The effect of a SiO2 layer on the performance of a ZnO-based SAW device for high sensitivity biosensorapplications

Abstract

The properties of ZnO/SiO2/Si surface acoustic wave (SAW) love mode biosensors are studied in this paper. This specificstructure is very suitable for biosensors since the reactive ZnO surface offers the opportunityfor effective bio–ZnO interfaces, and the development of sensors directly on Si substratesprovides the chance for full integration with read-out and signal processing circuitry in themature Si technology. However, investigations of the dependence of buffer layerSiO2 on the performance of biosensors are very few. Therefore, the main interest ofthis paper is to find the relation between the properties of biosensors and theSiO2 layer. Some important results are obtained by solving the coupled electromechanical fieldequations. It is found that the mass loading sensitivity can be further improved by adding theSiO2 layer; furthermore, the maximal sensitivity of the biosensors can be obtained byadjusting the thicknesses of the two layers. Accordingly, consideration of thebuffer layer is very important in the optimization of devices. On the otherhand, it is found that the thickness of the piezoelectric guiding layer has anevident effect on the electromechanical coupling coefficient, while that of theSiO2 layer has a tiny effect on it. Moreover, we find that the effect of initial stresses on theproperties of biosensors depends on the distribution of acoustic flow power in the twolayers. This analysis is meaningful for the manufacture and applications of theZnO/SiO2/Si structure love wave biosensor.