A 2D-MoS₂-Based Thin-Film Transistor for Trace-Level SO₂ Monitoring

An unconventional MoS2/MoO3 back-gated junctionless thin-film transistor (TFT) was proposed and experimentally demonstrated for highly selective trace-level sulfur dioxide (SO2) detection at room temperature. Few layered MoS2 nanoflakes were synthesized by a sonication-assisted liquid exfoliation technique of bulk MoS2, while MoO3 layer was formed by sustained calcination of exfoliated MoS2 flakes. The as-fabricated device was exposed to calculated amounts (680–800 ppb) of SO2 gas, and its sensing performance was studied. It was found that the response of the device can be enhanced by tuning the gate to source voltage, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {GS}}$ </tex-math></inline-formula>. A physics-based model was derived to predict the effect of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {GS}}$ </tex-math></inline-formula> on the output characteristics of the device and was validated by well-calibrated TCAD simulation deck. For 800-ppb SO2, the device showed the maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R} =1.316$ </tex-math></inline-formula> with response (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{r}$ </tex-math></inline-formula>) and recovery (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{s}$ </tex-math></inline-formula>) times of 229 and 112 s, respectively, under an optimized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {GS}} =5$ </tex-math></inline-formula> V at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {DS}} =10$ </tex-math></inline-formula> V. It was found to be highly selective toward SO2 over other chemically comparable gases (i.e., NO2, NO, Ethanol, 2-propanol, CO2, and so on) under the same bias voltages with good stability and reproducibility. The ultrahigh selectivity was observed to be specific toward the gases showing redox properties in comparison with purely oxidizing and reducing ones, and the physics of the same was adequately explained through the model. Hence, the proposed device could be a viable alternative to its conventional counterparts as an efficient CMOS integrable ultrasensitive SO2 sensor.