Effects of channel length on temperature dependence of apparent subthreshold swing in self-aligned top-gate coplanar IGZO thin-film transistors

Abstract This study investigates how channel length (L) affects the temperature dependence of the apparent subthreshold swing (SS *) in self-aligned top-gate coplanar indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). Our experimental results demonstrate that SS * increases with temperature for devices with L = 5 μm and 7 μm, yet decreases for devices with L = 10 μm. To elucidate this behavior, we developed a drain current model based on surface potential. Our analysis reveals that variations in the dominant carrier populations (trapped versus free electrons) within the SS * extraction range dictate the observed temperature dependence of SS *. Furthermore, the lateral diffusion of donor impurities in our fabricated structures leads to notable differences in the effective channel length across TFTs with varying Ls, thereby amplifying these trends. These findings offer crucial insights into the physical mechanisms underlying the channel-length-dependent temperature behavior of SS * in IGZO TFTs. This understanding is vital for enhancing the stability of active-matrix organic light-emitting diode displays that utilize IGZO TFTs as backplanes.