Short Channel Amorphous IGZO TFT Arrays: Electrical Properties, Stability, and Density-of-States
Soo Chang Kim and Jerzy Kanicki
The high-end displays with the ultra-high definition (UHD > ~4000×2000 pixels), large-area (>70 inches), and high frame rate (> 240 Hz) are being introduced to realize displays with more realistic visual images. To fabricate such displays, a-IGZO TFT has emerged as a powerful active-matrix array alternative in industrial display production. It is important to exactly understand fundamental electrical properties and stability of the a-IGZO TFT arrays with a UHD resolution.
As compared to the long channel devices, slightly different electrical characteristics such as non-saturation of output curve at high drain-to-source voltage (Vds), negative shift of threshold voltage with increasing Vds, and the mobility reduction at high gate voltage (Vgs) were observed. The second derivative method adopting Tikhonov’s regularization theory is suggested for the robust threshold voltage extraction. The threshold voltage shift by the AC bias-temperature stress had a dependency on the magnitude of drain bias stress, frequency, and duty cycle due to the impact ionization accelerated at high temperature. The effect of temperature on the electrical characteristics was also investigated. We observed that studied a-IGZO TFT arrays obeyed the Meyer-Neldel (MN) rule over a broad range of gate bias voltages. The MN rule and exponential subgap density of states (DOS) model were combined to extract the DOS distribution for the investigated a-IGZO TFT arrays.
