Tetsuya Hirashima

Acoustically-induced migration of thin film electrodes in SAW-resonator-coupled filters

The aging characteristics of recently developed SAW-resonator-coupled filters are discussed. The rejection level of the filter was decreased by applying power. This result means that the Q-factor of the surface acoustic wave (SAW) resonator decreases with applied power. This change was studied by means of resistivity measurement and microscopic observation. It was found that the resistivity of the thin film increases by stress-induced migration. The decrease of rejection level and the decrease of the resonators Q-factor are explained by the measurement resistivity. Voids and hillocks were observed on thin-film electrodes. These observations also support the resistivity increase caused by stress-induced migration. It was seen that the formation of voids and hillocks induced the resistivity increase in thin-film electrodes. It is concluded that the cause of electrical characteristics change is the resistivity increase in the thin-film electrodes.<<ETX>>

Precise Measurement of Leaky SAW Velocity on LiTaO3-36° YX Substrates Using a Comb-Filter Method

A precise measurement method for SAW velocity using a comb-filter is presented. Some of the points in this method are proper numbering of the comb-peaks, verification of the numbering, a calculation formula for phase velocity and consideration of measurement accuracy. Using the method, leaky SAW velocity on LiTaO3-36° YX substrates with Al film is determined up to 1 GHz. The studies reveal the following: dispersion of the wave is linear in frequency and film thickness, and the measurement accuracy at 840 MHz is ±0.3 m/s (±0.7×10-4).