Characteristics And Carrier Transport Mechanism Of Organic Thin Film Field Effect Transistors

Much attention has been attracted by organic thin-film field-effect transistors (OTFTs) in the past decade. Research on the performance of OTFTs and the mechanism of the carrier transport in tunnel is not only a significant topic related to physical chemistry, solid-state physics and microelectronics, but alsoone of the frontiers in the field of organic molecular electronics.In this dissertation, the effects of concentration of defeats, the inner electric field in tunnels, carrier distribution in semiconductor layer and the crystalline form of pentacene film on the performance of OTFTs have been studied. Fabrication conditions of OTFTs have been optimized and high performance OTFT based on glass substrate with a field-effect mobility of 0.71 cm2/Vs and on/off ratio of 104 have been obtained. At the same time, the optimum conditions were applied in fabrication process of flexible OTFTs based on plastic substrate. The curving characteristics of soft OTFTs were measured. It was found that the curvature paralleled to tunnel length would affect the performance of soft OTFTs due to the change of the pentacene layer morphology. Driving characteristics of OTFTs have also been measured. Organic lighting-emitting diodes (OLEDs) driven by one OTFT or an active-matrix driving circuit based on two OTFTs and one capacitance have been prepared. The change of the source-drain current of OTFTs connected in circuits, stability of OTFTs with long-time operation, responding and holding characteristics of active matrix driving circuits were investigated. Based on the discussion of the carrier transport mechanism in the tunnel, the effect of gas on the performance of OTFTs has also been studied. It was found that OTFTs degraded fast when exposed in atmosphere, the adsorption of H2O on pentacene surface was determined to be the main reason of the degradation. Remarkable improvement in the device stability was achieved by device encapsulation with UV curable resin. In addition, our work demonstrated that the carrier mobility of OTFTs increased with gas pressure in high pressure region, however, the mobility decreased with gas pressure in low pressure region. Bump of free gas molecules on pentacene particle and adsorption of gas molecules on pentacene film were considerd to be the two main factors that affected the carrier mobility. A model of gas related transports, including gas-assisted transport and barrier-blocked transport, was proposed. The relationship between gas pressure and source-drain current was presented by an equation.