Aluminum-based gate structure for active-matrix liquid crystal displays

This paper describes the development of an Al-based thin-film gate structure for use in large, high-resolution active-matrix liquid crystal displays (AMLCDs). Aluminum films are suitable for forming the data lines of such displays, but they are not suitable for forming the gate lines because of the hillock-induced shorts that can occur to overlying metal lines during the heating necessary for insulator deposition. Alloying with yttrium, gadolinium, and neodymium was examined with the aim of reducing hillock and whisker formation during such heating. Although Al films alloyed with 2 at.% of those metals exhibited low hillock densities (10-100 mm-2), the densities were not low enough for the fabrication of SXGA (1280 x 1024 pixels) panels. After investigation of several means to further reduce the formation of hillocks and whiskers, the most effective approach was found to be anodization of the Al-alloy gate lines, suitably patterned for anodization, followed by photoresist application and laser-cutting steps. Illustratively, by use of an anodized Al-Nd (2 at.%) thin-film gate structure, the short-circuit defect rate and contact defect rate for an 11.3-in.-diagonal experimental SVGA (800 x 600 pixels) display could be effectively reduced to zero.