Self-passivated copper gates for amorphous silicon thin-film transistors

A solution to the amorphous silicon transistor gate metallization problem in active matrix liquid crystal displays (AMLCD's) is demonstrated, in the form of a self-passivated copper (Cu) process. Cu is passivated by a self-aligned chromium (Cr) oxide encapsulation formed by surface segregation of Cr in dilute Cu-10-30at.%Cr alloys at 400 degrees C, solving the problems of chemical reactivity during the plasma deposition, diffusion, poor adhesion to the substrate, and oxidation. The performance of self-passivated Cu bottom-gate thin-film transistors (TFT's) and their stability during thermal bias stress testing is comparable to that of Cr-gate reference TFT's. The gate line resistivity (including encapsulation) is 4.5 mu Omega.cm at present.