Epitaxial growth and characterization of high quality ZnO films for surface acoustic wave applications

There has been increasing interest in high quality piezoelectric ZnO thin films. ZnO has a high coupling coefficient, which makes it promising for high frequency, low loss SAW devices when the film is deposited on top of a high-velocity substrate such as diamond or sapphire. It is well known that for these devices performance is critically dependent on the quality of ZnO films. We report the epitaxial growth of (1120) ZnO thin films on R-plane sapphire substrates using MOCVD technique. The films´ crystallinity and orientations were analyzed using X-ray diffractions. The smooth surface morphology and sharp interface properties were revealed by high-resolution cross-sectional TEM. Solid-electrode test transducers are used to characterize the surface wave velocity, the coupling coefficient and the electrode reflectivity. 10 μm. wavelength IDTs have been demonstrated to operate at 420 MHz and 560 MHz, with operating frequency being a function of film thickness. These correspond to SAW velocities of 4200 m/s and 5600 m/s, respectively. Coupling coefficients up to 6% and electrode reflectivity up to 8% per wavelength have been obtained