High Field Temperature-Independent Field-Effect Mobility of Amorphous Indium-Gallium-Zinc Oxide Thin-Film Transistors: Understanding the Importance of Equivalent-Oxide-Thickness Downscaling

Weinvestigate the temperaturedependenceof field-effect mobility (mu(eff)) on amorphous indium-gallium-zinc oxide (alpha-IGZO) thin-film transistors (TFTs) having 10-nm-thick HfO2. Thanks for the downscaling of the equivalent oxide thickness (EOT), we observe, for the first time, a temperature-independent mu(eff) at a high field or high carrier concentration (N-carrier) regime and a strong temperature-dependent mu(eff) at a low field or low N-carrier regime. The observation highlights the importance of EOT downscaling to enhance Ncarrier and facilitate the Fermi level (E-F) to approach and even exceed the potential barriers' peak (E-M), leading to a high and temperature-independent mu(eff) at high N-carrier. N-carrier at which E-F = E-M is extracted to be similar to 6 x 10(12) cm(-2). Adetailedstudy of the relationship-between EOT scaling and the gate bias voltage (V-GS) at which E-F equals to E-M is performed. alpha-IGZO TFTs with an ultrascaled gate dielectric are capable of alleviating the negative effects from the potential barriers at low V-GS and could enable low-power applications with high performance. Besides, a weak temperature-dependent subthreshold swing (SS) of alpha-IGZO TFT was observed and explained.