DC/AC Stability of In-Ga-Zn-O Thin-Film Transistors

Graduation date:2017This item has been restricted to the OSU Community at the request of the author until 2019-10-20The electrical stability of amorphous indium-gallium-zinc oxide (a-IGZO) thinfilm\ud transistors (TFTs) is investigated for flat-panel display applications. Although\ud products incorporating a-IGZO TFT backplanes are already commercially available,\ud e.g., iMac with 5K retina display, technical challenges need to be addressed for nextgeneration\ud applications, e.g., active-matrix organic light-emitting diode displays.\ud Device stability is one crucial issue. The objective of the research presented herein is\ud to provide an in-depth assessment of the effect of DC and AC bias temperature stress\ud on the stability of a-IGZO TFTs. It is found that TFT threshold voltage instability,\ud ΔVTH, is reduced by decreasing the unipolar AC duty ratio, decreasing the operation\ud temperature, using a bipolar AC waveform rather than a unipolar waveform, or\ud employing an optimized passivation layer that suppresses moisture incorporation into\ud the a-IGZO channel layer. A two-parameter stretched-exponential expression is used\ud to describe the time-dependent instability trend. The long-term reliability of an a-IGZO\ud TFT as a function of gate voltage, temperature, or duty ratio is successfully modeled\ud using the two-parameter stretched-exponential expression. The stretched-exponential\ud activation energy is correlated with the Meyer-Neldel rule activation entropy.\ud Technology computer-aided design (TCAD) simulation provides insight into the\ud natural of a-IGZO TFT instability from the perspective of the subgap density of states\ud (DOS). It is found that less DOS change results in a more stable TFT