Effect of Gate Conductance on Hygroscopic Insulator Organic Field-Effect Transistors

Hygroscopic insulator field-effect transistors (HIFETs) are a class of low-voltage-operation organic transistors that have been successfully demonstrated for biosensing applications through modification of the gate electrode. However, modification of the gate electrode often leads to nonideal transistor characteristics due to changes in its intrinsic electrical properties. This work investigates the effect of gate conductance in HIFETs using poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) as a model gate electrode. It is revealed that a reduction in gate conductance results in a reduction in the effective gate voltage and plays an important role in defining HIFET characteristics. Key figures of merit, including ON/OFF ratio, threshold voltage, transconductance, and saturation mobility increase with increasing gate conductance and reach a plateau once sufficient gate conductance is attained. This effect is attributed to a decrease in the effective gate voltage along the gate electrode arising from its resistivity when a gate leakage current is present. These results are widely applicable and serve as design rules for HIFET device optimization.