Feasibility of an Ag-alloy film as a thin-film transistor liquid-crystal display source/drain material

The Ag-alloy films have been investigated as source/drain materials applicable to thin-film transistor liquid-crystal displays (TFT-LCDs). The Ag-alloy consisting of 0.9at.%Pd, 1.7at.%Cu (designated APC) showed a resistivity that was lower than one-half that of AlNd. It also had good contact characteristics with amorphous Si (a-Si). In addition, the Ag/Si was stable after heating to above 700°C, requiring no diffusion barrier to prevent reaction between Ag and Si. Pure Ag films deposited on glass by DC magnetron sputtering showed severe hillock formation, hole growth, and agglomeration upon annealing in air. In comparison, the APC-alloy film exhibited improved resistance to agglomeration. Further, inverted-staggered back-channel-etch hydrogenated amorphous silicon (a-Si:H) TFTs using an APC-alloy film as a source/drain material had a threshold voltage of 4 V. A structure of single layers of gate-APC alloys and source/drain-APC alloys leads to lower costs and productivity improvements of large-area, high-resolution, active-matrix LCDs, such as 40-in. size panels through process simplification.