Tunable zinc oxide surface acoustic wave devices based on acoustoelectric interaction

Tunable surface acoustic wave (SAW) devices have been attracting considerable research efforts, as they are highly desired in advanced communication systems by offering versatile signal processing capability. Among various tuning mechanisms, the perturbation of the electrical boundary condition based on the acoustoelectric interaction in a semiconducting/piezoelectric multilayer structure is a promising approach to realize tunable SAW devices with low bias, large tunability, and small device dimension. To reduce the fabrication complexity and enhance the device reliability, the monolithic device structure is preferable.;This dissertation addresses the design and development of the tunable ZnO SAW devices based on the acoustoelectric interaction. Epitaxial ZnO and MgxZn1-xO multilayer structures grown by metal-organic chemical vapor deposition (MOCVD) on r-Al2O3 substrates are used as the basic structure, which offer advantages as high coupling coefficient and multimode SAW generation. The device related processing techniques, including wet chemical and dry etching of ZnO and MgxZn1-xO films, are investigated with respect to the etch rate, etch profile, surface morphology and process induced damage. The maximal 1:1 pattern edge slope has been achieved.;A prototype of ZnO UV SAW device has been demonstrated using semiconducting-piezoelectric ZnO multilayer structure, which enables the wireless output for sensor network. The interaction of the SAW with the UV induced carriers in the semiconducting ZnO layer results in a phase shift and an insertion loss change, as functions of the incident light wavelength and power. A phase shift of 107° is achieved at 365 nm for a light power of 2.32 mW/cm2.;A prototype of ZnO based voltage controlled multi-mode tunable SAW device has been demonstrated through the integration of a depletion-type MIS structure (Al/SiO2/semiconducting ZnO) and a piezoelectric ZnO/r-Al 2O3 system. The acoustic velocity tunability is achieved by changing the sheet conductivity of the semiconducting channel through the gate biasing. Due to the in-plane piezoelectric anisotropy of the ZnO/r-Al 2O3 system, the device can be operated with both Sezawa and Love mode for gaseous and liquid sensing, respectively. Under --18 V bias, 420° and 277.3° phase shifts are achieved for Sezawa and Love mode operation, respectively.