Polyimide as an acoustic absorber for high frequency SAW applications

A novel method is described for damping unwanted acoustic energy in high-frequency SAW (surface acoustic wave) devices through the use of a polyimide layer which is patternable with high resolution on the surface of the device. The polyimide layer maintains its absorptive acoustic properties after a high-temperature bakeout at 300 degrees C and exhibits excellent reliability. The application process and process tolerances are described. Experimental results for the acoustic attenuation factor are presented as a function of SAW frequency. The attenuation of 3.0-3.5- mu m-thick polyimide films for SAWs on LiNbO/sub 2/ was measured to be in the range of 10-20 dB/100 mu m at frequencies in the range of 300 MHz to 500 MHz.<>