Performance and Reliability Comparison of ZnO and IGZO Thin-Film Transistors and Inverters Fabricated at a Maximum Process Temperature of 115 °C

Abstract

Performance and reliability comparison of oxide-based thin-film transistors fabricated at a maximum process temperature of 115 °C is presented. A fully patterned and passivated process was successfully evaluated and implemented using polycrystalline ZnO and amorphous indium–gallium–zinc–oxide (IGZO) as an active layer in glass substrates. Saturation mobilities of 14.2 and 9.0 cm $^{{2}}\cdot \text{V}^{-{1}}\cdot \text{s}^{-{1}}$ were obtained for ZnO and IGZO, respectively, with threshold voltages of 2.2 and 2.0 V, an ON/ OFF ratio $> {1} \times 10^{{8}}$ , and an ${I}_{{\text {off}}} A. The small mobility change in IGZO with gate voltage is due to its amorphous character. Longer variation is observed in polycrystalline ZnO due to its grain boundaries. Reliability studies show a threshold voltage shifting of 0.4 and 1.8 V for ZnO and IGZO devices, testing after 1200-s stress. Devices were successfully implemented in ZnO- and IGZO-based inverters using saturation and zero-drive structures, showing a maximum dc gain of 2.4- and 25-V/V, respectively.