1.5 GHz SAW bandpass filter using poly-crystalline diamond

Due to its high Young modulus, diamond has the highest acoustic wave velocity among all materials and thus it can be expected to be a candidate of the substrate for high frequency surface acoustic wave (SAW) devices. 15 μm thick poly-crystalline diamond deposited on a silicon substrate by hot-filament CVD was used as a substrate. For the piezoelectric material, ZnO film was deposited by RF sputtering. A 1.5 GHz bandpass filter was successfully demonstrated using a 1.5 μm line and space single electrode; additionally a 12.1 dB insertion loss including a 6 dB bi-directional loss was observed. The phase velocity of 8900 m/s and an electro-mechanical coupling constant of 1.76% were obtained for this filter. The propagation loss of this structure was estimated to be 3.9 dB- most of this is presumably losses in ZnO. This loss can be reduced by process refinement of ZnO deposition