Study of aluminium nitride/freestanding diamond surface acoustic waves filters

Abstract

Highly oriented aluminium nitride (AIN) has been successfully deposited on silicon substrates and on the back side of unpolished, thick, freestanding, polycrystalline diamond films. Structural and electrical properties of the (0 0 2) oriented AIN films have been investigated. Using optimised AIN and chemical vapour deposited diamond films, high quality surface acoustic wave (SAW) filters were constructed by deposition of aluminium inter-digital transducers. The effects of the AIN thickness on the diamond-based SAW filter properties and the SAW propagation were investigated. A phase velocity of 17.1 km/s was observed, which is, to the best of our knowledge, the highest reported value for diamond. The dependence of the phase velocity (v) on the AIN thickness was compared to theoretical predictions. SAW filters with rather low insertion loss, high suppression and high electromechanical coefficient could be obtained. We also report on piezoelectric d(33) measurements of AIN films by atomic force microscopy. (C) 2002 Elsevier Science B.V. All rights reserved.