Aluminium nitride/nanodiamond structures for high-frequency surface acoustic wave nanotransducers

Surface acoustic waves (SAWs) have been used extensively for a variety of applications such as telecommunications, electronic devices and sensors. The emerging need for high-bit data processing at GHz frequencies and the requirement of high-sensitivity sensors demand the development of high-efficiency SAW devices. With the objective of exploiting the high acoustic velocity of diamond, the authors report on an optimally developed nanodiamond (ND) thin film with crystal size of 3-5-nm, embedded in an amorphous carbon matrix with grain boundaries of 1-1.5-nm, that is integrated with aluminium nitride (AlN) to extend the operating frequency of SAW transducers. The authors utilise this attractive property of diamond through facile synthesis of a bi-layer structure consisting of sputtered AlN deposited on ND. Deposition of ND was carried out using microwave plasma-enhanced chemical vapour deposition. AlN/ND-based SAW structures were fabricated using electron beam lithography to produce high acoustic velocity transducers. The fabricated SAW transducers were composed of two spatial periods of 1400 and 3200-nm devices. The fabricated devices exhibit an operating frequency of -2-GHz with an acoustic velocity of 8120 and 9280-m/s, respectively.