An integrated a-Si TFT demultiplexer for driving gate lines in active-matrix arrays

This paper reports on the analysis, design, and implementation of integrated amorphous silicon thin film transistor demultiplexers (a-Si TFT DEMUXs) for driving the gate lines in active matrix display/imaging board reduces the pin-count of the system, and consequently the system cost. Three different integrated a-Si TFT DEMUX are examined. The two-proposed a-Si TFT DEMUX circuits outperform previously proposed circuit by providing larger output voltage swings (OVSs), faster dynamic responses and less sensitivity to the device instability. The measurement result shows a 15 to 20 percent improvement in the OVS over that of a previous circuit under the same bias condition. As a key issue in the design of a-Si TFT circuits, the a-Si TFT instability, particularly the threshold voltage (V_T) shift, and its mechanisms are studied. Then, the expressions of circuit OVS sensitivity to the TFT´s V_T are derived and compared. Pulse-bias stress experiments, simulating the normal conditions of operation, are conducted on the a-Si TFT DEMUX circuits, and the deviations of the circuit electrical characteristics are measured over a period of 24hours. The measurement results are in agreement with the analysis in this work.