Impact of semiconductor/contact metal thickness ratio on organic thin-film transistor performance

Pentacene-based organic thin-film transistors have been fabricated using photolithography and the bottom contact structure using parylene as the gate dielectric. Device performance was optimized by varying the thickness ratio of pentacene to Au contacts. Contact resistance dependence on the pentacene/Au thickness ratio (r= tpen tAu) was extracted using the transfer-length method [D. K. Schroder, Semiconductor Material and Device Characterization (Wiley, New York, 2006), pp. 184-199; Necliudov, Solid-State Electron. 47, 259 (2003)]. In this paper, we show that the effect of parasitic resistance and pentacene film morphology on device performance can be decoupled. Film morphology and microstructure are reported as a function of pentacene thickness and the correlation with transistor field-effect mobility is discussed.