Abstract
A Finite Element Method (FEM) simulation study is conducted, aiming to scrutinize the sensitivity of Sezawa wave mode in a multilayer AlN/SiO2/Si Surface Acoustic Wave (SAW) sensor to low concentrations of Volatile Organic Compounds (VOCs), that is, trichloromethane, trichloroethylene, carbon tetrachloride and tetrachloroethene. A Complimentary Metal-Oxide Semiconductor (CMOS) compatible AlN/SiO2/Si based multilayer SAW resonator structure is taken into account for this purpose. In this study, first, the influence of AlN and SiO2 layers’ thicknesses over phase velocities and electromechanical coupling coefficients (k2) of two SAW modes (i.e., Rayleigh and Sezawa) is analyzed and the optimal thicknesses of AlN and SiO2 layers are opted for best propagation characteristics. Next, the study is further extended to analyze the mass loading effect on resonance frequencies of SAW modes by coating a thin Polyisobutylene (PIB) polymer film over the AlN surface. Finally, the sensitivity of the two SAW modes is examined for VOCs. This study concluded that the sensitivity of Sezawa wave mode for 1 ppm of selected volatile organic gases is twice that of the Rayleigh wave mode.
Highlights
The monitoring of volatile organic compounds (VOCs) is very crucial in various application fields like in industrial safety, fire detection, indoor air quality and health monitoring [1,2]
AlN/SiO2/Si structure and its potential to be used in gas sensing applications
AlN/SiO2 /Si structure and its potential to be used in gas sensing applications
Summary
The monitoring of volatile organic compounds (VOCs) is very crucial in various application fields like in industrial safety, fire detection, indoor air quality and health monitoring [1,2]. In SAW gas sensors, a thin film sensing layer coating is required over the acoustic path. A design of SAW gas sensor with PIB layer over LiNbO3 for the detection of VOCs is reported in Reference [12]. Sezawa mode devices [20,21,22] but none on AlN/SiO2 /Si. The Sezawa waves exist in layered SAW devices, when a substrate’s SAW velocity is greater than the overlaid piezoelectric film and exhibits higher velocity than Rayleigh mode for same IDTs configurations [23]. 2 thin film thicknesses on proposed SAW device propagation fast) in AlN/SiO2 /Si multilayer SAW for gas sensing application. SAW device and of present the comparative study of both surface modes surface (Rayleigh and Sezawa) in terms gas sensitivity. 2 /Si multilayer (Rayleigh and Sezawa) in terms of gas sensitivity
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