Simulation of two-transistor parallel and series circuits for gas sensing validated by experimental data

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.