(Invited) Technology Trend of Poly-Si TFT from Viewpoints of Crystallization and Device Performance

Abstract

TFTs utilizing the Low-Temperature Polycrystalline-Si (LTPS) are very crucial for the system-on-glass. The requirements for the LTPS are a high quality, a large grain size and a position control of the nucleation. To satisfy those requirements, the promising crystallization methods have been presented. In addition, the device structures such as the double gate TFT and the tunnel type TFT have been developed. The excimer laser annealing provided a large grained film with a high-quality. It was also clarified that hydrogens in a-Si film greatly accelerated the crystal velocity and improved the crystallinity of the poly-Si film. A soft X-ray crystallization (SXC) reduced the threshold temperature of crystallization for a-Si, Ge and SixGe1-x films by 100-150 oC as compared with the thermal crystallization. Although the high-performance TFT utilizing the large single crystalline grains has been intensively researched, it does not successfully operate from the productive viewpoint. Tunneling Dielectric Thin-Film Transistor (TDTFT) was proposed and fabricated. It reduced the gate-off current less than 1/10 in comparison with a conv. TFT. In addition, the TDTFT improved the hump effect. We conclude that TDTFT will be suitable as a promising candidate of the next generation poly-Si TFT structure.