Instability of an Amorphous Indium Gallium Zinc Oxide TFT under Bias and Light Illumination

Bias stabilities of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) under light illumination were examined. An unstable behavior was observed under a specific condition meditated by the polarity of the applied gate bias and the wavelength of the incident light. Under a positive gate bias stress, a-IGZO TFTs showed stable characteristics regardless of the light illumination. However, under a negative gate bias stress, a-IGZO TFTs showed a huge negative shift in the threshold voltage when illumination with light in the blue range was added. Hole trapping at the gate dielectric layer is believed to be one of the major causes of the degradation. Furthermore, a degradation in the subthreshold characteristics was simultaneously found, and could be attributed to changes in the subgap states.