Comparison of physical and electrical properties of GZO/ZnO buffer layer and GZO as source and drain electrodes of [alpha]-IGZO thin-film transistors

In this research, top-gate bottom-contact thin-film transistors (TFTs) made with amorphous indium gallium zinc oxide ([alpha]-IGZO) active layers were grown using the radio-frequency sputtering technique. Two kinds of source and drain (S/D) electrodes, namely bi-layer GZO/100-nm ZnO buffer layer/Corning 1737 and single-layer GZO/Corning 1737, used in the TFT devices and the electric characteristics of the devices were compared. To explain the differences in the TFT performances with these different S/D electrodes. X-ray reflectivity (XRR) and contact angles were measured. The [alpha]-IGZO TFT with the bi-layer GZO/100-nm ZnO buffer layer structure as S/D electrodes exhibited superior device performance compared to that of the TFT with a single-layer GZO structure, with a higher thin film density (5.94 g/cm super(3)), lower surface roughness (0.817 nm), and larger surface energy (62.07 mJ/m super(2)) and better adhesion properties of neighboring [alpha]-IGZO films. In addition, the mechanisms responsible for the GZO/100-nm ZnO buffer layer/Corning 1737 structure S/D electrodes improving the device characteristics were systematically investigated. The [alpha]-IGZO TFT saturation mobility, subthreshold voltage, on/off current ratio, and the trap density of the GZO/100-nm ZnO buffer layer/Corning 1737 S/D electrodes were 13.5 cm super(2)V super(-1)S super(-1), 0.43 V/decade, 3.56 x 10 super(7), and 5.65 x 10 super(12) eV super(-1) cm super(-2), respectively, indicating the potential of this bi-layer structure to be applied to large-area flat-panel displays.