Spherical /spl phi/ 1 mm SAW device based on Ball Semiconductor/MEMS technology

A ball SAW (surface acoustic wave) device was fabricated on a 1 mm /spl phi/ single crystal quartz sphere. On the z-axis cylinder, it has multiple roundtrips of more than 190 turns and a long propagation length of 157 mm at 150 MHz of driving frequency and 50 turns roundtrip. Using this device, we realized a hydrogen gas sensor as an application of a ball SAW device. Amplitude and delay time responses were measured under exposure to between 10 ppm and 3% H/sub 2/ in N/sub 2/ base gas by using a selective sensing film of 40 nm thick Pd/Ni alloy. The response time was about 30 sec in 3% H/sub 2/.