CN116722834B - A surface acoustic wave device based on periodic domain structure and its preparation method - Google Patents

Abstract

The application discloses a surface acoustic wave device based on a periodic domain structure and a preparation method thereof, comprising the following steps: preparing polarized electrode contours on the positive z-surface of the piezoelectric material crystal and the negative z-surface of the piezoelectric material crystal by using a photoetching method; dividing the positive z-surface of the piezoelectric material crystal and the negative z-surface of the piezoelectric material crystal by using a high-temperature adhesive tape to obtain different polarization areas; plating a first metal electrode on the outline of the polarized electrode; tearing off the high-temperature adhesive tape to obtain a polarized electrode structure; and preparing piezoelectric material crystals with partial domain overturning structures by using the polarized electrode structures, and finally obtaining the surface acoustic wave device based on domain structure excitation. The application firstly polarizes the piezoelectric material crystal of lithium tantalate or the piezoelectric material crystal of lithium niobate, then transfers the piezoelectric material crystal to a substrate through stripping, and plates an electrode on the surface of the piezoelectric material crystal to prepare the surface acoustic wave device.

Description

A surface acoustic wave device based on periodic domain structure and its preparation method

Technical Field

The invention relates to a surface acoustic wave device based on a periodic domain structure and a preparation method thereof, belonging to the technical field of surface acoustic wave device preparation.

Background Art

At present, it is a common method to use the surface coated with interdigital electrodes on piezoelectric thin films to excite surface acoustic waves to prepare acoustic resonators and filters. In addition, the periodic domain structure of piezoelectric thin films can also provide periodically changing piezoelectric coefficients, similar to the effect of the electric field of interdigital electrodes, thereby exciting surface acoustic waves and realizing the preparation of devices such as acoustic resonators and filters.

In conventional technology, multiple thin films are first prepared, and then each thin film is polarized separately to obtain multiple polarized thin films, thereby preparing an acoustic device. Since the polarization cost of piezoelectric thin films is relatively high, the preparation of multiple thin film polarization samples requires repeated preparation of polarization electrodes, and the polarization operation of multiple polarization electrodes is performed separately, which consumes time and manpower, resulting in a high polarization cost of the thin film. This results in a high cost of manufacturing of the existing technology, which is not conducive to mass production.

Summary of the invention

The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a surface acoustic wave device based on a periodic domain structure and a preparation method thereof. The present application first polarizes a piezoelectric material crystal of lithium tantalate or a piezoelectric material crystal of lithium niobate, and then transfers it to a substrate by peeling, and plates an electrode on the surface of the piezoelectric material crystal to prepare a surface acoustic wave device. The flat electrode prepared by the present invention is more conducive to controlling power consumption.

In a first aspect, the present invention provides a method for preparing a surface acoustic wave device based on a periodic domain structure, comprising:

Using photolithography to prepare polarization electrode contours on the positive z-plane of the piezoelectric material crystal and the reverse z-plane of the piezoelectric material crystal;

Using high temperature tape to separate the positive z-plane of the piezoelectric material crystal and the reverse z-plane of the piezoelectric material crystal to obtain different polarization regions;

Plating a first metal electrode on the polarization electrode contour;

The high temperature tape is removed to obtain a polarized electrode structure;

By using the polarized electrode structure, a piezoelectric material crystal with a partial domain inversion structure is prepared.

In combination with the first implementation of the first aspect, a piezoelectric material crystal having a partial domain reversal structure is prepared by using a polarized electrode structure, including:

Apply conductive tape to the electrode-free areas of different polarization regions in the polarization electrode structure;

Seal the piezoelectric material crystal with adhesive and wait for the adhesive to dry;

Connect the conductive tape on the positive z-plane of the piezoelectric material crystal to the positive electrode, and connect the conductive tape on the reverse z-plane of the piezoelectric material crystal to the negative electrode, and then apply an electric field between the positive electrode and the negative electrode to flip the domain between the positive electrode and the negative electrode;

Remove adhesive;

The positive electrode and the negative electrode are removed to obtain a piezoelectric material crystal with a domain inversion structure in some areas.

In a first embodiment combined with the first aspect, after preparing a piezoelectric material crystal having a partial domain reversal structure using a polarized electrode structure, at least one piezoelectric material crystal having a partial domain reversal structure is bonded to a substrate to obtain a film;

The electrode shape profile of the surface acoustic wave device is prepared on the surface of the film by photolithography;

A second metal electrode is plated on the electrode shape contour of the surface acoustic wave device to obtain a surface acoustic wave device based on domain structure excitation.

In combination with the second implementation of the first aspect, a piezoelectric material crystal having a partial domain reversal structure is prepared by using a polarized electrode structure, including:

Apply conductive tape to the electrode-free areas of different polarization regions in the polarization electrode structure;

Seal the piezoelectric material crystal with adhesive and wait for the adhesive to dry;

Connecting a positive electrode to one side of the third metal electrode, grounding the electrode to the other side of the third metal electrode, and then applying an electric field between the positive electrode and the grounding electrode to cause domain flipping between the positive electrode and the grounding electrode;

Remove adhesive;

The third metal electrode is removed to obtain a piezoelectric material crystal with a domain inversion structure in a partial region.

In a second embodiment combined with the first aspect, after preparing a piezoelectric material crystal having a partial domain flip structure by using a polarized electrode structure, the piezoelectric material crystal having a partial domain flip structure is cut to obtain a piezoelectric material crystal of a preset size;

The acoustic resonator profile is prepared on the surface of a piezoelectric material crystal of a preset size by photolithography;

A fourth metal electrode is plated on the contour of the acoustic resonator to obtain a surface acoustic wave device based on domain structure excitation.

In combination with the first aspect, the polarization electrode profile prepared on the positive z-plane of the piezoelectric material crystal and the reverse z-plane of the piezoelectric material crystal by photolithography has a period of 4.2 um.

In a second embodiment combined with the first aspect, the piezoelectric material crystal has a preset size of 1 cm×1 cm.

In the first embodiment or the second embodiment combined with the first aspect, the electric field applied between the positive electrode and the negative electrode is 100V to 400V.

In the first embodiment or the second embodiment combined with the first aspect, the photolithography method is electron beam lithography or ultraviolet lithography or a combination of the two.

In the first embodiment or the second embodiment combined with the first aspect, the piezoelectric material crystal is a z-cut lithium niobate crystal or a z-cut lithium tantalate crystal.

In a first embodiment in combination with the first aspect, the first metal electrode is aluminum, nickel, chromium or titanium.

In a first embodiment in combination with the first aspect, the second metal electrode is aluminum or gold.

In a second embodiment in combination with the first aspect, the third metal electrode is nickel.

In a second embodiment in combination with the first aspect, the fourth metal electrode is aluminum.

In the first embodiment or the second embodiment in combination with the first aspect, the conductive tape is a copper conductive tape.

In a second aspect, a surface acoustic wave device based on a periodic domain structure is manufactured using the manufacturing method of the first aspect.

The beneficial effects achieved by the present invention are:

The present application first polarizes a piezoelectric material crystal of lithium tantalate or lithium niobate, then transfers it to a substrate by peeling, and plates electrodes on the surface of the piezoelectric material crystal to prepare a surface acoustic wave device. Common surface acoustic wave devices such as resonator filters all use interdigitated electrodes on a thin film to excite acoustic waves. Compared with interdigitated electrode circuits, the flat plate electrodes prepared by the present invention are more conducive to controlling power consumption;

On the other hand, conventional polarized crystals are about 0.5 mm, which is relatively thick. Compared with conventional polarized thin film structures, the polarized lithium tantalate piezoelectric material crystals or lithium niobate piezoelectric material crystals in the present application can be bonded to a substrate. Many lithium tantalate piezoelectric material crystals or lithium niobate piezoelectric material crystals can be bonded to one substrate. The thickness of the thin film layer is less than 1 um. There is no need to depolarize the lithium tantalate piezoelectric material crystals or lithium niobate piezoelectric material crystals one by one. The polarized piezoelectric material crystals can be recycled many times and bonded to the substrate again, which greatly reduces the preparation cost caused by polarization. Therefore, it is feasible in industry.

The excitation of the domain structure in the present invention is very important for the preparation of acoustic devices. In addition, polarizing the piezoelectric material crystal first and then bonding it to the substrate also greatly saves the polarization cost, which is suitable for industrial applications.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

FIG1 is a front view of the outline of a polarization electrode in some embodiments of the present application;

FIG2 is a top view of different polarization regions in some embodiments of the present application;

FIG3 is a top view of regions with different polarizations divided in some embodiments of the present application;

FIG4 is a schematic diagram of the front angle of the conductive tape attached to the electrode-free area in some embodiments of the present application;

FIG5 is a theoretical diagram of a domain flipping structure in some embodiments of the present application;

FIG6 is a schematic diagram of a domain flip structure in a partial region in some embodiments of the present application;

FIG7 is a schematic diagram of a piezoelectric material crystal bonded to a substrate in some embodiments of the present application;

FIG8 is a structural diagram of a resonator prepared in some embodiments of the present application;

FIG9 is a theoretical simulation diagram of a surface acoustic wave device prepared in some embodiments of the present application;

FIG. 10 is a graph showing the test results of 800M lithium tantalate resonator in some embodiments of the present application.

Meaning of the reference numerals: 1-polarized electrode outline; 2-piezoelectric material crystal; 3-different polarization regions; 4-high temperature tape; 5-conductive tape; 6-electrode-free region; 7-surface acoustic wave device; 8-GSG radio frequency probe contact.

DETAILED DESCRIPTION

To facilitate the technical solution of the application, some concepts involved in the application are first explained below.

It should be noted that if there are directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention, they are only used to explain the relative position relationship and movement status of the various components under a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

In addition, if the descriptions of "first" and "second" etc. are involved in the present invention, they are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Embodiment 1

At present, most common piezoelectric thin film acoustic devices generate acoustic waves by alternating electric fields generated by interdigitated electrodes. This application proposes a solution for utilizing a periodic domain structure to provide a periodically varying piezoelectric coefficient, excite surface acoustic waves, and prepare acoustic devices such as resonators and filters.

Referring to Figure 1, an example of the present application provides a method for preparing a piezoelectric material thin film superlattice acoustic device, using photolithography to prepare polarization electrode contours on the positive z-plane of a piezoelectric material crystal (a z-cut lithium niobate crystal or a z-cut lithium tantalate crystal) and the reverse z-plane of the piezoelectric material crystal; wherein the photolithography may be electron beam lithography or ultraviolet lithography or a combination of the two; the piezoelectric material crystal may be a z-cut lithium niobate crystal or a z-cut lithium tantalate crystal.

Among them, piezoelectric material crystal refers to a non-centrosymmetric crystal. Under the action of mechanical force, it deforms, causing the charged particles to move relative to each other, resulting in positive and negative bound charges on the surface of the crystal. Such a crystal is called a piezoelectric crystal. The property of generating a potential difference at both ends of the polar axis of a piezoelectric crystal is called piezoelectricity.

As shown in Figures 2 and 3, different polarization regions are divided on the positive z-plane of the z-cut lithium tantalate crystal and the reverse z-plane of the z-cut lithium tantalate crystal by using high-temperature tape; a first metal electrode is plated on the polarization electrode contour of the photolithographic piezoelectric material crystal; the first metal electrode is aluminum, nickel, chromium or titanium.

In this embodiment, high temperature tape refers to adhesive tape used in high temperature working environment. It is mainly used in the electronic industry, and its temperature resistance is usually between 120 degrees and 260 degrees. It is often used for spray painting, baking varnish leather processing, coating masking, fixing in electronic parts manufacturing process, printed circuit boards and high temperature processing masking. High temperature tape includes KAPTON high temperature tape; Teflon high temperature tape; high temperature masking tape; PET green high temperature tape; high temperature double-sided tape, etc.

Tear off the high-temperature tape to obtain a polarized electrode structure; as shown in FIG4 , stick conductive tape on the electrode-free areas of different polarization areas in the polarized electrode structure, and the conductive tape can be a copper conductive tape; use ab glue (adhesive) to seal the piezoelectric material crystal, and wait for the ab glue to air-dry; connect the conductive tape on the positive z-face of the piezoelectric material crystal to the positive electrode, and connect the conductive tape on the reverse z-face of the piezoelectric material crystal to the negative electrode, and then apply an electric field between the positive electrode and the negative electrode to flip the domains between the positive electrode and the negative electrode; wherein the applied electric field is 100V to 400V, which is determined according to the period size and the coercive field.

Remove the ab glue; as shown in FIG6 , use dilute hydrochloric acid to remove the positive electrode and the negative electrode to obtain a piezoelectric material crystal with a domain inversion structure in some regions; the theoretical diagram of the domain inversion structure is shown in FIG5 .

Among them, AB glue is another name for two-liquid mixed hardening glue. One liquid is the glue and the other is the hardener. The two liquids can only be hardened when mixed. It does not need to be hardened by temperature, so it is a kind of room temperature hardening glue. It is sometimes used in model making. It is generally used in industry. AB glue is the name of two-component adhesive. AB glue with acrylic, epoxy, polyurethane and other ingredients are available on the market. When used in factories, in order to distinguish it from the conventional large canned (1 kg/2 kg set) epoxy resin, the toothpaste tube is referred to as AB glue (the eye-catching name on the packaging box).

As shown in FIG7 , at least one piezoelectric material crystal having a partial domain flip structure is bonded to a substrate to obtain a thin film; an electrode shape profile of a device such as an acoustic resonator or a filter is prepared on the surface of the thin film by photolithography, and the photolithography method may be electron beam lithography or ultraviolet lithography or a combination of the two;

A second metal electrode is plated on the electrode shape contour of the surface acoustic wave device; the second metal electrode is aluminum or gold, and a surface acoustic wave device (such as an acoustic resonator or filter) based on domain structure excitation is obtained.

As shown in FIG. 8 , the present invention can set a GSG radio frequency probe contact 8 on the surface acoustic wave device 7 .

This technology first polarizes lithium tantalate crystals or lithium niobate crystals, then transfers them to a substrate by peeling, and plates electrodes on the surface to prepare acoustic devices. General resonator filters and other structures all prepare interdigitated electrodes on a film to excite sound waves. Compared with interdigitated electrode circuits, the flat-plate electrodes prepared by the present invention are more conducive to controlling power consumption;

On the other hand, conventional polarized crystals are about 0.5 mm, which is relatively thick. Compared with conventional polarized thin film structures, the polarized lithium tantalate crystals or lithium niobate crystals in the present application can be bonded to the substrate. Many of them can be bonded, and the thin film layer is less than 1 um. There is no need to depolarize lithium tantalate crystals or lithium niobate crystals piece by piece. The polarized crystals can be used multiple times and bonded to the substrate, which greatly reduces the preparation cost caused by polarization. Therefore, it is feasible in industry.

In this embodiment, the present application provides a surface acoustic wave device based on a periodic domain structure, and an acoustic filter is manufactured using the above-mentioned manufacturing method.

The excitation of the domain structure in the present invention is very important for the preparation of acoustic devices. In addition, polarizing the crystal first and then bonding it to the substrate also greatly saves the polarization cost, which is suitable for industrial applications.

Embodiment 2

This embodiment part provides an acoustic resonator for domain structure excitation at a frequency of 800 MHz, which can verify that domain structure excitation is feasible; this application embodiment provides a method for preparing a lithium tantalate superlattice waveguide, including:

A polarization electrode profile with a period of 4.2 um is prepared on the front side of a z-cut lithium tantalate crystal by using photolithography; a polarization electrode profile with a period of 4.2 um is prepared on the back side of a z-cut lithium tantalate crystal by using photolithography; different polarization regions are separated on the front z-side and the back z-side of the z-cut lithium tantalate crystal by using high-temperature tape; a layer of third metal electrode is plated on the polarization electrode profile; the third metal electrode is nickel.

Tear off the high-temperature tape to obtain a polarized electrode structure; stick conductive tape on the electrode-free areas of different polarization areas in the polarized electrode structure; use ab glue (adhesive) to seal the z-cut lithium tantalate crystal, and wait for the ab glue to air-dry; connect the positive electrode to one side of the third metal electrode, and use the electrode to ground the other side of the third metal electrode, and then apply an electric field to flip the domains between the electrodes; wherein the applied electric field is 100V to 400V, which is determined according to the period size and the coercive field.

Remove the ab glue; use dilute hydrochloric acid to remove the first metal electrode to obtain a z-cut lithium tantalate crystal with a partial regional domain flip structure; cut the z-cut lithium tantalate crystal with a partial regional domain flip structure to obtain a 1cm*1cm piezoelectric material crystal (preset size piezoelectric material); use photolithography to prepare an acoustic resonator outline on the surface of the z-cut 1cm*1cm piezoelectric material crystal (preset size piezoelectric material); plate a fourth metal electrode on the photolithographic acoustic resonator outline, the fourth metal electrode can be aluminum, and obtain a surface acoustic wave device based on domain structure excitation.

In this embodiment, the present application provides an acoustic resonator based on a periodic domain structure, and the acoustic resonator is manufactured using the above-mentioned manufacturing method.

As shown in the theoretical simulation diagram of Figure 9, the surface acoustic wave device prepared in this application can be tested using a vector network analyzer. Using the aforementioned scheme, as shown in the test diagram of Figure 10, an acoustic resonator with a superlattice is prepared on the surface of z-cut lithium tantalate to verify the feasibility of domain structure excitation. The acoustic resonator prepared in this application has two inflection point coordinates (0.755, -0.75037) and (0.815, -2.77788), indicating that the main sound wave frequency excited by the acoustic resonator is 815MHz, which is close to the 824MHz frequency of the theoretical simulation.

The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention invented herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not invented by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

The above specific implementation methods further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above are only specific implementation methods of the present application and are not used to limit the protection scope of the present application. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solutions of the present application should be included in the protection scope of the present application.

Claims (9)

1. A method for manufacturing a surface acoustic wave device based on a periodic domain structure, comprising:

preparing polarized electrode contours on the positive z-surface of the piezoelectric material crystal and the negative z-surface of the piezoelectric material crystal by using a photoetching method;

dividing the positive z-surface of the piezoelectric material crystal and the negative z-surface of the piezoelectric material crystal by using a high-temperature adhesive tape to obtain different polarization areas;

Plating a first metal electrode on the outline of the polarized electrode;

tearing off the high-temperature adhesive tape to obtain a polarized electrode structure;

preparing a piezoelectric material crystal with a partial area domain overturning structure by using a polarized electrode structure;

Wherein, utilize polarized electrode structure, prepare the piezoelectric material crystal with some regional domain flip structures, include:

attaching conductive adhesive tapes to electrodeless areas of different polarized areas in the polarized electrode structure;

Sealing the piezoelectric material crystal by using an adhesive, standing and waiting for the adhesive to air-dry;

The method comprises the steps of connecting a conductive adhesive tape on the positive z-face of a piezoelectric material crystal to an electrode positive electrode, connecting a conductive adhesive tape on the negative z-face of the piezoelectric material crystal to an electrode negative electrode, and then applying an electric field between the electrode positive electrode and the electrode negative electrode to enable domains between the electrode positive electrode and the electrode negative electrode to be turned over;

Removing the adhesive;

and removing the positive electrode and the negative electrode of the electrode to obtain the piezoelectric material crystal with the partial area domain overturning structure.

2. The method for manufacturing a surface acoustic wave device based on a periodic domain structure according to claim 1, wherein,

After preparing a piezoelectric material crystal with a partial area domain inversion structure by utilizing a polarized electrode structure, bonding at least one piezoelectric material crystal with a partial area domain inversion structure to a substrate to obtain a film;

Preparing the electrode shape outline of the surface acoustic wave device on the surface of the film by adopting a photoetching method;

and plating a second metal electrode on the electrode shape outline of the surface acoustic wave device to obtain the surface acoustic wave device based on domain structure excitation.

3. The method for manufacturing a surface acoustic wave device based on a periodic domain structure according to claim 1, wherein,

Using the polarized electrode structure, a piezoelectric material crystal with a partial domain inversion structure is prepared, comprising:

attaching conductive adhesive tapes to electrodeless areas of different polarized areas in the polarized electrode structure;

Sealing the piezoelectric material crystal by using an adhesive, standing and waiting for the adhesive to air-dry;

an electrode positive electrode is connected to one side of the third metal electrode, the other side of the third metal electrode is grounded by adopting an electrode, and then an electric field is applied between the electrode positive electrode and the electrode ground, so that a domain between the electrode positive electrode and the electrode ground is turned over;

Removing the adhesive;

and removing the third metal electrode to obtain the piezoelectric material crystal with the partial area domain overturning structure.

4. The method for manufacturing a surface acoustic wave device based on a periodic domain structure according to claim 3, wherein after the piezoelectric material crystal having a partial area domain inversion structure is manufactured by using a polarized electrode structure, the piezoelectric material crystal having the partial area domain inversion structure is cut to obtain a piezoelectric material crystal of a preset size;

Preparing an acoustic resonator contour on the surface of a piezoelectric material crystal with a preset size by adopting a photoetching method;

and plating a fourth metal electrode on the outline of the acoustic resonator to obtain the surface acoustic wave device based on domain structure excitation.

5. The method of manufacturing a surface acoustic wave device based on a periodic domain structure according to claim 4, wherein the polarized electrode profile manufactured by photolithography on the positive z-plane of the piezoelectric material crystal and the negative z-plane of the piezoelectric material crystal is 4.2um period.

6. A method for manufacturing a surface acoustic wave device based on a periodic domain structure according to claim 1 or 3, wherein the electric field applied between the positive electrode and the negative electrode is 100V to 400V.

7. The method for manufacturing a surface acoustic wave device based on a periodic domain structure according to claim 2 or 4, wherein the photolithography is electron beam lithography or ultraviolet lithography or a combination of both.

8. The method for manufacturing a surface acoustic wave device based on a periodic domain structure according to claim 1, wherein the piezoelectric material crystal is a z-cut lithium niobate crystal or a z-cut lithium tantalate crystal.

9. A surface acoustic wave device based on a periodic domain structure, characterized in that the surface acoustic wave device is manufactured by the manufacturing method according to any one of claims 1 to 8.