We fabricated InGaZnO (IGZO) thin film transistors by the sol-gel 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 SiO(2)/Si substrate by spin coating, followed by heat treatment at 400 degrees C in an ambient atmosphere for 1-12 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(-10)-10(-11) A, 10(4)-10(5) A, and 7-15 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 cm(2)/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. (C) 2011 Elsevier B.V. All rights reserved.