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(-1)s(-1), while for channel lengths of 6 mu m, we obtain an effective mobility of 0.6 cm(2)V(-1)s(-1), in the saturated region and 0.5 cm(2)V(-1)s(-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.