Molecular sensing using monolayer gate fully depleted silicon on insulator nano MOSFETs

A novel hybrid structure has been proposed for highly selective and sensitive detection of specific molecules in the atmosphere. The proposed device structure is a silicon-on-insulator (SOI) based substrate gate controlled MOSFET device, with its top gate replaced with a self assembled molecular monolayer. Reactions occurring at the self assembled monolayer modulate the drain current established by the substrate back gate. Target molecules bind at the chemically sensitive molecular monolayer causing an increase or decrease in electron charge. This charge change at the top monolayer-native oxide interface is transduced by the SOI transistor with an increase or decrease in the device drain current. The selectivity of the sensor device is due to the specificity of the chemical interactions that occur at the molecular monolayer. Application of the device to sensing of ions in the liquid medium has been demonstrated by exposing the device to various pH buffer solutions. Detection of molecules in gas medium has been demonstrated by exposing zinc porphyrin monolayer coated devices to pyridine molecules. An increase in drain current of the device was observed when exposed to pyridine. When the device is exposed to bright light in a nitrogen purge, it is observed to drive off the molecules binding at the monolayer surface, enabling reuse of the sensor. Increased sensitivity of detection was observed by using parallel nanowires etched in the silicon channel. Resolution of detection of piperidine molecules up to a few parts per billion has been demonstrated using these nanowire devices. The observed response and the mechanism of transduction have been explained in terms of increase or decrease in work function of the molecular monolayer deposited on the active silicon surface. Due to the electrical coupling of the porphyrin monolayer and the fully depleted silicon channel below it, decrease in work function of the molecular monolayer draws electrons into the silicon channel from the source drain regions, resulting in an increase in channel drain current. This proposed mechanism of signal transduction by the SOI MOSFET structure was further confirmed by obtaining numerical simulation fits to experimental data using ATLAS device simulation software.