Piezoelectric Aluminum Nitride Films

Piezoelectric films of AlN and GaN were grown on sapphire substrates for use in the generation, propagation, and processing of surface acoustic waves. The films were grown by CVD heteroepitaxy using the metal-organic reactants trimethyl aluminum or trimethyl gallium. Greatest emphasis was placed on optimization of the aluminum nitride-sapphire system as determined by the (1,1,-2,0)AlN/(1,-1,0,2)Al2O3 epitaxial relationship. The films were examined with respect to crystallography, surface topography, optical properties, uniformity, and ease of polishing. A wide range of epitaxial growth temperatures was covered in order to establish optimum conditions for the growth of relatively thick films with minimum surface structure and residual composite strain. The possibility of growing silicon on the same substrate with AlN in a side-by-side configuration was examined and shown to be feasible. Aluminum transducer patterns were fabricated on some samples to form delay lines.