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 L s, 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.