Study Of Functional Organic Field Effect Transistors

Organic field effect transistors(OFET)have attracted great attention for potential application in basic switching elements, smart cards, sensing devices, ring-oscillators, ?at panel displays, identification tags and integrated circuit, due to their low cost processing, facile procedure, mechanical ?exibility, lightweight, large-area and chemical stability. By the development of over the last two decades, considerable improvements have been achieved. OFET becomes one of the most important electronical devices. Among the OFET devices, ambipolar OFET have become research targets since they are potentially available for complementary circuits in organic integrated circuits and organic light-emitting field effect transistors, which could achieve the function of field-effect and light emitting. Thus functional OFET are put on the agenda.Firstly, the evolution history in the latest two decades, application and research significance of OFET was summarized. The existing problem and developmental trends of OFET were discussed. Secondly, the basic structure and commonly used materials, such as organic semiconductor material, gate insulating layer material and electrode material of OFET were summarized. The principle and interface contact theory of OFET was studied in detail. Then some methods of improving performance of OFET were described.According to the research status and some existing issues of OFET, taking OFET as the object of study, pentacene OFET based on polymer gate insulator and ambipolar OFET based on a pentacene/C60 heterojunction were fabricated, respectively. Finally, quasi-ambipolar OFET based on aluminum electrode and single pentacene active layer were fabricated.The major work is summarized as follows:(1) Pentacene OFET based on PMMA and Polyimide gate dielectrics have been fabricated on ITO-coated glass substrate using ITO as gate electrode, respectively. Aluminum is using as source and drain electrodes. The devices exhibit typical P-channel characteristics. In addition, pentacene-based OFET using various thickness PMMA gate dielectrics are fabricated. The interface properties between gate insulator and pentacene active layer and the effects of the insulator thickness on the performance of the devices have been investigated, respectively.(2) Ambipolar OFET with a heterostructure of pentacene/C60 have been fabricated, in which the C60 layer functions as an n-type channel, while the pentacene layer functions as both a p-type channel and a sealing capsule for the C60 layer. PMMA is employed as gate insulating layer and low-cost Al is used as S/D electrodes. The ambipolar OFET, operating in an ambient atmosphere, exhibit a hole mobility of 1.0877×10-1cm2/V·s in the p-type operation and an electron mobility of 1.6186×10-2cm2/V·s in the n-type operation. Ambipolar OFET is the important part of functional OFET. (3) Single pentacene active layer-based quasi-ambipolar OFET have been fabricated. Firstly, the feasibility of the experimental program is confirmed by theoretical analysis. A thin PMMA-modified layer is spin-coated on SiO2 gate dielectric. The presence of ambipolar behavior is attributed to the relatively small surface energy on the PMMA-modified SiO2 gate dielectric as compared to that on the bare SiO2 surface. Thus the enhanced grain growth of pentacene takes place and hence reduce grain boundary density. Al is used as S/D electrodes, which possess a suitable work function to balance the hole and electron injection into the highest occupied and the lowest unoccupied molecular orbitals of pentacene, which lay the foundation for functional OFET.