Reduced Graphene-Oxide-Based Silk-FET: A Facile Platform for Low Power and Room Temperature Detection of Formaldehyde

Abstract

This article demonstrates the potential of silk film as gate dielectric in FET-based gas sensor. L-ascorbic acid (LAA) reduced graphene oxide (rGO) was used as semiconducting channel which acts as the sensing layer of the FET-based sensor. The morphology and capacitance of silk film were investigated to introspect two seldomly explored quantities: porosity and dielectric constant. The measured dielectric constant of silk film lies in the range of 32–13 in the low-frequency regime (40–100 Hz). Silk film also exhibited uniform, nonporous, smooth morphology. The Silk-FET device exhibited selective response toward formaldehyde (HCHO) among seven volatile organic compounds (VOCs), and rGO ensured room temperature sensing. During the adsorption of formaldehyde, electrons’ transfer takes place from formaldehyde to rGO, reducing the hole concentration of the channel. This leads to reduction in output current, revealing p-type characteristics of the device. The transfer and output characteristics also exhibited similar p-type nature. Device’s threshold voltage shift is also prominent with the exposure to formaldehyde. The gate bias played a pivotal role in improving the device performance. At 1.15-V gate voltage, the response was enhanced by 2.8 times for 45-ppm formaldehyde. The device exhibited maximum response at a gate voltage of 1.15 V, ensuring low-power operation of the FET device. The device’s response and recovery time were calculated as 97 and 280 s, respectively, at 180-ppm formaldehyde. The sensing behavior of the system was also reaffirmed through the TCAD SILVACO simulations. The energy band diagram revealed the depletion of carriers at rGO with adsorption of formaldehyde.