ZNO-on-nanocrystalline diamond lateral bulk acoustic resonators

This paper reports, for the first time, on thin-film piezoelectric-on-diamond composite bulk acoustic resonators. These resonators benefit from the large elastic modulus of the nano-crystalline diamond to increase the resonance frequency, and the high electromechanical coupling of the piezoelectric transduction to reduce the motional impedance. More than 1.8times increase in the resonance frequency is measured for devices fabricated on 2 mum thick diamond compared to the same size devices made on 6 mum thick silicon on insulator substrate. A device with 5 mum feature size exhibits a high resonance frequency of 1.2 GHz. A small motional impedance of 225 Omega is reported for a device operating at 173 MHz. The temperature coefficient of frequency (TCF) is measured to be as small as -2 ppm/degC as a result of including an oxide layer in the device structure.