Alkali ion drift model for data retention in stacked gate structures

Abstract

A model for data retention in stacked gate structures has been formulated, considering that an alkali ion drift toward the negatively charged floating gate is a cause of degradation. A charge conservation law is obtained for the alkali ions, which reduces to a differential equation concerning the threshold voltage variation. A simple analytical expression for the threshold voltage variation has been obtained whose form is identical to the conventional model; however, the physical meaning is quite different. In the proposed model, the low activation energy is attributed to the potential barrier height formed by silicon dioxide atoms for alkali ions and the inconsistency in the conventional model can be solved.