The effect of annealing temperature on the stability of gallium tin zinc oxide thin film transistors

Abstract

With the growing need for large area display technology and the push for a faster and cheaper alternative to the current amorphous indium gallium zinc oxide (a-IGZO) as the active channel layer for pixel-driven thin film transistors (TFTs) display applications, gallium tin zinc oxide (GSZO) has shown to be a promising candidate due to the similar electronic configuration of Sn4+ and In3+. In this work TFTs of GSZO sputtered films with only a few atomic % of Ga and Sn have been fabricated. A systematic and detailed comparison has been made of the properties of the GSZO films annealed at two temperatures: 140 °C and 450 °C. The electrical and optical stabilities of the respective devices have been studied to gain more insight into the degradation mechanism and are correlated with the initial TFT performance prior to the application of stress. Post deposition annealing at 450 °C of the films in air was found to lead to a higher atomic concentration of Sn4+ in these films and a superior quality of the film, as attested by the higher film density and less surface and interface roughness in comparison to the lower annealed temperature device. These result in significantly reduced shallow and deep interface traps with improved performance of the device exhibiting VON of −3.5 V, ION/IOFF of 108, field-effect mobility (μFE) of 4.46 cm2 V−1s−1, and sub-threshold swing of 0.38 V dec−1. The device is stable under both electrical and optical bias for wavelengths of 550 nm and above. Thus, this work demonstrates GSZO-based TFTs as a promising viable option to the IGZO TFTs by further tailoring the film composition and relevant processing temperatures.