An amorphous silicon thin-film transistor with fully self-aligned top gate structure

We have developed a novel fully self-aligned top gate amorphous silicon thin-film transistor, which shows excellent transistor characteristics. Self-alignment is achieved by patterning the gate electrode and then etching the silicon nitride gate insulator, followed by silicidation and ion implantation of the exposed a-Si in the contact regions. We obtain a long channel saturated mobility of 0.9 cm 2 V/sup -1/ s/sup -1/, while for channel lengths of 6 μm, we obtain an effective mobility of 0.6 cm 2 V/sup -1/ s/sup -1/, in the saturated region and 0.5 cm 2 V/sup -1/ s/sup -1/, in the linear region. This high level of performance, together with the negligible parasitic capacitance of the self-aligned structure, makes this transistor suitable for new demanding applications in active matrix liquid crystal displays and large area X-ray image sensors.