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Gate-bias controlled charge trapping as a mechanism for NO2 detection with field-effect transistors

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Author: Andringa, A.-M. · Meijboom, J.R. · Smits, E.C.P. · Mathijssen, S.G.J. · Blom, P.W.M. · Leeuw, D.M. de
Type:article
Date:2011
Source:Advanced Functional Materials, 1, 21, 100-107
Identifier: 461497
Keywords: Electronics · air quality sensors · charge trapping · field-effect transistors · NO2 sensors · ZnO · Ambipolar semiconductor · Chemiresistors · Commercial sensors · Detection mechanism · Electron trapping · Exponential time · Gate bias · Human health · Nitrogen dioxides · NO sensors · P-type · Positive gate bias · Sensing mechanism · Threshold voltage shifts · ZnO · Air quality · Bias voltage · Charge trapping · Nitrogen oxides · Sensors · Threshold voltage · Zinc oxide · Field effect transistors · Industrial Innovation · Mechatronics, Mechanics & Materials · HOL - Holst · TS - Technical Sciences

Abstract

Detection of nitrogen dioxide, NO2, is required to monitor the air-quality for human health and safety. Commercial sensors are typically chemiresistors, however field-effect transistors are being investigated. Although numerous investigations have been reported, the NO2 sensing mechanism is not clear. Here, the detection mechanism using ZnO field-effect transistors is investigated. The current gradually decreases upon NO2 exposure and application of a positive gate bias. The current decrease originates from the trapping of electrons, yielding a shift of the threshold voltage towards the applied gate bias. The shift is observed for extremely low NO2 concentrations down to 10 ppb and can phenomenologically be described by a stretched-exponential time relaxation. NO2 detection has been demonstrated with n-type, p-type, and ambipolar semiconductors. In all cases, the threshold voltage shifts due to gate bias induced electron trapping. The description of the NO2 detection with field-effect transistors is generic for all semiconductors and can be used to improve future NO2 sensors. The mechanism of NO2 detection is investigated using ZnO field-effect transistors. The transistor current gradually decreases upon NO2 exposure. The decrease originates from the trapping of electrons, which causes a shift of the threshold voltage towards the applied gate bias. The shift can be described by a stretched-exponential time relaxation and is observed for extremely low NO2 concentrations. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.