Simulation of two-transistor parallel and series circuits for gas sensing validated by experimental data
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Simulation of two‑transistor parallel and series circuits for gas sensing validated by experimental data W. Wondmagegn1 · Yingli Chu2 · Hui Li2 · Howard E. Katz2 · Jia Huang3 Received: 2 June 2020 / Accepted: 14 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Organic field effect transistors (OFETs) in parallel and series circuit configurations are simulated and tested for gas sensing activity. The devices are based on PQT12 and PQTS12 organic semiconductor thin films. A two-dimensional finite element simulation methodology is implemented. It is assumed that traps due to defects and grain boundaries are uniformly distributed throughout the semiconductor film. Gaussian trap distributions are used in the simulation. Gas sensing is accounted for by a doping-dependent hopping mobility model in the organic active material. Interface traps and charges at the interface between the polymer channel and gate insulator are incorporated. Transistors in both parallel and series configurations are studied. Compared to individual OFET-based sensors, the circuit configuration achieves significantly increased sensitivity to analyte, as indicated by the simulation and in agreement with experimental observations. This supports the concept of combining transistors to enhance analyte sensitivity and provides a method for advance screening of combinations of OFETs for high signal-to-drift ratios. The absolute value of drain currents for series circuits is lower than that of parallel circuits; however, the series circuits display higher analyte sensitivity. Keywords Organic transistor · Gas sensor · Simulation · Hopping mobility model
1 Introduction Conventionally, organic field effect transistors (OFETs) are envisioned for applications in flexible displays, electronic paper, radio frequency identification (RFID) tags, and smart cards [1–3]. A recent trend in the field includes involving organic field effect transistors in a variety of low-cost electronic gas sensing technologies for potential applications in environmental, biological, and industrial areas [4–10]. In some respects, the operation of organic electrochemical transistors (OECT) is analogous to that of conventional organic field effect transistors, though the complex interplay between ionic and electronic motion must be considered in a way that is much less applicable to OFETs [11, 12]. For * W. Wondmagegn [email protected] 1
Electrical and Computer Engineering Department, The College of New Jersey, Ewing Township, NJ 08628, USA
2
Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
3
School of Materials Science and Engineering, Tongji University, Shanghai 201804, People’s Republic of China
both OFETs and OECTs, charge carriers are injected into the channel of the transistor, by carrier injection or electrochemistry, respectively, thus changing its electrical conductivity [11]. While OFETs usually operate in accumulation mode, OECTs can be designed for either accumula
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