Soft Recovery Process of Mechanically Degraded Flexible a-IGZO TFTs With Various Rolling Stresses and Defect Simulation Using TCAD Simulation

Abstract

We examine the effects of repetitive rolling stress on thin-film transistors (TFTs) using various rolling radii, and evaluate the subsequent thermal treatment at var- ious temperatures. After applying repetitive rolling stress, the electrical characteristics of the TFTs changes. In partic- ular, change of subthreshold swing (SS) is significant than that of threshold voltage (Vth), and saturation mobility (μsat). We simulated the electrical performance of TFTs using technology computer-aided design (TCAD) to quantitatively ascertain the change to donor-like and acceptor-like defects in the active region. Both Gaussian donor-like defects (NGD) and acceptor-like defects (NGA) increased under mechanical strain due to the formation of oxygen-related defects, oxy- gen vacancy (Vo), and oxygen interstitials (Oi). In addition, negative bias illumination stress (NBIS) reliability results show that degraded TFTs at higher rolling stress yield more variation of threshold voltage ( Vth) and SS due to increase in interface trap site, and defect sites. The rolling stress generates more oxygen-related defects, Vo and Oi, which act as TFT degradation factors. Finally, we investigate the possible recovery mechanism of mechanically degraded TFTs through thermal treatment. Thermal treatment at 150 ◦ C and 250 ◦ C cannot recover the electrical performance of mechanically stressed TFTs and NBIS reliability to before rolling state. Therefore, we used TCAD simulation to specu- late the origin of incomplete recovery. We thought that this incomplete recovery originated from oxygen dimers (O-O) formed from Oi under mechanical stress.