We investigated the microstructure and electrical properties of Cu and Cu-Mn alloy on amorphous In-Ga-Zn-O (a-IGZO) oxide semiconductor in order to explore a high performance electrode material for thin film transistors (TFTs) in advanced flat panel displays. Current-voltage measurements of metal/semiconductor contact structure showed a non-linear behavior with Cu, while a good ohmic behavior [rho(C) = (1.2-2.9) x 10(-4) Omega.cm(2)] with the Cu-Mn alloy after annealing at 250 degrees C for 1 h. Transfer and output characteristics of TFT structure also showed excellent performance with the Cu-Mn alloy. The good electrical property was due to the formation of a highly doped n(+) a-IGZO layer with the carrier density of 1.4 x 10(20) cm(-3). The donor doping could be achieved simply by heat treatment to promote the oxidation of Mn and the reduction of a-IGZO. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3621723] All rights reserved.