阅读说明：本技术 一种制备压电复合薄膜的方法及压电复合薄膜 (Method for preparing piezoelectric composite film and piezoelectric composite film ) 是由 胡卉 李真宇 朱厚彬 张秀全 薛海蛟 于 2020-04-21 设计创作，主要内容包括：本发明公开了一种制备压电复合薄膜的方法及压电复合薄膜,在具有衬底层的原始压电复合薄膜内,通过离子注入法将离子注入到衬底层的表面区域,使得离子破坏衬底层表面处的晶格结构,造成一定的损伤进而形成损伤层,之后再对包含损伤层在内的原始压电复合薄膜进行低温退火处理,获得目标压电复合薄膜。本发明的方案可以在制备好整体的原始压电复合薄膜之后,通过离子注入法形成损伤层,再利用损伤层捕获衬底层与低声阻层之间的电荷,避免采用当前常用的方法,使得后形成低声阻层时对先生成的损伤层造成影响,本发明的方案能够保证损伤层捕获电荷的能力。(The invention discloses a method for preparing a piezoelectric composite film and the piezoelectric composite film. According to the scheme, after the integral original piezoelectric composite film is prepared, the damaged layer can be formed through an ion implantation method, the damaged layer is used for capturing electric charges between the substrate layer and the low-acoustic-resistance layer, the influence on the damaged layer generated earlier when the low-acoustic-resistance layer is formed later by adopting a current common method is avoided, and the capability of the damaged layer for capturing the electric charges can be guaranteed.)

1. A method of making a piezoelectric composite film, comprising:

preparing an original piezoelectric composite film, wherein the original piezoelectric composite film comprises a substrate layer;

ions penetrate through the original piezoelectric composite film by an ion implantation method and are implanted into the surface area of the substrate layer, so that a damaged layer is formed in the surface area of the substrate layer;

and carrying out low-temperature annealing treatment on the original piezoelectric composite film containing the damaged layer to obtain the target piezoelectric composite film.

2. The method of claim 1, wherein the original piezoelectric composite film further comprises a low acoustic resistance layer and a piezoelectric layer sequentially stacked on a surface of the backing layer.

3. The method of claim 2, wherein the step of preparing the original piezoelectric composite film comprises:

forming a low-acoustic-resistance layer on the substrate layer by a thermal oxidation method;

transferring the piezoelectric layer onto the low acoustic resistance layer by an ion implantation method and a bonding method;

and carrying out high-temperature annealing treatment on the whole structure of the substrate layer, the low-acoustic-resistance layer and the piezoelectric layer, and recovering the damage of the ion implantation method to the piezoelectric layer to obtain the original piezoelectric composite film.

4. The method according to any one of claims 1-2, wherein the ions implanted in the ion implantation process are H ions.

5. The method according to any of claims 1-2, wherein the ion implantation is performed at an ion implantation rate of 5x10¹¹-1x10¹⁵ions/cm²。

6. The method of any of claims 1-2, wherein the damage layer has a defect density of 1x10¹¹-1x10¹⁵/cm²And the thickness of the damage layer is 200-3000 nm.

7. The method according to any one of claims 1 to 2, wherein the temperature of the low temperature annealing treatment is in the range of 300 to 400 ℃.

8. The method according to any one of claims 2-3, wherein the material of the piezoelectric layer is lithium tantalate or lithium niobate, and the thickness of the piezoelectric layer is 100-2000 nm.

9. The method according to any one of claims 2 to 3, wherein the material of the low acoustic resistance layer is silicon dioxide, and the thickness of the low acoustic resistance layer is 100 to 5000nm, and the thickness uniformity of the low acoustic resistance layer is less than 2%.

10. A method according to any one of claims 1-3, characterized in that the material of the substrate layer is monocrystalline silicon having a resistivity of more than 5000 Ω -cm and that the thickness of the substrate layer is 150-1000 μm.

11. A piezoelectric composite film produced by the method according to any one of claims 1 to 10.

12. The piezoelectric composite film is characterized by comprising a substrate layer, a low-acoustic-resistance layer and at least one functional layer, wherein the surface area of the substrate layer is damaged by an ion implantation method to form a damaged layer.

Technical Field

The invention relates to the technical field of semiconductors, in particular to a method for preparing a piezoelectric composite film and the piezoelectric composite film.

Background

The piezoelectric composite film applied to the surface acoustic wave filter specifically comprises a piezoelectric layer, a low acoustic resistance layer and a high acoustic resistance substrate. The piezoelectric layer is a functional layer to realize the electro-acoustic interconversion, and is generally of an LN or LT piezoelectric single crystal structure; the material of the low-acoustic-resistance layer is generally SiO₂(ii) a The high-acoustic-resistance substrate is made of Si generally, and the structure of the high-acoustic-resistance substrate can greatly inhibit acoustic wave energy from leaking into the substrate and reduce the loss of devices.

Fig. 1 is a schematic diagram of a basic structure of a current piezoelectric composite film provided by the present invention, which includes a piezoelectric layer 100, a low acoustic resistance layer 200, and a substrate layer 300. As shown in FIG. 1, in the conventional piezoelectric composite thin film structure, due to the manufacturing process, in SiO₂A gap such as a bubble may exist between the layer and the Si layer. When the piezoelectric composite film is electrified, a voltage applied to the piezoelectric composite film generates an electromagnetic field, namely SiO₂There is a large amount of charge in the gap between the layer and the Si layer, which attracts the carriers in the Si layer to accumulate on the Si layer surface, forming a conductive layer. And the carriers in the conductive layer and the electromagnetic field are mutually influenced, so that the intensity of the electromagnetic field is weakened, and the loss of the electromagnetic field is caused.

To avoid forming a conductive layer on the surface of the Si layer, it is common practice to form the conductive layer on SiO₂A polysilicon layer is added between the layer and the Si layer, and the polysilicon layer has a certain density of defects and can capture SiO₂And electric charges between the layer and the Si layer are reduced, so that carriers accumulated on the surface of the Si layer are reduced, and the influence of the carriers on an external electromagnetic field is reduced. However, the addition of polysilicon requires the deposition of a polysilicon layer on a Si layer and then the thermal oxidation of a SiO layer on top of the polysilicon layer₂And (3) a layer. Although the thermal oxidation process can ensure SiO₂The layer has high compactness, uniformity, less defects and smaller surfaceRoughness but at oxidation temperature, SiO₂The polysilicon under the layer will re-crystallize, thereby reducing the trapping capability for charge; in addition, the thermal oxidation process also causes the surface roughness of the polysilicon to increase, which affects the charge trapping capability of the polysilicon.

Disclosure of Invention

The invention provides a method for manufacturing a piezoelectric composite film and the piezoelectric composite film, which aim to solve the problem of low charge capture capability caused by adding a polycrystalline silicon layer in the piezoelectric composite film at present.

In a first aspect, the present invention provides a method of making a piezoelectric composite film, comprising:

preparing an original piezoelectric composite film, wherein the original piezoelectric composite film comprises a substrate layer;

ions penetrate through the original piezoelectric composite film by an ion implantation method and are implanted into the surface area of the substrate layer, so that a damaged layer is formed in the surface area of the substrate layer;

and carrying out low-temperature annealing treatment on the original piezoelectric composite film containing the damaged layer to obtain the target piezoelectric composite film.

With reference to the first aspect, in an implementation manner of the first aspect, the original piezoelectric composite film further includes a low acoustic resistance layer and a piezoelectric layer sequentially stacked on the surface of the substrate layer.

With reference to the first aspect, in one possible implementation manner of the first aspect, the step of preparing the original piezoelectric composite thin film includes:

forming a low-acoustic-resistance layer on the substrate layer by a thermal oxidation method;

transferring the piezoelectric layer onto the low acoustic resistance layer by an ion implantation method and a bonding method;

and carrying out high-temperature annealing treatment on the whole structure of the substrate layer, the low-acoustic-resistance layer and the piezoelectric layer, and recovering the damage of the ion implantation method to the piezoelectric layer to obtain the original piezoelectric composite film.

With reference to the first aspect, in one possible implementation manner of the first aspect, the ions implanted in the ion implantation method are H ions.

In combination with the first aspect, in the first aspectIn one embodiment of the present invention, the ion implantation amount in the ion implantation method is 5 × 10¹¹-1x10¹⁵ions/cm²。

With reference to the first aspect, in one possible implementation manner of the first aspect, the defect density of the damaged layer is 1 × 10¹¹-1x10¹⁵/cm²And the thickness of the damage layer is 200-3000 nm.

With reference to the first aspect, in one possible implementation manner of the first aspect, the temperature range of the low-temperature annealing treatment is 300 to 400 ℃.

With reference to the first aspect, in an implementation manner of the first aspect, a material of the piezoelectric layer is lithium tantalate or lithium niobate, and a thickness of the piezoelectric layer is 100 to 2000 nm.

With reference to the first aspect, in an implementation manner of the first aspect, the material of the low acoustic resistance layer is silicon dioxide, the thickness of the low acoustic resistance layer is 100 to 5000nm, and the thickness uniformity of the low acoustic resistance layer is less than 2%.

With reference to the first aspect, in one possible implementation manner of the first aspect, the material of the substrate layer is monocrystalline silicon with a resistivity greater than 5000 Ω · cm, and the thickness of the substrate layer is 150-1000 μm.

In a second aspect, the present invention provides a piezoelectric composite film, which is prepared by the method of the first aspect, and specifically includes a piezoelectric layer, a low acoustic resistance layer, a damage layer, and a substrate layer, which are sequentially stacked.

In a third aspect, the invention further provides a piezoelectric composite film, which specifically comprises a substrate layer, a low-acoustic-resistance layer and at least one functional layer, wherein the surface area of the substrate layer is damaged by an ion implantation method to form a damaged layer.

According to the technical scheme, the invention discloses a method for preparing a piezoelectric composite film and the piezoelectric composite film. According to the scheme, after the integral original piezoelectric composite film is prepared, the damaged layer can be formed through an ion implantation method, the damaged layer is used for capturing electric charges between the substrate layer and the low-acoustic-resistance layer, the influence on the damaged layer generated earlier when the low-acoustic-resistance layer is formed later by adopting a current common method is avoided, and the capability of the damaged layer for capturing the electric charges can be guaranteed.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiment will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without any creative effort.

FIG. 1 is a schematic diagram of a basic structure of a present piezoelectric composite film according to the present invention;

fig. 2 is a schematic structural diagram of a piezoelectric composite film according to an embodiment of the present invention;

fig. 3 is a flowchart of a method for manufacturing a piezoelectric composite film according to an embodiment of the present invention.

Detailed Description

The surface acoustic wave filter is composed of a piezoelectric composite film and electrodes, the electrodes are manufactured on a piezoelectric layer of the piezoelectric composite film, and the piezoelectric layer and the electrodes can convert acoustic waves with specific frequency into electric signals through cooperation, so that a filtering function is achieved. The piezoelectric composite film commonly used at present specifically comprises a piezoelectric layer, a low-acoustic-resistance layer and a high-acoustic-resistance substrate. Wherein the piezoelectric layer is typically LN (lithium niobate, LiNiO)₃) Or LT (lithium tantalate, LiTaO)₃) A single crystal structure; the material of the low-acoustic-resistance layer is generally SiO₂(ii) a The material of the high acoustic resistance substrate is typically Si.

In the above-mentioned substrate layer structure, there is a certain requirement for the smoothness of the interface, generally the roughness of the interface<0.5nm, so as to avoid energy loss caused by scattering of sound waves on the interface and avoid subsequent light caused by rough interfaceLight scattering occurs during the etching process, which affects the lithography pattern. SiO of low acoustic resistance layer₂There are two main uses: on the one hand, as a low acoustic resistance layer, the acoustic resistance difference with the substrate layer is improved, and the effect of limiting energy leakage is improved, so that acoustic energy is mainly concentrated on the piezoelectric layer and SiO₂In the layer; on the other hand, SiO₂Has positive sound velocity temperature coefficient, which is opposite to that of common piezoelectric material, thus playing the role of reducing the frequency temperature drift coefficient of the final device, and the final compensation effect is mainly equal to that of SiO₂The thickness of the layer is relevant. Substrate layer pair SiO₂The layer has two requirements, one is SiO₂The layer has low acoustic transmission loss, on the one hand SiO₂The layer thickness is uniform. In the current process, thermal oxidation is usually used to produce SiO₂Layer of the substrate layer to SiO₂The two requirements of the layer. The oxidation temperature of the thermal oxidation method is higher, and the prepared SiO₂SiO with high compactness and less defects produced by thermal oxidation₂The thickness uniformity which cannot be achieved by other processes is also achieved, and can be generally controlled within 2%. Meanwhile, the thermal oxidation method is generally used for batch production by using a high-temperature oxidation furnace, and the used raw material only contains O₂And H₂O, has very low process cost and environment-friendly raw materials.

In conventional piezoelectric composite film structures, the SiO layer is present due to the fabrication process₂There are many defects and charges between the layer and the Si layer, resulting in SiO₂The concentration of carriers at the interface between the layer and the Si layer creates parasitic conductance, thereby creating additional losses in rf applications. To avoid the formation of parasitic conductance, it is conventional practice in the art to use SiO₂A polysilicon layer is added between the layer and the Si layer, and the polysilicon layer has a certain density of defects and can capture SiO₂And the current carriers between the layer and the Si layer are prevented from causing the current carriers to gather at the interface of the Si layer, so that the current carriers are prevented from weakening an electromagnetic field applied to the piezoelectric composite film.

However, the addition of polysilicon requires the deposition of a polysilicon layer on the Si layer and then over the polysilicon layerSiO production by thermal oxidation or deposition₂And (3) a layer. First, the raw material for making the polysilicon layer is generally a Si-containing gas or liquid, which is not environmentally friendly. Secondly, the manufactured polysilicon layer has grains with different sizes, so that the roughness of the surface of the polysilicon layer is difficult to control, and if the surface is smoothed by adopting a Chemical Mechanical Polishing (CMP) process after the manufacturing is finished, the process for manufacturing the piezoelectric composite film becomes complicated. Furthermore, SiO is formed on the polysilicon layer₂In the case of a layer, if a deposition method is employed, it is difficult to secure SiO₂Thickness uniformity of the layer; if a thermal oxidation method is adopted, because the polycrystalline silicon has grains with different sizes, the oxidation speed has orientation to the silicon crystal orientation, so that the final oxidized interface on the polycrystalline silicon layer becomes very rough and even reaches the level of dozens of nanometers; in addition, at the oxidation temperature, the polysilicon is crystallized again, reducing the carrier trapping effect.

It can be seen that the SiO is guaranteed at present₂Thickness uniformity of the layer, SiO is usually produced by thermal oxidation₂However, thermal oxidation causes polysilicon to recrystallize and increases the surface roughness of polysilicon, which in turn affects the charge trapping capability of polysilicon. Therefore, the invention provides a method for preparing a piezoelectric composite film, which is used for adding a new damaged layer, not only achieving the effect of capturing charges between a substrate layer and a low-acoustic-resistance layer, but also avoiding the influence of a thermal oxidation method on the damaged layer and ensuring the effect of capturing the charges.

Fig. 2 is a schematic structural diagram of a piezoelectric composite film provided in an embodiment of the present invention, and the piezoelectric composite film in fig. 2 is a target piezoelectric composite film prepared by the method provided in the present invention.

The piezoelectric composite film in the embodiment of the present invention includes a substrate layer 300 and a damaged layer 400, wherein the damaged layer 400 is formed by implanting ions into the surface of the substrate layer 300 by using an ion implantation method to damage the surface of the substrate layer 300. Specifically, the original piezoelectric composite film may further include a low acoustic resistance layer 200 and a piezoelectric layer 100 sequentially stacked on the surface of the substrate layer 300. Therefore, the structure of the target piezoelectric composite film prepared by using the original piezoelectric composite film according to the embodiment of the present invention can be as shown in fig. 2, where in fig. 2, the target piezoelectric composite film specifically includes a piezoelectric layer 100, a low acoustic resistance layer 200, a damaged layer 400, and a substrate layer 300. Wherein the damage layer 400 is formed on the surface area of the substrate layer 300 after ions pass through the piezoelectric 100 and the low-resistance layer 200.

In addition, in the target piezoelectric composite film prepared by the method for preparing a piezoelectric composite film in the embodiment of the present invention, the piezoelectric layer 100 may also be replaced by other functional layers capable of implementing electro-acoustic conversion, and the formed target piezoelectric composite film may specifically include a functional layer, a low acoustic resistance layer 200, a substrate layer 300, and a damaged layer 400, where the functional layer may be one or more layers. In the target piezoelectric composite thin film shown in fig. 2, the material of the piezoelectric layer 100 is preferably a lithium tantalate single crystal structure or a lithium niobate single crystal structure, and the thickness of the piezoelectric layer 100 is 100nm to 2000nm, more preferably 300nm to 1000nm, and specific values such as 600nm and 700nm may also be selected.

The material of the low-acoustic-resistance layer 200 is preferably SiO₂(silicon dioxide), and the low-acoustic-resistance layer 200 has a thickness of 100nm to 5000nm and a thickness uniformity of less than 2%. Because the low acoustic resistance layer 200 and the piezoelectric layer 100 have opposite acoustic velocity-temperature change coefficients, the thickness of the low acoustic resistance layer 200 needs to be matched with the thickness of the piezoelectric layer 100, and the more preferable thickness is the same as or similar to the thickness of the piezoelectric layer 100, so that temperature compensation can be better realized, the frequency temperature coefficient of the surface acoustic wave filter is reduced, and the device performance of the surface acoustic wave filter is ensured.

The material of the substrate layer 300 is preferably Si (single crystal silicon) having a resistivity of more than 5000 Ω · cm, and the thickness of the substrate layer 300 is preferably 150 μm to 1000 μm, and more preferably the thickness range is 250 μm to 500 μm.

Fig. 3 is a flowchart of a method for manufacturing a piezoelectric composite film according to an embodiment of the present invention. As shown in fig. 3, the method for preparing a piezoelectric composite film in the embodiment of the present invention specifically includes:

step S101, preparing an original piezoelectric composite film, where the original piezoelectric composite film includes a substrate layer 300.

The original piezoelectric composite film in the embodiment of the present invention includes a substrate layer 300, and on the substrate layer 300, the original piezoelectric composite film may further include a low acoustic resistance layer 200 and a piezoelectric layer 100 that are sequentially stacked, and the specific structure is as shown in fig. 1. In another embodiment, in the original piezoelectric film according to an embodiment of the present invention, the low-acoustic-resistance layer 200 is stacked on the substrate layer 300, and at least one other functional layer capable of performing electro-acoustic conversion may be stacked on the low-acoustic-resistance layer 200. For example, a lithium niobate layer is stacked on the low acoustic resistance layer 200, and a separation layer and a lithium tantalate layer are sequentially stacked on the lithium niobate layer.

Step S102, ions are implanted into the surface area of the substrate layer 300 through penetrating the original piezoelectric composite film by an ion implantation method, so that the surface area of the substrate layer 300 forms a damaged layer 400.

As shown in fig. 1, the original piezoelectric composite film in the embodiment of the present invention includes a substrate layer 300, a low acoustic resistance layer 200, and a piezoelectric layer 100. In step S102, ions need to be implanted between the substrate layer 300 and the low acoustic resistance layer 200 through the piezoelectric layer 100 and the low acoustic resistance layer 200 of the original piezoelectric composite film by an ion implantation method, so that the ions destroy the lattice structure on the surface of the substrate layer 300 to form the damaged layer 400.

In the embodiment of the present invention, the material of the piezoelectric layer 100 is preferably a lithium tantalate single crystal structure or a lithium niobate single crystal structure, and the material of the low acoustic resistance layer 200 is preferably SiO₂The material of the substrate layer 300 is preferably Si, and the contents of the following embodiments all use these preferred materials as examples, and further describe the piezoelectric composite thin film and the method for preparing the piezoelectric composite thin film provided by the present invention.

The method for preparing the piezoelectric composite film according to the embodiment of the present invention is different from the currently-used method in that, in the currently-used method, after the polysilicon layer is manufactured, the low-acoustic-resistance layer 200, such as SiO, is formed on the polysilicon layer₂A layer; in the present invention, ions are implanted into the original piezoelectric composite film on the basis of the original piezoelectric composite film on which the low acoustic resistance layer 200 has been formed, by an ion implantation method, so that the ions destroy the lattice structure at the interface of the substrate layer 300 to generateDefects, which form a damaged layer 400, are shown in fig. 2, wherein the direction indicated by the arrow is the direction of ion implantation. Defects within the damage layer 400 may attract charges between the low acoustic resistance layer 200 and the substrate layer 300, avoiding these charges from causing carrier aggregation at the interface of the substrate layer 300.

In the embodiment of the invention, the ion implantation method is used, so that the problem of recrystallization of the polycrystalline silicon caused by forming the low-acoustic-resistance layer 200 after forming the polycrystalline silicon layer in the conventional method is solved. In the ion implantation method, usable ions include H ions, Ar ions, and the like, but the effect of H ions is more excellent because H ions do not easily affect SiO₂Layer, even if H ions destroy SiO₂The lattice structure of the layer forms Si-H bonds, and H ions can easily form SiO during low-temperature annealing₂Diffusion out of the layer; and Ar ion is too large for SiO₂The damage of the layer is severe and the energy required for implanting Ar ions is large in the ion implantation operation. In addition, SiO₂The charge density in the layer is generally 10¹⁰～10¹³/cm²Level, the dose of implanted ions is 5x10 to achieve carrier trapping effect¹¹～1x10¹⁵ions/cm²That is, a more preferable range may be 1 × 10¹³～1x10¹⁵ions/cm²。

Step S103, performing low-temperature annealing treatment on the original piezoelectric composite film including the damaged layer 400 to obtain a target piezoelectric composite film.

The ions implanted in the embodiment of the present invention may damage the lattice structure of other layers of the original piezoelectric composite film, such as the piezoelectric layer 100, the low acoustic resistance layer 200, and the like. If H ions are used, the H ions will react with SiO₂Si ions in the layers form Si-H bonds, etc., and in order to avoid unnecessary chemical bonds between the piezoelectric layer 100 and the low acoustic resistance layer 200, the entire piezoelectric composite film after ion implantation needs to be annealed at a low temperature to restore the lattice structures of the piezoelectric layer 100 and the low acoustic resistance layer 200, for example, annealing at a low temperature to SiO₂H ions in Si-H bonds in the layer diffuse out. In the embodiment of the present invention, the temperature of the low temperature annealing is generally 200 ℃ or higher, and more preferably lowThe temperature range of the warm annealing treatment is 300-400 ℃.

At present, when the piezoelectric composite film is prepared, a polysilicon layer is generally prepared on a Si layer by adopting a deposition process, and then SiO is prepared on the polysilicon layer by adopting a thermal oxidation process₂Layer, thermal oxidation, however, affects the charge trapping capability of a previously grown polysilicon layer. The method for preparing the piezoelectric composite film provided by the embodiment of the invention can be used for preparing SiO by a thermal oxidation method₂Layer of not only the SiO produced₂The layer is more dense and has a more uniform thickness, while avoiding the effects of the high temperature of the deposition mode on the damaged layer 400. By means of ion implantation, in SiO₂After the layers are manufactured, the damaged layer 400 is formed, the damaged layer 400 is used for replacing a polycrystalline silicon layer in the target piezoelectric composite film, and the situation that the SiO is manufactured in a thermal oxidation and deposition mode after the damaged layer 400 is manufactured can be effectively avoided₂The layer prevents the damage layer 400 from being crystallized after passing through a high temperature environment.

In the piezoelectric composite film prepared by the method provided by the embodiment of the invention, the defect density of the damaged layer 400 is 1x10¹¹-1x10¹⁵/cm²And the thickness of the damaged layer 400 is about 200-3000 nm, preferably 300-1000 nm, the defect density of the damaged lattice in the damaged layer 400 is less than that of the polysilicon, furthermore, the damaged layer 400 is formed after the thermal oxidation method, the thermal oxidation method does not affect the charge trapping capability, and compared with the polysilicon layer in the present piezoelectric composite film, the damaged layer 400 can more effectively trap SiO₂Charge between the layer and the Si layer.

In another embodiment of the method for preparing a piezoelectric composite film provided by the present invention, the step of preparing the original piezoelectric composite film specifically includes:

in step S201, the low-resistance layer 200 is formed on the substrate layer 300 by a thermal oxidation method.

For example, SiO is formed on the Si layer by a thermal oxidation method₂Layer due to composite film pair SiO used in surface acoustic wave filter₂The layer requires low acoustic transmission loss and uniform thickness, so that the thermal oxidation method can ensure the production of SiO₂The layer meets the requirements, the process cost is low, and the process is relatively environment-friendly.

In step S202, the piezoelectric layer 100 is transferred onto the low acoustic resistance layer 200 by an ion implantation method and a bonding method.

In the embodiment of the present invention, the material of the piezoelectric layer 100 may be LN or LT, and before the piezoelectric layer 100 is fabricated on the low acoustic resistance layer 200, the piezoelectric layer 100 needs to be peeled off from the bulk material, wherein the peeling method includes two steps of an ion implantation method and a bonding method. For example, the peeling principle of a specific piezoelectric layer 100 may be: carrying out (hydrogen or helium) ion implantation on the LN wafer or the LT wafer, wherein after ions enter the wafer, energy is gradually lost, the speed is reduced, and finally, the ions stay on a layer surface with a certain depth to form an implantation layer; bonding the wafer to another piece covered with SiO₂The wafer group is then placed into an annealing furnace to be heated, ions injected into the injection layer are changed into hydrogen molecules or helium molecules in the heating process, the hydrogen molecules or the helium molecules are gradually gathered to form bubbles, the density of the bubbles is gradually increased along with the rise of the annealing temperature or the extension of the annealing time, the volume is gradually increased, all the bubbles are finally connected into a whole, the bubble layer is finally broken, and the piezoelectric layer 100 is stripped in the injection layer. It should be noted that the method for peeling off the piezoelectric layer 100 provided in the embodiment of the present invention is not the only method that can obtain the piezoelectric layer 100, but the present invention is only exemplary, and it is obvious to those skilled in the art that the method for peeling off the piezoelectric layer 100 can achieve the purpose of obtaining the piezoelectric layer 100 in the embodiment of the present invention.

Step S203, performing high-temperature annealing treatment on the whole structure of the substrate layer 300, the low acoustic resistance layer 200 and the piezoelectric layer 100, and recovering damage of the ion implantation method to the piezoelectric layer 100 to obtain the original piezoelectric composite film.

In the ion implantation process, ions passing through the piezoelectric layer 100 may damage the crystal structure in the piezoelectric layer 100 and affect the function of the piezoelectric layer 100, and therefore, after the ion implantation process, a high temperature annealing process is performed on the entire structure to release the ions in the piezoelectric layer 100 and restore the original crystal structure of the piezoelectric layer 100. In the embodiment of the present invention, the temperature of the high temperature annealing treatment is generally above 400 ℃, and more preferably, the temperature of the high temperature annealing treatment is about 450 to 550 ℃.

As can be seen from the above schemes, in the original piezoelectric composite film having the piezoelectric layer 100, the low acoustic resistance layer 200, and the substrate layer 300, ions are implanted into the surface area of the substrate layer 300 by an ion implantation method, so that the ions destroy the lattice structure on the surface of the substrate layer 300, and cause a certain damage, thereby forming the damaged layer 400, and then the original piezoelectric composite film including the damaged layer 400 is subjected to low temperature annealing treatment, so as to recover the damage caused by the ion implantation method to the lattice structures of the piezoelectric layer 100 and the low acoustic resistance layer 200, thereby obtaining the target piezoelectric composite film. According to the invention, after the low-acoustic-resistance layer 200 is formed, the damaged layer 400 is formed by an ion implantation method, and then the damaged layer 400 is used for capturing the electric charge between the substrate layer 300 and the low-acoustic-resistance layer 200, so that the influence on the damaged layer 400 generated in advance when the low-acoustic-resistance layer 200 is formed later is avoided, and the electric charge capturing capability of the damaged layer 400 is ensured.

In addition, the ion implantation method added in the method for preparing the piezoelectric composite film provided by the embodiment of the invention is finally added on the basis of the previously mature process for preparing the piezoelectric composite film, does not generate a process change process of an intermediate link, has good process stability, is easy to realize, and has low cost and good environmental protection effect for preparing the piezoelectric composite film. Meanwhile, the defect density, thickness, position and the like of the damaged layer 400 can be accurately controlled by an ion implantation method, and the final electric conduction inhibition effect is good, so that the surface acoustic wave filter using the piezoelectric composite film can meet the expected performance requirements.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.