Current instabilities in rare-earth oxides-HfO2 gate stacks grown on germanium based metal-oxide-semiconductor devices due to Maxwell–Wagner instabilities and dielectrics relaxation

Abstract

The authors report the current instabilities in rare-earth oxides-HfO2 gate stacks grown on Ge (001) based metal-oxide-semiconductor devices under constant voltage stress (CVS). The devices have been subjected to CVS and show relaxation effect and charge accumulation/trapping at the interface of the high-k bilayers known as Maxwell–Wagner (MW) polarization; both cause current instabilities (i.e., current decay). The experimental data can only be explained when co-occurrent effects of MW instability and dielectric relaxation are taken into consideration. On the contrary, any single effect alone is unable to fit and/or explain the results completely. It is interesting that these effects show field dependent behavior; that is, at low CVS, the authors observe the current instabilities (follow J∼t−n law), whereas at higher field, the charge trapping and/or the creation of new defects in the oxides, which eventually lead to breakdown, are significant. These results are also confirmed by capacitance-voltage (C−Vg) measurements in respective conditions.