Electrically erasable, directly overwritable, multibit single cell memory elements and arrays fabricated therefrom

An electrically operated memory array of directly overwritable, multibit, single-cell memory elements comprising:

• a substrate;
• a plurality of electrically activated, directly overwritable multibit single-cell memory elements spacedly disposed in rows and columns on said substrate;
• each of said memory elements having an isolation device associated therewith to electrically isolate each element from the remainder of said plurality of memory elements;
• each of said memory elements comprising a volume of memory material defining a single-cell memory element;
• said memory material constituting means for assuming a large dynamic range of electrical resistance values with the ability to be set directly to one of a plurality of resistance values within said dynamic range without the need to be set to a specific starting or erased resistance value, regardless of the previous resistance value of said material in response to a selected electrical input signal so as to provide said single cell with multibit storage capacities;
• and
• each of said memory elements having a pair of spacedly disposed contacts for supplying said electrical input signal to set said memory material means to a selected resistance value within said dynamic range;
• and
• address lines extending over the upper and lower portions respectively of said memory elements and making electrical contact on one side of each of said memory elements with said volume of memory material means and on the other side of each of said memory elements with said isolation device, thereby providing means for selectively and individually setting and reading said resistance values of each discrete memory element.