Enhancement of On/Off Current Ratio of Poly-Silicon TFT by Selective Laser-Induced Crystallization of Active Layer

Abstract

We have proposed the new poly-Si TFT which reduces the leakage current effectively by employing highly resistive a-Si region in the channel. The active layer of proposed device is crystallized selectively by employing excimer laser annealing while the both sides of channel near the source/drain are not recrystallized and remained as a-Si. Unlikely LDD or offset structure, the a-Si region which is designed to reduce the leakage current acts as the conduction channel of carriers under the ON state, so that the ON current is decreased very little. The selectively crystallized active layer can be fabricated by irradiating the excimer laser through ITO film of which transmittance at the wave length of laser is selectively adjusted. In the course of fabricating the proposed device, any additional photo masking step is not necessary and misalign problem is eliminated. The experimental results show that the ON/OFF current ratio of proposed poly-Si TFT is 106 while that of conventional one is 105.