Research Study in Growth of Aluminum-Nitride on Sapphire Piezoelectric Films.
Final rept. 1 Dec 74-31 Jul 76,
UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES ELECTRONIC SCIENCES LAB
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The growth and characterization of aluminum nitride epitaxial films on R-plane sapphire has been investigated in an eighteen month program aimed at improving the quality and uniformity of the material for use in microwave bandpass filters. This report details the entire process of AlN film processing starting from the polishing of sapphire wafers and ending with the electrical characterization of the resultant films. The polishing of sapphire proved to be a major effort because the constraints of wafer thickness optical flatness, wafer bowing due to thermal expansion stresses, and a defect free surface finish were not all compatible. Improvements were made in the A1N growth system and operating procedure which resulted in films of lower defect density, lower apparent strain, and improved acoustoelectric characteristics. Etching of the polished AlN surface followed by SEM examination was implemented as a means of checking crystal film perfection. Measurements made on the temperature coefficient of delay of the film composite have shown values as low as 13 ppm for a thickness to wavelength ratio of 0.66 and indicate that zero temperature coefficient will be obtained at a somewhat larger thickness. Author
- Solid State Physics