HIGH-FREQUENCY BANDPASS FILTER USING POLYCRYSTALLINE DIAMOND

Because of its high Young's modulus, diamond has the highest acoustic velocity of all materials, and thus for surface acoustic wave (SAW) de vices diamond can be expected to be one of the candidates for passive component applications. Polycrystalline diamond 40 mum thick was depos ited on a silicon substrate by hot-filament chemical vapour deposition . After the diamond surface had been polished, 100 nm of Al was deposi ted and fabricated into interdigital transducers, utilizing convention al photolithography and etching processes. This was followed by the de position of a ZnO thin film, which served as a piezoelectric material to generate SAWs. Finally, an SAW device using a ZnO/diamond system wa s fabricated for the first time. With the high SAW velocity of the ZnO /diamond system being up to 8600 m s,-1 a 1.07 GHz bandpass filter was successfully demonstrated using 2 mum line and space interdigital tra nsducers; additionally - 25 dB insertion loss was observed. This preli minary result suggests that, by utilizing diamond, high frequency (2-5 GHz) bandpass filters can be made available, and broad applications i n the optical and personal communication systems can be expected.