rf sputtering of ZnO shear-wave transducers

Thin films of ZnO with a large degree of preferred parallel orientation have been rf bias sputtered onto sputtered indium-tin oxide (ITO) on quartz. The orienting effect of the ITO film is partly due to some limited chemical reaction at the ZnO/ITO interface and partly due to a surface microtexture. An x-ray pole figure analysis indicates that the (10.0) planes of the ZnO are parallel to the substrate surface within ± 5° and that the direction of the c axes is parallel to the target surface within ± 20°. The preferred orientation of the c axes is only observed if both the ITO and the ZnO are sputtered onto the substrate at the same oblique incidence. The ZnO films have resistivities of the order of 108 to 1010 Ω cm. If the ITO/ZnO film couple is deposited onto a well-conducting ground electrode, efficient shear-wave transducers can be obtained.