Field-Emission Enhanced Contacts for Disordered Semiconductor based Thin-Film Transistors

Our presentation will report on substantial improvements to the performance characteristics of small channel length thin-film transistors (TFTs) made with disordered semiconductors such as amorphous indium gallium zinc oxide (IGZO) and pentacene with channel lengths in the range 10-200 nm. These improvements include reduced contact resistances that are deduced from the total channel resistance, increased effective carrier velocities, and improved sub-threshold response. The primary reason for these improvements is the improved carrier injection from source and drain contact metals to nominally undoped semiconductors resulting from using tapered geometries (nanospikes). Field emission, analogous to that seen in vacuum devices with sharp electrode tips, increases the local electric field at the contact tips and results in improved injection of charge from the metal contact to the band states or conducting states of the semiconductor. Conventional flat electrode devices have been fabricated alongside the nanospike TFTs for comparison. For all TFTs, a side guard electrode, held at the drain potential, was included that blocked spreading current from the source to the drain from regions away from the actual channel. This was necessary since the gate and the semiconductor were not patterned.