JPH0595249A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To eliminate the need for a package by forming sequentially a 1st high sound velocity film, a piezoelectric film and a 2nd high sound velocity film onto a substrate and providing an electrode to a border between the piezoelectric film and the 1st high sound velocity film and/or between the piezoelectric film and the 2nd high sound velocity film, thereby protecting the vicinity of the electrode. CONSTITUTION:A 1st high sound velocity film 1 is formed on a silicon substrate 4 by forming a diamond carbon film whose film thickness is 1-10mum by the ion vapor-deposit method or the like. An AIN piezoelectric film 3 is formed on the film 1 by the sputter method or the like and an aluminum electrode whose film thickness is nearly 200nm is formed on the film 3 by the vacuum vapor-deposition method. The electrode is processed into a fine interdigital electrode 5 by the photo lithography method to form both the input and output electrodes to be of the same shape as a pattern whose line and space are both 1.2mum. Moreover, a 2nd high sound velocity film 2 is formed onto the film 3 and the electrode 5 similarly to the case with the film 1. Thus, the vicinity of the electrode is protected and no package is required and the cost is reduced.

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 having a structure in which a piezoelectric layer is sandwiched between high-sonic materials in a sandwich shape so that acoustic waves can be confined inside a solid layer.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
A surface acoustic wave element is known as a device using an acoustic wave, and is used for a filter, a resonator, a delay line, and the like. In particular, application of this surface acoustic wave filter to a mobile communication terminal device such as an automobile phone / mobile phone has been studied, and a technique for increasing the frequency of such an element has been actively developed. By the way, the elastic wave propagation method of this element is called Rayleigh mode, and energy is concentrated and propagates near the substrate surface. This Rayleigh mode is characterized in that it can send and receive signals at any position on the substrate surface.
However, in order for the substrate surface of the device to vibrate, the substrate surface must be in contact with air or vacuum, which requires a hollow package structure. Further, if such a package is defective, there is a drawback that moisture or the like penetrates during long-term use and the surfaces of electrodes and the like are contaminated, resulting in deterioration of the characteristics of the device. Further, there is a problem that the packaging cost is high.

Accordingly, it is an object of the present invention to provide a surface acoustic wave device which eliminates various drawbacks caused by packaging.

[0004]

The inventors of the present invention have conducted extensive studies and research to solve the above-mentioned problems, and as a result, sandwiched the piezoelectric layer between the first and second high acoustic velocity material layers in a sandwich shape. By confining the elastic wave in the solid layer at
We have succeeded in developing a surface acoustic wave device that protects the vicinity of the electrode where energy is concentrated and does not require a hollow package.

That is, according to the present invention, at least a first high acoustic velocity film, a piezoelectric film and a second high acoustic velocity film are sequentially provided on a substrate,
An object of the present invention is to provide a surface acoustic wave device including electrodes at the interface between the piezoelectric film and the first high acoustic velocity film and / or the interface between the piezoelectric film and the second high acoustic velocity film.

One specific example of the surface acoustic wave device of the present invention is shown in FIG.
It shows in (a). In the figure, the element is formed by sequentially depositing a first high acoustic velocity film 1, a piezoelectric film 3 and a second high acoustic velocity film 2 on a substrate 4,
Interdigital electrodes 5 are formed at the interface between the piezoelectric film 3 and the second high acoustic velocity film 2 at a constant electrode finger interval. By adopting such a configuration, the energy of the elastic wave propagating through the element,
That is, the vibration intensity is distributed around the axis along the interface as shown in FIG. 7B, and the elastic wave is confined in the solid layer.

As the first and second high sound velocity film materials used in the present invention, SiC, c-BN, diamond-like carbon film,
Although a single crystal diamond film or the like can be used, a diamond-like carbon film or a single crystal diamond film is preferable in that a higher acoustic velocity can be obtained than other materials. In particular,
When AlN, which is advantageous for increasing the frequency of a surface acoustic wave device, is used as a piezoelectric film, diamond-like carbon and single crystal diamond, which are materials having a higher acoustic velocity than AlN, can be used to confine the acoustic waves in the high acoustic velocity layer Is required to be used. Such a high sonic velocity film can be formed by various methods, but when forming a diamond-like carbon film or a single crystal diamond, the ionization vapor deposition method is particularly preferable because a film having high smoothness can be obtained. About 1 to 10 μm is suitable as the thickness of each of the first and second films.

The piezoelectric material used in the present invention is Zn
O, AlN, ZnS, LiNbO ₃ , Pb (Zr, T
i) O ₃ , LiTaO ₃ , SiO ₂ , Ta ₂ O _{5 and the} like can be mentioned, but not limited thereto. AlN is Zn
This is advantageous because the sound velocity can be improved over O. These piezoelectric materials can be formed by various methods such as sputtering, vacuum deposition, and CVD.

In the device of the present invention, as shown in FIG. 1, an electrode is provided at the interface between the high acoustic velocity film and the piezoelectric film. The interface may be either the interface between the first high acoustic velocity film and the piezoelectric film formed on the substrate or the interface between the second high acoustic velocity film and the piezoelectric film formed on the piezoelectric film, or both interfaces may be formed. Is. In addition, as shown in FIG. 2, it is also possible to form a solid electrode 6 for electric field short circuit at an interface different from the interface at which the interdigital electrode 5 is formed. As the electrode used in the element of the present invention, a metal such as aluminum or gold can be used, but it is not particularly limited thereto, and various electrode materials capable of achieving the object of the present invention can be used. Generally, photolithography or etching can be used to form the electrode layer, and the shape of the electrode is generally a comb shape.

The substrate used for the surface acoustic wave device of the present invention includes ceramics such as alumina, SiC and Si ₃ N ₄ , metals such as Mo and W, alloys and glass containing at least one of Co, Ni and Fe, and Si. , Sapphire, GGG
Various materials such as can be used.

In order to manufacture the surface acoustic wave element of the present invention, the first high acoustic velocity film is formed on the above substrate by a method such as ion plating, and then the above piezoelectric film is formed. Form a film. At this time, the interdigital transducer is appropriately formed on the first high acoustic velocity film and / or the piezoelectric film. Then, the second high acoustic velocity material is formed on the piezoelectric film by the method as described above to achieve a structure in which the piezoelectric film having electrodes is sandwiched between the high acoustic speed materials.

In the surface acoustic wave device of the present invention as described above, in addition to the high acoustic velocity film and the piezoelectric film, an arbitrary layer such as a protective layer is inserted between arbitrary layers on the substrate or formed on the layer. Is also possible, and the first and second as described above are also possible.
It is also within the scope of the present invention to further laminate the combination of the high acoustic velocity film and the piezoelectric film on the substrate on which they are formed.

Examples of the present invention will be illustrated below, but the present invention is not limited thereto.

[0014]

Example A first diamond-like carbon film was formed on a silicon substrate by using an ionization vapor deposition device. The formation conditions are as follows.

Introducing methane gas into the ionization deposition apparatus,
A gas pressure was set to 0.1 Torr to cause discharge in the hot cathode filament. Magnetic flux density 400 gauss, substrate voltage Va
= -300V, and the substrate temperature was 200 ° C. Further, a current If = 25 A was applied to the filament. The filament was formed into a coil and had a width of 3 mm and an interval between the filament and the surrounding electrodes was 8 mm. The grid was vibrated at a speed of 5 mm / min.

Next, an AlN piezoelectric thin film was formed on the substrate having the diamond-like carbon film formed thereon by a sputtering method. Sputtering was performed in a nitrogen atmosphere with aluminum as a target. The substrate temperature was 250 ° C. and the gas pressure was 0.01 Torr.

An aluminum electrode was formed on this AlN piezoelectric thin film by a vacuum deposition method. At this time, the substrate temperature 25
0 ° C., ultimate pressure 1.2 × 10 ^- and ⁶ Torr, the formed film thickness was 200 nm. This aluminum electrode was processed into a fine interdigital electrode by photolithography.
The interdigital electrodes have the same shape as the input / output electrodes. The line and space were formed in a pattern of 1.2 μm using a contact exposure technique.

Here, the silicon substrate is divided into two,
One was evaluated as it was, and the other was further subjected to the ionization vapor deposition method to form a second diamond-like carbon film. Furthermore, the second diamond-like carbon film was removed by dry etching at the position corresponding to the lead-out electrode pad to the outside of the interdigital electrode so that connection was possible.

As described above, when the element in which only the first diamond-like carbon film was formed as the high acoustic velocity film and the element in which the piezoelectric film was sandwiched by the first and second diamond-like carbon films were compared, The element having the second diamond-like carbon coating formed operated at a higher frequency than the element having only the first diamond-like carbon coating. Furthermore, when an adhesive tape was adhered to both surfaces, the signal was greatly attenuated in the device having only the first diamond-like carbon film as the high acoustic velocity film, but the one having the first and second diamond-like carbon films was formed. There was no signal attenuation.

Therefore, the device of the present invention can be used by directly adhering it to a circuit board, or by directly molding it with resin or the like without forming a hollow, and simplifying the package and reducing the cost. Is achieved.

[0021]

In the surface acoustic wave device of the present invention, since the elastic wave vibration is confined inside the solid, the vicinity of the electrode where the energy is concentrated is protected. Further, the package is not required, there is no defect caused by defective packaging, and it is advantageous in terms of cost.

[Brief description of drawings]

FIG. 1A is a diagram showing an example of a surface acoustic wave device of the present invention. FIG. 2B is a graph showing the vibration intensity distribution regarding the longitudinal coordinate of the elastic wave propagating through the element of FIG.

FIG. 2 is a diagram showing a specific example of the surface acoustic wave device of the present invention in which a solid electrode for electrode short circuit is formed on an interface different from the interface on which the interdigital electrode is formed.

[Explanation of symbols]

 1 1st high sonic velocity film 2 2nd high sonic velocity film 3 Piezoelectric film 4 Substrate 5 Interdigital electrode 6 Solid electrode

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoshikazu Narimiya 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Terufumi Kamijo 1-13-11-1 Nihonbashi, Chuo-ku, Tokyo TDK Within the corporation

Claims (2)

[Claims] 1. A substrate having at least a first high acoustic velocity film,
A surface acoustic wave device comprising a piezoelectric film and a second high acoustic velocity film sequentially, and electrodes provided at the interface between the piezoelectric film and the first high acoustic velocity film and / or at the interface between the piezoelectric film and the second high acoustic velocity film. 2. The surface acoustic wave device according to claim 1, wherein at least one of the high acoustic velocity films is a diamond-like carbon film or a single crystal diamond film.