Katsuo Sato

Propagation Characteristics of Surface Acoustic Waves on Langasite

The propagation characteristics of surface acoustic waves (SAW) on La3Ga5SiO14 were investigated by both experimental and numerical methods. The experimental results of the SAW velocity and the coupling coefficient (k2) on X-cut and Y-cut substrates were in good agreement with the numerical results using the material constants reported previously. However, the experimental results of the temperature coefficient of delay (TCD) differed from that of the numerical calculations. So, a modification of the temperature coefficients of the material constants was performed numerically by the measured data using the direct search of optimization method. The numerical results obtained using the new constants were in good agreement with the experiment result on the X-cut and Y-cut substrates. Other cuts were also studied using the new constants. Then it was confirmed theoretically and experimentally that the temperature stable cut was located at (0°, 140°, 22.5°) cut with k2 of 0.32% and TCD (second-order coefficient) of 5.2×10-8/°C2.

The Power Durability of 900 MHz Band Double-Mode-Type Surface Acoustic Wave Filters and Improvement in Power Durability of Al–Cu Thin Film Electrodes by Cu Atom Segregation

The power durability of double-mode-type surface acoustic wave filters, which have recently seen wide use in cellular phones, is investigated. It was found that the lifetime of double-mode-type surface acoustic wave filters is reduced considerably when high input power is applied, due to non-linear behavior. Moreover, the authors demonstrate that the power durability of an Al–Cu thin film electrode is greatly improved by Cu atom segregation in the grain boundaries.

Power Durability of Al–W Alloy Electrodes Used in RF-Band Surface Acoustic Wave Filters

For the RF-band surface acoustic wave (SAW) filters, the power durability of Al–W alloy electrodes was studied. It was shown that the power durability of Al–0.5 at.% W alloy electrodes is superior to that of the Al–0.5 at.% Ti alloy electrodes which have been known as power-durable electrodes. The amount of hillocks decreases as the W content in the Al–W alloy increases, on the other hand, the lifetime of the electrodes is maximized at a W content of 0.5 at.%. These phenomena suggest that the whiskers, instead of hillocks, grown on the sides of the electrodes, cause the electrical short between the hot and the ground electrodes and suppress the lifetime increase.