JP2000261285A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface acoustic wave device which can be miniaturized without requiring a cover or a package. SOLUTION: A first insulating film 4 formed on input/output interdigital electrodes 2 and 3 and a surface acoustic wave propagation line and input/output interdigital electrodes 2 and 3 for surface acoustic wave transmission and reception are so formed that a film thickness h1 of the first insulating film 4 and a film thickness h2 of input/output interdigital electrodes 2 and 3 may satisfy h1/h2>=0.1 and parts other than parts on input/output interdigital electrodes 2 and 3 and the surface acoustic wave propagation line are formed with a second insulating film 5, and contact holes 10 are formed in the second insulating film 5 on input/output signal taking-out electrode pads 6 and 7 and plural input/output earth electrode pads 8 and 9, and plural input/output earth electrode pads 8 and 9 are connected through contact holes 10 by a common earth electrode pattern 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a surface acoustic wave device,
In particular, the present invention relates to a high-performance and small-sized surface acoustic wave device such as a SAW filter and a resonator used for a wireless communication device.

[0002]

2. Description of the Related Art In a conventional surface acoustic wave device, a method of mounting a surface acoustic wave element on a ceramic package or the like and obtaining a desired frequency characteristic, and wiring in the package,
There are known a method of mounting a surface acoustic wave element on a face-down type substrate, a method of forming an extraction electrode using a unique cover substrate while maintaining airtightness, and the like. As a prior art regarding such miniaturization, for example, Japanese Patent Publication No. 8-213
873 and JP-A-8-213874.

[0003]

The surface acoustic wave device is generally mounted on a ceramic package or the like in order to prevent the frequency characteristics from being deteriorated due to electrode corrosion due to external moisture or the like. However, development of a package-less surface acoustic wave device, that is, a chip-on-board type surface acoustic wave device is desired in order to cope with miniaturization and cost reduction.

In recent years, in response to this demand, downsizing using a face-down type or the like has been progressing. However, as the pattern becomes complicated, the number of Au bumps increases and a unique cover is required in terms of airtightness. There's a problem. Furthermore, with the demand for higher frequency and lower loss, the electrode pattern has become submicron, and the increase in defects due to foreign matter in the manufacturing process, the increase in the number of pads for connection with the outside, the increase in defects, and the decrease in work efficiency It is a problem.

An object of the present invention is to provide a surface acoustic wave device which solves the above-mentioned problems, does not require a cover and a package, and can be reduced in size.

[0006]

Means for Solving the Problems To achieve the above object, the first means is to provide an elastic surface propagation path on a piezoelectric substrate,
In a surface acoustic wave device having a plurality of input interdigital transducers and a plurality of output interdigital transducers for transmitting and receiving surface acoustic waves to and from each other, a first insulating film is provided on the input and output interdigital transducers and on the surface acoustic wave propagation path. A second insulating film other than the input and output interdigital transducers and the surface acoustic wave propagation path, and an input signal extraction electrode pad and an output signal extraction electrode pad for extracting a signal to the outside; A contact hole is formed in the second insulating film on the input ground electrode pad and the output ground electrode pad, and the input signal extraction electrode pattern, the output signal extraction electrode pattern, and the common ground electrode pattern connecting both electrode patterns are formed. And a bump is formed on a part of each electrode pattern.

In order to achieve the above object, a second means is the first means, wherein the thickness of the first insulating film is h.
1. When the thickness of the input and output IDT electrodes is h2, h
1 / h2 ≧ 0.1.

As described above, the present invention prevents the deterioration of the frequency characteristics due to external moisture and foreign substances by forming the first insulating film only on the input / output IDT electrodes and the surface acoustic wave propagation path. I have.

That is, the first insulating film is subjected to a standing test in a wet state. When the thickness of the insulating film is h1 and the thickness of the electrode for transmitting and receiving surface acoustic waves is h2, h1 / h2 ≧ 0.
1. As a result of the foreign matter resistance test, it was confirmed that there was no deterioration in the frequency characteristics when h1 / h2 ≧ 0.08. From the above, by defining the first insulating film thickness as h1 / h2 ≧ 0.1, the hermeticity of the surface acoustic wave device can be maintained without special treatment of the cover or the like.

Further, with respect to an increase in the number of external connection pads due to a complicated pattern such as a multi-electrode configuration, a contact hole is formed in a second insulating film formed on a plurality of input / output ground electrode pads. By separately forming a common ground electrode pattern through the contact hole and connecting a plurality of input and output ground electrode pads, the number of connection pads can be reduced.

With the above configuration, a small chip-on-board type surface acoustic wave device that does not require a cover or a package can be realized.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of the present invention, and FIG.
3 is a sectional view taken along the line XX 'of FIG. 1, and FIG. 3 is a sectional view taken along the line YY' of FIG.

The surface acoustic wave device has a structure in which an input interdigital transducer 2 for transmitting and receiving a surface acoustic wave and an output interdigital transducer 3 are provided on a piezoelectric substrate 1 made of lithium tantalate or lithium diobate. In order to obtain a desired frequency characteristic, a multi-electrode configuration in which a plurality of input interdigital transducers 2 and a plurality of output interdigital transducers 3 are formed.

This electrode pattern is formed by forming a film of Al or an Al-based alloy by EB evaporation or sputtering, and then performing a series of photolithography steps of exposure, development, and etching.

In the present invention, only the input and output IDTs 2 and 3 and the surface acoustic wave propagating portion are provided with the first insulating film (S) on the electrode pattern completed in the photolithography step.
An iO ₂ film or a ZnO film) 4 is formed. After that, the surfaces other than the input and output IDTs 2 and 3 and the surface acoustic wave propagating portion are covered with a second insulating film (SiO ₂ film or ZnO film).
Film 5) and an input signal extraction electrode pad 6
Above, on the output signal extraction electrode pad 7, on the plurality of input ground electrode pads 8, on the plurality of output ground electrode pads 9,
A contact hole 10 is formed in the upper second insulating film 5.

In the above process, first, an insulating film (Si
After forming an O ₂ film or a ZnO film), there is a step of protecting a portion requiring an insulating film using a resist as a mask, and a step of subsequently removing the insulating film by dry etching or wet etching. And a contact hole can be formed.

Further, after forming a contact hole 10 in the second insulating film 5, A is deposited by EB evaporation or sputtering.
A common ground electrode pattern 11, an input signal extraction electrode pattern 12, and an output signal extraction electrode pattern 13 made of 1 or an Al-based alloy are formed.

Thereafter, in order to mount the surface acoustic wave device on a chip, the input signal extraction electrode pattern 12, the output signal extraction electrode pattern 13, and the common ground electrode pattern 1
The Au bumps 14 are applied to a part of 1.

In the present embodiment, the first insulating film 4 has a thickness of 300 ° in consideration of moisture and foreign matter, and the second insulating film 5 has a common ground electrode pattern 11 and a lower layer. 5000 in consideration of the coupling with the electrode pattern formed in
Å

When the thickness of the insulating film is h1, and the thickness of the electrode for transmitting and receiving surface acoustic waves is h2, the ratio of the two is h1 / h.
FIG. 4 shows the relationship between No. 2 and the standing time in moisture. The test of leaving in the humidity was performed under the conditions of 40 ° C. and 95% RH, and the specification value was 50.
Under the condition that the filter frequency characteristics do not change for 0 hours or more, h1 / h2 needs to be 0.1 or more, particularly 0.15 or more, to satisfy the condition.

FIG. 5 shows the relationship between h1 / h2 and the foreign matter test. In this foreign matter test, Ni
In this test, the powder is dusted and the leakage current is measured to determine the insulation resistance value. The specification value of this test is that the insulation resistance value is 20M
Ω or more, and h1 / h2 is 0.0
It is necessary to be 8 or more, particularly preferably 0.15 or more. H1 / h2 is 0.1 or more, preferably 0.15 or more in order to satisfy the specification values of both the wet test and the foreign substance test.

In the present invention, the electrode pattern structure of the surface acoustic wave device has a multi-electrode structure. However, the same applies to a surface acoustic wave device such as a resonator structure which requires many input and output ground electrode pads. The effect is obtained.

In mounting the chip-on-board type surface acoustic wave device of the present invention on a substrate, if a distance in the height direction is required, it can be dealt with by forming Au bumps in two steps.

[0024]

As described above, according to the present invention,
When the thickness of the input / output interdigital transducer and the first insulating film formed on the surface acoustic wave propagation path is h1, and the thickness of the input / output interdigital transducer for transmitting and receiving surface acoustic waves is h2, h1 /
h2 ≧ 0.1, input and output interdigital electrodes, and input and output signal extraction electrode pads for extracting signals to the outside by forming a second insulating film other than on the surface acoustic wave propagation path; On the plurality of input and output ground electrode pads, the second
A contact hole is formed in the insulating film, and a plurality of input and output ground electrode pads are connected by a common ground electrode pattern via the contact hole;
A small chip-on-board type elastic surface with excellent airtightness and foreign matter resistance, and with a small number of bumps, with a configuration in which the input and output signal extraction electrode pads and a part of the common ground electrode pattern are bumped. A wave device can be realized.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view taken along the line XX ′ of FIG.

FIG. 3 is a sectional view taken along the line YY ′ of FIG. 1;

FIG. 4 is a characteristic diagram showing a relationship between h1 / h2 and a standing time in moisture.

FIG. 5 is a characteristic diagram showing a relationship between h1 / h2 and an insulation resistance value.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric substrate 2 input interdigital electrode 3 output interdigital electrode 4 first insulating film 5 second insulating film 6 input signal extraction electrode pad 7 output signal extraction electrode pad 8 input ground electrode pad 9 output ground electrode pad 10 contact Hall 11 Common ground electrode pattern 12 Input signal extraction electrode pattern 13 Output signal extraction electrode pattern 14 Au bump

Continuing on the front page (72) Inventor Seiichi Ogawa 1 Kitano Masaki, Mizusawa City, Iwate Prefecture Inside Hitachi Media Electronics Co., Ltd. F term (reference) 5J097 AA25 AA29 BB11 DD12 DD24 DD28 FF05 GG03 GG04 HA03 JJ06 KK09

Claims (2)

[Claims] 1. A surface acoustic wave device in which a plurality of input interdigital transducers and a plurality of output interdigital transducers for transmitting and receiving surface acoustic waves to and from each other on a surface acoustic path of a piezoelectric substrate are provided. A first insulating film is formed on the electrode and the surface acoustic wave propagation path, and a second insulating film is formed on the input and output interdigital transducers and the surface acoustic wave propagation path to take out a signal to the outside. A contact hole is formed in the input signal extraction electrode pad and the output signal extraction electrode pad, and a second insulating film on the plurality of input ground electrode pads and the output ground electrode pad, wherein the input signal extraction electrode pattern and the output signal extraction A surface acoustic wave device comprising: an electrode pattern; a common ground electrode pattern for connecting both electrode patterns; and a bump formed on a part of each electrode pattern. 2. The elasticity according to claim 1, wherein the ratio h1 / h2 of the thickness h1 of the first insulating film to the thickness h2 of the input and output interdigital transducers is 0.1 or more. Surface wave device.