Characterization of a Multi-Channel CMUT Gas Sensor

We report the design, the fabrication and the test of a multi-channel gas sensor based on Capacitive Micro-machined Ultrasonic Transducers (CMUT) functionalized with peptides as sensing material, dedicated to volatile organic compound (VOC) measurements in ambient air. The design, the fabrication and the electrical test of the CMUT device is reported, achieving a mass sensitivity per unit area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {5.9~Hz/(ag/{\mu }m^{2})}$ </tex-math></inline-formula>. The corresponding electronics, ensuring self-sustained oscillations of the loops, is described. Experimental characterization of the loops using a Vector Network Analyser (VNA) and associated simulations using Eldo software highlight how the Barkhausen criteria are fulfilled. A gas flow setup is used to expose the sensors to different gases. The three channels of the device reveal different sensitivities to gas, ranging from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {0.13~Hz/ppmv}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {0.41~Hz/ppmv}$ </tex-math></inline-formula> for nonane. This is attributed to different surface affinities towards nonane, confirming the potential of CMUT devices for electronic noses. [2024-0089]