ZNO FILMS ON (001)-CUT [110]-PROPAGATING GAAS SUBSTRATES FOR SURFACE-ACOUSTIC-WAVE DEVICE APPLICATIONS

A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered stru cture is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut [110]-pro pagating GaAs substrates are investigated in this article, including S AW velocity, effective piezoelectric coupling constant, propagation lo ss, diffraction, velocity surface, and reflectivity of shorted and ope n metallic gratings. The measurements of these essential SAW propertie s for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for him thicknesses over the range of 1 .6-4 mu m and with films of different grain sizes. The high quality of de triode sputtered films was observed as evidenced by high K-2 and l ow attenuation, The measurements of the velocity surface, which direct ly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on {001}-cut GaAs samples are reported using two different te chniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acous tic microscope. It was found that near the [110] propagation direction , the focusing SAW property of the bare GaAs changes into a nonfocusin g one for the layered structure, but a reversed phenomenon exists near the [100] direction. Furthermore, to some extent the diffraction of t he substrate can be controlled with the film thickness. The reflectivi ty of shorted and open gratings are also analyzed and measured. Zero r eflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.