Differential studies of dual-dielectric charge-storage cells

Abstract

By means of novel differential techniques, we have studied the writing and erasing dynamics of DDC cells and, in the process, uncovered a number of unexpected phenomena which play an important role in these processes. For example, we find writing currents qualitatively similar to, but considerably in excess of, those predicted earlier by Fowler‐Nordheim studies on similar MOS structures. We find that these devices can be written with high and undiminished efficiency to 7–10 V of flatband shift depending on insulator thickness, and we determine the limiting source of efficiency degradation beyond these levels. In erase, we find an interesting enhancement due, we believe, to electron‐electron repulsion of the net stored charge. By studying the reversible motion of the stored‐charge centroid at high temperatures, we determine that the effect of the interfacial dopant on the outer insulator extends about 80 Å into this layer. Other studies indicate an effect on the thin oxide to be less than 20 Å. Low‐field long‐time charging results point to a Fowler‐Nordheim–like writing current versus oxide field extending at least from 4.2 to 10 MV/cm, a range of no less than 10⁹ in current density for oxide thicknesses of 80 Å or more. All these features and others were found and investigated using quite standard flatband measurements, albeit, by the use of novel patterns of writing and erasing.