Fabrication of Sputtered Aluminum Nitride on Sapphire for Application in UHF SAW Frequency Filters.

Single crystal AlN films were grown by sputtering on single crystal (0001) oriented sapphire substrates. The substrate size was 25.4 x 9.0 x 2.0 mm. This size was chosen as a convenient size for the fabrication of UHF SAW frequency filters. The AlN was synthesized by reactive rf diode sputtering of a pure aluminum target in an ammonia atmosphere. Growth conditions were established which yielded clear, uniform, single crystal AlN films. Films were evaluated through microscopic examinations, interference spectrophotometric thickness measurement and electron channeling and X-ray diffractometer crystallographic analysis. Films ranged from 2 micrometers to 2.3 micrometers in thickness and were uniform to less than 0.1 micrometers across the long dimension of the substrate. Films were single crystal with the (0001) A1N direction parallel to the (0001) Al2O3 direction. Films were clear and smooth replicating the surface of the substrate. Twelve samples were delivered in accordance with the requirements of this program. Surface acoustic wave interdigital electrode transducers and delay lines were fabricated on samples identical to those delivered. Measurements of delay line performance at 201, 477, and 848 MHz were made to provide an estimate of the basic constants for surface acoustic wave excitation and wave propagation. Relatively low acoustic propagation loss was observed for all AlN on sapphire delay lines studied. (Author)