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

Abstract

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.

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.