Interface traps analysis in p-type poly-Si TFTs under hot carrier stress using the charge pumping method

In this research, we investigated the interface traps of poly-Si TFTs using charge pumping methods and analyzed effect of hot carrier stress by comparing interface trap distribution. These methods applied three types of pulse shapes, which were square, triangular, and trapezoidal. The interface state density, D_it, was measured by varying the frequency, pulse amplitude, and rise/fall times from the square pulse method. We found that D_it decreased due to the decreasing recombination of trapped carriers, and the majority carriers decreased by thermal emission depending on the temperature. We also confirmed the relation between space charge region and source–drain region according to reverse bias. Additionally, the mean interface-state density and capture cross-section, Q_ss, were extracted from the recombined charge versus pulse frequency curve created by the triangle pulse method. To explain the effects of the HC stress of poly TFTs, the interface trap states were measured before and after application of the hot carrier stress. The experimental results showed that the capture cross-section was doubled from 1.1×10^-14 cm² to 2.27×10^-14 cm² and interface trap distribution was changed after the HC stress. Finally, we confirmed that, after applying the hot carrier stress, the energy distribution of the interface state reflected the location of the induced damage region caused by the hot carrier stress and the observed shift of deep trap states affected the drain current in the subthreshold region and increased the subthreshold swing.