Temperature modulated graphene oxide resistive humidity sensor for indoor air quality monitoring.
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 degC, resulting in a sensor DC power consumption of only 2.75 mW at 50 degC. 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.
Nanoscale