阅读说明：本技术 一种压电复合薄膜及其制备方法 (Piezoelectric composite film and preparation method thereof ) 是由 李真宇 朱厚彬 张秀全 杨超 李洋洋 于 2020-04-21 设计创作，主要内容包括：本发明公开了一种压电复合薄膜及其制备方法,压电复合薄膜具体包括依次叠加的衬底层、低声阻层以及压电层,其中,低声阻层中掺有一定含量的氯离子,氯离子均匀分布在低声阻层之中或者位于低声阻层中的局部区域。本发明的技术方案中,加入氯离子能够有效地捕获低声阻层中的可移动的碱金属离子,形成中性的氯化物,避免低声阻层中的碱金属离子对声表面波滤波器激发的电磁场造成影响,保证声表面波滤波器的稳定性。(The invention discloses a piezoelectric composite film and a preparation method thereof, wherein the piezoelectric composite film specifically comprises a substrate layer, a low-acoustic-resistance layer and a piezoelectric layer which are sequentially stacked, wherein the low-acoustic-resistance layer is doped with chloride ions with certain content, and the chloride ions are uniformly distributed in the low-acoustic-resistance layer or in a local area in the low-acoustic-resistance layer. In the technical scheme of the invention, the chloride ions are added, so that the movable alkali metal ions in the low-acoustic-resistance layer can be effectively captured to form neutral chloride, the influence of the alkali metal ions in the low-acoustic-resistance layer on an electromagnetic field excited by the surface acoustic wave filter is avoided, and the stability of the surface acoustic wave filter is ensured.)

1. A piezoelectric composite film comprises a substrate layer (300), a low-acoustic-resistance layer (200) and a piezoelectric layer (100) which are sequentially stacked, and is characterized in that the low-acoustic-resistance layer (200) is doped with chloride ions which are uniformly distributed in the low-acoustic-resistance layer (200) or are positioned in a local area in the low-acoustic-resistance layer (200).

2. The piezoelectric composite film according to claim 1, wherein the content of chloride ions in the low-acoustic-resistance layer (200) is more than 2x10¹⁸ atoms/cm³。

3. The piezoelectric composite film according to claim 1, wherein a material of the piezoelectric layer (100) is single-crystal lithium tantalate or single-crystal lithium niobate, and a thickness of the piezoelectric layer (100) is 100 to 2000 nm.

4. The piezo-electric composite film according to claim 1, characterized in that a trapping layer (400) with a predetermined defect density is arranged between the substrate layer (300) and the low-acoustic-resistance layer (200).

5. The piezoelectric composite film according to claim 4, wherein the trapping layer (400) is formed on a surface area of the substrate layer (300).

6. The piezoelectric composite film according to any one of claims 4 to 5, wherein the trapping layer (400) has a defect density of more than 1x10¹¹/cm²And the thickness of the trapping layer (400) is 200-3000 nm.

7. The piezoelectric composite film according to claim 1, wherein the material of the low-acoustic-resistance layer (200) is silicon dioxide, the thickness of the low-acoustic-resistance layer (200) is 100-5000 nm, and the thickness uniformity of the low-acoustic-resistance layer (200) is less than 1%.

8. The piezoelectric composite film according to claim 1, wherein the substrate layer (300) is made of single crystal silicon having a resistivity of more than 5000 Ω -cm, and the substrate layer (300) has a thickness of 150 to 1000 μm.

9. A method for preparing a piezoelectric composite film is characterized by comprising the following steps:

forming a low-acoustic-resistance layer containing chlorine ions on the substrate layer by an chlorine-doping oxidation method or a chlorine-doping deposition method;

moving 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 piezoelectric composite film.

10. A method for preparing a piezoelectric composite film is characterized by comprising the following steps:

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

injecting chloride ions into the low-acoustic-resistance layer by an ion injection method to form a low-acoustic-resistance layer containing chloride ions;

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 piezoelectric composite film.

Technical Field

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

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. Fig. 1 is a schematic diagram of a basic structure of a present piezoelectric composite thin film provided by the present invention, and as shown in fig. 1, a piezoelectric layer is a functional layer to implement electro-acoustic interconversion, and is generally an LN or LT piezoelectric single crystal structure.

However, the SiO of the present piezoelectric composite thin film₂In the layer, there will usually be some mobile positively charged alkali metal ions, such as Na⁺，Li⁺Etc. of Na⁺Mainly comes from Na in air and in the expired air of operators in the production process of the piezoelectric composite film⁺The content is also higher; li⁺Mainly from LT materials, in the manufacturing process of the piezoelectric composite film, the bonding process and the ion implantation process both need to carry out high-temperature annealing on the film, and Li in the piezoelectric layer can be promoted at the moment⁺To SiO₂The layer is diffused. The alkali metal ions are in SiO₂The diffusion coefficient in the layer is large, and particularly, the movement phenomenon is more obvious when the temperature is high or under the action of an electric field, and the surface acoustic wave filter generates energy loss during working to cause temperature rise, so that the surface acoustic wave filter is beneficial to movement of alkali metal ions. Meanwhile, lithium tantalate used as the piezoelectric layer is also a pyroelectric material, and the change of the environmental temperature of the piezoelectric composite film can cause the two surfaces of the piezoelectric composite film to generate electric charges, namely SiO₂The movement of alkali metal ions in the layer is facilitated.

On one hand, the movable alkali metal ions can interact with a radio frequency electromagnetic field excited by the surface acoustic wave filter to generate loss, and on the other hand, the concentration of the alkali metal ions at different positions in the piezoelectric composite film can bring different influences on the surface acoustic wave filter, so that the stability of the surface acoustic wave filter is poor.

Disclosure of Invention

The invention provides a piezoelectric composite film and a preparation method thereof, which are used for solving the problem of poor stability of a surface acoustic wave filter caused by alkali metal ions existing in the conventional piezoelectric composite film.

In a first aspect, the present invention provides a piezoelectric composite film, which includes a substrate layer, a low acoustic resistance layer, and a piezoelectric layer stacked in sequence, and is characterized in that the low acoustic resistance layer is doped with chloride ions, and the chloride ions are uniformly distributed in the low acoustic resistance layer or in a local area in the low acoustic resistance layer.

With reference to the first aspect, in one implementation manner of the first aspect, the content of chloride ions in the low-acoustic-resistance layer is greater than 2x10¹⁸ atoms/cm³。

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

With reference to the first aspect, in an implementable manner of the first aspect, a trapping layer having a preset defect density is disposed between the substrate layer and the low-acoustic-resistance layer.

With reference to the first aspect, in one implementation manner of the first aspect, the capture layer is formed on a surface area of the substrate layer.

With reference to the first aspect, in an implementation manner of the first aspect, the trapping layer has a defect density of more than 1 × 10¹¹/cm²And the thickness of the trapping layer is 200-3000 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, a thickness of the low acoustic resistance layer is 100 to 5000nm, and a thickness uniformity of the low acoustic resistance layer is less than 1%.

With reference to the first aspect, in an 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 to 1000 μm.

In a second aspect, the present invention provides a method for preparing a piezoelectric composite film, including:

forming a low-acoustic-resistance layer containing chlorine ions on the substrate layer by an chlorine-doping oxidation method or a chlorine-doping deposition method;

moving 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 composite film.

In a third aspect, the present invention provides another method for preparing a piezoelectric composite film, including:

forming a low-acoustic-resistance layer on the substrate layer by thermal oxidation or deposition

Injecting chloride ions into the low-acoustic-resistance layer by an ion injection method to form a low-acoustic-resistance layer containing chloride ions;

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 piezoelectric composite film.

In a fourth aspect, the present invention provides another method for preparing a piezoelectric composite film, including:

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

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

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;

and injecting chloride ions into the low-acoustic-resistance layer through the piezoelectric layer by an ion injection method to obtain the piezoelectric composite film.

According to the technical scheme, the invention discloses a piezoelectric composite film and a preparation method thereof, and the piezoelectric composite film specifically comprises a substrate layer, a low-acoustic-resistance layer and a piezoelectric layer which are sequentially stacked, wherein the low-acoustic-resistance layer contains a certain content of chloride ions, and the chloride ions are uniformly distributed in the low-acoustic-resistance layer or in a local area in the low-acoustic-resistance layer. In the technical scheme of the invention, the chloride ions are added, so that the movable alkali metal ions in the low-acoustic-resistance layer can be effectively captured to form neutral chloride, the influence of the alkali metal ions in the low-acoustic-resistance layer on an electromagnetic field excited by the surface acoustic wave filter is avoided, and the stability of the surface acoustic wave filter is ensured.

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 schematic structural diagram of another piezoelectric composite film provided in an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a piezoelectric composite film incorporating a trapping layer according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of another piezoelectric composite film with a trapping layer added 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 low acoustic resistance layer 200 of the present piezoelectric composite film, for example, SiO₂Layer, usually in the presence of some mobile positively charged alkali metal ions, e.g. Na⁺，Li⁺Etc. of Na⁺Mainly comes from Na in air and in the expired air of operators in the production process of the piezoelectric composite film⁺The content is also higher; li⁺Mainly from LT materials, in the manufacturing process of the piezoelectric composite film, the bonding process and the ion implantation process both need to carry out high-temperature annealing on the film, and Li in the piezoelectric layer can be enhanced or accelerated at the moment⁺To SiO₂Diffusion of the layer. In addition, since these alkali metal ions are in SiO₂The diffusion coefficient in the layer is larger, and especially the movement phenomenon is more obvious at higher temperature or under the action of an electric field. The surface acoustic wave filter generates energy loss during operation to cause temperature rise, thereby facilitating the movement of alkali metal ions. Meanwhile, lithium tantalate used as the piezoelectric layer is also a pyroelectric material, and the change of the environmental temperature of the piezoelectric composite film causes the two surfaces of the piezoelectric composite film to generate electric charges, thereby promoting the SiO₂Movement of alkali metal ions in the layer. These mobile alkali metal ions interact with the rf electromagnetic field excited by the saw filter to produce losses.

In addition, the stability of the surface acoustic wave filter is related to the loss of its radio frequency electromagnetic field, and if the loss is stable, the stability of the surface acoustic wave filter is good, but the alkali metal ions can move freely under the condition of temperature rise and are in SiO₂The different positions of the layers are gathered, so that the radio frequency electromagnetic field excited by the surface acoustic wave filter is subjected to different losses, and if the losses are small and large, the stability of the surface acoustic wave filter is poor.

The embodiment of the invention provides a piezoelectric composite film, on the basis of the existing piezoelectric composite film, a chlorine doping process is used, a certain amount of chloride ions are added into a low-acoustic-resistance layer 200, and the chloride ions are negatively charged, so that alkali metal ions with positive charges in the low-acoustic-resistance layer 200 can be effectively captured, and the adverse effect of the alkali metal ions on a surface acoustic wave filter is avoided.

Fig. 2 is a schematic structural diagram of a piezoelectric composite thin film according to an embodiment of the present invention. As shown in fig. 2, the piezoelectric composite film comprises a substrate layer 300, a low acoustic resistance layer 200 and a piezoelectric layer 100 which are sequentially stacked, wherein chloride ions Cl are doped in the low acoustic resistance layer 200^-Said chloride ion Cl^-Uniformly distributed in the low-acoustic-resistance layer 200 or located at a local position in the low-acoustic-resistance layer 200.

In the embodiment of the present invention, a chlorine doping oxidation method, a chlorine doping deposition method, a chlorine ion implantation method, etc. may be used to fabricate the low acoustic resistance layer 200 containing chlorine ions. If chlorine doping method or chlorine doping deposition method is adopted, the source of the chloride ions can be chlorine-containing gas or liquid such as hydrogen chloride, dichloroethylene, trichloroethylene and the like, and if the chloride ion injection method is adopted, the source of the chloride ions is mainly chlorine gas or hydrogen chloride. Chloride ion Cl added to the low acoustic resistance layer 200^-The position and the content of (C) can be determined by a method of doping chlorine, and in the examples of the present invention, chloride ion Cl is doped^-Is preferably greater than 2x10¹⁸ atoms/cm³。

Fig. 3 is a schematic structural diagram of another piezoelectric composite film according to an embodiment of the present invention. After adding chloride ions to the piezoelectric layer 200, chloride ions Cl are added as shown in fig. 3^-And alkali metal ions Na originally in the piezoelectric layer 200⁺、Li⁺And the like to generate neutral NaCl, LiCl and the like.

In the embodiment of the present invention, the material of the piezoelectric layer 100 may be single-crystal lithium tantalate or single-crystal lithium niobate, and after factors in process possibility, cost and performance are fully considered, the most preferable material of the piezoelectric layer 100 in the embodiment of the present invention is single-crystal lithium tantalate. The thickness of the piezoelectric layer 100 is about 100nm to 2000nm, more preferably 300nm to 1000nm, and specific values such as 600nm and 700nm may 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 1%. Since the low acoustic resistance layer 200 has an opposite acoustic velocity-temperature coefficient of variation to that of the piezoelectric layer 100, lowThe thickness of the acoustic resistance layer 200 needs to be matched with the thickness of the piezoelectric layer 100, and more preferably, the 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 further 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.

In addition, due to the fabrication process, in the low acoustic resistance layer 200 (e.g., SiO)₂Layer) and substrate layer 300 (e.g., a Si layer) may have many defects and charges that cause carrier concentration at the interface between substrate layer 300 and low-acoustic-resistance layer 200, resulting in parasitic conductance and thus additional losses in rf applications. To avoid parasitic conductance formation, embodiments of the present invention may also include a low-acoustic-resistance layer 200 (e.g., SiO)₂Layer) and a substrate layer 300 (e.g., a Si layer) with a trapping layer 400 having a predetermined defect density, the trapping layer 400 having a trapping low-acoustic-resistance layer 200 (e.g., SiO) due to certain defects in the trapping layer 400₂Layer) and substrate layer 300 (e.g., a Si layer) to prevent these carriers from causing carrier aggregation at the interface of substrate layer 300 (e.g., a Si layer), thereby preventing the carriers from attenuating the electromagnetic field applied to the piezoelectric composite thin film.

Fig. 4 is a schematic structural diagram of a piezoelectric composite film with a trapping layer added according to an embodiment of the present invention, in the embodiment of the present invention, a trapping layer 400 may be formed on a substrate layer 300 by a deposition method, and then a low acoustic resistance layer 200 and a piezoelectric layer 100 are sequentially formed on the trapping layer 400, so as to manufacture the piezoelectric composite film shown in fig. 4. However, in this manufacturing method, the thermal oxidation method for forming the low-resistance layer 200 deteriorates the charge trapping capability of the trapping layer 400 formed first. Therefore, in the embodiment of the present invention, ions may also pass through the piezoelectric layer 100 and the low acoustic resistance layer 200 by an ion implantation method, so as to destroy the lattice structure of the surface area of the substrate layer 300, generate defects, and further form a trapping layer 400 on the surface area of the substrate layer 300, and the structure of the piezoelectric composite film formed in this way is shown in fig. 5.

The defect density of the trapping layer 400 formed by the above-described embodiment is greater than 1 × 10¹¹The thickness of the trapping layer 400 is 200 to 3000nm, preferably 300 to 1000 nm. The defect density of the damaged crystal lattice in the trapping layer 400 is smaller than that of the currently commonly used polysilicon, and the thickness of the damaged crystal lattice is also smaller than that of the polysilicon, so that the energy for manufacturing the trapping layer 400 is less than that required for manufacturing the polysilicon. Furthermore, if the low-acoustic-resistance layer 200 is formed by a thermal oxidation method and then the trapping layer 400 is formed by an ion implantation method, the thermal oxidation method does not affect the charge trapping capability of the trapping layer 400, and the trapping layer 400 can trap charges between the low-acoustic-resistance layer 200 and the substrate layer 300 more effectively than a polysilicon layer in the conventional piezoelectric composite thin film.

As can be seen from the above, in the piezoelectric composite thin film provided in the embodiment of the present invention, a certain amount of chloride ions are doped in the low acoustic resistance layer 200, so that the chloride ions can capture alkali metal ions that originally move in the low acoustic resistance layer 200, and since the chloride ions are negatively charged and the alkali metal ions are positively charged, the chloride ions and the alkali metal ions can neutralize each other to form a neutral chloride, thereby avoiding loss of the free alkali metal ions to the radio frequency electromagnetic field excited by the surface acoustic wave filter. In addition, since chlorine ions are hardly diffused in the low acoustic resistance layer 200, the chlorine ions that are hard to move do not affect the performance of the surface acoustic wave filter.

The embodiment of the invention also provides a preparation method of the piezoelectric composite film, which is used for preparing the piezoelectric composite film in the embodiment, and the specific steps comprise:

in step S101, a low acoustic resistance layer 200 containing chlorine ions is formed on the substrate layer 300 by an chlorine doping oxidation method or a chlorine doping deposition method.

In the chlorine doping method and the chlorine doping deposition method, the source of the chloride ions can be chlorine-containing gas or liquid such as hydrogen chloride, dichloroethylene, trichloroethylene and the like. The manufacturing material is SiO₂For example, the chlorine doping method is performed based on a thermal oxidation method, in which O is added to Si₂Or H₂O, etc. oxygen-containing gas or liquid is subjected to high-temperature oxidation reaction to generateSiO₂At the same time, chlorine-containing gas or liquid is mixed in, and chlorine ions are generated when the chlorine-containing gas or liquid is at high temperature, so that the generated SiO₂The chlorine ions are doped in the solution; the chlorine-doped deposition method is carried out on the basis of a chemical vapor deposition method and utilizes O₂When the oxygen-containing gas or steam oxidizes the Si surface, a chlorine-containing gas or liquid is added to generate chlorine ions in the chlorine-containing gas or liquid, thereby growing SiO on the Si₂In which chloride ions are doped.

The chlorine doping method and the chlorine doping deposition method described above can specifically determine whether the positions of the chlorine ions added to the low acoustic resistance layer 200 are uniformly distributed or distributed in a certain local area. The amount of chloride ion added to the low acoustic resistance layer 200 may also be determined, and in embodiments of the present invention, the amount of chloride ion is preferably greater than 2x10¹⁸ atoms/cm³。

If the chlorine-containing gas or liquid is continuously doped at a fixed doping rate during the entire process of the thermal oxidation method or the chemical vapor deposition method, the generated chlorine ions can be uniformly distributed in the low-resistance layer 200; if chlorine-containing gas or liquid is intermittently introduced during the entire process of the thermal oxidation method or the chemical vapor deposition method, a part of the low acoustic resistance layer 200 generated during the period of introducing the chlorine-containing gas or liquid contains chlorine ions. The chlorine ions are uniformly distributed or locally distributed in the low acoustic resistance layer 200, so that the time for capturing the alkali metal ions is influenced to a certain extent, if the chlorine ions are uniformly distributed, when the surface acoustic wave filter works, the alkali metal ions just start to move and can be captured by the chlorine ions, and the capturing time is short; if the surface acoustic wave filter is locally distributed, when the surface acoustic wave filter works, alkali metal ions can be captured only when the surface acoustic wave filter moves to a chlorine ion distribution area, and when the surface acoustic wave filter works for a certain time, the alkali metal ions can be completely captured, so that the capturing time is longer. However, the alkali metal ion capturing ability of the chloride ions is not affected whether the chloride ions are uniformly distributed or locally distributed.

Step S102, 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 put into an annealing furnace to be heated, ions injected into an 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 annealing temperature or the extension of annealing time, the volume is gradually increased, all the bubbles are finally connected into one piece, the bubble layer is finally broken, and the piezoelectric layer 100 is stripped from 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 for those skilled in the art, 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.

And S103, 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 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 invention, the temperature of the high-temperature annealing treatment is about 450-550 ℃.

It can be seen that, when the low acoustic resistance layer 200 is fabricated on the substrate layer 300 by the above method for fabricating a piezoelectric composite thin film, chloride ions are doped into the low acoustic resistance layer 200, and then the piezoelectric layer 100 is fabricated on the low acoustic resistance layer 200. In the piezoelectric composite film finally prepared by the method, alkali metal ions in the low acoustic resistance layer 200 are captured by chloride ions to generate neutral compounds, so that the influence of the alkali metal ions on a radio frequency electromagnetic field of the surface acoustic wave filter is effectively avoided.

The embodiment of the invention also provides another preparation method of the piezoelectric composite film, which is used for preparing the piezoelectric composite film in the embodiment, and the specific steps comprise:

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

In the embodiment of the present invention, it is preferable to form the low acoustic resistance layer 200 by using the thermal oxidation method because the thermal oxidation method has a relatively high oxidation temperature, the low acoustic resistance layer 200 has a high density and few defects, and the low acoustic resistance layer 200 formed by the thermal oxidation method has a thickness uniformity that cannot be achieved by other processes, such as SiO₂The thickness uniformity of the layer can be controlled to within 1%. 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 step S202, chloride ions are implanted into the low acoustic resistance layer 200 by an ion implantation method, thereby forming the low acoustic resistance layer 200 containing chloride ions.

Wherein, the ion implantation method can determine the position of the chloride ion added into the low acoustic resistance layer 200 by controlling the speed of the chloride ion implantation, and the position of the chloride ion implantation is deeper when the implanted ion moves fast; the implanted ions have a slow moving speed, and the implanted chlorine ions have a shallow position. If chloride ions are continuously injected into the low-acoustic-resistance layer 200 at a speed having a certain decreasing rule or an increasing rule, the chloride ions will be uniformly distributed in the low-acoustic-resistance layer 200; if only one implantation rate is used, the chloride ions will be concentrated in a certain local area in the low acoustic resistance layer 200; if the injection speed is used faster or slower, the chlorine ions will be randomly distributed in the low-resistance layer 200. No matter which distribution state of the chloride ions is, the chloride ions do not influence the alkali metal ionsThe capture capacity of the seed only influences the length of the capture time. In addition, the ion implantation method may also determine the content of chloride ions added to the low acoustic resistance layer 200, and in the embodiment of the present invention, the content of chloride ions is preferably more than 2 × 10¹⁸ atoms/cm³。

In step S203, the piezoelectric layer 100 is transferred onto the low acoustic resistance layer 200 by an ion implantation method and a bonding method.

The material of the piezoelectric layer 100 may be LN or LT, and the specific peeling method and the manufacturing method of the low acoustic resistance layer 200 are as described in the above embodiments, and are not described herein again.

Step S204, carrying out 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 the damage of the ion implantation method to the piezoelectric layer 100 to obtain the piezoelectric composite film. In the embodiment of the invention, the temperature of the high-temperature annealing treatment is about 400-550 ℃.

It is worth to be noted that, the chlorine doping oxidation method, the chlorine doping deposition method or the ion implantation method can be used to uniformly distribute or locally distribute the chlorine ions in the low acoustic resistance layer 200, the capture time of the uniformly distributed chlorine ions to the alkali metal ions is short, and further the loss time of the alkali metal ions to the radio frequency electromagnetic field of the surface acoustic wave filter is short, so that the surface acoustic wave filter can keep stable performance from the beginning of operation; the capture time of the locally distributed chloride ions to the alkali metal ions is longer, the loss time of the alkali metal ions to the radio frequency electromagnetic field of the surface acoustic wave filter is shorter and longer, the performance of the surface acoustic wave filter is gradually improved in work, and finally, the stability is achieved. No matter the chloride ions are uniformly distributed or locally distributed, the capacity of capturing alkali metal ions is not influenced, the loss of a radio frequency electromagnetic field finally formed by the surface acoustic wave filter can be reduced, and the stable performance of the surface acoustic wave filter is ensured.

The embodiment of the invention also provides another piezoelectric composite film preparation method, which is used for preparing the piezoelectric composite film in the embodiment, and the specific steps comprise:

in step S301, the low-acoustic-resistance layer 200 is formed on the substrate layer 300 by a thermal oxidation method or a deposition method. The specific formation is described in the above embodiments.

In step S302, the piezoelectric layer 100 is transferred onto the low acoustic resistance layer 200 by an ion implantation method and a bonding method.

The material of the piezoelectric layer 100 may be LN or LT, and the specific peeling method and the manufacturing method of the low acoustic resistance layer 200 are described in the above embodiments.

In step S303, a high temperature annealing process is performed on the entire structure of the piezoelectric layer 100, the low acoustic resistance layer 200, and the substrate layer 300, so as to recover the damage of the piezoelectric layer 100 caused by the ion implantation method.

In step S304, chloride ions are implanted into the low acoustic resistance layer 200 through the piezoelectric layer 100 by an ion implantation method, so that a piezoelectric composite film is obtained. The specific manner of the ion implantation method is described in the above examples.

Compared with the above embodiments, the present embodiment is different in that, in the present embodiment, after the substrate layer 300, the low acoustic resistance layer 200, and the piezoelectric layer 100 are manufactured, chloride ions are implanted into the low acoustic resistance layer 200 through the piezoelectric layer 100 by an ion implantation method, so that the piezoelectric composite film in which the chloride ions are doped in the low acoustic resistance layer 200 is obtained. Since the implantation dose and the implantation depth of the chloride ions are controllable in the ion implantation method, in this embodiment, the manner in which the chloride ions are doped into the low acoustic resistance layer 200 through the piezoelectric layer 100 by the ion implantation method is controllable.

According to the technical scheme, the invention discloses a piezoelectric composite film and a preparation method thereof, and the piezoelectric composite film specifically comprises a substrate layer 300, a low-acoustic-resistance layer 200 and a piezoelectric layer 100 which are sequentially stacked, wherein a certain content of chloride ions are doped in the low-acoustic-resistance layer 200, and the chloride ions are uniformly distributed in the low-acoustic-resistance layer 200 or in a local area in the low-acoustic-resistance layer 200. In the technical scheme of the invention, the chloride ions are added, so that the movable alkali metal ions in the low-acoustic-resistance layer 200 can be effectively captured to form neutral chloride, the alkali metal ions in the low-acoustic-resistance layer 200 are prevented from influencing an electromagnetic field excited by the surface acoustic wave filter, and the stability of the surface acoustic wave filter is ensured.

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.