Excimer laser processing for a-Si and poly-Si thin film transistors for imager applications

Pulsed excimer laser annealing (ELA) has become an important technology by which to produce high performance thin film transistors (TFTs) for large area electronics. The applications of these advanced TFTs in flat-panel displays and flat-panel imagers for two-dimensional x-ray imaging have attracted much interest. TFTs made from excimer laser crystallized poly-Si thin films with mobilities higher than ${\mathrm{100\hspace{0.17em}cm}}^2\mathrm{/V s}$ and off-state leakage currents lower than 2 fA/μm at drain voltage $V_D\text{=5}$ V have recently been achieved. The improved off-state leakage current enables one to consider making flat-panel imagers based on poly-Si TFT technology. Laser doping or dopant activation is another important application of the ELA process. Using a laser doping process, we have fabricated a-Si TFTs with self-aligned poly-Si source/drain contacts. These new devices have reduced source/drain parasitic capacitance and their channel length can easily be scaled down. In this article, we will review the excimer laser processing technology for both the poly-Si TFT technology and self-aligned a-Si:H TFT technology and report the current status of developing flat-panel imagers using these new TFT technologies.