CN114592172A

CN114592172A - Interdigital electrode of surface acoustic wave filter, preparation method thereof and surface acoustic wave filter

Info

Publication number: CN114592172A
Application number: CN202210229923.9A
Authority: CN
Inventors: 翁志坤
Original assignee: Guangdong Guangnaixin Technology Co ltd
Current assignee: Guangdong Guangnaixin Technology Co ltd
Priority date: 2022-03-10
Filing date: 2022-03-10
Publication date: 2022-06-07

Abstract

The preparation method of the interdigital electrode of the surface acoustic wave filter comprises the following steps: forming an alloy electrode layer made of an alloy including at least aluminum (Al) and copper (Cu) on a substrate, wherein the aluminum is deposited on the substrate at a predetermined first deposition rate by a first evaporation system, and the copper is deposited on the substrate at a predetermined second deposition rate by a second evaporation system; and forming the alloy electrode layer with a prescribed thickness into a pattern shape of the interdigital electrode.

Description

Interdigital electrode of surface acoustic wave filter, preparation method thereof and surface acoustic wave filter

Technical Field

The invention relates to a preparation method of an interdigital electrode of a surface acoustic wave filter, the interdigital electrode prepared by the preparation method and the surface acoustic wave filter with the interdigital electrode, in particular to a technology for improving the power tolerance of the surface acoustic wave filter.

Background

With the rapid development of information technology, especially in the field of wireless communication, it is increasingly important to widely apply to the radio frequency front end of various communication devices, data transmission devices, audio-visual devices, positioning navigation devices, and the like. The radio frequency front end is a functional area between a radio frequency transceiver and an antenna and consists of devices such as a power amplifier, an antenna switch, a filter, a duplexer, a low noise amplifier and the like. In order to adapt to the rapid development of the communication field, higher requirements are put forward on various performances of the radio frequency front end.

A Surface Acoustic Wave (SAW) filter is used as a key device of a radio frequency front end, works based on the piezoelectric effect of a piezoelectric material and through the SAW, converts an input electric signal into an acoustic wave signal or converts the acoustic wave signal into the electric signal by using an interdigital transducer (IDT) formed on the surface of the piezoelectric material so as to extract and process the signal, and has the advantages of small size, low cost, light weight, good consistency and semiconductor process compatibility, and is suitable for mass production. With the current further development of electronic systems in the directions of miniaturization, high reliability, strong anti-interference capability, and the like, SAW filters are more and more favored.

In the SAW filter, the interdigital transducer usually uses a material with excellent conductivity and small acoustic impedance to convert an acoustic wave signal and an electric signal, and at present, materials such as aluminum (Al), copper (Cu), or aluminum-copper (Al — Cu) alloy are often used. Existing interdigital transducers (also referred to as interdigital electrodes) are typically found in LiTaO₃Or LiNiO₃After a thin Ti or Cr film is evaporated on the surface of the wafer, a pure Al or Al-Cu alloy film is coated on the thin Ti or Cr film. The strong texture Al film is obtained by strictly controlling the growth of the Al film, or the AlCu alloy film with high Cu content is prepared.

However, for the interdigital electrode of the SAW filter applied to high frequency, under the action of the alternating repetitive stress of the high frequency sound wave, Al atoms are easy to migrate along the grain boundary, and the thin film bulges or locally forms holes, which causes the short circuit failure of the electrode, so that a film layer with higher power tolerance than that of the traditional electrode is required.

Patent document 1 describes an interdigital electrode having a multilayer structure with improved power tolerance, which is a 42 ° oriented LiTaO₃After a Ti electrode is plated on the substrate, an Al-Mg alloy electrode is plated on the Ti electrode, so that the obtained multilayer film has low resistivity and excellent power tolerance. However, Al-Mg alloy has high activity, is easy to oxidize, is difficult to control the coating process, and is not suitable for large-scale mass production.

Moreover, in the interdigital electrode having a multilayer structure disclosed in patent document 1, the content of Mg element doped in the Al — Mg alloy is limited, and when the content of Mg element exceeds a certain degree, there is a significant difference in alloy content between product batches due to segregation effect between different metals of Al and Mg, which presents a certain challenge in controlling the consistency of products. Therefore, in order to obtain the interdigital electrode with excellent performance and better product consistency, the stability of alloy components needs to be strictly controlled.

Documents of the prior art

Patent document 1: CN106603035A

Disclosure of Invention

In view of the above problems, the present invention is directed to ensuring uniformity of a metal thin film of an IDT electrode, improving mechanical strength and high power durability of an alloy, and reducing resistivity of the thin film. In this regard, the present inventors have used a dual-evaporation-source evaporation coating apparatus to evaporate pure Al by electron beam heating, and to evaporate pure Cu by induction heating. The composition ratio of the alloy elements is controlled by controlling the respective coating rates of the two evaporation sources. In the Al — Cu alloy, in order to increase the mechanical strength of the thin film, the resistivity of the thin film also increases, that is, the mechanical strength and the resistivity of the thin film are in an opposite relationship. In general, the higher the Cu content, the higher the second phase Al₂The denser the Cu distribution, the higher the mechanical strength of the alloy, the higher the resistivity, and the larger the electrode loss, that is, the conventional Al-Cu alloy with high Cu content cannot satisfy both the conditions of high mechanical strength and low resistivity.

Therefore, an object of the present invention is to provide a method for manufacturing an interdigital electrode for a surface acoustic wave filter having high power durability, low loss factor, and high stability, an interdigital electrode manufactured by the manufacturing method, and a surface acoustic wave filter having the interdigital electrode.

The preparation method of the interdigital electrode of the surface acoustic wave filter comprises the following steps: forming an alloy electrode layer made of an alloy including at least aluminum (Al) and copper (Cu) on a substrate, wherein aluminum is deposited on the substrate at a predetermined first deposition rate by a first evaporation system, and copper is deposited on the substrate at a predetermined second deposition rate by a second evaporation system; and forming the alloy electrode layer with a prescribed thickness into a pattern shape of an interdigital electrode.

In the preparation method of the interdigital electrode of the surface acoustic wave filter, the first evaporation system is an electron beam evaporation system, and the second evaporation system is a high-temperature evaporation system.

In the method for preparing the interdigital electrode of the surface acoustic wave filter, the high-temperature evaporation system evaporates copper by using induction heating.

In the method for manufacturing the interdigital electrode of the surface acoustic wave filter, the evaporation distances, which are the distances from the evaporation source of the first evaporation system and the evaporation source of the second evaporation system to the evaporation position on the substrate, are equal.

In the method for preparing the interdigital electrode of the surface acoustic wave filter, the first evaporation rate is

The second evaporation rate is

In the preparation method of the interdigital electrode of the surface acoustic wave filter, the first evaporation rate and the second evaporation rate are determined in the respective evaporation systems before the first evaporation system and the second evaporation system are subjected to simultaneous evaporation.

In the preparation method of the interdigital electrode of the surface acoustic wave filter, the mass fraction of copper in the alloy electrode layer is 2-8%.

In the preparation method of the interdigital electrode of the surface acoustic wave filter, the substrate is LiNiO₃Or LiTaO₃A substrate.

The preparation method of the interdigital electrode of the surface acoustic wave filter further comprises the step of carrying out heat treatment on the formed alloy electrode layer.

In the method for preparing interdigital electrode of surface acoustic wave filter, N is thermally treated in vacuum environment₂Is carried out in an atmosphere.

In the method for manufacturing the interdigital electrode of the surface acoustic wave filter of the present invention, the heat treatment comprises:

heating the alloy electrode layer to a first heating temperature and then preserving heat for a first time; further heating to a second heating temperature and then preserving heat for a second time period; and cooling to room temperature.

The method for preparing the interdigital electrode of the surface acoustic wave filter further comprises the step of forming a transition layer on the substrate before forming the alloy electrode layer.

In the method for manufacturing the interdigital electrode of the surface acoustic wave filter, the transition layer is made of any one of Cr, Ni and Ti.

The preparation method of the interdigital electrode of the surface acoustic wave filter further comprises the step of forming a copper metal layer on the alloy electrode layer.

The preparation method of the interdigital electrode of the surface acoustic wave filter further comprises the step of further forming a protective layer on the copper metal layer.

In the method for manufacturing the interdigital electrode of the surface acoustic wave filter, the protective layer is made of any one of Cr, Ni and Ti.

The interdigital electrode of the surface acoustic wave filter of the present invention comprises: an alloy electrode layer formed on the piezoelectric substrate and prepared by the above preparation method, the alloy electrode layer being composed of an alloy including at least aluminum (Al) and copper (Cu), and the alloy electrode layer having a prescribed thickness and being formed in a pattern shape of the interdigital electrode.

The interdigital electrode of the surface acoustic wave filter of the present invention further comprises: a transition layer formed between the piezoelectric substrate and the alloy electrode layer; a copper metal layer formed on the alloy electrode layer; and a protective layer formed on the copper metal layer.

The surface acoustic wave filter of the present invention includes: a piezoelectric substrate; and the interdigital electrode described above.

According to the preparation method of the interdigital electrode of the surface acoustic wave filter, the interdigital electrode prepared by the preparation method and the surface acoustic wave filter with the interdigital electrode, the power tolerance of the interdigital electrode and the surface acoustic wave filter with the interdigital electrode and other devices can be improved, the loss of the interdigital electrode can be reduced, the stability of components in the interdigital electrode is ensured, the migration of Al atoms along a crystal boundary caused by the repetitive stress of the surface acoustic wave under high power is prevented, and the failure of the surface acoustic wave filter caused by high temperature caused by high power can be prevented.

Drawings

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which specific embodiments of the invention are shown. The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to embodiments of the present application. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to refer to like parts throughout the drawings. The drawings are only schematic and are not to be construed as limiting the actual dimensional proportions.

Fig. 1 is a schematic view of a film layer structure of an interdigital electrode of a surface acoustic wave filter according to an embodiment of the present invention.

FIG. 2 is a schematic view of an Al-Cu alloy plating system according to an embodiment of the present invention.

Fig. 3 is a flowchart of a method for manufacturing an interdigital electrode according to an embodiment of the present invention.

Fig. 4 is a graph showing a heat treatment process of the IDT electrode according to the embodiment of the present invention.

Fig. 5 is a microstructure diagram of the IDT electrode of the present embodiment after heat treatment.

Detailed Description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which specific embodiments of the invention are shown. Various advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the specific embodiments. It should be understood, however, that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. The following embodiments are provided so that the invention may be more fully understood. Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meaning as understood by those of skill in the art to which this application belongs.

Fig. 1 is a schematic diagram showing a film layer structure of an interdigital electrode (hereinafter also referred to as an IDT electrode) of a surface acoustic wave filter according to an embodiment of the present invention. As shown in fig. 1, the film structure of the IDT electrode of this example is composed of four layers C2 to C5.

In the figure, C1 is used as the bottom layer of the IDT electrode, and a LiNiO3 or LiTaO3 piezoelectric substrate is used in the present embodiment.

The C2 is used as a primer layer (also referred to as an intermediate layer, a buffer layer, or a transition layer) and is formed of a thin film of any one metal selected from Cr, Ni, and Ti, and has a thickness in the range of 2 to 10nm, for the purpose of enhancing the adhesion between the thin film C3 described later and the substrate C1.

C3A thin Al-Cu alloy film was used as an alloy film of the IDT electrode, wherein the mass fraction of Cu was in the range of 2% to 8%. The Al-Cu alloy has high electrical conductivity and small acoustic impedance, and is a preferred material for realizing the conversion between an acoustic wave signal and an electric signal.

C4 is a Cu metal film with a thickness in the range of 5-20 nm. An alloy layer is formed between the interface of the two films of the Cu metal film C4 and the Al-Cu alloy film C3 below the Cu metal film through the atomic diffusion effect, Cu atoms distributed between grain boundaries of the alloy layer can effectively prevent Al atoms in the Al-Cu alloy film C3 from moving upwards, electrode short circuit failure caused by the fact that a thin film in the IDT electrode protrudes or a hole is formed locally is avoided, and moreover, due to the fact that the heat conductivity of Cu is good, temperature rise of the IDT electrode caused by resistance heat can be reduced, and therefore atom migration can also be reduced. That is, the Cu metal film C4 can improve the high power withstand performance of the IDT electrode.

C5 is a protective layer, and is a thin film of any one metal selected from Cr, Ni and Ti, and has a thickness in the range of 2-10 nm. The purpose is to protect the Cu metal film C4 from oxidation or corrosion.

The basic structure of the IDT electrode shown in the embodiment of the present invention is configured by the four thin-film structure of the primer layer C2, the Al — Cu alloy film C3, the Cu metal film C4, and the protective layer C5, but the number of the thin-film structure may be five or more, or three, and the primer layer C2 and the protective layer C5 may be appropriately provided as needed.

Other piezoelectric substrates such as silicon (Si), silicon carbide (SiC), zinc oxide (ZnO), Langasite (LGS), etc. may be selected for the bottom layer C1.

In the present invention, in order to ensure product uniformity of IDT electrodes, to improve the component stability of the Al-Cu alloy film C3, and to improve the high power durability of the surface acoustic wave filter, the co-evaporation system shown in fig. 2 was used to prepare an Al-Cu alloy film C3.

FIG. 2 is a schematic view of an Al-Cu alloy plating system according to an embodiment of the present invention. As shown in FIG. 2, the Al-Cu alloy coating system of the present invention comprises a wafer 1, an umbrella stand 2, a high temperature evaporation system 3 and an electron beam evaporation system. Among them, a Si wafer, a SiC wafer, the LiNiO3 described above, a LiTaO3 piezoelectric substrate, or the like can be used as the wafer 1. The umbrella stand 2 adopts a cambered surface structure, and is provided with a plurality of bearing holes for bearing the wafer 1. The umbrella stand 2 can rotate around the central axis thereof to ensure the uniformity of the coated layer.

The Al-Cu alloy coating system adopts a co-evaporation coating mode, namely, two independent evaporation systems, namely a high-temperature evaporation system 3 and an electron beam evaporation system 4, are utilized to carry out evaporation respectively. Specifically, a high-temperature evaporation system 3 is used for evaporating Cu metal, an electron beam evaporation system 4 is used for evaporating Al metal, and an Al-Cu alloy film is obtained by evaporation on the wafer 1 by controlling the technological parameters of the two evaporation systems.

The high-temperature evaporation system 3 generates Cu atoms by heating a Cu ingot of an evaporation source placed in a crucible, and evaporates the Cu ingot at a high temperature to deposit the Cu atoms on the wafer 1. The heating method may be resistance (for example, tungsten wire) heating, induction heating, or the like.

The electron beam evaporation system 4 heats an Al ingot as an evaporation source by impinging a high-energy electron beam (for example, several thousand eV) thereto, thereby evaporating and generating Al atoms and depositing them on the wafer 1. The high-energy electron beam may be a thermal electron generated by a high-temperature metal or an electron generated by a cathode discharge.

As shown in fig. 2, in order to ensure uniformity and consistency of the Al — Cu alloy film C3, the distance from the evaporation source Cu ingot of the high-temperature evaporation system 3 to the wafer 1 and the distance from the evaporation source Al ingot of the electron beam evaporation system 4 to the wafer 1, that is, the evaporation distance, were set to be the same.

Before vapor deposition, the vapor deposition rates of the two evaporation systems are set. For example, the high temperature evaporation system 3 can be independently started, the evaporation source Cu ingot thereof is heated to raise the temperature thereof, and the evaporation rate of Cu atoms reaches a preset value by adjusting parameters. And then independently starting the electron beam evaporation system 4, impacting an electron beam on an Al ingot of the evaporation source to heat the Al ingot, and adjusting parameters to enable the evaporation rate of Al atoms to reach a preset value.

After the evaporation is started, the timing of opening the shutter in front of the evaporation source Cu ingot in the high-temperature evaporation system 3 and the timing of opening the shutter in front of the electron gun emitting the electron beam in the electron beam evaporation system 4 are controlled, thereby ensuring that the high-temperature evaporation system 3 and the electron beam evaporation system 4 can simultaneously form a film on the wafer 1 to form a uniform and stable Al — Cu alloy film C3.

According to the co-evaporation system of the embodiment, the Cu metal and the Al metal are evaporated by the independent high-temperature evaporation system 3 and the independent electron beam evaporation system 4, and parameters of the high-temperature evaporation system 3 and the electron beam evaporation system 4 are controlled to make respective evaporation rates reach preset values, so as to realize the Al-Cu alloy film with the Cu content (mass fraction) of 2% to 8%, so that the Al-Cu alloy film can be stable in composition and uniform in film formation, and further the high power tolerance of the surface acoustic wave filter having the interdigital electrode formed by the Al-Cu alloy film is improved.

Next, a specific flow of a method for manufacturing an interdigital electrode according to an embodiment of the present invention will be described. Fig. 3 is a flow chart of a method for manufacturing an interdigital electrode according to an embodiment of the present invention.

First, in the stepIn S101, cleaning is performed before the substrate is coated. Specifically, a piezoelectric substrate, such as a LiNiO3 or LiTaO3 piezoelectric substrate in fig. 1, is selected as the substrate, the substrate is sequentially soaked and cleaned with a mixed solution of acetone, sulfuric acid and hydrogen peroxide, and after cleaning, the substrate is placed in N₂Drying in an atmosphere or an inert gas atmosphere, and then mechanically polishing the substrate to ensure the cleanliness and the flatness of the surface of the substrate and improve the quality of subsequent film formation.

In step S102, the high-temperature evaporation system is started. In this step, the high temperature evaporation system 3 in fig. 1 is independently started, so that the speed of Cu atoms generated by heating and evaporating the evaporation source Cu ingot, i.e. the evaporation speed, reaches a preset condition, and the evaporation rate of Cu in this embodiment is controlled to be 0.1 to 0.2A/S. The Cu atom beam in step S102 is not deposited on the wafer 1. In this embodiment, when the high temperature evaporation system 3 is started, the temperature of the evaporation source Cu ingot is raised, and the temperature is kept for 1h after the temperature reaches 1150-1200 ℃, and the vacuum degree in the chamber during the temperature raising process is controlled at 1 × 10-⁴Pa～2×10-⁴Pa. Thereafter, a standby shutter (not shown in fig. 1, for example, a shutter provided in the emission direction of Cu atomic beams, which are evaporation source Cu ingots) is opened to deposit Cu atomic beams on the wafer 1. Step 102 may be performed separately in the high temperature evaporation system 3 before the co-evaporation system of the present invention shown in fig. 2 is assembled, or may be performed by controlling the opening and closing of the shutter after the assembly is completed.

In step S103, the electron beam evaporation system is started. In this step, the electron beam evaporation system 4 in fig. 1 is separately started, so that the speed of Al atoms generated by the impact heating of the evaporation source Al ingot by the high-energy electron beam, i.e. the evaporation speed, reaches the preset condition, and the evaporation rate of Al in this embodiment is controlled to be 5 to 10A/s. The Al atom beam in step S103 is not deposited on the wafer 1. In this embodiment, when the electron beam evaporation system 4 is started, the evaporation source Al ingot is heated up, and the temperature is kept for 1h after the temperature reaches 1150-1200 ℃, and the vacuum degree in the chamber during the heating up process is controlled at 1 × 10-⁴Pa～2×10-⁴Pa. Then, a standby shutter (not shown in FIG. 1, for example, may be provided at the outlet of an electron gun for emitting a high-energy electron beamThe shutter of the nozzle) is opened to evaporate the Al atomic beam onto the wafer 1. Step 103 may be performed separately in the electron beam evaporation system 3 before the co-evaporation system shown in fig. 2 of the present invention is assembled, or may be performed by controlling the opening and closing of the shutters after the assembly is completed.

In step S104, the respective shutters of the high-temperature evaporation system 3 and the electron beam evaporation system 4 are opened to start co-evaporation of the film. At this time, the vacuum degree in the coating chamber of the co-evaporation system is controlled at 1 × 10-⁴Pa～2×10-⁴Pa, and controlling the temperature of the respective Cu ingot and Al ingot of the evaporation source to 1150-1200 ℃. By controlling the opening time of the baffle in front of the electron gun of the electron beam evaporation system 4 and the baffle in front of the evaporation source of the high-temperature evaporation system 3, the simultaneous film formation of the electron beam evaporation system 4 and the high-temperature evaporation system 3 on the wafer 1 is ensured. In this embodiment, the deposition rate of Cu is controlled to 0.1 to 0.2A/S, and the deposition rate of Al is controlled to 5 to 10A/S, whereby an Al-Cu alloy film having a Cu content (mass fraction) of 2 to 8% is obtained. In the present embodiment, the thickness of the Al — Cu alloy film is in the range of 100 to 150nm, and the thickness can be appropriately changed according to the operating frequency of the surface acoustic wave filter in which the IDT electrode made of the Al — Cu alloy film is located.

In step S105, the evaporated sample is taken out of the coating chamber and peeled in a stripper, thereby completing the coating of the IDT electrode.

Then, in step S106, the electrode obtained in step S105 is patterned, and an interdigital pattern is formed by, for example, etching or the like.

As shown in fig. 1, the IDT electrode according to the present embodiment has a multilayer structure, and therefore, in step S107, SiO may be formed on the electrode on which the interdigital pattern is formed as needed₂And the protective layer, the Cu metal film C4 shown in fig. 2 may also be formed before the protective layer is formed. The film formation method described here can be any of various film formation methods such as PVD (physical vapor deposition), CVD (chemical vapor deposition), MBE (molecular beam epitaxy), and the like.

Next, in step S108, the IDT electrode having a multilayer film structure is subjected to heat treatment. For example, willThe electrode is placed in a vacuum atmosphere protective furnace for protective heat treatment, and the atmosphere of the heat treatment can be N under a vacuum environment₂The atmosphere may be other inert atmosphere such as inert gas Ar atmosphere.

The heat treatment process of this example is shown in fig. 4. Fig. 4 is a graph showing a heat treatment process of the IDT electrode according to the embodiment of the present invention. As shown, the heat treatment of the present invention is carried out in three stages. Firstly, heating the IDT electrode from normal temperature to 100-150 ℃, then preserving heat for 0.5-1 h, then continuously heating to 200-250 ℃, preserving heat for 1-2 h, finally directly cooling to room temperature, and finishing heat treatment. In the heat treatment process shown in FIG. 3, the sample chambers of the IDT electrodes are all in a vacuum environment N₂Atmosphere, and the vacuum degree of the sample chamber reaches 2X 10^-3Pa～4×10^-3After Pa, start to feed N₂Gas, and N₂The flow rate of the gas is controlled to be 5-20L/min.

Returning to fig. 2, after the heat treatment of step S108, the resistivity of the IDT electrode may be measured by four probes, and the microstructure of the prepared IDT electrode may be photographed by an SEM (scanning electron microscope) and also the withstand power of the IDT electrode may be tested in step S109. By performing various tests on the IDT electrode, packaging is performed in a condition that the product requirements are met.

The resistivity of the Al-Cu alloy thin film obtained by the preparation method shown in fig. 2 and the heat treatment method shown in fig. 5 of this example was reduced by 30% to 40% compared to the resistivity of the Al-Cu alloy thin film not subjected to the above heat treatment, and the overall resistivity of the IDT electrode thus obtained was also reduced by 20% to 30%. This is because the proper heat treatment process can dissolve Cu atoms in the Al-Cu alloy thin film into the Al matrix to reduce the second phase Al₂The precipitation of Cu lowers the film resistivity. And the solid-solution Cu atoms can improve the mechanical property of the film through a solid-solution strengthening effect. That is, the heat treatment can significantly improve the resistivity.

Further, as described above, the mechanical strength and the resistivity of the Al — Cu alloy thin film are in an opposite relationship. In general, the higher the Cu content, the higher the second phase Al₂The denser the Cu distribution, the stronger the mechanical strength of the alloyThe higher the resistivity is, the higher the loss of the electrode is, and the conventional Al-Cu alloy with high Cu content cannot satisfy both the conditions of high mechanical strength and low resistivity. However, by adopting the manufacturing method described in the above embodiment of the present invention, not only a reduction in resistivity but also an improvement in mechanical strength can be achieved.

Fig. 5 is a microstructure diagram of the IDT electrode of the present embodiment after heat treatment. As can be seen from the figure, no significant second phase Al was found at the grain boundary of the Al-Cu alloy₂Particle distribution of Cu. The power tolerance of the IDT electrode prepared by the method is 33.32dBm at 55 ℃ for more than 5min, and is obviously improved compared with the conventional tolerant power of about 28 dBm.

The preparation method of the interdigital electrode provided by the embodiment of the invention is to utilize evaporation coating equipment with double evaporation sources to evaporate pure Al in an electron beam heating mode and simultaneously evaporate pure Cu in an induction heating mode. The element composition ratio of the alloy film obtained by evaporation is controlled by controlling the coating rate of each evaporation source. The preparation method of the interdigital electrode comprises the steps of preparing the Al-Cu alloy electrode film with stable components by using a coating device of electron beams and high-temperature thermal evaporation of a double-evaporation source, and using an inactive atmosphere such as N in a vacuum environment₂And the atmosphere heat treatment furnace is used for carrying out heat treatment after coating on the electrode prepared by the coating equipment with the double evaporation sources, and finally obtaining the power tolerance film with high strength and low resistivity, thereby improving the power tolerance of the IDT alloy electrode of the surface acoustic wave filter.

The preparation method of the interdigital electrode of the surface acoustic wave filter comprises the following steps: forming an alloy electrode layer made of an alloy including at least aluminum (Al) and copper (Cu) on a substrate, wherein aluminum is deposited on the substrate at a predetermined first deposition rate by a first evaporation system, and copper is deposited on the substrate at a predetermined second deposition rate by a second evaporation system; and forming the alloy electrode layer with a prescribed thickness into a pattern shape of an interdigital electrode. As described above, by simultaneously depositing two metal components constituting the alloy thin film by the co-evaporation system, the elemental composition ratio in the alloy thin film can be controlled in accordance with the respective deposition rates, so that the composition ratio in the alloy thin film is stabilized.

In the preparation method of the interdigital electrode of the surface acoustic wave filter, the first evaporation system is an electron beam evaporation system, and the second evaporation system is a high-temperature evaporation system. That is, the Al-Cu alloy thin film is evaporated by evaporating Al with an electron beam and evaporating Cu by induction heating, and the respective evaporation speeds are easier to control, so that an alloy thin film having stable components can be prepared.

In the method for preparing the interdigital electrode of the surface acoustic wave filter, the high-temperature evaporation system evaporates copper by using induction heating. But may also be evaporated by means of resistive heating.

In the method for manufacturing the interdigital electrode of the surface acoustic wave filter, the evaporation distances, which are the distances from the evaporation source of the first evaporation system and the evaporation source of the second evaporation system to the evaporation position on the substrate, are equal. The reason why the evaporation distances of the two evaporation sources are equal is to match the respective evaporation speeds, so that the film evaporated on the substrate is more uniform and the composition is more stable.

The second evaporation rate is

And the two evaporation rates are determined in their respective evaporation systems before simultaneous evaporation. The thickness of the interdigital electrode can be designed according to the working frequency of the surface acoustic wave device, so that the evaporation rate of two alloy elements is determined, and the alloy film with stable components and simple preparation process is obtained.

In the preparation method of the interdigital electrode of the surface acoustic wave filter, the mass fraction of copper in the alloy electrode layer is 2-8%. The higher the Cu content is, the second phase Al in the Al-Cu alloy film₂The denser the Cu distribution, the higher the mechanical strength of the alloy, but the higher the resistivity, the greater the loss of the electrode. To be mechanically strongThe optimal alloy film is obtained by balancing the degree and the resistivity, and the mass fraction of Cu is controlled within the range of 2-8 percent, so that the alloy film with high mechanical strength and low resistivity is obtained, and further the interdigital electrode and the surface acoustic wave filter with high mechanical strength and low resistivity are obtained.

In the preparation method of the interdigital electrode of the surface acoustic wave filter, the substrate is LiNiO₃Or LiTaO₃A substrate. Other substrates, such as Si substrates, SiC substrates, ZnO substrates, LGS substrates, and the like, may also be used. The substrate may be other than the piezoelectric substrate, and other substrates suitable for forming an Al — Cu alloy thin film may be used. However, since the Al — Cu alloy thin film is to be eventually used together with the piezoelectric substrate to form a surface acoustic wave device, it is preferable to form the Al — Cu alloy thin film on the piezoelectric substrate.

The preparation method of the interdigital electrode of the surface acoustic wave filter further comprises the step of carrying out heat treatment on the formed alloy electrode layer. By heat-treating the prepared electrode, the mechanical strength, power durability and loss of the film can be improved at the same time, and the components of the alloy film can be further stabilized.

The method for preparing the interdigital electrode of the surface acoustic wave filter further comprises the step of forming a transition layer on the substrate before forming the alloy electrode layer. The transition layer can enhance the adhesive force between the Al-Cu alloy film and the substrate and prevent the alloy film from being stripped in the coating process.

The preparation method of the interdigital electrode of the surface acoustic wave filter further comprises the step of forming a copper metal layer on the alloy electrode layer. The Cu metal layer and the interface of the Al-Cu alloy film can form an alloy layer through the atomic diffusion effect, Cu atoms distributed among grain boundaries of the alloy layer can effectively prevent Al atoms in the Al-Cu alloy film from moving upwards, electrode short circuit failure caused by protruding or local forming of cavities of the alloy film is avoided, and temperature rise of the alloy film due to resistance heating can be reduced due to the good thermal conductivity of Cu, so that atom migration can also be reduced. Therefore, the Cu metal layer can improve the high power withstand performance of the Al — Cu alloy thin film and the IDT electrode.

The preparation method of the interdigital electrode of the surface acoustic wave filter further comprises the step of further forming a protective layer on the copper metal layer. So that the IDT electrode thus manufactured can be protected from oxidation or corrosion.

The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present disclosure, and the present disclosure should be construed as being covered by the claims and the specification.

Reference numerals

1 wafer

2 umbrella stand

3 high temperature evaporation system

4 electron beam evaporation system.

Claims

1. A method for preparing an interdigital electrode of a surface acoustic wave filter is characterized by comprising the following steps:

forming an alloy electrode layer made of an alloy including at least aluminum (Al) and copper (Cu) on a substrate, wherein aluminum is deposited on the substrate at a predetermined first deposition rate by a first evaporation system, and copper is deposited on the substrate at a predetermined second deposition rate by a second evaporation system; and

and forming the alloy electrode layer with a specified thickness into the pattern shape of the interdigital electrode.

2. The method according to claim 1, wherein the reaction mixture,

the first evaporation system is an electron beam evaporation system, and the second evaporation system is a high-temperature evaporation system.

3. The method according to claim 2,

the high temperature evaporation system uses induction heating to evaporate the copper.

4. The production method according to any one of claims 1 to 3,

and the evaporation distances, namely the distances from the evaporation source of the first evaporation system to the evaporation position on the substrate, are equal to each other.

5. The production method according to any one of claims 1 to 3,

the first evaporation rate is

The second evaporation rate is

6. The method according to claim 5,

the first evaporation rate and the second evaporation rate are determined in the respective evaporation systems before the simultaneous evaporation is performed in the first evaporation system and the second evaporation system.

7. The production method according to any one of claims 1 to 3,

the mass fraction of copper in the alloy electrode layer is 2% -8%.

8. The production method according to any one of claims 1 to 3,

the substrate is LiNiO₃Or LiTaO₃A substrate.

9. The production method according to any one of claims 1 to 3,

further comprising the step of heat treating the formed alloy electrode layer.

10. The method according to claim 9,

n of the heat treatment in a vacuum environment₂Is carried out in an atmosphere.

11. The method according to claim 10,

the heat treatment comprises:

heating the alloy electrode layer to a first heating temperature, and then carrying out heat preservation for a first time;

further heating to a second heating temperature and then preserving heat for a second time period; and

and (5) cooling to room temperature.

12. The production method according to any one of claims 1 to 3,

the method further comprises the step of forming a transition layer on the substrate before forming the alloy electrode layer.

13. The method according to claim 12,

the transition layer is made of any one of Cr, Ni and Ti.

14. The production method according to any one of claims 1 to 3,

the method also comprises the step of forming a copper metal layer on the alloy electrode layer.

15. The method according to claim 14,

further comprising the step of forming a protective layer on the copper metal layer.

16. The method according to claim 15,

the protective layer is made of any one metal of Cr, Ni and Ti.

17. An interdigital electrode for a surface acoustic wave filter, comprising:

an alloy electrode layer formed on a piezoelectric substrate and produced by the production method according to any one of claims 1 to 16, the alloy electrode layer being composed of an alloy including at least aluminum (Al) and copper (Cu), and the alloy electrode layer having a prescribed thickness and being formed in a pattern shape of the interdigital electrode.

18. The interdigital electrode of claim 17, further comprising:

a transition layer formed between the piezoelectric substrate and the alloy electrode layer;

a copper metal layer formed on the alloy electrode layer; and

a protective layer formed on the copper metal layer.

19. A surface acoustic wave filter, comprising:

a piezoelectric substrate; and

the interdigital electrode of claim 17 or 18.