Durability of aluminum-alloy electrodes for high power SAW filters which are used for antenna duplexers in cellular portable telephones is experimentally investigated. Titanium added aluminum is deposited by DC magnetron sputtering. The new alloy expands the limitation on the driving power of the filters. Temperature, particularly, accelerates the degradation of the high power filters, the film resistance causes an even greater increase in temperature. Thus, optimum value for titanium of 0.4 wt.% can be achieved for high durability filters.

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DC magnetron sputtering and Ti addition for A 1 electrodes are studied to achieve higher durability of SAW devices operating at high frequency and high power. Experiments on SAW resonators and ladder type SAW filters obtain the following results. The sputtering is better than conventional e-gun evaporation for both reproducibility of film composition and durability. The sputtered A 1 films with 0.4 wt% to 0.8 wt% Ti addition lead to durability for three times larger power than 0.7 wt% Cu addition to evaporated A 1 films.

Intel-modulation between transmission and spurious signals in multi-IDT-type SAW filters on 36° Y–X LiTaO3 substrate, which are used for antenna duplexers in cellular telephones, is studied. The experiments used two input signals of 835 MHz transmission and 790 MHz spurious signals applied to the filter, and a third-order intermodulation signal at 880 MHz caused by the nonlinear effect coming into the receiving band. These intermodulation characteristics are influenced by applied power and ambient temperature. The experimental results show that intermodulation level is closely related to applied power level and temperature of the filter.

The influences of the internal stress of the film, annealing treatment and a sputtered Ti-added Al electrode on 36° rotated Y-X LiTaO3 substrates were investigated. Higher activation energy of the time to failure (TF) was obtained when the amount of internal stress was decreased. The annealing temperature is limited to below 400°C because of discoloration and phase change of the substrate. TF with Al-0.6 wt%Ti electrodes in IIDT filters became ten times that obtained with Al-0.2 wt%Ti electrodes. By the increase of the amount of Ti, the grain size and the standard deviation were decreased.