Piezoelectric aluminum nitride films deposited by triode sputtering for surface acoustic wave devices

Abstract

Aluminium nitride(A1N) thin films have ben widely used in various applications due to their excellent properties such as chemical stability, electrical isolation, high acoustic wave velocity and large electromechanical coupling coefficient. For surface acoustic wave (SAW)applications, structures having A1N films on high acoustic velocity substrates such as diamond or sapphire offer much interest in forming high frequency SAW devices with phase velocities greater than 10000m/s. In this study, A1N films have been deposited on (001) sapphire and (100)silicon substrates by triode sputtering at low temperature in argon-nitrogen gas mixture. The crystal orientation, stoechiometry, optical acoustic and electrical properties were investigated. Dense AIN layers with very high electrical resistivity were obtained at high deposition rates. SAW filters were formde by development of interdigital transducers on the A1N/Silicon and A1N/Sapphire structures. The phase velocity was measured by a network analyzer as a function of A1N film thickness and substrate type.