Tantalum doping to improve switching characteristics and bias stress stability of amorphous indium-gallium-zin oxide thin-film transistors

In this study, Ta atoms were incorporated into amorphous indium-gallium-zinc oxide (a-IGZO) films to improve the subthreshold switching (SS) characteristics and bias stress stability of thin-film transistors (TFTs). As the Ta content (C_Ta) was increased, field-effect mobility gradually was decreased and threshold voltage (V_TH) was shifted toward positive value. Further, the IGZO TFTs with C_Ta ≤ 0.2 at% exhibited smaller SS, and bulk channel layer trap and interfacial trap densities than the undoped IGZO TFTs. Further, the undoped-IGZO TFT experienced a large positive V_TH shift during the positive and negative tests. However, the IGZO TFTs with C_Ta = 0.15 and 0.2 at% demonstrated smaller V_TH shift than the undoped sample. X-ray photoemission spectroscopy results showed that the optimum content of Ta (C_Ta) (e.g., C_Ta = 0.15 and 0.2 at%) could effectively reduce the carrier trapping defects by suppressing the formation of oxygen vacancies and reducing the impurities in the IGZO films. These results indicate that optimum Ta content is effective in improving the bias stress stability and SS of the IGZO TFTs.