Study On The Operating Mechanism And Fabrication Of Organic Thin Film Transistors

Organic Thin Film Transistor (OTFT), a kind of transistor, can be made into large area device during low temperature. As a result of that, it has the advantages such as low cost and flexibility. With the performance developing, it has been a promising technique in electric label, radio frequency identification card and the driver circuit in flat panel display. Recently, researchers are paying more attention to the theory of OTFT at the same time as they try to improve the performance of it. Until now, researchers have made some progress, such as the influence of the energy level matching in the contact between the electrode and organic semiconductor on the injection of carriers, the formation of contact resistor, the transmission mechanism of the carriers and the working mechanism of OTFT. In this paper, the further theory study on OTFT is carried out. The specific work is as follows.First, the parameters of OTFT are researched. We analyze the error of the fitting method on Ⅰ/Ⅴ characteristic, which is used to get the field effect mobility and the threshold voltage. As a result, we get a conclusion that it is better to calculate the performance parameters through the least square method for its more precision. In addition, a new parameter, alternating resistance, is introduced to characterize the OTFT. Through the changing of the parameter above, it can be shown whether the ohmic or non-ohmic contact between organic semiconductor and electrode, that the resistance in the channel, and that the emergence of the saturation phenomenon. With this parameter, thus, the characteristics of OTFT can be completely described.Second, the principle of capacitance modulation is used to deduce a model of OTFT. Comparing to the characteristics of OTFT device, we find that they match well in the linear region, so the conclusion is drawn that the electronic process of OTFT in linear region is modulated by the capacitance principle. With the model analyzing the performance of OTFT, it is understood that the gate capacitance and the mobility of the organic semiconductor impact more on the characteristics of OTFT, namely, the insulating layer with higher dielectric constant and the organic layer with higher mobility will improve the performance of OTFT greatly.Third, the finite element method is used to simulate the OTFT on the potential and the carrier concentration in active layer. As we can see from the simulation result, the distribution of potential and carrier concentration are shown directly. With the changing of the electrodes, the process of channel formation and emergence of pinch-off with the increasing drain voltage can be seen clearly. Hence the simulation has proved the idea to the mechanism of OTFT. Besides, the simulation based on the change of gate capacitance and initial carrier concentration is implemented. As the simulation shows, higher capacitance and initial carrier concentration will enhance the characteristics of OTFT.Finally, OTFT of composite structure is put forward, and6composite structures arising from4typical structures of OTFT are mentioned. We also introduce the preparation process and mask methods of them. Based on the design plans, we succeed to fabricate one of the structures. The device presents a better performance than the single layer device when testing. In details, we can see from the transfer characteristic curve, in which the gate controlling source-drain current of composite structure is higher than that of the single part formed it. To further study the mechanism, the finite element method is used again to investigate the distribution of carrier concentration in organic layer. As the simulation result shows, the reason why composite structure device performs better is due to the formation of two channels.