title: Temperature-modulated graphene oxide resistive humidity sensor for indoor air quality monitoring.
abstract: In this paper we present a temperature-modulated graphene oxide (GO) resistive humidity sensor that employs complementary-metal-oxide-semiconductor (CMOS) micro-electro-mechanical-system (MEMS) micro-hotplate technology for the monitoring and control of indoor air quality (IAQ). GO powder is obtained by chemical exfoliation, dispersed in water and deposited via ink-jet printing onto a low power micro-hotplate. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) show the typical layered and wrinkled morphology of the GO. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red (FTIR) spectroscopy indicate that the GO flakes possess a significant number of oxygen containing functional groups (epoxy, carbonyl, hydroxyl) extremely attractive for humidity detection. Electro-thermal characterisation of the micro-hotplates shows a thermal efficiency of 0.11 mW per °C, resulting in a sensor DC power consumption of only 2.75 mW at 50 °C. When operated in an isothermal mode, the sensor response is detrimentally affected by significant drift, hysteretic behaviour, slow response/recovery times and hence poor RH level discrimination. Conversely, a temperature modulation technique coupled with a differential readout methodology results in a significant reduction of the sensor drift, improved linear response with a sensitivity of 0.14 mV per %, resolution below 5%, and a maximum hysteresis of ±5%; response and recovery times equal to 189 ± 49 s and 89 ± 5 s, respectively. These performance parameters satisfy current IAQ monitoring requirements. We have thus demonstrated the effectiveness of integrating GO on a micro-hotplate CMOS-compatible platform enabling temperature modulation schemes to be easily applied in order to achieve compact, low power, low cost humidity IAQ monitoring.
authors: Department of Engineering, Electrical Engineering Division, University of Cambridge, 9 JJ Thomson Avenue, CB3 0FA, Cambridge, UK. ad597@cam.ac.uk.
authors: A
authors: A
authors: De Luca
authors: Department of Physics, Indian Institute of Technology, Kharagpur, 721302, India.
authors: S
authors: S
authors: Santra
authors: E&ECE Department, Indian Institute of Technology, Kharagpur, 721302, India.
authors: R
authors: R
authors: Ghosh
authors: Cambridge CMOS Sensors Ltd, Deanland House, 160 Cowley Road, CB4 0DL, Cambridge, UK.
authors: S Z
authors: SZ
authors: Ali
authors: Cambridge CMOS Sensors Ltd, Deanland House, 160 Cowley Road, CB4 0DL, Cambridge, UK and School of Engineering, University of Warwick, CV4 7AL, Coventry, UK.
authors: J W
authors: JW
authors: Gardner
authors: E&ECE Department, Indian Institute of Technology, Kharagpur, 721302, India.
authors: P K
authors: PK
authors: Guha
authors: Department of Engineering, Electrical Engineering Division, University of Cambridge, 9 JJ Thomson Avenue, CB3 0FA, Cambridge, UK. ad597@cam.ac.uk and Cambridge CMOS Sensors Ltd, Deanland House, 160 Cowley Road, CB4 0DL, Cambridge, UK.
authors: F
authors: F
authors: Udrea