June 19, 2009 - Dr. Hagen Klauk
Systems on Plastic (SoP), such as flexible displays, require field effect transistors that can be manufactured at temperatures below about 150 °C, to be compatible with plastic substrates. Such low temperature transistors can be made using conjugated organic semiconductors, semiconducting carbon nanotubes, or inorganic semiconducting nanowires. However, most organic transistors and many of the nanotube and nanowire transistors developed to date employ relatively thick gate dielectrics with a capacitance typically below 0.3 µF/cm2, so the transistors usually require operating voltages of more than 5 V. In order to take full advantage of low voltage (<3 V), high efficiency (>100 lm/W) organic light emitting diodes (OLEDs) for the realization of ultra low power flexible emissive displays, field effect transistors that can be operated with 3 V or less are needed. This requires a low temperature processable gate dielectric with a capacitance greater than about 0.5 µF/cm2. A promising approach is the combination of a thin plasma grown metal oxide and a molecular self-assembled monolayer. These hybrid dielectrics are prepared at temperatures below 100 °C, have a thickness of about 5 to 6 nm (depending on the plasma power and the choice of the self assembling molecules), and provide a capacitance close to 1 µF/cm2 that allows transistors as well as unipolar and complementary logic circuits based on organic semiconductors, carbon nanotubes, and inorganic nanowires to operate with voltages between 2 and 3 V.