Development of ZnO/SiO/sub 2//Si love mode surface acoustic wave devices with high sensitivity for biosensor applications

ZnO with a high piezoelectric coefficient is capable of generating very high frequency (GHz) surface acoustic wave devices and when combined with a SiO2/Si substrate it can be an excellent material of choice for Love mode propagation. Mass sensitivity for a Love mode device is found to be a function of the frequency of operation of the device and the slope of the dispersion curve. We have developed a ZnO/SiO2/Si based high frequency Love mode surface acoustic wave (L-SAW) device operating with a resonant frequency as high as 1.5 GHz and yielding a phase velocity of 4814.4m/s in the ZnO guiding layer. We have studied the change in the phase velocity of the acoustic waves as a function of the thicknesses of the guiding layer. The mass sensitivities of the system have been modeled and experimentally verified. We have used two parameters to improve the mass sensitivity effectively. One is the ability to increase the frequency of operation of the device with smaller finger geometries, and the other is to increase the slope of the dispersion curve at a constant frequency by optimizing the guiding layer thickness. We find that the mass sensitivity that can be achieved in this system is more than double that seen in a PMMA guiding layer based Love mode device.