Coupling coefficient, temperature stability and mass sensitivity of the Rayleigh-type mode an (001) [110] AlAs/GaAs

The use of AlAs/GaAs layered structures for SAW sensor applications is discussed with the aim of exploring the potential of the material system for the integration of SAW and electronic devices. Based on the acoustic wave spectrum on the (001) cut of GaAs the development of the Rayleigh-type mode in the [110] direction of the AlAs/GaAs structure is described. Using a transfer matrix algorithm the phase velocity and the coupling coefficient of the dispersive structure are calculated as a function of the relative layer thickness kh(AlAs), with k being the wave number and h(AlAs) the layer thickness. Results of SAW phase velocity measurements carried out by a thermoelastic laser excitation method and a time delay technique are presented. The coupling coefficient has a maximum at kh = 1.8 being twice as high as the coefficient of bare GaAs. The temperature stabilization with SiO2 and Au layers is calculated and the relation between kh(SiO2) and kh(Au) is determined for a vanishing temperature coefficient of delay (TCD), The mass sensitivity is increased by the application of the temperature stabilizing layers. It reaches a maximum value at kh(Au) = 0.0881 and kh(SiO2) = 1.054. Some aspects of optimization procedures including the AlAs layer thickness are discussed.