Characteristics of ZnO Thin Film Surface Acoustic Wave Devices Fabricated Using Al2O3 Films on Silicon Substrates.

ZnO films with a c-axis (0002) orientation have been successfully grown by RF magnetron sputtering on interdigital transducer (IDT)/Al₂O₃/SiO₂/Si substrates. Al₂O₃ films were deposited on SiO₂/Si substrates by electron beam evaporation. The crystalline structure and surface roughness of the films were investigated by X-ray diffraction and atomic force microscopy, respectively. The second-order phase velocity of a surface acoustic wave (SAW) device with a 7.5-µm-thick Al₂O₃ film was measured to be about 5432 m/s, which approaches (93%) that (5840 m/s) of ZnO/IDT/sapphire. This experimental result indicates that a low-cost Al₂O₃ film can be used to replace an expensive single-crystalline sapphire substrate for the fabrication of high-frequency SAW devices and is also useful in the integration of semiconductor and high-frequency SAW devices on the same Si substrate. [ABSTRACT FROM AUTHOR]