JPH0897673A - Surface acoustic wave element and its manufacture - Google Patents

Abstract

PURPOSE: To provide an element by which a noise component of an electric signal is considerably reduced by providing a sound absorption section having a Young's modulus able to absorb a surface acoustic wave to an outer side of a piezoelectric substrate and allowing the end of the substrate to absorb the surface acoustic wave. CONSTITUTION: A single crystal of LiNbO3 of Y direction cut Z axis propagation is used for a piezoelectric substrate 1 and an upper face of the substrate 1 is mirror-finished by a lapping machine. Then an aluminum film 6 is formed on the substrate 1, a photo resist is coated and an ultraviolet ray is emitted via a photo mask, the substrate 1 is developed to obtain a photo resist pattern of a prescribed electrode shape. An interdigital electrode is adopted for an input electrode 2 and an output electrode 3. Then a photosensing polyimide resin is coated onto the substrate 1 to obtain a photosensing polyimide resin film 7, an ultraviolet ray is emitted to the film 7 via the photo mask, after the film 7 is cured, an undesired part is removed by heat treatment and a sound absorption section 5 with a Young's modulus of 350kg/mm<2> is obtained. A surface acoustic wave is absorbed at the end of the substrate 1 to reduce a noise in the electric signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter used in electronic circuits such as mobile phones and televisions, and a built-in integrator circuit (hereinafter referred to as a convolver) used in a communication device in the field of mobile communication. The present invention relates to a surface acoustic wave element used and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a surface acoustic wave device has attracted attention because it has a relatively simple structure and can be made compact and lightweight. In particular, it is expected to be used as a noise filter or a convolver capable of responding to downsizing and weight saving of electronic devices.

A conventional surface acoustic wave device will be described below with reference to the drawings. FIG. 7 is a plan view of a conventional surface acoustic wave device. In FIG. 7, 1 is a piezoelectric substrate, 2 is a pair of input electrodes formed in a comb shape on the upper surface of the piezoelectric substrate 1, 3
Is a pair of output electrodes formed in a comb shape on the upper surface of the piezoelectric substrate 1 at a predetermined interval from the input electrode 2, and 4 is provided at the end of the piezoelectric substrate 1 facing the input electrode 2 and the output electrode 3. It is the sound absorption part.

A method of manufacturing the surface acoustic wave device having the above structure will be described below. First, the piezoelectric single crystal is cut out in a predetermined crystal orientation to form the piezoelectric substrate 1. Next, the upper surface of the piezoelectric substrate 1 is mirror-finished by lapping. Next, a metal film is formed on the upper surface of the piezoelectric substrate 1 by using a vapor deposition method, a sputtering method, an ion plating method, or the like. The input electrode 2 and the output are formed by a method of etching the electrode film into a predetermined shape using a resist or the like after forming this metal film, or a method of first forming the predetermined shape with a resist or the like and then forming an electrode film and lifting off. The electrode 3 is formed. Next, the sound absorbing portion 4 made of an organic polymer resin is formed at the end of the piezoelectric substrate 1 for the input electrode 2 and the output electrode 3.

The operation of the surface acoustic wave device manufactured as described above will be described below. First, an electric signal is applied to the input electrode 2. The electric signal applied to the input electrode 2 is converted into a surface acoustic wave by the piezoelectric effect of the piezoelectric substrate 1 and propagates on the upper surface of the piezoelectric substrate 1. Output electrode 3
At, the surface acoustic wave is converted into an electric signal again.
At this time, the surface acoustic wave propagates to both sides of the piezoelectric substrate 1, but the surface acoustic wave propagating to the side opposite to the output electrode 3 causes noise. Therefore, the sound absorbing portion formed at the end of the piezoelectric substrate 1 By being absorbed by 4, an electric signal containing no noise is generated at the output electrode 3.

[0006]

However, in the above-mentioned conventional surface acoustic wave device, the crystal orientation of the piezoelectric substrate is slightly different from the design, or the installation angle of the input electrode and the output electrode is slightly different from the design. There are cases. In this case, the surface acoustic wave propagates in a direction other than the output electrode, and the surface acoustic wave is reflected at the end of the piezoelectric substrate and enters the output electrode,
It has a problem that it causes noise. Further, since the area from the electrode to the end of the piezoelectric substrate is provided as the attenuation area in order to remove the noise caused by the reflected wave, there is a problem that the size of the surface acoustic wave element must be increased. . Further, when vibration from the outside is transmitted to the piezoelectric substrate, there is a problem that surface acoustic waves, which become noise in the output electrode, are generated in the piezoelectric substrate.

Further, in the conventional method of manufacturing a surface acoustic wave element, it is not possible to remove the noise due to the reflected wave of the surface acoustic wave caused by the minute displacement of the arrangement angle of the piezoelectric substrate, the input electrode and the output electrode. Had.
Further, there is a problem that noise caused by external vibration cannot be removed.

The present invention solves the above-mentioned conventional problems, and provides a surface acoustic wave device capable of removing a reflected wave of a surface acoustic wave and noise caused by vibration from the outside, and a surface acoustic wave It is an object of the present invention to provide a method of manufacturing a surface acoustic wave device, which can easily manufacture a sound absorbing portion that can be absorbed into a high yield with high productivity.

[0009]

To achieve this object, a surface acoustic wave device according to a first aspect of the present invention comprises a piezoelectric substrate for converting an input electric signal into a surface acoustic wave, and an electric signal. A pair of input electrodes provided on the piezoelectric substrate for inputting, a pair of output electrodes provided on the piezoelectric substrate for converting surface acoustic waves into electric signals, and sound absorption for absorbing the surface acoustic waves of the input electrodes. A surface acoustic wave element including a portion, and the sound absorbing portion is formed on an outer portion of the piezoelectric substrate.

According to a second aspect of the surface acoustic wave device of the first aspect, the sound absorbing portion is made of a photosensitive polyimide resin.

A method of manufacturing a surface acoustic wave element according to a third aspect is the method of manufacturing a surface acoustic wave element according to any one of the first aspect and the second aspect, wherein the sound absorbing portion is piezoelectrically formed by photolithography. It is formed on the outer side of the flexible substrate.

Here, as the piezoelectric substrate, LiNbO is used.
₃ , LiTaO ₃ , B ₁₂ GeO ₂₀ , SiO ₂ , Pb (Z
r, Ti) O ₃ , ZnO or the like is used. The input and output electrodes are Al, Au, Cu, Ag, Ni, P
d, Pt, or the like is used. As the sound absorbing part, polyimide resin, polyethylene resin, polypropylene resin, polystyrene resin, polytetrafluoroethylene resin, polyacrylonitrile resin, polyvinyl chloride resin, polyvinyl acetate resin, polymethylmethacrylate resin, polyoxymethylene resin, polyethylene Terephthalate resin, polyamide resin, polycarbonate resin, polyester resin,
An organic polymer resin such as polyurethane resin, an inorganic polymer resin such as silicon resin, or a composite thereof is used.

The photolithography method is a thin film forming method in which after applying a photoresist, only a pattern to be formed is irradiated with light such as ultraviolet rays and only a portion to be formed is cured and other portions are removed to form a pattern. is there. There are two types of photoresist, positive type and negative type. In the case of negative type photoresist, the mask on which the pattern is formed may be inverted. As the photoresist, water-soluble colloid-based, polycinnamic acid-based, cyclized rubber-based, quinonediazide-based materials and the like are used. In particular, since the photosensitive polyimide resin can directly form a pattern, pattern formation is easy, and the Young's modulus of the formed sound absorbing portion is suitable for absorbing surface acoustic waves and has excellent durability. Because it is preferred.

[0014]

According to the surface acoustic wave element of the present invention, since the sound absorbing portion is provided on the outer side portion of the piezoelectric substrate and the sound absorbing portion has an appropriate hardness, other than the surface acoustic wave directed to the output electrode. It is possible to absorb all the surface acoustic waves in the sound absorbing section, and it is possible to prevent generation of noise in the output electrode. In addition, vibrations from the outside can be absorbed by the sound absorbing portion, and noise can be prevented from occurring.

Further, since the sound absorbing portion provided on the outer side of the piezoelectric substrate can be manufactured with extremely high positional accuracy by the photolithography method, the sound absorbing portion can be provided in the vicinity of the input electrode and the output electrode. Therefore, the size of the surface acoustic wave element can be reduced. Further, it is possible to manufacture the sound absorbing section with a high manufacturing yield and a low manufacturing cost.

[0016]

【Example】

Example 1 and Comparative Example FIG. 1 is a plan view of a surface acoustic wave device according to Example 1 of the present invention.

In FIG. 1, 1 is a piezoelectric substrate, 2 is a pair of input electrodes, and 3 is a pair of output electrodes. These are the same as in the conventional example, and the same reference numerals are given and the description thereof is omitted. Reference numeral 5 is a sound absorbing portion provided on the outer side of the piezoelectric substrate 1.

A method of manufacturing the surface acoustic wave device having the above structure will be described below with reference to the drawings. 2A is a perspective view of a piezoelectric substrate having an Al film according to the present invention, and FIG. 2B is a perspective view of a piezoelectric substrate having an input electrode and an output electrode according to the present invention. FIG. 3A is a perspective view of a piezoelectric substrate on which the photosensitive polyimide resin film of the present invention is formed, and FIG. 3B is a perspective view of a piezoelectric substrate on which the sound absorbing portion of the present invention is formed. Here, 6 is an Al film, and 7 is a photosensitive polyimide resin film.

First, the piezoelectric substrate 1 has a thickness of 0.5 mm.
Y-direction cut Z-propagation LiNbO ₃Using a single crystal of
The average surface roughness of the upper surface of the piezoelectric substrate 1 is measured by a lapping machine.
It is a 12Å mirror surface. Next, as shown in FIG.
Then, a 5000 Å thick Al film 6 is formed on the piezoelectric substrate 1.
did. Al film 6 has an ultimate vacuum of 5 × 10^-6Torr
After that, at a film-forming rate of 30Å / s by electron beam evaporation method
Formed. Next, apply a photoresist on the Al film 6.
After that, irradiate UV light through the photomask 1
8 mJ / cm²After irradiation for 5 hours at
A polar photoresist pattern was obtained. Then oxygen
Al is etched with an etchant and unnecessary
I / O electrodes are obtained by removing the photoresist.
It was As shown in FIG. 2B, the input electrode 2 and the output electrode 3
Line and space is 4μm, input electrode 2 and output power
The electrodes 3 were formed in a comb shape with a gap of 1.6 mm. Next, FIG.
As shown in (a), a photosensitive polyimide resin is used as a piezoelectric group.
It is coated on the plate 1 to a thickness of 2 μm and is made of a photosensitive polyimide resin.
The film 7 was formed. Predetermined shape on the photosensitive polyimide resin film 7
18mJ / cm through the photo mask of²20 of ultraviolet rays
After irradiating for 2 seconds to cure the photosensitive polyimide resin film 7,
-Methyl-2-pyrrolidone photosensitive polyimide resin
The removed portion of the membrane 7 was removed. Next, in FIG.
As shown, heat treatment at 400 ℃ for 1 hour
The unnecessary solvent in the light-sensitive polyimide resin film 7 is removed,
Rate 350kg / mm²The sound absorbing part 5 having the hardness of was obtained.

Next, the filter characteristics of the comparative example in which the sound absorbing portion 4 was provided at the end of the piezoelectric substrate 1 facing the surface acoustic wave element and the input electrode 2 and the output electrode 3 in the first embodiment were measured. The filter characteristic was measured by inputting a signal having a center frequency of 215 MHz and a span of 100 MHz and a signal level of 0 dBm. FIG. 4A is a diagram showing the filter characteristics of the surface acoustic wave element according to the first embodiment of the present invention, and FIG.
FIG. 4 is a diagram showing filter characteristics of a surface acoustic wave device according to a comparative example of the present invention.

As is apparent from FIGS. 4 (a) and 4 (b), the surface acoustic wave device according to the present embodiment has an excellent effect in that the output electric signal has little noise. It was

As described above, according to this embodiment, the sound absorbing portion 5 made of the photosensitive polyimide resin is provided on the outer portion of the piezoelectric substrate 1.
Since the surface acoustic wave that causes noise can be absorbed in the sound absorbing portion 5 and the vibration from the outside can be absorbed in the sound absorbing portion 5, the noise included in the output electric signal can be extremely reduced. It turns out that it can be reduced.

Further, according to the manufacturing method of this embodiment, since the sound absorbing portion 5 made of the photosensitive polyimide resin is provided on the outer portion of the piezoelectric substrate 1 by the photolithography method, the sound absorbing portion 5 is provided near the input electrode 2 and the output electrode 3. The sound absorbing part 5 can be provided, and the size of the surface acoustic wave element can be reduced. Further, it has been found that the sound absorbing portion having a high Young's modulus capable of absorbing surface acoustic waves can be manufactured with high yield and high productivity, so that the manufacturing cost can be reduced.

(Embodiment 2) FIG. 5 is a plan view of a surface acoustic wave device which is a convolver in the second embodiment.

In FIG. 5, reference numeral 1 is a piezoelectric substrate, 5 is a sound absorbing portion provided on the outer side of the piezoelectric substrate 1, 8 and 9 are a pair of input electrodes provided in the vicinity of both sides of the piezoelectric substrate 1, 1
Reference numeral 0 denotes an output electrode provided in a substantially central portion of the piezoelectric substrate 1, and a ground electrode (not shown) is provided on the back surface side of the piezoelectric substrate 1.

The operation of the surface acoustic wave device constructed as above will be described below. First, an input electric signal is applied to each of the input electrodes 8 and 9. Each input electric signal generates a surface acoustic wave in the piezoelectric substrate 1. The two surface acoustic waves generated by the respective input electric signals propagate through the piezoelectric substrate 1 and are superposed below the output electrode 10. At this time, if the two input signals are sufficiently large, the convolution integration of the two input signals is performed and the electric signals are extracted from the output signal 10.

As described above, according to this embodiment, since the sound absorbing portion 5 is provided on the outer side of the piezoelectric substrate 1, the surface acoustic wave reflected at the end portion of the piezoelectric substrate 1 is absorbed by the sound absorbing portion 5. It has been found that since the vibrations from the outside can be absorbed by the sound absorbing portion 5, an output electric signal with extremely little noise can be obtained.

(Embodiment 3) FIG. 6 is a plan view of a surface acoustic wave element which is a waveguide type convolver in the third embodiment.

In FIG. 6, reference numeral 1 is a piezoelectric substrate, 5 is a sound absorbing portion provided on the outer side of the piezoelectric substrate 1, 8 and 9 are a pair of input electrodes provided in the vicinity of both sides of the piezoelectric substrate 1, 1
Reference numerals 0 and 11 denote a pair of output electrodes provided above and below the substantially central portion of the piezoelectric substrate 1, and 12 denotes a plurality of waveguides provided at the substantially central portion of the piezoelectric substrate 1.

The operation of the surface acoustic wave device having the above structure will be described below. First, an input electric signal is applied to each of the input electrodes 8 and 9. Each input electric signal generates a surface acoustic wave in the piezoelectric substrate 1. The two surface acoustic waves generated by the respective input electric signals propagate in the direction perpendicular to the waveguide 12 by being subjected to convolution integration while being guided to the waveguide 12 in the piezoelectric substrate 1 and propagated. A surface acoustic wave is generated. The surface acoustic wave is converted into an electric signal by the output electrode 10.

As described above, according to this embodiment, since the sound absorbing portion 5 is provided on the outer side of the piezoelectric substrate 1, it is possible to absorb the surface acoustic wave that causes noise propagating in the piezoelectric substrate 1. You can Further, it has been found that since the vibration from the outside can be absorbed by the sound absorbing unit 5, it is possible to reduce the noise component in the convolution-integrated output electric signal.

[0032]

As described above, according to the present invention, since the sound absorbing portion having the Young's modulus capable of absorbing the surface acoustic wave is provided on the outer side portion of the piezoelectric substrate, the surface acoustic wave is absorbed at the end portion of the piezoelectric substrate. be able to. Therefore, since it is possible to absorb the surface acoustic wave which is reflected at the end portion of the piezoelectric substrate and becomes the noise component of the electric signal at the output electrode, the noise component of the electric signal can be remarkably reduced. In addition, since vibration that enters the surface acoustic wave element from the outside can be absorbed by the sound absorbing portion provided on the outer side of the piezoelectric substrate, it is possible to prevent the noise of the electric signal due to the external vibration. The surface acoustic wave element can be realized.

Further, according to the present invention, since the sound absorbing portion provided on the outer side portion of the piezoelectric substrate is formed by the photolithography method, the sound absorbing portion can be accurately provided in the vicinity of the input electrode and the output electrode. The size of the element can be reduced. Further, since the sound absorbing portion capable of sufficiently absorbing the surface acoustic wave can be easily manufactured with high yield and high productivity, it is possible to realize the excellent manufacturing method of the surface acoustic wave element with low manufacturing cost.

[Brief description of drawings]

FIG. 1 is a plan view of a surface acoustic wave device according to a first embodiment of the present invention.

2A is a perspective view of a piezoelectric substrate on which an Al film of the present invention is formed. FIG. 2B is a perspective view of a piezoelectric substrate on which an input electrode and an output electrode of the present invention are formed.

3A is a perspective view of a piezoelectric substrate on which a photosensitive polyimide resin film of the present invention is formed. FIG. 3B is a perspective view of a piezoelectric substrate on which a sound absorbing portion of the present invention is formed.

FIG. 4A is a diagram showing a filter characteristic of a surface acoustic wave element according to a first embodiment of the present invention. FIG. 4B is a diagram showing a filter characteristic of a surface acoustic wave element according to a comparative example of the present invention.

FIG. 5 is a plan view of a surface acoustic wave device that is a convolver according to a second embodiment of the present invention.

FIG. 6 is a plan view of a surface acoustic wave element that is a waveguide type convolver according to a third embodiment of the present invention.

FIG. 7 is a plan view of a conventional surface acoustic wave device.

[Explanation of symbols]

 1 Piezoelectric Substrate 2 Input Electrode 3 Output Electrode 4 Sound Absorption Part 5 Sound Absorption Part 6 Al Film 7 Photosensitive Polyimide Resin Film 8, 9 Input Electrode 10, 11 Output Electrode 12 Waveguide

Claims (3)

[Claims] 1. A piezoelectric substrate for converting an input electric signal into a surface acoustic wave, a pair of input electrodes provided on the piezoelectric substrate for inputting an electric signal, and the surface acoustic wave as an electric signal. A surface acoustic wave device comprising: a pair of output electrodes provided on the piezoelectric substrate for conversion; and a sound absorbing portion that absorbs a surface acoustic wave of the input electrode, wherein the sound absorbing portion is the piezoelectric substrate. A surface acoustic wave element formed on the outer side of the. 2. The surface acoustic wave device according to claim 1, wherein the sound absorbing portion is made of a photosensitive polyimide resin. 3. The method of manufacturing a surface acoustic wave device according to claim 1, wherein the sound absorbing portion is formed on an outer portion of the piezoelectric substrate by photolithography. And a method for manufacturing a surface acoustic wave device.