Amorphous oxide thin film transistors (TFTs) were fabricated with 0.5 wt% silicon doped zinc tin oxide (a-0.5SZTO) thin film deposited by radio frequency (RF) magnetron sputtering. In order to investigate the effect of annealing treatment on the electrical properties of TFTs, a-0.5SZTO thin films were annealed at three different temperatures (300 o C, 500 o C℃ , and 700 o C) for 2 hours in a air atmosphere. The structural and electrical properties of a-0.5SZTO TFTs were measured using X-ray

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... raction and a semiconductor analyzer. As annealing temperature increased from 300 o C to 500 o C, no peak was observed. This provided crystalline properties indicating that the amorphous phase was observed up to 500℃ o C. The electrical properties of a-0.5SZTO TFTs, such as the field effect mobility (μ FE ) of 24.31 cm 2 / Vs, on current (I ON ) of 2.38×10 -4 A, and subthreshold swing (S.S) of 0.59 V/decade improved with the thermal annealing treatment. This improvement was mainly due to the increased carrier concentration and decreased structural defects by rearranged atoms. However, when a-0.5SZTO TFTs were annealed at 700 o C, a crystalline peak was observed. As a result, electrical properties degraded. μ FE was 0.06 cm 2 /Vs, I ON was 5.27×10 -7 A, and S.S was 2.09 V/decade. This degradation of electrical properties was mainly due to increased interfacial and bulk trap densities of forming grain boundaries caused by the annealing treatment.