Effect of Ga content and sintering time on electrical properties of InGaZnO thin film transistors fabricated by solgel process

We fabricated InGaZnO (IGZO) thin film transistors by the solgel method and evaluated the effects of the Ga content and sintering time on their electrical properties. The IGZO precursor solution was prepared by mixing In-nitrate, Ga-nitrate, and Zn-acetate at an atomic ratio of In:Ga:Zn=3:x:1 (x=0.5, 1.0, and 1.5) and deposited on a SiO₂/Si substrate by spin coating, followed by heat treatment at 400 °C in an ambient atmosphere for 112 h. All of the devices behaved as n-channel transistors and the off current, on-to-off current, and threshold voltage were measured to be in the ranges of 10 ^-1010^-11 A, 10⁴10⁵ A, and 715 V, respectively. In addition, we found that the electrical properties were sensitive to the Ga ratio and sintering time of the IGZO film. The saturation mobility was the highest (3.11 cm²/V s) when the Ga ratio was 1.0 and the sintering time was 1 h, and it decreased as the Ga ratio or sintering time increased. This decrease is probably due to the presence of excess oxygen vacancies and/or Ga phase as an impurity.