Giant Transconductance of Organic Field-Effect Transistors in Compensation Electric Fields

In field-effect transistors (FETs) that typically have three electrodes, the charge density and electrical conductance of semiconductor films are tuned by an electric field provided by the gate electrode. However, the other two electrodes (source and drain) are inevitably applied with different voltages to generate a source-drain current to make the FET work, which causes a continuous evolution of charge accumulation (or depletion) in the three-dimensional semiconducting films during gate-voltage scanning and thus leads to an intrinsic delay between on and off states. To avoid the delay and accelerate the switching speed, here we propose that transconductance of semiconducting films can be significantly increased (denoted as "giant transconductance" here) when the transport channel is within extra static compensation electric fields and experimentally verify it in organic FETs. The giant transconductance is theoretically derived as super transconductance, corresponding to an abrupt current variation at a fixed gate voltage and thus ideally zero subthreshold swing as well as infinite effective field-effect mobility (μFET). Giant transconductance is compatible with high temperature (up to 400 K), but both the doping concentration and the film thickness should be synergically optimized to warrant the super-rapid switching. For practical applications, we choose poly(3-hexylthiophene) and 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene to experimentally demonstrate the giant transconductance and its capability of current modulation. Giant transconductance could be potentially used in oscillator circuits, sensors, and high-performance circuits.