Pentacene films deposited with molecular beam deposition have been fabricated and characterized with respect to structure and morphology using x-ray diffraction and scanning electron microscopy. Metal-insulator semiconductor field-effect transistor devices based on such films were used to study their transport properties. A maximum field-effect mobility of 0.038 cm−2 V−1 s−1 is reported for devices incorporating pentacene films deposited at room temperature. The structural characterization revealed the coexistence of two phases: the thermodynamically stable single-crystal phase and the kinetically favored, metastable thin-film phase. Such mixed phase films were produced when low deposition rates were used in combination with a substrate temperature of 55 °C. Mixed phase films had transport properties inferior to films consisting solely of one phase, while amorphous films deposited at low surface mobility conditions had extremely low conductivity. Use of prepurified pentacene as source material resulted in an order of magnitude lower free-carrier concentration in the pentacene film as compared to films made with as-received pentacene.
Metal-insulator-semiconductor field-effect transistors have been fabricated from polymer semiconductors that can be processed from solution. The performance of these transistors is sufficient to allow the construction of simple logic gates that display voltage amplification. Successful coupling of these gates into ring oscillators demonstrates that these logic gates can switch subsequent gates and perform logic operations. The ability to perform logic operations is an essential requirement for the use of polymer-based transistors in low-cost low-end data storage applications.
Metal-insulator-semiconductor field-effect transistors have been constructed with pentacene as the active semiconductor. The pentacene is processed by spin coating from a soluble precursor. A simple thermal conversion yields transistors with carrier mobilities as high as 9×10−3 cm2 V−1 s−1 and current modulations of the order of 105. Depletion of charge is essential to the device operation. Data for an invertor exhibiting voltage amplification are presented.
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