Dynamics of charge carrier trapping in NO2 sensors based on ZnO field-effect transistors

Abstract

Dynamics of charge carrier trapping in NO2 sensors based on ZnO field-effect transistors Andringa, Anne-Marije; Vlietstra, Nynke; Smits, Edsger C. P.; Spijkman, Mark-Jan; Gomes, Henrique L.; Klootwijk, Johan H.; Blom, Paul W. M.; de Leeuw, Dago M. Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Andringa, A-M., Vlietstra, N., Smits, E. C. P., Spijkman, M-J., Gomes, H. L., Klootwijk, J. H., ... de Leeuw, D. M. (2012). Dynamics of charge carrier trapping in NO2 sensors based on ZnO field-effect transistors. Sensors and actuators b-Chemical, 171(27), 1172-1179. DOI: 10.1016/j.snb.2012 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Here we investigate the dynamics of charge trapping and recovery as a function of temperature by monitoring the threshold voltage shift. The threshold voltage shifts follow a stretched-exponential time dependence with thermally activated relaxation times. We find an activation energy of 0.1 eV for trapping and 1.2 eV for detrapping. The attempt-to-escape frequency and characteristic temperature have been determined as 1 Hz and 960 K for charge trapping and 10 11 Hz and 750 K for recovery, respectively. Thermally stimulated current measurements confirm the presence of trapped charge carriers with a trap depth of around 1 eV. The obtained functional dependence is used as input for an analytical model that predicts the sensor's temporal behavior. The model is experimentally verified and a real-time sensor has been developed. The perfect agreement between predicted and measured sensor response validates the methodology developed. The analytical description can be used to optimize the driving protocol. By adjusting the operating temperature and the duration of charging and resetting, the response time can be optimized and the sensitivity can be maximized for the desired partial NO 2 pressure window.

Real-time NO2 detection at ppb level with ZnO field-effect transistors

“…To set the operating temperature, the pulse time and duty cycle for a reversible, calibrated sensor we first have modeled the temporal behavior of the threshold voltage as reported in Ref [10]. To this end, charging and recovery measurements have been performed on ZnO field-effect transistors as a function of temperature and NO 2 pressure as described previously [10].…”

“…To this end, charging and recovery measurements have been performed on ZnO field-effect transistors as a function of temperature and NO 2 pressure as described previously [10]. For a given NO 2 content the threshold voltage as a function of time during charging with a continuous applied gate bias at various temperatures follows a stretched-exponential time dependence:…”

“…The only change is the threshold voltage, here empirically taken as the onset of current modulation. The mechanism is due to gate bias controlled charge trapping of electrons at the gate dielectric ZnO interface [9,10]. When the gate bias is turned off, the trapped electrons are thermally released and the threshold voltage recovers to its original value as schematically depicted in Fig.…”

“…Previously, we have modeled the temporal behavior of the threshold voltage to set the operating temperature and cycle time to obtain a reversible sensor [10]. The model uses as input the threshold voltage dynamics as a function of temperature and NO 2 pressure as measured for both charging and recovery.…”

Localizing trapped charge carriers in NO2 sensors based on organic field-effect transistors

“…7,8 An important factor for the sensing in a field-effect transistor is the gate bias, which sets the electron density. Without applying a gate bias transistors are stable in NO 2 ambient.…”