced reduces the existence of the acoustic wave of the spurious mode of the surface acoustic wave filter, thereby enabling more acoustic wave energy to be transmitted through a desired transmission path (surface transmission path), thereby improving the Q value and insertion loss of the SAW filter.

In the embodiment shown in fig. 1, the interdigital transducer 202 is not in contact with the substrate 10, and a certain gap is present therebetween, so that the possibility of leakage of acoustic wave energy from the substrate 10 side can be reduced.

As another embodiment of the present application, as shown in fig. 3, the interdigital transducer 202 is in contact with the substrate 10, so that the mechanical supporting force of the cavity 30 can be increased, and the structural stability of the SAW filter can be improved.

Note that in the embodiment of the present application, whether the interdigital transducer 202 is in contact with the substrate 10 or not can be realized by adjusting the heights of the interdigital transducer 202, the first pad 101, and the second pad 201. Specifically, when the height of the interdigital transducer 202 is equal to the sum of the heights of the first pad 101 and the second pad 201, the contact of the interdigital transducer 202 with the substrate 10 can be achieved. When the height of the interdigital transducer 202 is smaller than the sum of the heights of the first pad 101 and the second pad 201, it can be achieved that the interdigital transducer 202 does not contact the substrate 10.

In addition, as an implementation of the present application, in the SAW filter shown in fig. 3, a buffer layer (not shown in fig. 3) may be disposed on a surface of the substrate 10 facing the piezoelectric material layer 20, and the buffer layer may relieve stress between the interdigital transducer 202 and the substrate 10, so as to prevent damage to the piezoelectric material layer 20 and the interdigital transducer 202 caused by excessive stress therebetween.

As an example, the material of the buffer layer may be capable of softening during the bonding process of the substrate 10 and the piezoelectric material layer 20, thereby ensuring sufficient bonding between the interdigital transducer 202 and the buffer layer, while preserving the cavity between the substrate 10 and the piezoelectric material layer 20. As a specific example, the buffer layer may be made of a resin material.

It should be noted that the problem of the passband frequency of the SAW filter drifting with temperature changes is serious due to the negative temperature coefficient characteristics of the conventional piezoelectric material used for forming the piezoelectric material layer 20, such as lithium niobate or lithium tantalate. In order to alleviate the problem of the passband frequency of the SAW filter drifting with temperature changes, the application also provides a further embodiment of the SAW filter.

Referring to fig. 4, the SAW filter may further include a temperature compensation layer 206 in addition to the structures shown in fig. 1, wherein the temperature compensation layer 206 is located on the surface of the piezoelectric material layer 20 opposite to the substrate 10.

Note that, in fig. 4, the third pad 203 is located on the surface of the temperature compensation layer 206 opposite to the substrate 10, and the conductive via 204 penetrates the temperature compensation layer 206 up and down in addition to the piezoelectric material layer 20.

When the piezoelectric material layer 20 has a negative temperature coefficient characteristic, the temperature compensation layer 206 has a positive temperature coefficient characteristic, which can alleviate the problem of the passband frequency of the SAW filter drifting with temperature changes to some extent. As an example, the material of the temperature compensation layer 206 may be silicon dioxide.

It should be noted that, since the surface of the piezoelectric material layer 20 opposite to the substrate 10 is a completely flat plane, there are many options for the Deposition process for forming the temperature compensation layer 206, and Plasma Enhanced Chemical Vapor Deposition (PECVD), LPCVD, or Physical Vapor Deposition (PVD) can be used as an example.

In addition, the thickness and compactness of the temperature compensation layer 206 may affect the equivalent sound velocity of the sound wave, and if the thickness is too thin or the compactness is too poor, the problem of insignificant temperature compensation effect may occur, and if the temperature is too thick, the interdigital transducer electrode with a large density needs to be prepared, resulting in a complex preparation process. Thus, as an example, the temperature compensation layer 206 may be at a thickness of

In order to take account of the above problems.

It should be noted that the SAW filter shown in fig. 4 is an improvement of the SAW filter shown in fig. 1, and actually, as an extension of the embodiment of the present application, a SAW filter provided with a temperature compensation layer may be an improvement of the SAW filter shown in fig. 3.

In the SAW filter structures shown in the above respective embodiments, the leakage of acoustic wave energy on the substrate 10 side can be reduced, thereby improving the Q value and insertion loss of the SAW filter. In order to further reduce the leakage of acoustic wave energy and further improve the Q value and insertion loss of the SAW filter, the present application provides yet another embodiment of the SAW filter to reduce the leakage of acoustic wave energy at the piezoelectric material layer side, thereby further improving the Q value and insertion loss of the SAW filter.

Referring to fig. 5, the SAW filter provided in the embodiment of the present application may further include a sound speed increasing layer 207, in addition to the structures shown in fig. 4, where the sound speed increasing layer 207 is located on a surface of the temperature compensation layer 206 opposite to the substrate 10. The sound velocity increasing layer 207 can increase the equivalent sound velocity of the surface acoustic wave.

As an example, the sound speed increasing layer 207 may be provided only on a surface area of the temperature compensation layer 206 facing away from the interdigital transducer 202, instead of covering the entire surface of the temperature compensation layer 206.

As another example, the sound speed increasing layer 207 may also cover the entire surface of the temperature compensation layer 206.

As an example, the material of the sound velocity increasing layer 207 may be a high acoustic resistance material, such as AlN or Al₂O ₃SiC, SiN, SiON, and the like. The sound velocity increasing layer 207 may have a thickness of

In the SAW filter shown in fig. 5, on the one hand, acoustic wave energy is not easily leaked from the substrate 10 side through the cavity 30. On the other hand, the temperature compensation layer 206 and the acoustic velocity increasing layer 207 provided on the surface of the piezoelectric material layer 20 opposite to the substrate 10 can confine acoustic energy between the temperature compensation layer 206 and the acoustic velocity increasing layer 207, and thus, acoustic energy is not easily leaked from the piezoelectric material layer 20 side. Therefore, in the SAW filter shown in fig. 5, the acoustic wave energy does not leak out not only from the substrate side but also from the piezoelectric material layer side, and therefore, the SAW filter further reduces the leakage of the acoustic wave energy, and further improves the Q value and insertion loss of the SAW filter.

In addition, as another implementation manner of the present application, in order to improve the heat dissipation performance of the device, the sound speed increasing layer 207 shown in fig. 5 may be replaced with a heat dissipation layer, and the heat dissipation layer may be made of a high thermal conductivity material. As an example, the high thermal conductivity material may be AlN, A_l2O ₃SiC, SiN, SiON, and the like. The heat dissipation layer may have a thickness of

In addition, since the high acoustic resistance material used for preparing the sound speed increasing layer 207 and the heat dissipation material used for preparing the heat dissipation layer may be the same material, the sound speed increasing layer 207 and the heat dissipation layer may have the same layer structure.

In addition, when the high acoustic resistance material used for preparing the sound speed increasing layer 207 and the heat dissipation material used for preparing the heat dissipation layer are different materials, as another implementation manner of the present application, the sound speed increasing layer and the heat dissipation layer that are stacked may be simultaneously formed on the surface of the temperature compensation layer 206 that faces away from the substrate 10. In the embodiments of the present application, the relationship between the upper and lower positions of the sound velocity increasing layer and the heat dissipation layer is not limited.

In addition, in order to prevent moisture or external environment from influencing the internal structure of the SAW filter and improve the reliability of the SAW filter, the application also provides another implementation mode of the SAW filter.

Referring to fig. 6, the SAW filter provided in the embodiment of the present application may further include, in addition to the structures shown in fig. 5:

an encapsulation protection layer 208, the encapsulation protection layer 208 covering the sound speed increasing layer 207 and the surface of the temperature compensation layer 206 opposite to the substrate 10 not covered by the sound speed increasing layer 207.

On one hand, the packaging protection layer 208 can prevent the damage of the packaging process to the internal structure of the SAW, and on the other hand, the packaging protection layer 208 can isolate the influence of external environments such as external water vapor on the internal structure of the SAW, thereby improving the reliability of the device. In addition, the encapsulation protection layer 208 can also increase the mechanical strength of the thin film piezoelectric structure and suppress the generation of lamb wave (lamb wave) mode.

As an example, the material of the encapsulation protection layer 208 may be selected from at least one of Poly-p-Phenylene Benzobisoxazole (PBO) or Polyimide (PI).

In addition, in the SAW filter shown in fig. 6, the leakage of the acoustic wave from the package protection layer 208 is avoided to some extent due to the presence of the sound speed increasing layer 207.

Note that, in the SAW filter shown in fig. 6, the third pad 203 is located on the surface of the package protective layer 208 opposite to the substrate 10, and the conductive via 204 penetrates the package protective layer 208 up and down in addition to the piezoelectric material layer 20 and the temperature compensation layer 206.

The above provides a plurality of specific implementations of the SAW filter according to the embodiments of the present application. In these embodiments, the electrical signals inside the piezoelectric element can be electrically connected to an external circuit through the first pad 101, the second pad 201, and the third pad 203, and the metal solder ball disposed on one side of the piezoelectric material layer 20. In fact, in a plurality of specific implementation manners of the application, the packaging form can be more flexible. As another alternative implementation manner of the present application, a conductive plunger may be disposed on the substrate 10, and an electrical signal inside the SAW filter may be led out through the first pad 101, the second pad 201, the third pad 203, and the conductive plunger, so as to be electrically connected to an external circuit.

In addition, in the embodiments, the SAW filters may be combined with each other, and the combined SAW filter structure is within the scope of the present application.

Based on a plurality of specific implementations of the SAW filter provided by the above embodiments, accordingly, the present application also provides a specific implementation of a manufacturing method of the SAW filter.

Referring to fig. 7 to 8(7), a method for manufacturing a SAW filter according to an embodiment of the present disclosure includes:

s701: a first bonding pad is formed on a surface of the first substrate.

As an example, a conductive layer may be grown on a surface of the first substrate 10 using an LPCVD process, and then the first pad 101 may be formed on a surface of the first substrate 10 by an etching method.

As an example, the material of the conductive layer may be polysilicon, or may be a conductive metal. The first substrate 10 is a support substrate, which may be a silicon substrate, a glass substrate, or a sapphire substrate.

The schematic cross-sectional structure after the step is performed is shown in fig. 8 (1).

As another example, a passive device (not shown in fig. 8 (1)) which can be used for matching with the SAW filter may be further formed on at least one surface of the first substrate according to the need of the SAW filter to be manufactured. By way of example, the passive device may be a capacitive or inductive device.

S702: and performing ion implantation on the first surface of the second substrate to form a piezoelectric material layer close to the first surface side of the second substrate.

The step may specifically be: according to the designed thickness of the piezoelectric material layer, the ion implantation energy is acquired, and according to the acquired ion implantation energy, ion implantation is performed from the first surface of the second substrate 20 ' to the inside of the second substrate 20 ', so that the piezoelectric material layer 20 is formed on the side close to the first surface of the second substrate 20 '. For example, the implantation energy may be 100-150KeV, and the ion dose may be 3 × 10e 16-8 × 10e16atoms/cm²。

The second substrate 20' may be a piezoelectric material substrate, for example, a lithium niobate substrate or a lithium tantalate substrate.

The schematic cross-sectional structure after the step is performed is shown in fig. 8 (2).

In fig. 8(2), the dotted line represents the position where the ion concentration is highest. When subsequently subjected to a high temperature process, the second substrate 20 'generates micro-bubbles at the dotted line, thereby separating the piezoelectric material layer 20 from the second substrate 20'.

S703: forming a second pad and an interdigital transducer on the piezoelectric material layer; when the first substrate and the second substrate are stacked and the surface of the first substrate, on which the first welding pads are formed, faces the piezoelectric material layer, the first welding pads and the second welding pads correspond to each other one by one.

The step may specifically be: the second pads 201 and the interdigital transducers 202 are formed on the surface of the piezoelectric material layer 20 by a patterning process.

In the embodiment of the present application, the metal material and the processing method used for the interdigital transducer 202 are not particularly limited, and the preparation of the interdigital transducer 202 may be completed by a lift-off process (lift-off), as an example. AsFor another example, in order to suppress the spurious mode, the metal material used in the interdigital transducer 202 may be a metal material with a relatively large density, such as Au, Ta, W, or Cu. As yet another example, the thickness of interdigital transducer 202 may be in the range of 1000A to

In the meantime.

As a more specific example, the second pad 201 may be formed using an electroplating process or an electron beam evaporation deposition process. The thickness of the second pad may be 2000 to

In the meantime.

The schematic cross-sectional structure after the step is performed is shown in fig. 8 (3).

S704: and bonding the first bonding pad and the second bonding pad which are in one-to-one correspondence, so that the interdigital transducer is positioned in a cavity formed by the first bonding pad and the second bonding pad.

The step may specifically be: the first substrate 10 and the second substrate 20 ' are oppositely placed in such a manner that the surface of the first substrate 10 on which the first pads 101 are formed faces the piezoelectric material layer on the second substrate 20 ', and the first pads 101 and the second pads 201 corresponding to each other are aligned one by one, and then the first pads 101 and the second pads 201 corresponding to each other are bonded together by a bonding process, thereby forming the cavity 30 between the first substrate 10 and the second substrate 20 '. Wherein the first pad 101 and the second pad 201 form sidewalls of the cavity 30 and the interdigital transducer 202 is located within the cavity 30.

As an example, the bonding process employed in this step may be a eutectic bonding process. As a more specific example, the bonding temperature may be 300-400 ℃ for 30-60 min.

The schematic cross-sectional structure after the step is performed is shown in fig. 8 (4).

S705: and carrying out heat treatment on the second substrate to separate the piezoelectric material layer from the second substrate.

The step may specifically be: the structure formed in S704 is subjected to a heat treatment at 250 to 400 c, during which the second substrate 20 'generates microbubbles from the position where the concentration of the implanted ions is the highest, and the piezoelectric material layer 20 is separated from the second substrate 20' after applying stress.

The schematic cross-sectional structure after the step is performed is shown in fig. 8 (5).

S706: the piezoelectric material layer is subjected to heat treatment to improve the piezoelectric characteristics of the piezoelectric material layer.

It should be noted that the implanted ions may damage the piezoelectric performance of the second substrate 20', and thus, in order to improve the performance of the SAW filter, the embodiment of the present application may improve the piezoelectric characteristics of the piezoelectric material layer by performing a heat treatment on the piezoelectric material layer.

As an example, the temperature range of the heat treatment employed in this step is between 300-600 deg.C, more specifically, the temperature range of the heat treatment is between 400-500 deg.C for 2-4 hours.

S707: and forming a through hole in the area of the piezoelectric material layer opposite to the second welding pad.

The step may specifically be: a via hole 204' is formed on a region of the piezoelectric material layer 20 opposite to the second pad 201 using an etching process.

The schematic cross-sectional structure after the step is performed is shown in fig. 8 (6).

S708: and forming a third bonding pad above the through hole.

As an example, the step may specifically be: first, a conductive material layer is formed on the surface of the piezoelectric material layer 20 opposite to the first substrate 10, wherein the conductive material layer is formed while filling the through hole 204 ', so that the through hole 204' forms the conductive through hole 204.

Then, the conductive material layer is etched using a patterning process, thereby forming a third pad 203 over the via hole 204'. The cross-sectional structure of the step is shown in fig. 8 (7).

S709: and forming a metal solder ball electrically connected with an external circuit on the surface of the third pad opposite to the piezoelectric material layer.

The schematic cross-sectional structure after the step is performed is shown in fig. 1.

The foregoing is a specific implementation manner of the SAW filter provided in the embodiments of the present application.

It should be noted that, in a specific implementation manner of the SAW filter provided in the embodiment of the present application, the SAW filter shown in fig. 1 or fig. 3 may be formed. Wherein, whether the interdigital transducer 202 is contacted with the substrate 10 or not can be realized by adjusting the heights of the interdigital transducer 202, the first pad 101 and the second pad 201. When the height of the interdigital transducer 202 is smaller than the sum of the heights of the first pad 101 and the second pad 201, it can be achieved that the interdigital transducer 202 does not contact the substrate 10, thereby forming the structure shown in fig. 1. When the height of the interdigital transducer 202 is equal to the sum of the heights of the first pad 101 and the second pad 201, the contact of the interdigital transducer 202 with the substrate 10 can be achieved, thereby forming the structure shown in fig. 3.

In addition, when the SAW filter structure shown in fig. 3 is formed, in order to relieve stress between the interdigital transducer 202 and the substrate 10 and prevent damage to the piezoelectric material layer 20 and the interdigital transducer 202 caused by excessive stress therebetween, before S704, the following steps may be further included:

a buffer layer is formed on a surface of the first substrate 10 on which the first pad is formed.

The material of the buffer layer may soften during the bonding process of the substrate 10 and the layer of piezoelectric material 20, thereby ensuring sufficient bonding between the interdigital transducer 202 and the buffer layer, while preserving the cavity between the substrate 10 and the layer of piezoelectric material 20. As a specific example, the buffer layer may be made of a resin material.

In the method of manufacturing the SAW filter according to the above-described embodiment, the interdigital transducer 202 may be placed in the cavity 30, and the inside of the cavity may be a vacuum environment or a gas environment. Since the acoustic wave cannot propagate in a vacuum and the acoustic wave has a lower propagation capacity in a gas medium compared to a solid medium, the acoustic wave energy is not easily leaked out from the substrate 10 side through the cavity 30, and thus, the cavity 30 formed between the substrate 10 and the piezoelectric material layer 20 can reduce the existence of the acoustic wave in a stray mode, reduce the possibility of the acoustic wave energy leaking from the substrate 10, and thus improve the Q value and insertion loss of the SAW filter.

It should be noted that the problem of the passband frequency of the SAW filter drifting with temperature changes is serious due to the negative temperature coefficient characteristics of the conventional piezoelectric material used for forming the piezoelectric material layer 20, such as lithium niobate or lithium tantalate. In order to alleviate the problem that the passband frequency of the SAW filter drifts along with the temperature change, the application also provides another SAW filter manufacturing method.

Referring to fig. 9 to 10(4), another method for manufacturing a SAW filter provided by the present application includes the following steps:

s901 to S906 are the same as S701 to S706 described above, and for the sake of brevity, are not described in detail here.

S907: and forming a temperature compensation layer on the surface of the piezoelectric material layer opposite to the first substrate.

It should be noted that, since the surface of the piezoelectric material layer 20 opposite to the substrate 10 is a completely flat plane, the temperature compensation layer 206 may be formed on the surface of the piezoelectric material layer 20 opposite to the first substrate 10 by using a conventional thin film deposition process in this step.

There are many options for the deposition process used to form the temperature compensation layer 206, and PECVD, LPCVD or PVD may be used as examples.

In addition, the thickness and compactness of the temperature compensation layer 206 may affect the equivalent sound velocity of the sound wave, and if the thickness is too thin or the compactness is too poor, the problem of insignificant temperature compensation effect may occur, and if the temperature is too thick, the interdigital transducer electrode with a large density needs to be prepared, resulting in a complex preparation process. Therefore, the temperature of the molten metal is controlled,as an example, the temperature compensation layer 206 may be of a thickness

In order to take account of the above problems.

The schematic cross-sectional structure after the step is performed is shown in fig. 10 (1).

As another alternative embodiment of the present application, in order to implement the adjustment of the passband frequency of the SAW filter, after S907, the following steps may be further included:

s908: and trimming the thickness of the temperature compensation layer according to design requirements.

The step may specifically be: after the temperature compensation layer 206 is formed, the performance of the SAW filter is tested, the designed target performance of the SAW filter is compared with the actual performance obtained through testing, if the actual performance tested is not consistent with the target performance, the thicknesses of the temperature compensation layers on different areas of the first substrate can be differentially trimmed through a particle grinding process, so that the passband frequencies of the SAW filters in different areas are consistent, the passband frequency of the SAW filter is adjusted, and the uniformity and the product yield of the SAW filter are improved.

As another optional implementation manner of the present application, in order to further reduce leakage of acoustic wave energy and further improve the Q value and insertion loss of the SAW filter, after S908, the method may further include the following steps:

s909: a sound speed increasing layer is formed on a surface of the temperature compensation layer facing away from the first substrate.

As an implementation manner, in this step, a PECVD process may be adopted to form the sound velocity increasing layer 207 on the surface of the temperature compensation layer 206 opposite to the first substrate 10, and the sound velocity increasing layer 207 may increase the equivalent sound velocity of the surface acoustic wave.

As an example, the sound speed increasing layer 207 may be provided only on a surface area of the temperature compensation layer 206 facing away from the interdigital transducer 202, rather than covering the entire surface of the temperature compensation layer 206.

In addition, when the sound speed increasing layer 207 is made of a material with a high thermal conductivity, the sound speed increasing layer 207 can also serve as a heat dissipation layer, thereby improving the heat dissipation performance of the SAW filter.

The schematic cross-sectional structure after the step is performed is shown in fig. 10 (2).

As another implementation, in order to improve the heat dissipation performance of the SAW filter, S909 may be replaced with: and forming a heat dissipation layer on the surface of the temperature compensation layer opposite to the first substrate.

In addition, when the high acoustic resistance material used for preparing the sound velocity increasing layer 207 and the heat dissipation material used for preparing the heat dissipation layer are different materials, in order to enable the prepared SAW filter to reduce the leakage of acoustic energy on the piezoelectric material layer side and improve the heat dissipation performance of the SAW filter, as another implementation manner of the present application, the sound velocity increasing layer and the heat dissipation layer which are stacked may be simultaneously formed on the surface of the temperature compensation layer 206 facing away from the substrate 10. In the embodiments of the present application, the relationship between the upper and lower positions of the sound velocity increasing layer and the heat dissipation layer is not limited.

S910: the thickness of the sound velocity increasing layer is trimmed according to design requirements.

The step may specifically be: after the sound velocity increasing layer 207 is formed, the performance of the SAW filter is tested, the designed target performance of the SAW filter is compared with the actual performance obtained through the test, if the tested actual performance is not consistent with the target performance, the thickness of the sound velocity increasing layer 207 on different areas of the first substrate can be trimmed on different areas of the first substrate by utilizing a particle grinding process, so that the passband frequencies of the SAW filters in different areas are consistent, the passband frequency of the SAW filter is adjusted, and the uniformity and the product yield of the SAW filter are improved.

As another optional implementation manner of the present application, in order to prevent moisture or an external environment from affecting an internal structure of the SAW filter and improve reliability of the SAW filter, on the basis of the above optional implementation manner, after S910, the method may further include:

s911: an encapsulation protection layer 208 is formed on the surface of the sound speed increasing layer 207 and the surface of the temperature compensation layer 206 opposite to the substrate 10, which is not covered by the sound speed increasing layer 207.

As an example, the material of the encapsulation protection layer 208 may be selected from at least one of PBO or PI.

The schematic cross-sectional structure after the step is performed is shown in fig. 10 (3).

S912: and etching the packaging protection layer, the temperature compensation layer and the piezoelectric material layer to form a through hole.

The step may specifically be: the encapsulation protection layer 208, the temperature compensation layer 206 and the piezoelectric material layer 20 are etched over the second bonding pads 201 to form through holes 204' penetrating the encapsulation protection layer 208, the temperature compensation layer 206 and the piezoelectric material layer 20. The via 204' communicates with the second pad 201.

The schematic cross-sectional structure after the step is performed is shown in fig. 10 (4).

S913 to S914 are the same as S708 to S709, and for the sake of brevity, will not be described in detail herein. Finally, the SAW filter structure shown in fig. 6 is formed.

It should be noted that, in the embodiment of the present application, the third pad 203 may be used as a test pad, and the performance of the SAW filter may be tested by using the third pad 203, so as to obtain a test result of the performance of the SAW filter.

The above is a specific implementation manner of another SAW filter manufacturing method provided in the embodiments of the present application. The specific implementation manner of the manufacturing method has the following effects in addition to the beneficial effects of the manufacturing method provided by the above embodiment:

1. because the surface of the piezoelectric material layer 20 opposite to the first substrate 10 is a flat surface, there are many choices for the process for forming the temperature compensation layer 206, and the process for forming the temperature compensation layer 206 is less difficult, and it is not necessary to perform a grinding process after the temperature compensation layer 206 is formed, thereby reducing the chemical mechanical polishing process, simplifying the process flow, and reducing the manufacturing cost.

2. Since the equivalent acoustic velocity of the surface acoustic wave is related to the thicknesses of the temperature compensation layer 206, the acoustic velocity increasing layer 207 and the heat dissipation layer disposed on the surface of the piezoelectric material layer 20 opposite to the interdigital transducer, in the manufacturing method of the SAW filter provided in the embodiment of the present application, after the temperature compensation layer 206, the acoustic velocity increasing layer 207 or the heat dissipation layer is formed, a trimming process can be inserted to trim the thicknesses of the layers, so that the product yield and the performance of the SAW filter are improved.

In the two implementations of the above-provided SAW filter manufacturing method, the electrical signal inside thereof can be electrically connected to an external circuit through the first pad 101, the second pad 201, and the third pad 203, and the metal solder ball disposed on the side of the piezoelectric material layer 20. In fact, in a plurality of specific implementation manners of the application, the packaging form can be more flexible. As another alternative implementation manner of the present application, a conductive plunger may also be disposed on the first substrate 10, and an electrical signal inside the SAW filter may be led out from a side of the first substrate 10 opposite to the piezoelectric material layer 20 through the first pad 101, the second pad 201, the third pad 203, and the conductive plunger, so as to be electrically connected to an external circuit.

In the above method of manufacturing the SAW filter, pads for bonding are formed on the surfaces of the first and second substrates 10 and 20'. In fact, as an extended embodiment of the present application, a pad may be formed only on the first substrate 10, and directly soldered on the surface of the second substrate 20'. As another expanded embodiment of the present application, a pad may be formed on the surface of the second substrate 20', and the pad may be directly soldered on the surface of the first substrate 10.

The above is a specific implementation manner of the SAW filter and the manufacturing method thereof provided by the embodiment of the application.

Based on the SAW filter provided by the above embodiment, the application also provides a radio frequency front end chip. As shown in fig. 11, the rf front-end chip includes a surface acoustic wave filter 111, a low noise amplifier 112, a power amplifier 113, and a data transmission interface 114;

wherein, the surface acoustic wave filter is the surface acoustic wave filter of any one of the above embodiments. As an example, the surface acoustic wave filter shown in fig. 11 is the surface acoustic wave filter shown in fig. 1 described above.

Wherein the low noise amplifier 112, the power amplifier 113 and the data transmission interface 114 are located inside the cavity 30 and on the surface of the substrate 10 facing the piezoelectric material layer 20.

The application also provides a specific implementation mode of the mobile terminal.

Referring to fig. 12, the mobile terminal provided in the embodiment of the present application includes a communication module 121, where the communication module 121 includes a surface acoustic wave filter 1211, and the surface acoustic wave filter 1211 may be a surface acoustic wave filter provided in any of the above implementation manners.

By way of example, the mobile terminal according to the embodiment of the present application may be a mobile phone, a tablet computer, and the like.

The above provides a specific implementation manner for the embodiment of the present application.

Claims

A surface acoustic wave filter, comprising:

the piezoelectric transducer comprises a substrate and a piezoelectric material layer which are oppositely arranged, wherein a cavity is arranged between the substrate and the piezoelectric material layer; a welding pad used for bonding the substrate and the piezoelectric material layer is arranged on the side wall of the cavity;

an interdigital transducer is arranged on the surface, facing the substrate, of the piezoelectric material layer; the interdigital transducer is located within the cavity.
The filter according to claim 1, wherein the pads comprise first pads located on a surface of the substrate facing the piezoelectric material layer, and/or second pads located on a surface of the piezoelectric material layer facing the substrate;

the first welding pad and the second welding pad are arranged in a stacked mode.
The filter of claim 1, further comprising: the temperature compensation layer is positioned on the surface of the piezoelectric material layer, which faces away from the substrate.
The filter of claim 3, further comprising: a sound speed increasing layer covering at least a surface area of the temperature compensation layer facing away from the interdigital transducer.
The filter of claim 3, further comprising:

and the heat dissipation layer at least covers the surface area of the temperature compensation layer back to the interdigital transducer.
The filter of claim 4, further comprising:

and the packaging protection layer covers the sound velocity increasing layer and the surface, opposite to the substrate, of the temperature compensation layer which is not covered by the sound velocity increasing layer.
The filter of claim 5, further comprising:

and the packaging protective layer covers the heat dissipation layer and the surface, back to the substrate, of the temperature compensation layer which is not covered by the heat dissipation layer.
The filter of any of claims 1-7, wherein the interdigital transducer is in contact with the substrate.
The filter of claim 8, wherein a buffer layer is disposed on a surface of the substrate facing the layer of piezoelectric material.
A filter according to any of claims 3-7, wherein the thickness of the temperature compensation layer is between 1000 and 7
In the meantime.
A method of manufacturing a surface acoustic wave filter, comprising:

forming a first bonding pad on a surface of a first substrate;

performing ion implantation on the first surface of the second substrate to form a piezoelectric material layer on one side close to the first surface of the second substrate;

forming a second pad and an interdigital transducer on the piezoelectric material layer; when the first substrate and the second substrate are stacked and the surface of the first substrate, on which the first welding pads are formed, faces the piezoelectric material layer, the first welding pads and the second welding pads correspond to each other one by one;

bonding the first bonding pad and the second bonding pad which are in one-to-one correspondence, so that the interdigital transducer is positioned in a cavity formed by the first bonding pad and the second bonding pad;

and carrying out heat treatment on the second substrate to separate the piezoelectric material layer from the second substrate.
The method of claim 11, wherein after thermally treating the second substrate to separate the layer of piezoelectric material from the second substrate, further comprising:

and carrying out heat treatment on the piezoelectric material layer so as to improve the piezoelectric property of the piezoelectric material layer.
The method according to claim 11, wherein the heat treating the piezoelectric material layer comprises:

the piezoelectric material layer is heat-treated at a temperature ranging from 400 to 500 ℃.
The method of claim 11, wherein after thermally treating the second substrate to separate the layer of piezoelectric material from the second substrate, further comprising:

and forming a temperature compensation layer on the surface of the piezoelectric material layer opposite to the first substrate.
The method of claim 14, further comprising, after forming a temperature compensation layer on a surface of the piezoelectric material layer facing away from the first substrate:

and trimming the thickness of the temperature compensation layer according to design requirements.
The method of claim 14, further comprising, after forming a temperature compensation layer on a surface of the piezoelectric material layer facing away from the first substrate:

and forming a sound velocity increasing layer or a heat dissipation layer on the surface of the temperature compensation layer, which is opposite to the first substrate, wherein the sound velocity increasing layer or the heat dissipation layer only covers part of the surface area of the temperature compensation layer, which is opposite to the substrate.
The method of claim 16, further comprising, after forming a sound speed increasing layer or a heat dissipation layer on a surface of the temperature compensation layer facing away from the first substrate:

the thickness of the sound velocity increasing layer and/or the heat dissipation layer is trimmed according to design requirements.
The method according to claim 16 or 17, further comprising, after forming a sound speed increasing layer and/or a heat dissipating layer on a surface of the temperature compensation layer facing away from the first substrate:

and annealing the sound velocity increasing layer and/or the heat dissipation layer to eliminate stress in the layer.
The method of claim 11, wherein after thermally treating the second substrate to separate the layer of piezoelectric material from the second substrate, further comprising:

and forming an encapsulation protection layer on the surface of the piezoelectric material layer opposite to the first substrate.
The method of any of claims 11-19, further comprising, prior to bonding the first pad and the second pad:

a buffer layer is formed on a surface of the first substrate on which the first pad is formed.
A radio frequency front-end chip is characterized by comprising a surface acoustic wave filter, a low noise amplifier, a power amplifier and a data transmission interface;

the surface acoustic wave filter as set forth in any of claims 1 to 10, wherein the low noise amplifier, the power amplifier and the data transmission interface are located inside the cavity and on a surface of the substrate facing the piezoelectric material layer.
A mobile terminal, comprising: a communication module comprising a surface acoustic wave filter therein, the surface acoustic wave filter being as claimed in any one of claims 1 to 10.