JPH09312547A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small insertion loss and an excellent characteristic by configuring the element with a 1st layer being a piezoelectric layer, a 2nd layer being an electrode layer and a 3rd layer being a diamond layer from the side of a non-piezoelectric substrate. SOLUTION: A piezoelectric layer 2 as a 1st layer is formed on a sapphire substrate 1. A zinc oxide is used for the piezoelectric layer 2. Then an electrode layer 3 being a 2nd layer is formed on the piezoelectric layer 2. A copper film is used for the electrode layer 3. After the electrode layer 3 is formed over the piezoelectric layer 1, the layer 3 is shaped as desired by a chemical method. Succeedingly, a diamond layer 4 being a 3rd layer is formed by the chemical gas phase growing method into a thickness of about 5μm. A single crystal zinc oxide film is used for the piezoelectric layer 2. Thus, the propagation attenuation of a surface acoustic wave by the piezoelectric layer 2 is very small and an excellent piezoelectric characteristic is obtained, the insertion loss of the element in the case of a filter for 1.9GHz band is about 2dB and the loss is improved by 3dB more than that of a conventional device.

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 device used in mobile communication devices such as paging systems and cordless telephones, general wireless communication systems, and devices such as TV / VTRs.

[0002]

2. Description of the Related Art In a conventional surface acoustic wave device, an electrode layer and a piezoelectric layer such as zinc oxide are formed on a single crystal diamond layer as described in, for example, Japanese Unexamined Patent Publication No. 7-273591. Was the way to do it. Also, Japanese Patent Application Laid-Open No.
As described in Japanese Patent No. 39715, a structure is proposed in which a diamond layer, an electrode layer, and a piezoelectric layer are sequentially provided on a piezoelectric substrate.

[0003]

The above-mentioned prior art has the following problems.

First, in the structure described in Japanese Patent Laid-Open No. 7-273591, it is necessary to flatten the diamond layer because the electrode layer is formed after the diamond layer is formed. This flattening is performed by polishing or the like, but there is a problem that polishing takes a very long time because the diamond layer has high hardness. Another problem is that since the piezoelectric layer is formed on the electrode layer, the crystallinity of the piezoelectric layer is poor and the insertion loss becomes large. This is because the diamond layer and the electrode layer are separated by processing the electrode layer into a predetermined shape prior to the formation of the piezoelectric layer, and the crystallinity is disturbed because the piezoelectric layer is formed on a different base material. .

Next, in the structure disclosed in Japanese Patent Laid-Open No. 2-239715, since a piezoelectric substrate is used, 800 degrees Celsius necessary for forming a diamond layer is used.
There is a problem that the diamond layer becomes incomplete because the temperature cannot be raised to a high temperature. Therefore, characteristic defects such as a large insertion loss still occur.

An object of the present invention is to solve the above problems and to form a surface acoustic wave element having a small insertion loss and excellent characteristics.

[0007]

A surface acoustic wave device having a small insertion loss, which is an object of the present invention, is a non-piezoelectric substrate and a surface acoustic wave device comprising a diamond layer, an electrode layer and a piezoelectric layer. From the side, the first layer is a piezoelectric layer, the second layer is an electrode layer, and the third layer is a diamond layer from the side. Further, the electrode layer is characterized by being made of copper or an alloy of copper and silicon. Further, an intermediate layer is provided between the electrode layer and the diamond layer, between the piezoelectric layer and the electrode layer, or both.

[0008]

As described above, according to the present invention, since the piezoelectric layer is formed as the first layer on the non-piezoelectric substrate, the piezoelectric layer can have good crystallinity. Also, as the second electrode layer,
Since copper or an alloy of copper and silicon is used, 80 degrees Celsius
It can be maintained at a high temperature of 0 degree or more, and the quality of the diamond film of the third layer can be optimized. As described above, the surface acoustic wave device according to the present invention can have excellent characteristics with small insertion loss.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred examples of the present invention will be described in detail below.

FIG. 1 is a sectional view of a first preferred example of a surface acoustic wave device according to the present invention. The substrate 1 is a sapphire substrate. Piezoelectric layer 2 as first layer on sapphire substrate 1
To form In the first preferred example, the piezoelectric layer 2 uses zinc oxide. The piezoelectric layer 2 is formed by a sputtering method which is a vacuum film forming technique, and the forming temperature is about 300 degrees Celsius. In this example, the thickness of the piezoelectric layer 2 is about 3 micrometers, but it is not limited to this.

Next, the second electrode layer 3 is formed on the piezoelectric layer 2. In the first preferred example, this electrode layer 3
In addition, a copper film is used. After being formed on the entire surface of the piezoelectric layer 2 by a sputtering method, it is formed into a desired shape by a chemical corrosion method. The thickness of the electrode layer 3 is about 0.01 micrometer.

Subsequently, the diamond layer 4 which is the third layer
Are formed by chemical vapor deposition to a thickness of about 5 micrometers. The formation temperature of the diamond layer 4 is about 8 degrees Celsius.
It is 00 degrees.

Here, the reason why the copper film is used for the second electrode layer 3 will be described. In a general surface acoustic wave element, aluminum is used for the electrode layer, but the melting temperature of aluminum is 600 degrees Celsius, and as in the first preferred example, when the temperature is raised to 800 degrees Celsius thereafter, it melts. It cannot be used because it is lost.

Therefore, the material of the electrode layer 3 has a melting temperature of 80 degrees Celsius which is the formation temperature of the diamond layer 4.
It must be 0 degrees or more. Therefore, refractory metals such as copper, gold and tungsten are suitable. Since a metal having a low specific gravity is suitable for the surface acoustic wave element among them, the copper film is used in the first preferred example. Of course, gold, tungsten, tantalum, titanium, etc. may be used depending on the characteristics.

The electrode layer 3 may be made of aluminum as long as the diamond layer 4 can be formed at 600 ° C. or lower.

As the zinc oxide of the piezoelectric layer 2, a single crystal film is used in the first preferred example. Therefore, since the propagation attenuation of the surface acoustic wave by the piezoelectric layer 2 is extremely small and the piezoelectric characteristics are excellent, the insertion loss of the surface acoustic wave element according to the first preferred example is about 2 dB in the filter of 1.9 GHz band. Is 3d compared to about 5dB in the past.
B can be improved.

Although the sapphire substrate is used as the substrate 1 in the first preferred example, a quartz substrate can be used. In this case, the piezoelectric property of quartz is not used, and it can be used only as a substrate for growing a single crystal of zinc oxide. Therefore, it is considered as a non-piezoelectric substrate.

Further, the piezoelectric layer 2 may be a piezoelectric material other than zinc oxide, such as aluminum nitride and tantalum pentoxide.

Next, FIG. 2 shows a sectional view of a surface acoustic wave device of a second preferred example. In the second preferred example, the intermediate layer 5 is formed between the piezoelectric layer 2 and the electrode layer 3 and between the electrode layer 3 and the diamond layer 4.

The intermediate layer 5 is for preventing the adhesion failure of the diamond layer 4, and silicon is used in the second preferred example. Propagation loss increases at the interface where surface acoustic waves propagate if there is poor adhesion. Therefore, it is important to secure adhesion. Since silicon has high adhesiveness to the diamond film, it is possible to form a surface acoustic wave element having very small propagation loss.

The thickness of the intermediate layer 5 in the second preferred example is about 100 angstroms, and does not deteriorate the piezoelectric conversion characteristics of the zinc oxide of the piezoelectric layer 2 and the electrode layer 3. The thickness is not limited to this.

Silicon is a material that can withstand the formation temperature of the diamond layer 4 sufficiently. The silicon of the intermediate layer 5 in the second preferred example can be formed by a sputtering method, a chemical vapor deposition method, or the like. The material of the intermediate layer 5 is not limited to silicon.

In addition to the second preferred example, the intermediate layer 5 is formed only between the piezoelectric layer 2 and the electrode layer 3, or between the electrode layer 3 and the diamond, as shown in FIGS. Layer 4
It can also be formed only during the period.

A third preferred example according to the present invention is one in which the electrode layer 3 in the first preferred example shown in FIG. 1 is an alloy of copper and silicon. In the case of the third preferred example, the silicon of the intermediate layer 5 in the second preferred example is mixed in the electrode layer 3 in advance, which also improves the adhesion of each layer.

The alloy composition is such that copper is the main component and silicon is about 1% to 20% by weight. However, it is not limited to these.

[0026]

As described above, according to the present invention, since the piezoelectric layer is formed on the first layer on the substrate, there is an effect that it is not necessary to flatten the diamond layer and the process can be simplified. Further, since the piezoelectric layer can have good crystallinity, it has an effect of reducing the insertion loss of the surface acoustic wave element, and thus has an effect of reducing the power consumption of the device.

Further, since copper is used as the second electrode layer, it can be maintained at a high temperature of 800 ° C. or higher, so that the quality of the diamond film of the third layer can be optimized.

Further, the use of the intermediate layer and the electrode layer made of an alloy of copper and silicon can improve the adhesiveness of the diamond layer and can reduce the insertion loss as a surface acoustic wave element. Have.

[Brief description of drawings]

FIG. 1 is a sectional view of a surface acoustic wave device according to a first preferred example of the present invention.

FIG. 2 is a sectional view of a surface acoustic wave device according to a second preferred example of the present invention.

FIG. 3 is a sectional view of a surface acoustic wave device having another structure according to a second preferred example of the present invention.

FIG. 4 is a sectional view of a surface acoustic wave device having another structure according to a second preferred example of the present invention.

[Explanation of symbols]

 1 Substrate 2 Piezoelectric layer 3 Electrode layer 4 Diamond layer 5 Intermediate layer

Claims (5)

[Claims] 1. A surface acoustic wave device comprising a non-piezoelectric substrate, a diamond layer, an electrode layer and a piezoelectric layer, wherein the first layer is a piezoelectric layer, the second layer is an electrode layer and the third layer is from the non-piezoelectric substrate side.
A surface acoustic wave device, wherein the layer is a diamond layer. 2. The surface acoustic wave device according to claim 1, wherein the electrode layer is made of copper. 3. The surface acoustic wave device according to claim 1, wherein the electrode layer is an alloy of copper and silicon. 4. The surface acoustic wave device according to claim 1, wherein an intermediate layer is provided between the electrode layer and the diamond layer. 5. The surface acoustic wave device according to claim 1, wherein an intermediate layer is provided between the piezoelectric layer and the electrode layer.