Fig. 2: Structure and characterization of the MEMS gas sensor array.
a Design of a single MEMS gas sensor comprises, from top to bottom, a heating resistance wire, an isolation layer, interdigital electrodes, an insulated layer, and a deep cavity within the silicon substrate. b Corresponding fabrication process of the microsensor array in cross-sectional views. (i) Deposition of SiO2 via dry etching. (ii) Patterning 30/300 nm Ta/Pt interdigital electrode through sputtering and a lift-off process. (iii) Deposition of SiO2 and SiNx through plasma enhanced chemical vapor deposition (PECVD); then electrode pads of interdigital electrode are expose by dry etching. (iv) Patterning Ta/Pt heating resistor through sputtering and lift-off process. (v) Deep etch for silicon from the back of wafer. (vi) Release of the suspended membrane in TMAH solution. (vii) Au bumping with a diameter of ~50 μm and inkjet printing with metal oxide sensing materials. (viii) MEMS gas sensor array connected to a CMOS device by flip-chip bonding. c Optical image of the fabricated MEMS gas sensor array. d Backside view of the 16 independent gas sensing channels, 1 temperature sensor, and 1 humidity sensor. e Infrared thermal image under a total current of 0.32 A with the temperature distribution along the white dotted line. f Scanning electron microscopy images of the metal oxide-sensing nanomaterials. g Single-channel gas sensor for 10 ppm acetone. h Platinum resistance against temperature. i Test results of the humidity sensor
