Micromachined thin film bulk acoustic resonators

We have fabricated thin film bulk acoustic resonators (FBARS) with measured Q's of over 1000 and resonant frequencies as low as 1.5 GHz and as high as 7.5 GHz. The device, as currently fabricated, consists of the piezoelectric material aluminum nitride (AlN) sandwiched between electrodes all of which lie on a thin low-stress silicon nitride (Si/sub x/N/sub y/) membrane. Integrated on the membrane are small microheaters for frequency tuning and/or temperature stabilization. We have observed frequency shifts of 50 to 80 ppm per degree C depending on relative material thicknesses. Maximum temperature excursions over 580 C could be achieved using the microheaters. We have also observed frequency shifts of 5 to 10 ppm per volt depending on harmonic.<
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