JP2002076828A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave element with a simple configuration that can easily improve an attenuation characteristic in the vicinity of its bandwidth. SOLUTION: In the surface acoustic wave element where metallic film interdigital IDTs 12a, 13a are formed to one side 11a of a piezoelectric substrate 11, a conductor pattern 14 is formed to the other side 11b of the piezoelectric substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interdigital converter (IDT) on a piezoelectric substrate.
The present invention relates to an improvement of a surface acoustic wave device formed by forming a plurality of comb-like electrodes for forming a sducer.

[0002]

2. Description of the Related Art As is well known, a SAW (Surface Acoustic Wave) device on which a surface acoustic wave element as described above is mounted has been widely used, for example, as a surface acoustic wave filter or a delay circuit. In recent years, it has been widely used as an electronic component of a mobile wireless communication device because of its merit that it can be made thinner and smaller.

In this SAW device, a surface acoustic wave element is adhered to a ceramic package, and a bonding pad of the surface acoustic wave element is connected to a signal terminal in the package.
For example, it is configured to be electrically connected by a wire such as gold (Au) or aluminum (Al).

In the SAW device, a bonding wire is used for electrical connection between the surface acoustic wave element and the package. Therefore, signal terminals in the package must be arranged so as to surround the outer periphery of the surface acoustic wave element. Therefore, the configuration is not suitable for miniaturization.

On the other hand, recently, in order to further reduce the size of the SAW device, the bonding pad of the surface acoustic wave element and the signal terminal of the package are replaced with gold (A).
Mounting using a face-down bonding technique, which electrically connects via bumps made of u) or the like, has been put to practical use.

More specifically, the surface on which the bonding pads of the piezoelectric substrate constituting the surface acoustic wave element are formed is opposed to the surface on which the metal pads serving as signal terminals of the package are formed. The bumps are electrically connected to each other, and the surface acoustic wave element is sealed by covering the package with a ceramic cap.

According to such face-down bonding mounting, since no bonding wire is used for electrical connection between the surface acoustic wave element and the package, the signal terminals in the package are arranged so as to surround the outer periphery of the surface acoustic wave element. Since it is not necessary to dispose the SAW device, the size of the SAW device can be reduced.

[0008]

However, the conventional surface acoustic wave device as described above has a problem that it is very difficult to obtain a desired attenuation characteristic near a band as a SAW device. I have.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a very good surface acoustic wave device capable of easily improving the attenuation characteristics near a band with a simple configuration. Aim.

[0010]

A surface acoustic wave device according to the present invention is directed to a surface acoustic wave device in which a comb-like electrode is formed of a metal thin film on one surface of a piezoelectric substrate. And
A conductive pattern is formed on the other surface of the piezoelectric substrate.

According to the above configuration, the stray capacitance component formed between the comb-teeth-shaped electrode and the conductive pattern couples with the impedance component of the surface acoustic wave element. It is possible to improve the attenuation characteristics near the band.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG.
Shows one surface 11a of the piezoelectric substrate 11 constituting the surface acoustic wave element described in this embodiment. That is, two surface acoustic wave filters 12 and 13 are formed in parallel on one surface 11a of the piezoelectric substrate 11.

One surface acoustic wave filter 12 includes a plurality (three in the illustrated case) of IDTs 12a formed of a metal thin film,
The reflectors 12b provided on both sides of the IDT 12a
And a terminal electrode 12c connected to each comb-like electrode constituting the IDT 12a.

The other surface acoustic wave filter 13
A plurality (three in the illustrated case) of IDTs 13 made of metal thin films
a and the reflectors 1 disposed on both sides of the IDT 13a.
3b and a terminal electrode 13c connected to each comb-like electrode constituting the IDT 13a.

These surface acoustic wave filters 12, 13
Are formed, for example, by depositing an aluminum alloy film on the piezoelectric substrate 11 by a sputtering method and then using a photolithography technique.

On the other hand, FIG.
The other surface 11b of FIG. That is, the other surface 11b of the piezoelectric substrate 11 has the IDTs 12a, 1
A conductive pattern 14 serving as a floating electrode is formed in a region corresponding to 3a. This conductive pattern 14
Is also formed by the same photolithography technique as the method of forming the surface acoustic wave filters 12 and 13.

The process for forming the surface acoustic wave filters 12 and 13 and the conductive pattern 14 is as follows.
An aluminum electrode layer having a thickness of about 50 nm is formed on the other surface 11b of the substrate 1 by vapor deposition. Thereafter, an aluminum alloy electrode layer is formed on one surface 11a of the piezoelectric substrate 11 by sputtering.

In the piezoelectric substrate 11 having the aluminum layers formed on both sides as described above, first, the other surface 11b
Is formed by photolithography. Thereafter, while protecting the electrode layer on the other surface 11b by resist coating, surface acoustic wave filters 12, 13 are formed on one surface 11a by photolithography technology, and a surface acoustic wave element is formed here. You.

The surface acoustic wave device configured as above is
As shown in FIG. 2, a stray capacitance component C is present between the conductive patterns 14 and the IDTs 12 a and 13 a forming the surface acoustic wave filters 12 and 13. In other words, the formation of the conductive pattern 14 on the other surface 11b of the piezoelectric substrate 11 increases the stray capacitance component of the surface acoustic wave element.

And the increased stray capacitance component:
By coupling with the impedance component of the surface acoustic wave element, attenuation near the band can be obtained as a SAW device. The stray capacitance here is about 0.3 pF.

FIG. 3A shows the conductive pattern 1
FIG. 3B shows a wide-band frequency characteristic of a SAW device using the surface acoustic wave element on which the conductive pattern 14 is formed. FIG.
4 shows the broadband frequency characteristics of the device. As is clear from the comparison between the two, the SAW device using the surface acoustic wave element on which the conductive pattern 14 is formed has improved low-frequency attenuation characteristics.

The surface acoustic wave device having the conductive pattern 14 formed thereon has a terminal electrode 1 as shown in FIG.
A bump 15 made of gold (Au) or the like is formed on 2c and 13c. When the bonding of the bumps 15 is performed by a machine, since the patterns on the IDTs 12a and 13a are used, the positional accuracy is high, and the accuracy within about 30 μm can be realized.

After the bumps 15 are bonded,
The piezoelectric substrate 11 enters a flip chip process in which the piezoelectric substrate 11 is bonded to the package 16 through a timing process in which the piezoelectric substrate 11 is divided into individual pieces. That is, the diced surface acoustic wave element is carried on a dedicated tray, and the bump 15 is flip-chip bonded to the connection electrode 16a formed on the package 16 by pressure and load by a flip chip device.

After that, a ceramic cap 17 covering the surface acoustic wave element is put on the package 16 and
The surface acoustic wave element is sealed by bonding with an adhesive 18, and a SAW device is configured here.

Here, the other surface 11b of the piezoelectric substrate 11
The conductive pattern to be formed is not limited to the shape shown in FIG. 1B. For example, as shown in FIG. 5B, the conductive patterns are individually formed in regions corresponding to the surface acoustic wave filters 12 and 13, respectively. The conductive patterns 19a and 19b may be formed.

In short, the conductive pattern is the piezoelectric substrate 1
As long as the IDTs 12a and 13a forming the surface acoustic wave filters 12 and 13 formed in 1 have an action of giving a necessary stray capacitance component C, their shapes and positions are not particularly limited. Various settings can be made as necessary, for example, for convenience in manufacturing.

It should be noted that the present invention is not limited to the above-described embodiment, and can be variously modified and implemented without departing from the spirit and scope of the present invention.

[0028]

As described in detail above, according to the present invention,
It is possible to provide an extremely good surface acoustic wave element that can easily improve the attenuation characteristics near the band with a simple configuration.

[Brief description of the drawings]

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

FIG. 2 is a sectional side view for explaining a stray capacitance component in the embodiment.

FIG. 3 is a view for explaining wideband frequency characteristics in the embodiment.

FIG. 4 is a sectional side view for explaining flip chip mounting in the embodiment.

FIG. 5 is an exemplary plan view shown for explaining a modification of the conductive pattern in the embodiment;

[Explanation of symbols]

 11: Piezoelectric substrate, 12, 13: Surface acoustic wave filter, 14: Conductive pattern, 15: Bump, 16: Package, 17: Cap, 18: Adhesive 19a, 19b: Conductive pattern.

Claims (5)

[Claims] 1. A surface acoustic wave device having a comb-shaped electrode formed of a metal thin film on one surface of a piezoelectric substrate, wherein a conductive pattern is formed on the other surface of the piezoelectric substrate. . 2. The piezoelectric device according to claim 1, wherein the conductive pattern is formed on substantially the entire other surface of the piezoelectric substrate.
The surface acoustic wave device as described in the above. 3. The device according to claim 1, wherein the conductive pattern is formed at a position facing the comb-shaped electrode.
The surface acoustic wave device as described in the above. 4. The surface acoustic wave device according to claim 1, wherein the conductive pattern is formed at a position facing at least a part of the comb-shaped electrode. 5. The surface acoustic wave device according to claim 1, wherein the conductive pattern forms a stray capacitance with the comb-like electrode.