Unified model for QBD prediction for thin gate oxide MOS devices with constant voltage and current stress

Abstract

A unified thin oxide breakdown model based on anode hole injection is presented for calculating the charge to breakdown Q BD for constant voltage and current stress. The oxide breakdown strength Q BD for thin oxide MOS devices can be predicted at different constant voltage and current levels based on the proposed breakdown model. The oxide electric field which determines the tunneling current, electron energy, oxide degradation and hence the lifetime of the device is properly calculated in this model. The voltage drop due to the poly depletion effect has been carefully taken into account while calculating the oxide voltage to determine the oxide electric field. Moreover, the impact of poly depletion on quasi static C– V curves of a thin ( t ox=25–70 Å) gate oxide MOS device is studied using the 2-D device simulator medici. The model also accounts for the energy-dependent relaxation length for calculating the electron energy and the quantum yield in silicon for calculating the barrier height for hot hole tunneling from the anode side. These quantities are then used to compute the anode hole current which is linked to the time-dependent dielectric breakdown.