X-ray reflectivity and surface energy analyses of the physical and electrical properties of α-IGZO/GZO double active layer thin film transistors

In this research, bottom-gate thin film transistors (TFTs) of amorphous indium gallium zinc oxide (α-IGZO)-based active layers were grown by the radio-frequency sputtering technique. The device characteristics of two kinds of TFT structures, namely α-IGZO/GZO double active layer TFT and α-IGZO single active layer TFT, were compared. To explain the differences in the TFT performances of these different structures, X-ray reflectivity (XRR) and contact angles of the active layer were measured. The α-IGZO/GZO double active layer TFT exhibits superior device performance as compared to the other TFT structure because of its highest thin film density (5.87 g/cm3), lowest surface roughness (1.89 nm), and largest surface energy (60.07 mJ/m2). Also, the mechanisms of this double active layer to improve the device characteristics were systematically investigated. The improved saturation mobility, sub-threshold voltage, on/off current ratio, and trap density of the α-IGZO/GZO double active layer TFT were 18.92 cm2 V−1 S−1, 0.33 V/decade, 1.33×108, and 4.25×1012 eV−1 cm−2, respectively, indicating the potential of this structure to be applied on large-area-flat-panel displays.