Ambipolar pentacene field-effect transistor with double-layer organic insulator

Ambipolar conduction in organic field-effect transistor is very important feature to achieve organic CMOS circuitry. We fabricated an ambipolar pentacene field-ef fect transistors consisted of gold source-drain electrodes and double-layered PMMA (Polymethylmethacrylate) / PVA (Polyvinyl Alcohol) organic insulator on the ITO(Indium-tin-oxide)-patterned glass substrate. These top-contact geometry field-effect transistors were fabricated in the vacuum of 10 -6 Torr and minimally exposed to atmosphere before its measurement and characterized in the vacuum condition. Our device showed reasonable p-type ch aracteristics of field-effect hole mobility of 0.2-0.9 cm 2 /Vs and the current ON/OFF ratio of about 10 6 compared to prior reports with similar configurations. For the n-type characteristics, field-effect electron mobility of 0.004-0.008 cm 2 /Vs and the current ON/OFF ratio of about 10 3 were measured, which is relatively high performance for the n-type conduction of pentacene field-effect transistors. We attributed these ambipolar properties mainly to the hydroxyl-free PMMA insulator interface with the pentacene active layer. In addition, an increased insulator capacitance due to double-layer insulator structure with high-k PVA layer also helped us to observe relatively good n-type characteristics. Keywords: pentacene, OTFT, field-effect transistor, ambipolar, mobility