The effects of channel length and film microstructure on the performance of pentacene transistors

With the use of the stencil lithography, we fabricated pentacene thin-film transistors pre- pared directly on thermally oxidized silicon gates with channel lengths ranging from 2 to 600 lm. By performing 4-probe measurements or by using the transfer line method on these field-effect transistors, we were able to separate the respective contributions of the channel and the contacts to the transistor performance. The contact resistance depends strongly on the gate voltage and on the grain size and morphology; this behavior has been attributed to screening effects at the contact barriers. The low-field mobility in the channel is 0.5–0.6 cm2/Vs in long-channel transistors and reaches mobility in the order of 10 cm2/ Vs in short-channel transistors consisting essentially of a single grain.