Numerical calculation of SAW sensitivity: application to ZnO/LiTaO3 transducers

A technique for analysing the sensitivity of a surface acoustic wave (SAW) device is presented, based on the numerically obtained Green's function. It is applied to devices based on a 36degrees-YX LiTaO3 substrate with a ZnO guiding layer. The capability of these devices for gas and liquid sensing is shown by studying parameters such as mass sensitivity and electromechanical coupling coefficient. Devices were fabricated with film thicknesses ranging from 0 to 8 mum yielding operating frequencies between 101.5 and 78.5 MHz. Phase velocity is calculated as a function of ZnO guiding layer thickness by searching for singularities of the Green's function in wavenumber domain. The calculations were confirmed by measuring the change in centre frequency of fabricated devices. Electromechanical coupling coefficient was measured and found to have a maximum of 7.5% at thickness of h/lambda(0) = 0.05. Mass sensitivity was measured as a function of layer thickness, and found to have a maximum of 70 cm(2)/g