Design and Analysis of SAW Gas Sensor Utilizing AIN/Diamond/Si Multilayered Structure for VOCs Detection

This study provides insights into the design and analysis of surface acoustic wave sensors customized for detecting volatile organic compounds (VOCs), utilizing an innovative AlN/diamond/Si multilayered configuration. The results are explored numerically using finite element method simulation within the COMSOL Multiphysics package. The potential of the AlN piezoelectric thin film on diamond on Si substrates for sensor development is examined. The phase velocities, electromechanical coupling coefficient, K2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${K}<^>{2}$$\end{document}, and reflectivity are examined versus the normalized thicknesses of the substrates, considering both Rayleigh and Sezawa wave modes. Additionally, the temperature coefficient of frequency (TCF) is investigated. The results show that the TCF increases with reducing the thickness of the diamond. For instance, at khAIN = 2 where the maximum K2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${K}<^>{2}$$\end{document} can be observed, the TCF increases from -17 to -14 to 3 ppm/degrees C for khdiamond = 0.5, 0.2, and 0.05, respectively. Furthermore, the sensor sensitivity to gas concentration in the air is examined for several VOCs using a thin polyisobutylene (PIB) layer for sensor demonstration. The study shows a remarkable sensitivity enhancement in sensor sensitivity achieved through the Sezawa wave mode compared to the Rayleigh counterpart. For example, in the case of tetrachloroethene gas (PCE), the sensor sensitivity reaches 197.73 Hz/ppm for the Sezawa mode, as opposed to 62.15 Hz/ppm for the Rayleigh mode.