Influence of diamond matrix morphology on ZnO surface morphology and preferred orientation

Abstract

The signal propagation loss and conversion efficiency are two critical performances of diamond/ZnO film-based surface acoustic wave (SAW) device, and depend on roughness and preferred orientation degree (POD) of ZnO surface layer at plane (002). In-situ improvement of operational performance of ZnO layer is achieved by adjusting morphology of diamond matrix layer via diamond particle size. Diamond layer is deposited on silicon substrate using hot-filament chemical vapor deposition (HFCVD) technique by varying Ar/(Ar+H2) ratio. The ZnO layer is then deposited on the diamond film using radio-frequency magnetron sputtering (RFMS). The results show that, by regulating the diamond particle size, it is possible to adjust morphology of the diamond layer and facilitate variation in morphology and preferred orientation of ZnO layer for a better operational performance of SAW device. When the diamond particle size is decreased from 1.38 to 0.12 µm, the root-mean-square (RMS) roughness of ZnO layer initially drops and then rises, and the lowest roughness is 6.4 nm. Also, POD of ZnO (002) increases from 2.61 to 2.89, and then drops to 2.83. For a diamond particle size of 0.35 µm, the RMS roughness of ZnO layer has minimum value of 6.4 nm, and the POD of ZnO (002) approaches the maximum of 2.89 with a half-peak width of 0.36˚. The influence of diamond layer morphology on ZnO morphology and POD is thus proposed.