FINITE ELEMENT ANALYSIS OF MULTILAYERED ZnO/AIN/Si STRUCTURE SAW SENSOR FOR EFFICIENT VOCs GAS DETECTION

Surface Acoustic Wave (SAW) gas sensor device based on the ZnO/AIN/Si structure is numerically studied using the Finite Element Method (FEM) simulations employed by the Comsol Multiphysics package. The analyses of the device performance concerning the phase velocities and electromechanical coupling factor, K-2, are carried out and discussed for both Rayleigh and Sezawa wave modes. The structure is initiated by studying the ZnO/Si model, and the obtained results are validated by comparison to previously reported experimental results that match our numerical simulations. To enhance the performance of the SAW device, an AlN layer is inserted between ZnO and Si layers. The influence of ZnO and AIN layer thickness of the two SAW modes is analyzed. The obtained results reveal that, for Sezawa mode, high velocities of up to 5800 m/s is achieved through optimizing the thickness ratio of AlN/ZnO. The sensor sensitivity to gas concentration in the air is examined for seven Volatile Organic Compounds (VOCs) using a thin Polyisobutylene (PIB) layer for sensor demonstration. The results show a linear dependence of the sensitivity over the investigated gas concentrations. The study shows a remarkable sensitivity improvement of the SAW sensor achieved by the Sezawa wave mode compared to the Rayleigh one. For instance, a sensor sensitivity of 1.097 Hz/ppm for Sezawa mode is compared to 0.692 Hz/ppm for Rayleigh mode for the standard Dichloromethane gas (DCM).