Degradation of Metal-Induced Laterally Crystallized n-Type Polycrystalline Silicon Thin-Film Transistors Under Synchronized Voltage Stress

Abstract

Device degradation of n-type metal-induced laterally crystallized polycrystalline silicon thin-film transistors is systematically investigated under synchronized V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> pulse stresses. ON-state degradation is dominated by a pulse duty-time-related self-heating (SH) mechanism for low-frequency stresses whereas by a pulse transient time-related dynamic hot carrier (HC) mechanism for high-frequency stresses. OFF-state degradation is dominated by the dynamic HC effect, irrespective of stress frequency. It is first observed that such dynamic HC degradation is independent of the pulse falling time (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> ) but dependent on the rising time (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ). During t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , HCs are generated in the drain depletion region by a high transient coupling electric field arising from V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> switching. However, during t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> , the HC effect is screened by SH that caused high temperature rise. Device saturation is confirmed to play a key role in dynamic HC degradation under synchronized stresses. The proposed degradation model is verified by comparing it with various stress test results.