Double-gate poly-Si thin-film transistors fabricated using self-aligned technology

摘要

Double-gate TFTs having a buried bottom-gate were fabricated using a new self-aligned process. The photolithography for the top-gate was performed using the bottom-gate as the photo-mask and by exposing from the backside of the quartz wafer. We have been able to fabricate perfectly self-aligned double-gate TFTs using 4 photo-masks; bottom-gate, field isolation, contact hole and metalization. Drain current of about 3-fold the drain current of single-gate operation was obtained by double-gate operation. Current drive was also increased by thinning TFT active layer. The threshold voltage for the single-gate operation was able to be varied by changing the bias of the other gate. Uniformity in threshold voltage was improved by double-gate operation.