Developments in Dual Dielectric Charge-Storage (DDC) REPROM (REProgrammable Read Often Memories)

There has been an increasing interest in recent months in the dual dielectric metal insulator semiconductor (MIS) cell as a nonvolatile semiconductor memory element. A true nonvolatile semiconductor memory could replace the omnipresent magnetic memory because associated with it one also expects fast access capability as well as interface compatibility with other semiconductor logic circuits. Key features in such a semiconductor memory cell, then are; true nonvolatility, high-speed access capability and ease of write-erase operations. The development of the dual-dielectric charge-storage (DDC) cells have followed two parallel paths, both enjoying a limited success yielding commercial products. The first centers around the concept of the floating gate, an artificially created metallic charge-storage site located at the dual dielectric interface. The second uses the naturally occurring interfacial states existing at the dual-dielectric interface as the charge storage sites, as in metal-nitride-oxide-semiconductor (MNOS) memory transistors. The advantages and disadvantages of these two approaches to the realization of DDC cells is reviewed briefly. And then the concept of the interfacial dopants, l the heart of this paper, emerges as a particularly beneficial compromise between these two concepts, resulting in an optimum DDC cell, with true nonvolatility, yet with undemanding write-eras conditions.