Pentacene OFETs of bottom-gate/bottom-contact were fabricated with three types of pentacene organic semiconductors and cross linked Poly(4-vinylphenol) or polycarbonate as gate dielectric layer. Two different processes were used to prepare the pentacene active channel layers: (1) spin-coating on dielectric layer using two different soluble pentacene precursors of SAP and DMP; (2) vacuum evaporation on PC insulator. X-ray diffraction studies revealed coexistence of thin film and bulk phase of pentacene from SAP and thin film phase of pentacene from DMP precursors. The field effect mobility of 0.031？cm2/Vs and threshold voltage of ？12.5？V was obtained from OFETs fabricated from SAP precursor, however, the pentacene OFETs from DMP under same preparation yielded high mobility of 0.09？cm2/Vs and threshold value decreased to ？5？V. It reflects that the mixed phase films had carrier mobilities inferior to films consisting solely of single phase. For comparison, we have also fabricated pentacene OFETs by vacuum evaporation on polycarbonate as the gate dielectric and obtained charge carrier mobilities as large as 0.62？cm2/Vs and threshold voltage of ？8.5？V. We demonstrated that the spin-coated pentacene using soluble pentacene precursors could be alternative process technology for low cost, large area and low temperature fabrication of OFETs. 1. Introduction Organic electronics are receiving great attention as emergent technology because of their inherent capacity to realize different electronic devices on desirable and flexible substrates. Organic molecular semiconductors and polymers used as active elements in optoelectronic devices have attracted great deal of attention today. Various organic molecular semiconductors and polymers have now demonstrated performance, which makes them suitable for application in thin-film-based devices via solution processes and cost-effective methods [1, 2]. Organic field effect transistors (OFETs) paved a new way due to their application to flexible, low cost, and large area thin film devices for various kinds of sophisticated organic electronic devices such as organic light emitting diodes (OLEDs), organic photovoltaic cells (OPV), drivers for electronic papers (e-papers), radio frequency identification tag (RFID), flexible memory, and flat panel displays [3, 4]. OFETs were organic active layers deposited upon gate dielectrics, for example, silicon dioxide (SiO2) or polymer dielectrics fabricated by vacuum evaporation, chemical vapour deposition; hot wall epitaxy and spin-coating have been reported to show good working
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