To study the interface effects on the device performance, we fabricated indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) with a two-stack gate-insulator structure. The two-stack gate insulator was composed of a thick main insulator and a thin interfacial insulator; the main insulator determines the effective permittivity of the gate insulator, and the interfacial insulator regulates the gate/active interface properties. The a-IGZO TFTs had about 10cm2 V−1 s−1 field effect mobility (μ FE) values and 107–108 switching ratios. The dependences of μ FE and threshold voltage, V TH, on the channel width to length ratio were different according to the electron affinity, χ, of the interfacial insulator. The contact resistance between the source/drain electrode and the active layer, and the electron-injection barrier height from the active layer to the interfacial gate insulator layer could explain this finding. In this work, we successfully demonstrated the method to distinguish the interface-related phenomena from the insulator permittivity-related phenomena. 
Analysis of the dependence of indium–gallium–zinc oxide thin-film transistor properties on the gate interface material using a two-stack gate-insulator structure