Subthreshold Swing of 59 mV decade−1 in Nanoscale Flexible Ultralow-Voltage Organic Transistors

Abstract

Organic thin-film transistors (TFTs) that provide subthreshold swings near the theoretical limit together with large on/off current ratios at very low operating voltages require high-capacitance gate dielectrics with a vanishingly small defect density. A promising approach to the fabrication of such dielectrics at temperatures sufficiently low to allow TFT fabrication on polymeric substrates are hybrid dielectrics consisting of a thin metal oxide layer in combination with a molecular self-assembled monolayer (SAM). Here, the electrical and surface properties of titanium oxide produced by the plasma-assisted oxidation of the surface of vacuum-deposited titanium gate electrodes and its use as the first component of a hybrid TiOx/SAM gate dielectric in flexible organic TFTs are investigated. These transistors have a gate-dielectric capacitance of about 1 µF cm−2, a subthreshold swing of 59 mV decade−1 (within measurement error of the physical limit at room temperature) for a wide range of channel lengths as small as 0.7 µm, and an on/off current ratio of 107 for a gate-source-voltage range of 1 V.