A Current Estimation Method for Bias-Temperature Stress of a-Si TFT Device

We have studied the time-dependence degradation of ON current of amorphous silicon thin-film transistors (a-Si:H TFTs), which is a function of stress duration, stress temperature, and stress bias. A simple method with stretched-exponential equation and current-voltage function is used to characterize and predict the TFT performance. Bias-temperature stress at different stress voltages has been performed on a-Si:H TFTs. A new method using ON current degradation to analyze TFT device performance is presented, which is different from the conventional threshold-voltage shift method. We have also observed that the beta value in the ON current degradation method compared to the threshold-voltage shift method, with a stretched-exponential stress time, is related to beta~beta₀-T_ST/T₀. Finally, we have also used the new equation to evaluate the performance of the gate-driver-on-array circuit in our products. If the limitation of the current for the pull-down device is 1times10^-6 A, then the operation time of the pull-down device can be estimated to about 1219 h when key pulled-down TFT is operating at 60degC.