A Study on Highly Reliable Integrated Gate Driver using a-Si TFTs

Abstract

MasterIntegrating gate driver circuits simultaneously with pixel TFTs on the glass is very important in the LCD technology, because it can reduce total cost of production by reduce driver IC and its bonding process. Poly-Si technology has been regarded as the most promising candidate for this purpose because it gives superior device performance to a-Si TFT. However the main stream in active matrix LCD is a-Si based technology, a-Si based integrated circuits are expected to replace poly-Si technology to a certain extent.When it comes to a-Si-based circuit integration, there are two issues of great importance. First, a-Si TFT has low mobility. It is about 0.5cm2/Vs, an order of a hundredth of that of poly-Si TFT. A handy solution is to increase the size of transistors. So the width of the TFT should extend to a degree of thousands of microns. Large a-Si TFTs are yet to be well characterized. Instability of a-Si TFT is a more serious problem. When a TFT is biased for a long time, the electrical properties change. Threshold voltages of a-Si TFTs in a circuit increase with time while the circuit is working. The circuit finally ceases proper operation. Insufficient life time of circuits has been the critical barrier to prevent a-Si TFT gate drivers from being practical technology.In this paper, we studied how to improve long-term reliability at high temperature for integrated gate driver circuit and verified by test samples. Then we fabricated 7.0” WVGA sample with enhancement integrated gate driver circuit technology and verified. In addition, dual VSS technology can improve the reliability was demonstrated