JPH09321564A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost by applying dealkali processing to a glass substrate of the surface acoustic wave and to reduce the propagation loss of the surface acoustic wave with respect to the glass substrate. SOLUTION: The surface acoustic wave element 6 has a base consisting of a glass substrate 1 whose surface is subject to dealkali processing, a piezoelectric film 2 formed on the surface of the glass substrate 1, and interdigital electrodes 3a, 3b in contact with the piezoelectric film 2. Furthermore, opposed electrodes 4a, 4b are provided to the piezoelectric film 2 in opposition to (via the piezoelectric film 2) the interdigital electrodes 3a, 3b. The dealkali processing is conducted by immersing the glass substrate 1 into a dilute oxidation water solution at a temperature between the room temperature and 100 deg.C. As a result alkaline metals such as lithium and potassium and alkaline earth metals such as beryllium and magnesium are removed from the glass substrate 1. The propagation loss coefficient for the surface acoustic wave of the glass substrate 1 is reduced through the conduction of the dealkali processing as above.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a surface acoustic wave device using a dealkalized glass substrate.

[0002]

2. Description of the Related Art A surface acoustic wave device that allows signals to be easily input and output on a surface acoustic wave propagation path is used for an intermediate frequency filter, an oscillator, a resonator, and the like of a television, and is disclosed in JP-A-5-90860. In addition to the piezoelectric body that excites surface acoustic waves and the comb-shaped electrode on the piezoelectric body that applies an electric signal, an insulating layer on the substrate that accelerates the propagation velocity of surface acoustic waves, for example, a diamond layer. As disclosed in JP-B-61-35716, zinc oxide (ZnO) as a piezoelectric film is formed on a silicon (Si) substrate, and a propagation loss of zinc oxide is formed on the zinc oxide layer. It is known to dispose silicon dioxide (SiO ₂ ) as a small dielectric film and a comb-shaped electrode.

As a new application field of the above-mentioned surface acoustic wave device, Japanese Patent Application Laid-Open Nos. 4-15146 and 7-22.
Japanese Patent No. 3512 and Japanese Patent Application Laid-Open No. 7-223513 disclose a device that uses surface acoustic waves to remove water droplets on a window glass of an automobile or a mirror.

[0004]

Conventionally, in order to reduce the propagation loss of surface acoustic waves, a diamond or silicon dioxide film is provided on the substrate. However, when forming a film of diamond or silicon dioxide on the substrate, Requires large-scale manufacturing equipment, which leads to cost increase. On the other hand, when a surface acoustic wave device without such a film is attached to a window glass or a mirror of an automobile and the dirt and water droplets are removed by using the vibration, the propagation loss of the surface acoustic wave is large. However, a large amount of power consumption is required to uniformly remove dirt and water droplets on the entire window glass and mirrors. Therefore, an attempt is made to reduce the propagation loss by forming a layer of a material having a small propagation loss on the window glass as the substrate. However, it is not practical to combine a material having a small propagation loss with a glass substrate in terms of the adhesion to the glass of that material and the complexity of the manufacturing process. Therefore, an object of the present invention is to solve the above-mentioned disadvantages of the related art.

[0005]

In order to solve the above-mentioned problems, the present invention is one in which a glass substrate of a surface acoustic wave device is subjected to dealkalization treatment.

According to the present invention, the propagation loss of surface acoustic waves on the glass substrate is reduced by subjecting the glass substrate to dealkalization treatment. Preferably, the dealkalization treatment in the present invention involves immersing the glass substrate in an acid or an aqueous solution containing an acid and an alkali metal salt or an alkaline earth metal salt, or an acidic substance on the glass substrate, or an acidic substance and an alkali metal salt or alkali. Contact with an earth metal salt is preferred.
Among them, acid, when the glass substrate is immersed in an aqueous solution containing an alkali metal salt or an alkaline earth metal salt, or when the glass substrate is brought into contact with an acidic substance, an alkali metal salt or an alkaline earth metal salt, The propagation loss of the surface acoustic wave on the glass substrate is further reduced as compared with the case where the dealkalization treatment is performed by using the acid alone or the acid substance alone. The component removed from the glass substrate by the dealkalization treatment is an alkali metal or an alkaline earth metal, and in this case, the amount removed from the glass substrate is the content of the alkali metal or the alkaline earth metal on the glass surface. 1% by weight or more, or the depth from the glass surface (depth in the plate thickness direction) 200μ
It is more effective if the content of alkali metal or alkaline earth metal contained up to m is 0.1% by weight or more.
In this dealkalization treatment, it is not necessary to use an expensive device. Further, the glass substrate may be subjected to dehydration treatment after dealkalization treatment, the glass substrate, soda lime glass containing an alkali metal or alkaline earth metal,
Either borosilicate glass or aluminoborosilicate glass can be used.

According to the present invention, since the surface of the glass substrate of the surface acoustic wave device is dealkalized, the propagation loss coefficient of the surface acoustic wave of the glass substrate can be suppressed, and dirt or water droplets attached to the window glass or mirror of the automobile can be suppressed. Can be uniformly removed with less power consumption, and the practical value of the present invention is high.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A surface acoustic wave element 6 comprises a glass substrate 1 whose surface is dealkalized, as shown in FIG.
It has a basic structure including a piezoelectric film 2 formed on the surface of the glass substrate 1 and comb-shaped electrodes 3 a and 3 b in contact with the piezoelectric film 2. Opposed electrodes 4a and 4b are provided on the piezoelectric film 2 so as to face the comb-teeth electrodes 3a and 3b (the piezoelectric film 2 is interposed). In the example of FIG. 1, the comb-teeth electrodes 3a and 3b are interposed between the glass substrate 1 and the piezoelectric film 2, and in the example of FIG. 2, the counter electrodes 4a and 4b are between the glass substrate 1 and the piezoelectric film 2. Intervening. 3 and 4 show the comb-teeth electrodes 3a, 3b.
The comb tooth electrodes 3a and 3b are provided only between the glass substrate 1 and the piezoelectric film 2 or on the surface of the piezoelectric film 2 by using only the above.

In this case, the dealkalization treatment removes alkali metal or alkaline earth metal from the glass substrate 1. The components removed from the glass substrate 1 are, for example, lithium, sodium, potassium, rubidium and cesium. Or an alkaline earth metal such as beryllium, magnesium, calcium, strontium, or barium. From this, glass containing either an alkali metal or an alkaline earth metal is used for the glass substrate 1, and for example, inexpensive soda lime glass, borosilicate glass, aluminoborosilicate glass, or the like can be used. .

As is well known, the dealkalizing treatment is carried out by immersing glass in a dilute acidic aqueous solution such as hydrochloric acid, nitric acid or sulfuric acid at room temperature to about 100 ° C.
Alternatively, the glass is an acidic substance containing sulfur near its transition temperature, for example, sulfur powder, ammonium sulfate, sulfurous acid gas,
By contacting with potassium pyrosulfate or the like, the components of alkali metal and alkaline earth metal on the glass surface are removed.

A more preferable dealkalization treatment is to immerse the glass substrate in an aqueous solution containing an acid and an alkali metal salt or an alkaline earth metal salt at room temperature to about 100 ° C., or to add acid to the glass substrate containing sulfur near its transition temperature. Substance,
It may be brought into contact with an alkali metal salt or an alkaline earth metal salt. Acids used here include hydrochloric acid, sulfuric acid,
Nitric acid or the like is used, and examples of the alkali metal salt or alkaline earth metal salt include sodium chloride, lithium chloride, sodium hydroxide, lithium hydroxide, potassium chloride, potassium hydroxide, magnesium chloride, magnesium hydroxide, calcium chloride. , Calcium hydroxide and the like can be used. The amount of the alkali metal or alkaline earth metal removed from the glass substrate 1 by the dealkalization treatment is, for example, at least 1% by weight or more of the content of the above substance on the glass surface, or the depth from the glass surface is 2% or more.
It is preferable that the content of the above substances is 0.1% or more in the range of up to 00 μm, and further, the dehydration treatment performed after the dealkalizing treatment is performed in the air at 300 to 6%.
The heat treatment is performed at 00 ° C. or 50 to 200 ° C. in vacuum for about 3 hours, and this dehydration treatment can further reduce the propagation loss of surface acoustic waves.

As is well known, the piezoelectric film 2 is made of zinc oxide, aluminum nitride, lead zirconate titanate or the like, and its glass substrate 1 is used.
There are no particular restrictions on the method of forming the above-mentioned material, which is a known sputtering method, vapor deposition method, ion plating method, CVD method, or the like. The comb-teeth electrodes 3a, 3b and the counter electrodes 4a, 4b are made of a metal such as aluminum or an alloy thereof, and can be formed by a method generally used for forming an integrated circuit or the like.

[0013]

【Example】

[Example 1] A glass substrate made of soda lime glass having a thickness of 1.9 mm was immersed in a 0.1 N hydrochloric acid solution at 96 ° C for 48 hours, and its surface was dealkalized. The sodium content on the surface of the glass substrate was 9.8 wt% as measured by EPMA analysis (before the dealkalization treatment, it was 10.4 wt%. In this case, the propagation loss was reduced. For this purpose, it is better that the amount of alkali metal or alkaline earth metal is smaller, and calcium is the only component other than sodium, and this calcium content did not change at 5.3% by weight, but sodium is a glass substrate. 1 depth 5
It was removed up to 00 μm). As shown in FIG. 1, a comb-shaped electrode made of aluminum having a gap and a line width of 20 μm, a logarithm of 83 pairs, a cross width of 1 mm and a film thickness of 0.1 μm was formed on one surface of a glass substrate. A zinc oxide film having a film thickness of 2 μm was formed on the comb-teeth electrode by a sputtering method, and a counter electrode made of aluminum having a film thickness of 0.1 μm was formed on the zinc oxide film to obtain a surface acoustic wave device.
The propagation loss coefficient of surface acoustic wave in this device is 2.86.
It was dB / cm.

[Embodiment 2] In Embodiment 1, a glass substrate is used.
A surface acoustic wave device was manufactured through the same steps, except that it was immersed in a 2N hydrochloric acid solution at 8 ° C. for 79 hours and dealkalized. The calcium content on the glass substrate surface was 5.3% by weight, which was unchanged, but the sodium content on the substrate surface was 9.
7% by weight, depth 700 from the surface of the glass substrate 1
Sodium was almost uniformly removed to a depth deeper than μm. The surface acoustic wave propagation loss coefficient of this device was 2.99 dB / cm.

[Embodiment 3] In Embodiment 1, the glass substrate is replaced by 9
4 at 0.1C hydrochloric acid and 1N sodium chloride solution at 6 ℃
The surface acoustic wave device was formed by immersing for 8 hours for dealkalization, and through the same steps as above. The sodium content on the surface of the glass substrate 1 was 9.5% by weight and the calcium content was 5.1% by weight (before the dealkalization treatment, the calcium content was 5.3%).
Wt%). Sodium of 600 μm and calcium of 100 μm were removed in the depth direction of the glass substrate 1. The propagation loss coefficient of the surface acoustic wave of this device in this case was 2.37 dB / cm. Apart from this, Example 1
In the case where the glass substrate 1 obtained by the dealkalization treatment is heat-treated in vacuum at 100 ° C. for 3 hours to dehydrate the surface of the glass substrate 1 and form a surface acoustic wave device through the same steps, Wave propagation loss coefficient is 2.78 dB / cm
Met.

[Comparative Example] The same surface acoustic wave device as that of Example 1 was obtained by using a glass substrate (sodium content: 10.4% by weight) not subjected to dealkalization treatment. The surface acoustic wave propagation loss coefficient of this device was 3.54 dB / cm. The sodium content in the examples means the weight% of sodium in the five elements of sodium, potassium, calcium, silicon and oxygen.

[0017]

[Effect] The surface acoustic wave device using the glass substrate subjected to dealkalization does not require a device for forming a film for reducing the propagation loss, so that cost increase can be suppressed. Furthermore, since the propagation loss of surface acoustic waves is reduced and surface acoustic waves are generated with low power consumption,
It can be used in new applications such as removing dust and water droplets from mirrors. Further, the present invention can be applied not only to such a field but also to a material using glass as a propagation material for transmitting a surface acoustic wave.

[Brief description of drawings]

FIG. 1 is a sectional view of an element of an example of the present invention.

FIG. 2 is a cross-sectional view of an example in which a comb tooth electrode is used on the surface of a piezoelectric film.

FIG. 3 is a sectional view of an example in which a counter electrode is not used.

FIG. 4 is a cross-sectional view of an example in which the comb-teeth electrode is arranged on the surface of the piezoelectric film in the example of FIG.

FIG. 5 is a graph showing changes in sodium or calcium content in the depth direction of a glass substrate in dealkalization treatment.

[Explanation of symbols]

 1 Glass Substrate 2 Piezoelectric Films 3a, 3b Comb Tooth Electrodes 4a, 4b Counter Electrodes

Front Page Continuation (72) Inventor Toshihiko Tani, Nagakute-cho, Aichi-gun, Aichi Prefecture 41, Nagachoji, Yokochi Central Research Institute, Ltd. (72) Inventor Yasushi Saito, 41, Nagakute-cho, Aichi-gun, Nagakute-machi Address 1 Toyota Central Research Institute Co., Ltd.

Claims (5)

[Claims] 1. A surface acoustic wave element having a piezoelectric film formed on a glass substrate, wherein an electrode is provided on the glass substrate or on the piezoelectric film to generate a surface acoustic wave.
A surface acoustic wave device, characterized in that the glass substrate is subjected to dealkalization treatment. 2. The dealkalizing treatment is an acid or an acid,
2. The glass substrate is immersed in an aqueous solution containing an alkali metal salt or an alkaline earth metal salt, or the glass substrate is contacted with an acidic substance or an acidic substance and an alkali metal salt or an alkaline earth metal salt. Surface acoustic wave device. 3. The component removed from the glass substrate by the dealkalizing treatment is an alkali metal or an alkaline earth metal, and the amount removed from the glass substrate is the alkali metal or alkaline earth on the glass surface. 3. 1% by weight or more of the content of the group metal, or 0.1% by weight or more of the content of the alkali metal or alkaline earth metal contained up to a depth of 200 μm from the glass surface. Surface acoustic wave device. 4. The surface acoustic wave device according to claim 3, wherein the glass substrate is dehydrated after dealkalization. 5. The surface acoustic wave device according to claim 4, wherein the glass substrate is made of soda lime glass, borosilicate glass, or aluminoborosilicate glass.