A Unified Degradation Model of Elevated-Metal Metal Oxide (EMMO) TFTs Under Positive Gate Bias With or Without an Illumination

Abstract

Degradations of elevated-metal metal oxide (EMMO) thin-film transistors (TFTs) under positive bias stress (PBS) and positive bias illumination stress (PBIS) are systematically investigated and compared. An intrinsic correlation between PBS and PBIS degradation is demonstrated. Continuous negative threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) shift is observed under both stresses, with similar time-dependent V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> shift and recovery behavior. Characterization parameters for dependencies of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> shift on both stress V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> and temperature are also very close for the two degradations. PBS and PBIS degradation of EMMO TFTs and their correlation can be consistently understood based on a unified model, which emphasizes stress-induced accumulation of doubly-ionized V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sub> traps at the back-channel interface, and is verified with simulation.