Current Temperature Stress Study of Amorphous In-Ga-Zn-O Thin Film Transistors

Charlene Chen and Jerzy Kanicki

The thin-film transistor (TFT) long term reliability is a critical issue, especially in certain applications such as AM-OLEDs, where the drive TFT constantly supplies a current to the organic light-emitting diode (OLED) instead of just acting like a switch.

In this project we study the electrical stability of a-IGZO TFTs by performing current temperature stress (CTS) measurements, and investigate factors affecting the CTS including stress time, stress current, stress temperature, and TFT biasing conditions. We observed that the threshold voltage shift (ΔV_T) follows a power-law relationship with tSTR and ISTR, and that maintaining a lower temperature and smaller V_GS is beneficial to the TFT’s electrical stability. We also found that for the same level of I_D, the TFTs are more stable when operating in the saturation regime then in the linear regime. The a-IGZO TFTs exhibit ΔV_T ~1V under 10000s stress with ISTR = 100μA, and T_STR = 60°C. The subthreshold slope, off-current, and field- effect mobility remain almost unchanged during the stress. The stretched-exponential model modified for CTS describes very well ΔV_T as a function of t_STR, T_STR, and I_STR, suggesting that charge trapping near interface or in gate dielectric is at the origin of the a-IGZO TFT electrical instability. This work was supported by Canon Corp., Japan.

C. Chen et al., Journal of the SID, 17/6 (2009) 525.

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