Electrical, optical, and structural properties of indium zinc oxide (IZO) films grown by a box cathode sputtering (BCS) were investigated as a function of oxygen flow ratio. A sheet resistance of 42.6 Omega/square, average transmittance above 88% in visible range, and root-mean-square roughness of 2.7 angstrom were obtained even in the IZO layers grown at room temperature. The top-emitting organic light-emitting diodes (TOLEDs) with the IZO top cathode layer were prepared and their electrical properties compared with TOLEDs with Mg-Ag/indium tin oxide (ITO) cathode layer and TOLEDs with only thermally evaporated Mg-Ag cathode layer. In addition, the effects of oxygen flow ratio in IZO films are investigated, based on X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet/visible (UV/VIS) spectrometer, scanning electron microscopy (SEM), and atomic force microscopy (AFM) analysis results. (c) 2005 The Electrochemical Society.