Zero Temperature Coefficient Surface-Acoustic-Wave Devices Using Epitaxial AlN Films

Abstract

Until now, very few papers have appeared on the temperature coefficient of delay (TCD) for surface acoustic waves (SAW) on A1N films. We report that A1N has a negative TCD of \-30 ppm/C, and that the A1N layer of appropriate thickness cancels the first-order temperature coefficient for sapphire and silicon. A1N films on sapphire substrates. A1N films were single-crystal films grown by metalorganic chemical vapor deposition. The experimental value of TCD at 25OC decreased with increasing kH (k: wave number, H; thickness of A1N film). With the (0001)AlNl (0001) [1100]~1~0~.structure a zero temperature COefficient SAW oscillator of 1.139 GHz was obtained at kH-b3.75, and with the (1120) [0001]A1N/(01~2) [0I11]Al2O3 structure a negative TCD (-7.5 ppm/'C) was obtained at kHn,3.0. Next, by computer fitting, we have determined the first-order temperature COefficients of elastic constants of AlN, and then calculated all the zero TCD characteristics of A1N/A1203, AlN/Si, AlN/SOS and A1N/Si02/Si combinations. We have measured the TCD's for