Improved signal-to-noise-ratio of FET-type gas sensors using body bias control and embedded micro-heater

摘要

This paper investigates the effects of body-to-source junction bias (V_(BS)) on signal-to-noise-ratio (SNR) of Si metal-oxide-silicon field effect transistor (FET)-type gas sensor with a localized embedded micro-heater. Sensing material, 12 nm-thick n-type semiconducting In_2O_3, is prepared through radio frequency magnetron sputtering. NO_2 is used as a test gas to investigate the gas sensing characteristics of the sensor. By using the embedded micro-heater, the temperature of the sensing area can be raised to an extent required for the gas reaction (150 °C) while maintaining the temperature of the FET channel at 27 °C. The 1/f noise of the FET-type gas sensor is dominated by the carrier number fluctuation (CNF) in all operation regions. The effects of V_(BS) on low-frequency noise (LFN) characteristics are demonstrated by the CNF model with correlated carrier mobility fluctuation. When a forward V_(BS) of 0.5 V is applied to the sensor, the 1/f noise decreases by the factor of ~10 and the SNR of the sensor increases by ~2 times compared to when a V_(BS) of 0 V is applied. It is shown that the limit of detection (LOD) of the gas sensor for NO_2 gas can be improved from 0.55 ppb to 0.27 ppb by applying a forward V_(BS) of 0-5 V.