Abstract
Pentacene-based planar- and vertical-type organic thin-film transistors (OTFTs) are investigated in this paper. High operation voltages are observed for the planar-type OTFTs with top source/drain electrodes, which results from the limitations of channel length and low material mobility. With a reduced channel length, a LiF hole-injection enhancement layer, and a thin metal gate, the vertical-type pentacene OTFTs exhibit a low-voltage operation of less than 5 V and a compatible on/off ratio of larger than 10 2 . The smaller current gain observed from the device under current modulation is attributed to the increase of base recombination current under the common-emitter mode. © 2007 IEEE.