IMPROVED METALLIZATION FOR SURFACE ACOUSTIC-WAVE DEVICES

Surface acoustic wave (SAW) resonators operating at frequencies in the range 100-500 MHz employ lightly coupled high Q (10 000-20 000) acoustical cavities. Resonators fabricated with pure aluminum transducers showed the formation of dendrite-like growths and a degraded electrical response after a relatively short operating time at high power levels. The similarity to thermally induced metal migration led to identifying the problem as stress-induced material migration. Resonator devices fabricated with 2% copper-doped aluminum films showed up to 65 times greater lifetime than the devices fabricated with pure aluminum. The unique amplitude and frequency conditions present in SAW resonators make them useful for evaluating films for their resistance to stress migration. © 1979.