Gate Stack Dielectric Degradation of Rare-Earth Oxides Grown on High Mobility Ge Substrates

TL;DR

This paper investigates dielectric degradation mechanisms in rare-earth oxide/HfO2 gate stacks on high-mobility Ge substrates, introducing a new Maxwell-Wagner instability model to explain observed charge trapping and breakdown phenomena.

Contribution

It presents a novel model based on Maxwell-Wagner instabilities to explain dielectric degradation in REO/HfO2 stacks on Ge, supported by experimental CVS stress data.

Findings

Charge trapping varies with CVS conditions.

Degradation involves relaxation, charge trapping, and leakage.

Hard breakdown occurs after prolonged stress.

Abstract

We report on the dielectric degradation of Rare-Earth Oxides (REOs), when used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2) on high mobility Ge substrates. Metal-Oxide-Semiconductor (MOS) devices with these stacks,show dissimilar charge trapping phenomena under varying levels of Constant- Voltage-Stress (CVS) conditions, which also influences the measured densities of the interface (Nit) and border (NBT) traps. In the present study we also report on C-Vg hysteresis curves related to Nit and NBT. We also propose a new model based on Maxwell-Wagner instabilities mechanism that explains the dielectric degradations (current decay transient behavior) of the gate stack devices grown on high mobility substrates under CVS bias from low to higher fields, and which is unlike to those used for other MOS devices. Finally, the time dependent degradation of the corresponding devices revealed an initial current decay due to relaxation, followed by charge trapping and generation of stress-induced leakage which eventually lead to hard breakdown after long CVS stressing.