We report two measurement methods, named positive gate pulse mode (PGPM) and double sweeping mode (DSM), which can estimate the hysteresis induced by hole trapping in a gate insulator ( V hole ) and by defect creation in the IGZO channel ( V defect ). The effects of IGZO deposition temperature and of stress temperature on defect creation in the channel under negative bias and illumination stress (NBIS) are investigated. The results show that high deposition temperature of IGZO reduces defect creation in the channel under NBIS. The average activation energy for hole trapping in a GI under NBIS has been calculated to be 0.39 eV. InGaZnO (IGZO) thin-film transistors (TFTs) with field effect mobility >10 cm 2 /(V · s) are now used in high definition, large area ether active matrix liquid crystal displays (AMLCD) and active matrix organic light emitting diode displays (AMOLED).1,2 However, the reliability of IGZO TFTs under negative bias and illumination stress (NBIS) still requires improvement. Three possible reasons for NBIS instability in IGZO TFTs have been reported: (i) hole trapping in a gate insulator (GI), 3,4 (ii) donor like defect creation in the IGZO channel, [5][6][7] and (iii) electron trapping at a back channel interface. 8 Many efforts to improve NBIS reliability of IGZO TFT have been reported. 9-14 Hole trapping at front channel interface could be reduced by using AlO x as a gate insulator 9 or by using TiO 2 as a hole blocking layer. 14 The donor like state creation could be reduced by annealing IGZO TFTs in a high pressure water vapor, 10 wet O 2 , 11 hydrogen environment. 12 An AlO x , SrO x passivation layer could be used to suppress deep subgap defects in the IGZO channel. 13 In our previous study, 8 both hole trapping in a GI and donor like state creation in an IGZO channel induced hysteresis (V h ) in an IGZO TFT under NBIS. However, unlike a-Si TFT, the NBIS degradation mechanism in IGZO TFT is not consistent. It depends on the TFT structure, 15 the IGZO composition 16 and the fabrication process.17 Therefore, an understanding of the contribution of hole trapping in a GI and donor like state creation in an IGZO channel to V h is essential in the work to improve oxide TFT stability.Capacitance-voltage measurement is usually used to detect defect creation in the IGZO channel. 18,19 Subthreshold voltage swing [Ss = dV g /d log I D (V/decade)] could also be used to estimate the total number of generated defects ( N defect ) using the equation:[1]The threshold voltage shift induced by generated defects ( V defect ) can be calculated using the following equation:where C i is gate capacitance per unit area, q is the elementary charge, K is the Boltzmann constant and T is the absolute temperature (K). However, to the best of our knowledge, there is no direct method for separately measuring of hysteresis induced by trapped hole in a gate insulator ( V hole ) and hysteresis induced by defect creation in a channel ( V defect ). In this study, we demonstrate our developed measurement method, referred to i...