Fine-Patterned Organic Thin Film Transistors using Solution Organic Semiconductor Materials

To integrate solution-processible organic semiconductors in the array of thin-film transistors, fine-patterned organic thin-film transistors were fabricated by photolithography. Gold, which has a high work function, was used as a source–drain electrode to reduce the energy barrier between the organic semiconductor and the source–drain. Stacked double layers of gold and chromium were deposited and etched on a glass substrate to enhance the poor adhesion of gold on glass, and then a self-assembled monolayer was formed on them. Solutions of an organic semiconductor and a low-k organic gate insulator were spun by a spin coater and patterned by dry etching using a gate metal as a mask. The devices fabricated by this method show good electrical properties, average field effect mobilities of 0.2–0.3 cm2 V-1 s-1, and an on/off current ratio of over 105 in device dimensions of W/L=84/6 µm. The leakage current through the gate insulator between the gate and the source–drain was similar to that of SiNx in amorphous silicon thin-film transistor (a-Si TFT), which is lower than 10 pA. When the bias-stress stability of organic thin film transistors (OTFTs) was compared with that of a-Si TFT, the threshold voltage shift of OTFT was comparable to that of a-Si TFT, which is smaller than 1 V. However, the stability of OTFT should be further improved and discussed.