Hiroshi Tsutsu

Effect of Residual Phosphorus on Amorphous Silicon Thin Film Transistors

Effects of residual phosphorus in the channel region of amorphous silicon thin film transistors(a-Si TFTs) on the TFT characteristics were quantitatively investigated. Concentration and the depth profile of the residual phosphorus were measured by high resolution secondary ion mass spectroscopy(SIMS). The OFF characteristics of a-Si TFTs were also measured. The SIMS data showed that the phosphorus exists about 100nm deep into intrinsic a-Si(i-a-Si), but the OFF characteristics showed that the activity of the residual phosphorus is 4 order of magnitude lower than that of heavily phosphorus doped a-Si( + -a-Si). The residual phosphorus is found to be inactive and stable, and has little effect on a-Si TFT characteristics. These results enabled us to fabricate inverted staggered a-Si TFTs by the simplest process using only 2 photo-mask steps and 1 self-aligned exposure.

Development of a new design simulator for poly-Si TFTs to optimize the lightly doped drain structure

A new design simulator to simulate the characteristics of poly-Si TFTs taking into account its physical structure was developed. By using the simulator, we can optimize the length and the sheet resistance of the LDD region in order to obtain sufficient ON currents and to suppress OFF currents under both dark and illuminated conditions.