Geometric Effect of Channel on Device Performance in Pentacene Thin-Film Transistor

We fabricated pentacene thin film-transistors on a glass substrate with a SiO2 layer via thermal evaporation in ultrahigh vacuum. We investigated the influence of channel length, channel width, and the deposition rate of a pentacene layer on organic thin film transistors (OTFTs) performance. Field-effect mobility of the transistors markedly increased as channel width decreased and channel length increased. The maximum drain current of OTFTs increased as channel length decreased. These observations indicate that the grain boundary scattering of charge carriers in the pentacene layer is a major hurdle in charge conduction, similarly to the observation in poly-Si TFTs. The maximum field-effect mobility was 0.69 cm2/Vs for a device prepared at 0.1 A/s with a 50 µm channel length and a 20 µm channel width. Channel width/length ratio (W/L) as well as the deposition rate of the pentacene layer should be carefully chosen to increase field-effect mobility and maximum drain current in OTFTs.