Effects of various gate materials on electrical degradation of a-Si:H TFT in industrial display application

Both aluminum (Al) and copper (Cu), acting as transmission lines in the hydrogenated amorphous silicon of a thin film transistor (a-Si:H TFT), were studied to investigate electrical degradation including electron-migration (EM) and threshold voltage (V-t) stability and recovery performance. Under long-term current stress, the Cu material exhibited excellent resistance to EM properties, but a passivated SiNx crack was observed due to fast heat conductivity. By applying electrical stress on the gate and drain for 5 x 10(4) s, the power-law time dependency of the threshold voltage shift (Delta V-t) indicated that the defective state creation dominated the TFT device's instability. The presence of drain stress increased the overall Delta V-t because the high longitudinal field induced impact ionization and then, enhanced hot-carrier-induced electron trapping within the gate SiNx dielectric. An annealing effect prompted a stressed a-Si:H TFT back to virgin status. This study proposes better Delta V-t stability and excellent resistance against electron-migration in a Cu gate device which can be considered as a candidate for a transmission line on prolonged TFT applications. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.