Studies And Fabrication Of Organic Field Effect Transistor

Organic Filed Effect Transistor (OFET), namely Organic Thin-film Filed-effect Transistor (OTFT), is one of the most important research subjects in organic electronics. Considerable improvements have been achieved since it was invented, and it is hopefully to be applied to many fields in commercial scale. Concerning about this, the study on OFET is quite significant. In this thesis, it was performed in theory, by experiment and simulation, respectively.Firstly, the evolution history of OFET was reviewed. The different problems appeared at different stages of OFET were summarized. The existing questions and hot topics for the future study were also discussed. In fact, some of them, e.g., the influence of interaction of semiconductor/insulator on OFET performance, became the important subjects investigated in the thesis.Then, the materials widely used in OFET, including organic field-effect material, electrode material and insulator material, were summarized in detail, in which the organic field-effect material was classified into n-type, p-type and bipolar-type to be carefully analyzed, respectively.The operation principle of OFET was demonstrated mainly from the following two aspects. First, the transport mechanism of carrier in organic semiconductor was discussed. It is commonsense that the different transport mechanism of carrier is the primary factor which differentiates organic semiconductor from inorganic semiconductor. Thus there were many transport mechanisms for organic semiconductor had been proposed and they are carefully generalized and analyzed. Second, the â… -â…¤ equations of OFET were deduced. As we know, OFET is operated under enhancement mode, distinguished from the inversion mode of other Si-basedField-effect transistors, resulting in the different I-V equations. In this article, the principle of OFET and I-V equations were analyzed and deduced.Several kinds of OFETs with different configurations were fabricated. During the process, ITO was employed as the substitute of Au to act as the Source/Drain materials. It didn't deteriorate OFET performances and the principle was demonstrated. Moreover, in order to farthest utilize the ITO performance, the photolithography process of ITO thin film was studied, which is one crucial step to fabricate one new configuration, namely "reversed top-contact" OFET. This kind of OFET has some advantages than "top-contact" and "bottom-contact" OFET, it is potentially to be used in light-emitting OFET (bipolar), etc.The influence of insulator on OFET was also studied, which aimed to analyze the influence of insulator layer thickness, and of insulator/semiconductor interaction on the OFET's performances. Experimental results showed that, when insulator thickness decreased, both carrier density and electric filed in semiconductor would be enhanced greatly, which further changed the carrier mobility via traps-filled mechanism and Poole-Frenkel mechanism, respectively. Besides this, the surface and interface electron states of insulator/semiconductor were characterized. The O element diffused from insulator layer was proved to have great bearing on the chemical shift of other elements, which may degrade the performance of OFET.Finally, the numerical simulation of OFET was also performed, focusing its analysis on the influence of "contact resistance (Re)" on OFET performances. Analyzed results showed that when carrier mobility exceed 10"1 cm2/V.s, great negative effect will be brought about by Re. To avoid this effect, Re should be reduced to one fifteen of the intrinsic resistance (the Channel Resistance when the maximum Gate voltage, zero Drain voltage were applied). In addition, if the contact resistance is inevasible, it seems a good measure to reduce the operating voltage to guarantee the basic I-V characteristic of OFET, while this will degrade the performance of OFET.