Growth of AlN piezoelectric films on diamond for high frequency SAW devices

Diamond-like-carbon (DLC) films are very attractive for SAW devices applications because of their high SAW velocity, which can allow high frequency operation at moderate line-width resolution. Use of AlN as piezoelectric layer on DLC is also attractive because of its high SAW velocity: the highest among all piezoelectric materials, together with its excellent electrical, mechanical and chemical properties. The problem arising in the growth of AlN films on DLC have prevented, up to now, the use of this materials combination. In this paper we report our recent results on the growth of highly oriented, low stressed AlN films on DLC. SAWs propagation on AIN/DLC has been theoretically investigated together with the electromechanical coupling for both the Rayleigh and Sezawa modes. The theoretical calculations show how high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted k² = 2.2 and 4 for the Rayleigh and Sezawa wave, respectively, comparable to those observed in strongly piezoelectric single crystal such as LiNbO₃, but with SAW velocities approximately twice. Experiments performed on AIN/DLC/Si SAW test devices have shown a good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.