Fe<inf>3</inf>O<inf>4</inf> magnetic enhanced CMOS MEMS compatible gas sensor

Abstract

A new magnetic-catalytic sensing mechanism to increase sensitivity for CMOS MEMS gas sensor with mesh stacked sensing electrodes is proposed. Beyond the conventional power dissipation of heating to maintain a certain working temperature, a novel gas sensor with magnetic-catalytic mechanism works at the ambient temperature without the consideration of active heating. The design and fabrication is realized by the standard 0.35μm CMOS process to fabricate a gas sensor with mesh stacked electrodes. For the preparation of magnetic sensing material, a prepared solution of sol-gel SnO2 is mixed at SnO2 : Fe3O4 = 3:1, which was deposited onto mesh stacked electrodes. Moreover, to obtain a stable gas sensing signal, a pulse sampling scheme is proposed in this research work. Since the resistance of sensing material with sol-gel deposition shows a drift behavior under a DC bias circuit. We have proposed a new signal reading scheme with a pulse-type bias for a bridge sensing circuit. Only under the sampling phase, the sensing current flows through the sensing material which induces a voltage drop across the resistance. For the CO concentration measurement, the sample is tested and verified inside a CO gas chamber with a magnetic field generator of solenoid coil. A careful investigation of measurement results, at horizontal magnetic field, the sensitivity of proposed CO gas sensor reaches 0.492%/ppm under the 12.12 Gauss which shows widely applicable for an ultra-low power chemical microsensor with high sensitivity.