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 cm(2) V-1 s(-1), and an on/off current ratio of over 105 in device dimensions of W/L = 84/6 mu m. 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 1V. However, the stability of OTFT should be further improved and discussed.