A self-passivated Cu(Mg) gate electrode for an amorphous silicon thin-filmtransistor

The feasibility of using Cu(Mg) alloy film as a gate electrode for thin-fil m transistor (TFT) liquid crystal displays has been investigated. When pure Cu was used as a gate electrode, severe interdiffusion occurred between Cu and the gases SiH4, NH3, and CF4 during plasma-enhanced chemical vapor dep osition of a gate dielectric, SiNx, and dry etching of the SiNx. On the oth er hand, the deposition of a Cu(Mg) alloy film gives rise to the formation of a MgO/Cu bilayer structure with low Cu resistivity, good adhesion to SiO 2, higher leakage current density, and excellent passivation capability. A hydrogenated amorphous silicon TFT with a MgO encapsulated Cu gate exhibite d a gate voltage swing of 0.91 V/dec. and a threshold voltage of 6.8 V, res ulting in a reduction of process steps and better performance. (C) 2001 Ame rican Institute of Physics.