Study On The Lateral And Vertical Structure Of Organic Field Effect Transistors

Organic Filed Effect Transistor (OFET) is one of the most important research subjects in organic electronics. Considerable improvements have been achieved since it was invented. Because of their low cost and low temperature in fabricating, as well as better flexibility OFETs are considered to be useful in driving liquid crystal display, organic light-emitting diodes(OLEDs), smart cards, smart price and inventory tags, and large-area sensor arrays. Firstly, the evolution history of OFET was reviewed and the different problems appeared at different stages of OFET were summarized. The existing questions and hot topics for the future study were also discussed. Then, the materials were summarized in detail. The principle of OFET and I-V equations were analyzed and deduced.In this paper, OFETs with lateral and vertical structures have been fabricated by rational designs. The major work is summarized as the followings:(1) OFETs based on pentacene with copper (Cu) as source and drain (S-D) electrodes have been fabricated and investigated. Compared with the as-prepared devices, the stored devices exhibit preferable electrical characteristics after ten hours. The mobility increases from 0.012 to 0.03 cm2 V-1 s-1, and the threshold voltage downshifts from ?14 to ?9 V. The on/off current ratio is improved to 104. The improved performance of the stored devices is attributed to the formation of thin oxide. The role of the thin oxide has been discussed. The results suggest a simple way to optimize device properties and reduce the fabrication cost.(2) OLEDs with a configuration of top-contact field-effect transistor (FET) using LiF/Al as source and drain electrodes have been fabricated. Both an electro-optical transfer characteristic of OLEDs and a field effect behavior of FETs are shown in these devices. Five organic layers are expected to play respective function for FET and OLED. As a result, an unipolar field-effect behavior is presented experimentally. Furthermore, the field effect behavior has been analyzed. These multifunctional devices will provide an alternative way for fabricating OLETs and investigating the foundational mechanism about injection, transportation and recombination of charge carriers in organic optoelectronic devices.(3) A vertical organic light-emitting transistor (VOLET) was fabricated by stacking a capacitor cell on top of an organic light emitting cell joined by a common source electrode. This unique device has double functions, emitting light and switch current. When the capacitor is under bias, the storage charges modulate the charge injection of the OLED active unit. This device structure provide an extremely short channel and large conduction area (0.04 cm2), which supply enough output current.(up to 0.2mA). As a result, this device provides a solution for an active-matrix OLED display application.