Effects of lattice mismatches in ZnO/substrate structures on the orientations of ZnO films and characteristics of SAW devices

Polycrystalline ZnO films are deposited using RF magnetron sputtering on various substrate materials including AlN/Si-(111), sapphire, DLC/Si-(100), SiO2/Si-(100) and Si-(111). The structural parameters of deposited ZnO films, such as texture coefficient (TC) value for (002)-orientation, crystallite size and full-width at half-maximum (FWHM) at ZnO (002)-peak, are compared. Surface acoustic wave (SAW) devices are also fabricated by using a lift-off method, with the configuration of IDT/ZnO/substrate. The frequency response characteristics (including S21) of the fabricated SAW devices are measured and the device parameters, such as insertion losses and side-lobe rejection level, are estimated in terms of the substrate materials. Experimental results indicate that the lattice matching as well as the structural similarity between ZnO and substrate may be essential for determining the SAW device characteristics.