Ultrathin MoO_x/Graphene Hybrid Field Effect Transistor Sensors Prepared Simply by a Shadow Mask Approach for Selective ppb‐Level NH₃ Sensing with Simultaneous Superior Response and Fast Recovery

Abstract

approaches compatible with the conventional semiconductor processes include patterning, etching, and evaporation, which would give rise to the contamination, the structural and chemical changes, and the damages of the sensing chip surface of sensors due to the unavoidable resist residues and/or thermal and radiative effects during fabrication processes. In sharp contrast, shadow mask approach may be adopted as an alternative of sensor fabrication like gas sensors etc. that could protect the sensing chip surface against the contamination, the unwanted structural and chemical changes, and the damages, which would guarantee a clean sensing chip surface with good enough reactivity with the gas molecules, particularly the one with a weak charge transfer nature like NH 3 . NH 3 , a kind of weak electron donor air pollutant, released as an industrial and combustion waste, is a serious threat to the human health and environment. [1] Many diversified gas sensors based on metal oxides, graphene/reduced graphene oxide (RGO), transition metal dichalcogenides and their reasonable hybrids etc., fabricated in chemiresistor or/and field effect transistor (FET) configurations have been reported for NH 3 detection. For instance, a gas sensor based on atomic layers of MoS 2 shows Both simultaneous achievement of high response, low limit of detection, and full recovery at room temperature (RT) for weak reducing gases like NH 3 and facile and batchable fabrication approach are quite challenging for sensors. Herein, ultrathin MoO x layers are hybridized with mono layer graphene with different coverage percentages, into MoO x /GFET (graphene field effect transistor) devices for selective NH 3 sensing fabricated by a facile, cost effective, and contamination-free shadow mask approach instead of conventional lithography processes. A response of −18.10% for 12 ppm NH 3 with full recovery of 356 s, superior repeatability, low detection limit of 310 ppb, and strong selectivity is simultaneously achieved for MoO x /GFET sensors at RT. The superior sensing and recovery performance of MoO x /GFET sensors is predominantly attributed to the effective tuning of Schottky barrier height and the Coulomb interaction between charged polar donor molecules and positively polarized surface enhanced by the positive bias voltage. The energy band diagrams well explain the sensing mechanism for reducing/oxidizing gases. The idea proposed in this study offers a feasible solution for highly selective sensing of different gases by oxides/graphene hybrid FET based gas sensors with superior RT performances fabricated by a facile, contamination-free, batchable, and generalized approach.A. Falak

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization

“…Attempts have also been made with real-time monitoring of NH 3 -like reducing gases such as hydrogen (H 2 ), carbon monoxide (CO), sulfuretted hydrogen (H 2 S) and others. ,, NH 3 , which has been an indispensable component in modern industry, is a weak electron donor air pollutant and ecological threat. − The past decade has witnessed the rapid development of 2D FET NH 3 sensors. ,, For instance, Afazal and co-workers designed an ultrafast FET gas sensor based on vertically stacked 2D n-WS 2 /p-GeSe/n-WS 2 vdW heterojunction (Figure d) . Due to the strong electronegativity of n-WS 2 , NH 3 gases were readily absorbed on the edge sites of WS 2 and this led to electron doping.…”

1D and 2D Field Effect Transistors in Gas Sensing: A Comprehensive Review

“…Similar results were obtained by the same research group using MoO x /graphene FETs for detection of NH 3 . [ 297 ]…”

Research Progress of Graphene and Its Derivatives towards Exhaled Breath Analysis

“…Falak et al used a simple and contamination-free shadow mask approach to hybridize an ultra-thin MoO x layer with a single layer of graphene with different molybdenum oxide coverage [ 66 ]. The MoO x /GFET (graphene field-effect tube) showed a response recovery time of 356 s to 12 ppm NH 3 , and a lower detection limit of 310 ppb.…”

“… ( a ) Fermi-level tuning diagram in MoOx/graphene composite field-effect transistor sensor (D100) (back gate voltage V GS from −50 to +75 V, electron transfer from NH3 to p-type graphene) [ 66 ]. Copyright (2020), used with permission from Elsevier.…”