JPH0238494Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a surface acoustic wave device, and particularly relates to an electrode structure of a surface acoustic wave device.

[Technical background of the invention and its problems]

Among the surface acoustic wave devices, for example, a surface acoustic wave resonator will be explained with reference to FIG. A surface acoustic wave resonator 7 consisting of an interdigital electrode 5 (hereinafter referred to as IDT) and a pair of grating reflective electrodes 6, 6 sandwiching the IDT 5 is formed on the mirror-finished main surface of the piezoelectric substrate 1. ing.

Between these two grating reflective electrodes 6, 6, a standing wave of a surface wave excited and radiated from the IDT 5 is caused to resonate, thereby acting as a high-Q resonator.

However, the IDT 5 and the grating reflective electrodes 6, 6 are generally made of aluminum, and when the surface acoustic wave resonator 7 is operated for a long time,
There is a problem that the resonance loss level gradually deteriorates due to the deterioration of the reflecting surface, and the function of the surface acoustic wave resonator 7 deteriorates significantly.

Therefore, in order to prevent the long-term resonance loss from deteriorating, an example has been proposed in which the IDT 5 and the grating reflective electrode 6 are made of an aluminum-copper alloy with a copper content ratio of 0.1 to 5.0%. However, although the resonance characteristics of this surface acoustic wave resonator are improved over long-term operation than those using IDTs made of aluminum and grating reflective electrodes, the initial characteristics are on the contrary deteriorated. was confirmed. For example, if the thickness of piezoelectric substrate 1 is 0.3 to 0.5 mm, IDT5
and the grating reflective electrode 6 have a thickness of 1.0~
1.5μm surface acoustic wave resonator with resonance frequency of 100MHz
When used in the band, the initial characteristics deteriorate by about 0.2 to 0.5 dB.

The cause of this is when using an aluminum-copper alloy.
This is thought to be because the electrode edges of the IDT 5 and the grating reflective electrode 6 have more irregularities than those formed of aluminum, which reduces reflection of surface acoustic waves.

[Purpose of invention]

The present invention has been devised in view of the above-mentioned problems, and is intended to provide a surface acoustic wave device that has low resonance loss in its initial characteristics and does not degrade over long periods of actual use.

[Summary of the idea]

In this invention, by forming the interdigital electrode and reflective electrode from two layers of aluminum and copper alloy with a copper weight composition ratio of 0.1 to 5.0, the initial characteristics have low resonance loss and long-term resistance. This is a surface acoustic wave device with little deterioration in actual use.

[Example of idea]

An embodiment of the present invention will be described with reference to FIGS. 2 and 3. Here, a surface acoustic wave resonator, for example, will be described as an example of the surface acoustic wave device. Further, FIGS. 2 and 3 are schematic diagrams of a surface acoustic wave resonator in which an IDT and a grating reflective electrode are enlarged to explain an embodiment of the present invention. Note that the structure of the surface acoustic wave resonator is the same as that of the surface acoustic wave resonator shown in FIG. 1 except for the electrode structure of the IDT and the grating reflective electrode, so a detailed explanation will be omitted.

In FIGS. 2 and 3, an aluminum electrode 11 having a height h ₂ or a thickness of 5000 Å is formed on a piezoelectric substrate 1 having a thickness of 0.3 mm. Further, on the aluminum electrode 11, an aluminum-copper alloy electrode 10 having a height _h1 , that is, a thickness of 5000 Å and containing copper in a weight composition ratio of approximately 2% is formed. This two-layer structure of aluminum electrode 11 and aluminum-copper alloy
An IDT 5 and grating reflective electrodes 6, 6 are configured.

Briefly, the method for manufacturing the surface acoustic wave resonator 7 is as follows: Aluminum with a thickness of about 5000 Å is deposited on a LiTa0 ₈ single crystal wafer with a thickness of 0.3 mm. On top of that, an aluminum-copper alloy containing 2 wt% copper is deposited to a thickness of about 5000 Å, and a resist is applied. Next, the surface acoustic wave resonator 7 is obtained by exposing to light through a mask, developing and etching, and then peeling off the resist.

Here, as shown in Figure 4, the thickness of the piezoelectric substrate is
0.3mm, electrode thickness is 1.0μm, and IDT5 and grating reflective electrode6 are made from conventional aluminum.
A 100MHz band surface acoustic wave resonator consisting of
The resonance characteristics of the 22 when a power of 1 mW was applied and a mounting test was conducted for 500 hours resulted in a resonance loss of approximately 2 dB during the mounting test for 500 hours. On the other hand, when the surface acoustic wave resonator 7 of the present invention shown in FIGS. 2 and 3 is subjected to a mounting test for 500 hours under the same conditions as described above, the same resonance characteristic 21 is obtained. As shown in characteristic 21 in FIG. 4, the resonance loss was extremely small even after a long-term mounting test, and the initial characteristics were also good. Incidentally, as a matter of course, the initial characteristics of the surface acoustic wave resonator of the above example are as follows:
It was confirmed that the IDT 5 and the grating reflective electrodes 6 and 6 were much improved compared to the surface acoustic wave resonator 7 in which the IDT 5 and the grating reflective electrodes 6 were formed of an aluminum-copper alloy containing 2% copper by weight. This is because the lower portions of the IDT 5 and the grating reflective electrodes 6, 6, that is, the surface of the aluminum electrode 11, are smooth and have no unevenness, so that surface acoustic waves are reflected well.

In the above example, the weight composition ratio of copper in the aluminum-copper alloy was 2%.
Remarkable effects were also seen at weight composition ratios of about 0.1 to 5.0%. This is because if the weight composition ratio of copper in the aluminum-copper alloy electrode is less than 0.1wt%, significant resonance loss will occur during a long-term mounting test, and if it exceeds 5.0wt%, the unevenness of the aluminum-copper alloy electrode will occur. This is because the reflection of surface waves becomes significant, the reflection of surface waves decreases, and the deterioration of the initial characteristics becomes noticeable.
Furthermore, IDT5 and grating reflective electrode 6,
Although the height _h2 of the aluminum electrode 11 and the height _h1 of the aluminum-copper alloy electrode 10 are ₁ : ₁ , the present invention is not limited to this. The ratio can be arbitrarily selected. In other words, when the weight composition ratio of copper to the total aluminum of the IDT 5 and the grating reflective electrode 6 was about 1%, the initial characteristics were good and no reduction in resonance loss was observed. Also, the one of this invention
Similar effects can be obtained in surface acoustic wave resonators with different electrode configurations, such as a surface acoustic wave resonator in which two IDTs are arranged, and a ring-shaped resonator in which a large number of IDTs are arranged.

[Effect of idea]

According to the present invention, since the interdigital electrode and the grating reflective electrode are formed from an aluminum electrode and an aluminum-copper alloy electrode, there is little reduction in resonance loss in the initial characteristics, and moreover, the resonance loss is reduced during long-term actual use. A surface acoustic wave device with very little deterioration can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a conventional surface acoustic wave resonator, FIG. 2 is a schematic plan view showing an embodiment of the surface acoustic wave resonator of the present invention, and FIG.
FIG. 4 is a cross-sectional view showing a cross section taken along X', and is a resonance characteristic diagram of the surface acoustic wave resonator. DESCRIPTION OF SYMBOLS 1...Piezoelectric substrate, 5...Interdigital electrode, 6...Grating reflective electrode, 7 ...Surface acoustic wave resonator, 10...Aluminum-copper alloy electrode, 11...Aluminum electrode.

Claims (1)

[Claims for Utility Model Registration] (1) A surface acoustic wave device comprising reflective electrodes sandwiching interdigital electrodes disposed on a piezoelectric substrate at predetermined intervals, wherein the interdigital electrodes and the reflective electrodes is a first layer formed of aluminum;
The weight composition ratio of the copper placed on this first layer is
A surface acoustic wave device comprising a second layer made of an aluminum-copper alloy of 0.1 to 0.5%. (2) The ratio of the thicknesses of the first layer and the second layer is 1:
1. A surface acoustic wave device according to claim 1, characterized in that: 1.