Study On Performances Of OFET Based Copper Phthalocyanine

Today, with the high development of information industry, large scale integrated circuits technology and displays technology become the two major techniques in information society. Disadvantages, such as higher invest cost, complicated preparation techniques, not suit to flexible substrate and large area production, exist in traditional Si-based semiconductor techniques. A novel, low-cost electronic device, i.e. organic field-effect transistor, experienced a rapid development in last decades, which drawn a tremendous attention of scientists and manufacturers. This kind of organic electronic devices have the characteristics of low cost, simple techniques, lower preparation temperature (lower than 150℃ ), and compatible with the flexible substrates, and match completely the need of low-end electronic products. So, it are the best solved schemes to achieve lower cost, flexible substrates, larger area flat displays array and low end integrated circuits. However, the rapid improvements of OFET's performances mostly profit from research achievements in new organic semiconductor materials. Oppositely, there are just little studies on improving structur(?) and optimizing parameter of OFET devices and on carrier transport mechanism in organic materials.Therefore, our study focuses on integrate performances of OFET devices. The whole contents of study as follow:First, we fabricated high performance OFET device based CuPc.We investigated the effect of different gate insulators and substrate temperature on morphology of CuPc evaporated film and properties of CuPc-OFET. The results indicated that all CuPc films present α -phase in structure and polycrystalline in morphology on all chosen gate insulator, and grain size increase as substrate temperature go up. The performance of OFET device is optimum when substrate temperature was hold at 150℃ on same gate insulator. Closer to the value of CuPc film the value of surface energy of insulator, easier the larger grain size CuPc film beobtained, and better the properties of OFETs based CuPc are. We think that the surface energy of gate insulator not only affect nuclear density of CuPc films, but affect defect states of intragrain and intergrain of CuPc films also.We also investigated the instabilities of OFET that is characteristic of threshold voltage shift. Through studying the relations of threshold voltage shift versus stress voltages, stress times and temperature, we concluded that the instabilities are due to carrier trapping into trap site in the insulator by direct tunneling model. Through studying the I-V property of insulator MIM and C-V property of MIS based CuPc, we concluded that trapped carriers have a redistribution process by Pool-Frankel mode, and that the value of threshold voltage shift is related to insulating ability of insulators, the OFET with good insulating ability gate insulator(SiO2) have small shift value and he OFET with poor insulating ability gate insulator(TaOx) have large shift value.We invented a novel structure OFET, which belong to bottom contact structure but with a layer of low dielectric insulator under source and drain electrodes. It has the advantages of a bottom-contact device for easy integration, and has the high performance of a top-contact device. The low-dielectric insulating layer reduces leakage current and parasitic capacitances derived from gate/source and gate/drain overlap. The experimental results indicated that good performances of the normal top contact OFET and our novel structure OFET is due to that changes of source/drain contact position can change the electrical field distribution and help carriers injecting into channel region. And poor performance of normal bottom contact devices is injection limited. In addition, we optimized devices parameter of active layer thickness. When the thickness active layer is 20nm, the performance of OFET based CuPc become best.Finally, we investigated dependences of field-effect mobility of CuPc-FET on gate voltage, doping and measure temperature. We also simulated relation of field-effect mobility and temperature using grain boundary potential well model, and simulate results and experiment results have a good fit. So we think that grain boundary potential well model dominated the carrier transport in the CuPc polycrystalline film.