82 made of lt 100 gt gallium arsenide gaas was coated with an insulating film 83 of silicon dioxide the silicon dioxide film 83 was formed by the plasma cvd using a reactive gas of silane and oxide at 300 u00b0 c a lower electrode thin film in a double layer structure of a titanium film 84 of 30 nm in thickness and platinum film 85 of 70 nm in thickness was formed on the insulating film 83 by the evaporation the lower electrode thin film was patterned by the lift off to form a lower thin film electrode 86 simultaneously an electrical connection 88 was formed between the lower electrode pad 87 and the lower thin film electrode 86 on the substrate 82 outside a region for a piezoelectric thin film the piezoelectric thin film 89 of aluminum nitride of about 2 u03bcm in thickness was formed on the lower thin film electrode 86 the piezoelectric thin film 89 was formed by the sputtering using a mixture of argon and nitrogen under the pressure of 1 pa in pressure with keeping the temperature of the substrate at 300 u00b0 c a portion of the piezoelectric thin film 89 was etched by the ion milling using a resist mask into a rectangular shape of 200 u03bcm u00d7 200 u03bcm further a metal film having the same composition as the lower electrode thin film 86 was deposited by the use of the same processes as those used for the formation of the lower electrode thin film 86 then an upper thin film electrode 90 was formed by the lift.