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Organic Transistors

The past decade has seen an upsurge in academic and commercial interest in the field of organic electronics. Devices such as organic light emitting displays, and chemical and physical sensors are already in the marketplace, while others, including photovoltaic cells and smart cards, are developing fast. This project focuses on the development of organic thin-film transistors (OTFTs) using a particular organic semiconductor combination – pentacene/PMMA. The interface between these two organic materials is relatively trap-free, leading to devices with excellent electrical performance, with high carrier mobilities and large on/off ratios.

In particular, we are attempting to fabricate transistors that operate at relatively low voltages. The electrical characteristics of pentacene OTFTs  using cross-linked poly(methyl methacrylate) (PMMA) as the gate dielectric are currently under study. Ultra-thin films of cross-linked PMMA can be obtained by spin-coating and subsequent irradiation using a 1.515 MeV 4He+ ion beam. The resulting film, with a thickness of 33 nm, possesses a low leakage current density of about 10-6  A cm-2 for fields up to 2 MV cm-1. Transistors incorporating the cross-linked dielectric operated at relatively low voltages, <10 V, and exhibit a mobility of 1.1 cm2 V-1 s-1, a threshold voltage of -1 V, a subthreshold slope of 220 mV per decade and an on/off current ratio of 1.0x106.

  1. Y Yun, C Pearson and M C Petty, Pentacene thin film transistors with a poly(methyl methacrylate) gate dielectric: optimization of device performance, J. Applied Physics, 105 (2009) 034508.
  2. M F Mabrook, Y Yun, C Pearson, D A Zeze and M C Petty, A pentacene-based  organic thin film memory transistor, Appl. Phys. Lett., 94 (2009) 173302.
  3. Y Yun, C Pearson and M C Petty, Bootstrapped inverter using a pentacene thin-film transistor with a poly(methyl methacrylate) gate dielectric, IET Circuits, Devices & Systems, 3 (2009) 182-186.
  4. Y Yun, C Pearson, D H Cadd, R L Thompson and M C Petty, A cross-linked poly(methyl methacrylate) gate dielectric by ion-beam irradiation for organic thin-film transistors, Organic Electronics, 10 (2009) 1596-1600.

Contact: Mike Petty ( for more details.

diagram of Organic Transistors