Investigation of grain boundary control in the drain junction on laser-crystalized poly-Si thin film transistors

This letter investigates the influences of grain boundaries in the drain junction on the performance and reliability of laser-crystalized poly-Si thin film transistors (TFTs). A unique test structure where the channel region includes 150-nm-thick laser-crystalized poly-Si with small grain sizes and a 100-nm-thick one with large grain sizes is fabricated. Different behaviors in the electrical characteristics and reliability of a single TFT are observed, first under measurements of the forward mode and then under measurements of the reverse mode. This is due to the different number of grain boundaries in the drain junction. Grain boundaries in the drain junction were found to cause reduced ON/OFF current ratio, variations in threshold voltage with drain bias, significantly increased kink effect in the output characteristics, and poor hot-carrier stress endurance.