ANODIC OXIDE-FILMS AS A GATE DIELECTRIC FOR A THIN-FILM-TRANSISTOR

A comprehensive study is made of the anodization behavior and electrical and physicochemical properties of anodic oxides for use as thin film transistor (TFT) gate dielectrics. The matrix metals examined are pure Al, Al-1.1 atom percent (a/o) Ta, Al-0.5 a/o Ti, and Al-1.0 weight percent Si, and electrolytes in aqueous solution are ammonium tartrate, triammonium citrate, diammonium hydrogenphosphate, and ammonium tetraborate-boric acid. Breakdown voltage in anodization, which corresponds to maximum formable thickness, was highest for the oxide of Al-Ta for all solutions. A dielectric strength of over 7.0 x 10(6) V/cm was achieved for oxides of the combinations Al-Ta and Al-Ti/inorganic solution. Leakage current in the anodic oxide annealed at 300-degrees-C was lowest for the combination Al/inorganic solution. The oxide of Al-Si for all solutions was no better than that of Al for any of the properties investigated. The most promising combination for gate dielectries was Al-Ta and Al-Ti/inorganic solution, giving a field effect mobility of 1.0 to 1.5 cm2/Vs and an on-off current ratio of more than 10(8) for TFTs fabricated with a double-layer gate dielectric structure of an anodic oxide layer/a plasma chemically vapor deposited SiN(x) layer.