JP2003115742A - Surface acoustic wave transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a means for preventing corrosion of an IDT (Interdigital Transducer) electrode due to a battery effect, the electrode being constituted by stacking different kinds of metals to improve current resistance. SOLUTION: In a surface acoustic wave transducer which is formed by stacking and bonding different kinds of metallic films on a piezoelectric substrate, a thin film of an insulating material is deposited so as to cover the top surface and both side surfaces of electrode fingers constituting the transducer, thereby forming the transducer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave converter, and more particularly to preventing corrosion of a metal film caused by a so-called battery effect which occurs in a surface acoustic wave converter (IDT electrode) formed by laminating different kinds of metals. The present invention relates to the structure of a surface acoustic wave converter.

[0002]

2. Description of the Related Art In recent years, SAW devices have been widely used in the field of communication and have excellent characteristics such as high performance, small size and mass productivity, and are therefore widely used especially in mobile phones. FIG. 4 (a) shows a first-order used in an RF filter of a mobile phone.
FIG. 3 is a plan view showing the configuration of a third-order longitudinally coupled dual-mode SAW filter (hereinafter referred to as a dual-mode SAW filter), in which the IDT electrode 12 is provided on the main surface of the piezoelectric substrate 11 along the propagation direction of the surface wave. 13 and 14 are placed close to each other,
Grating reflectors (hereinafter referred to as reflectors) 15a and 15b are arranged on both sides of the IDT electrodes 12, 13 and 14, respectively. Each of the IDT electrodes 12, 13, and 14 is formed of a pair of comb-shaped electrodes having a plurality of electrode fingers which are inserted into each other, and one of the comb-shaped electrodes of the central IDT electrode 12 is connected to the input terminal IN by wire bonding or the like. Connect and ground the other comb electrode. Furthermore, the outer ID
The comb electrodes of the T electrodes 13 and 14 are connected to each other by the lead electrodes formed on the piezoelectric substrate 11, and one of the lead electrodes is connected to the output terminal OUT and the other lead electrode is grounded to form a double layer. Configure a mode SAW filter.

FIG. 4B is an enlarged view of a part of the sectional view taken along the line Q-Q in FIG. 4A, showing electrode fingers 12 'of the IDT electrode 12.
It is a figure which shows the cross section of. IDT electrodes 12, 13, 14
As the electrode material of the reflectors 15a and 15b, aluminum (Al) or an aluminum alloy in which a very small amount of a different metal (copper or the like) is added to aluminum is generally used because of its low electric resistance and small mass. Target.

Since a few years ago, mobile phones have become smaller,
In order to reduce the weight, attempts have been made to replace the dielectric filter used in the antenna duplexer with a SAW filter. For this purpose, it is particularly necessary to improve the power resistance of the SAW filter used for transmission in the RF stage, and various power resistance improvements have been proposed. For example, Japanese Patent Laid-Open No. 7-122961 discloses a piezoelectric substrate 1 as shown in FIG.
The electrode fingers 16, 16 formed on 1 have a three-layer film electrode structure of aluminum-copper alloy 17, copper 18, and aluminum-copper alloy 19, and the heat treatment temperature is appropriately selected to reduce the grain size of aluminum, and It is described that by appropriately setting the film thickness of each electrode, the internal stress was controlled and the life for electric power could be extended.

[0005]

However, SAW
In the process of cutting the wafer when manufacturing the device and dividing it into chip pieces, cooling water for the dicing device,
Due to a moisture absorption effect while being in contact with air, moisture adheres to the electrode film in which different metals are laminated. For example, on an electrode film where different metals such as aluminum and copper are laminated,
When water adheres, there is a problem that a potential difference is generated between different kinds of metals due to an ionization tendency and a current flows, so that the laminated electrode film is corroded due to a so-called battery effect. The present invention has been made to solve the above problems, and an object of the present invention is to provide a surface acoustic wave converter that prevents a battery effect.

[0006]

In order to achieve the above object, the invention of claim 1 of the surface acoustic wave converter according to the present invention is a laminated thin film in which a plurality of different metal thin films are laminated on a piezoelectric substrate. A surface acoustic wave converter having a formed electrode pattern, wherein a thin film of an insulating material is attached so as to cover at least the upper surface and side surfaces of the electrode fingers of the electrode pattern. Is. Claim 2
The invention described is a surface acoustic wave converter having an electrode pattern formed by laminating a thin film of aluminum or an aluminum alloy and another metal thin film on a piezoelectric substrate, wherein the thin film of the aluminum or aluminum alloy is A surface acoustic wave converter having a surface covered with an insulating material obtained by anodic oxidation. According to a third aspect of the present invention, there is provided a surface acoustic wave converter having an electrode pattern formed of a laminated thin film in which a plurality of thin films of different kinds of metals are laminated on a piezoelectric substrate, wherein at least an upper surface of an electrode finger of the electrode pattern and The surface acoustic wave converter is characterized in that a metal film having a large electric resistance is attached so as to cover the side surface.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the drawings. FIG. 1 is an enlarged cross-sectional view showing a part of the configuration of the surface acoustic wave converter according to the present invention, in which an aluminum alloy film 2 is formed on a piezoelectric substrate 1 by using a vapor deposition device, a sputtering device or the like. Along with
A copper thin film 3 is laminated on the alloy film 2, and an aluminum alloy film 4 is further laminated on the alloy film 2, which is then etched using a photolithography technique to provide a surface acoustic wave transducer (IDT electrode) having a predetermined electrode pattern. To form. Further, an insulator 5, for example, a thin film of silicon dioxide (SiO ₂ ) is attached to cover the upper and side surfaces of the electrode fingers 6, 6 ... Of the surface acoustic wave converter (IDT electrode) in a vacuum device. Constitutes a surface acoustic wave converter.

The feature of the present invention is that the electrode fingers 6 and 6 of the IDT electrode.
Since the upper and side surfaces of the are covered with an insulating material, even when the wafer is divided into chip pieces by using a dicing saw, moisture only adheres to the insulating layer and spreads across different kinds of metals. There is no such thing. Therefore, the battery effect does not occur and the IDT electrode film does not corrode.

FIG. 2 is a cross-sectional view showing another embodiment according to the present invention. For example, a three-layer film of aluminum-copper alloy, copper, and aluminum-copper alloy is formed on the piezoelectric substrate 1, and a photo film is formed. The steps up to forming a surface acoustic wave transducer (IDT electrode) by etching using a lithography technique are the same as those in FIG. 1, but after forming the surface acoustic wave transducer,
In sulfuric acid solution or ammonium borate solution ((NH4) ₂
By applying an electric field in B ₄ O ₇ · 4H ₂ O) and anodizing the surface of the aluminum-copper alloy thin film to form an insulating film, the battery effect will not occur even if the aqueous solution adheres to the laminated film. In addition, the IDT electrode film does not corrode.

FIG. 3 is a sectional view showing another embodiment according to the present invention, in which aluminum-copper,
A three-layer film of copper and aluminum-copper is formed and etched using a photolithography technique, and then the surface acoustic wave transducer (I
The steps up to forming the DT electrode) are the same as those in FIG. 1, but after forming the surface acoustic wave converter, the metal film 8 having a very high electric resistance is thinned by a vapor deposition method, a sputtering method, or the like.
By adhering to the upper surface and the side surface of the electrode finger, the battery effect does not occur even when the aqueous solution adheres between different kinds of metals, and the IDT electrode film does not corrode. As the metal material, there are materials such as tungsten and nickel.

Further, instead of thinly depositing an insulating material or a metal material having high electric resistance by vapor deposition or sputtering, the same effect can be obtained by thinly plating an IDT electrode having a three-layer film structure in an electrolytic solution. Is obtained. However, if the method described above is applied to the IDT electrode, silicon dioxide (Si
The frequency of the SAW device slightly decreases due to the respective mass loads of O ₂ ), aluminum dioxide, metal thin film, etc. Therefore, it is not necessary to set the electrode pattern dimension of the surface acoustic wave transducer in advance in consideration of the frequency decrease amount. Needless to say.

[0012]

Since the present invention is configured as described above, the invention described in claim 1 has an excellent effect of preventing the corrosion of the IDT electrode. The invention according to claim 2 exhibits an excellent effect of preventing the corrosion of the IDT electrode by using a simple method of anodic oxidation. Claim 3
The invention described in 1) brings about an excellent effect of preventing the corrosion of the IDT electrode only by thinly adhering a metal having an extremely high electric resistance.

[Brief description of drawings]

FIG. 1 is a partially enlarged cross-sectional view showing the structure of a surface acoustic wave converter according to the present invention.

FIG. 2 is a partially enlarged sectional view showing the structure of a surface acoustic wave converter according to a second embodiment of the present invention.

FIG. 3 is a partially enlarged sectional view showing the structure of a surface acoustic wave converter according to a third embodiment of the present invention.

FIG. 4A is a conventional first-third order longitudinally coupled dual mode S.
The top view which shows the structure of an AW filter, (b) has expanded and shown a part of sectional view of an IDT electrode.

FIG. 5 is an enlarged view showing a part of a cross-sectional view of an IDT electrode having a three-layer film structure.

[Explanation of symbols]

1 ... Piezoelectric substrate 2, 3, 4 ... Electrode film forming electrode fingers of IDT electrodes 5 ... Insulating material film 6 ... Electrode fingers 7 ... Aluminum oxide film 8 ... High resistance metal film

Claims (3)

[Claims] 1. A surface acoustic wave converter having an electrode pattern formed of a laminated thin film in which a plurality of different metal thin films are laminated on a piezoelectric substrate, wherein at least an upper surface and a side surface of an electrode finger of the electrode pattern are covered. A surface acoustic wave converter characterized in that a thin film of an insulating material is attached thereto. 2. A surface acoustic wave converter having an electrode pattern formed by laminating a thin film of aluminum or an aluminum alloy and another metal thin film on a piezoelectric substrate, the thin film comprising the thin film of aluminum or aluminum alloy. A surface acoustic wave converter having a surface covered with an insulating material obtained by anodic oxidation. 3. A surface acoustic wave converter having an electrode pattern formed of a laminated thin film in which a plurality of different metal thin films are laminated on a piezoelectric substrate, and at least the upper surface and the side surface of the electrode finger of the electrode pattern are covered. A surface acoustic wave converter characterized in that a metal film having a large electric resistance is attached thereto.