Origin of the Alternative Current (AC-) Gate Bias Improving the NBIS Stability of IGZO TFTs

The alternative current (AC-) and direct current (DC-) NBIS degradation mechanism of IGZO TFT were investigated. Negative shift in transfer characteristic with subthreshold swing (Ss) degradation was observed under DC-NBIS testing. However, the Ss degradation disappeared under AC-NBIS testing. The generated defects and trapped holes were reasons for DC-NBIS instability. On the other hands, trapped holes were the main reason for AC-NBIS instability. The generated defects were unstable and act as midgap trap states for hole generation. AC-gate bias reduced density of midgap trap state, resulting in a reduction of hole generation.