Surface acoustic wave devices based on nanocrystalline diamond and aluminium nitride

Abstract

Due to its high-acoustic velocity, diamond, when combined with piezoelectric material, has a promising potentiality for high frequency surface acoustic wave (SAW) devices. In the present work, low-surface roughness nanocrystalline diamond (NCD) were deposited on silicon substrate by microwave plasma assisted chemical vapour deposition process and piezoelectric aluminium nitride films were grown by DC reactive magnetron sputtering. For the first time, SAW devices based on AlN/NCD/Silicon layered structure were successfully performed. The influence of inter-digital transducers periodicity and NCD film thickness on the acoustic velocity of the layered structure was studied. The high frequency characterisation showed that NCD presents a high-surface acoustic velocity similar to that of polycrystalline CVD diamond. Thus, taking advantage of the remarkable surface smoothness of as-grown NCD films, the polishing step of diamond substrates may be no more required prior to SAW device achievement.