FIG. 21A shows a conventional conductive bridging random access memory (CBRAM) type element 2100 having a bottom cathode (i.e., inert electrode) 2199, an ion conducting layer (solid electrolyte) 2197, and a top anode (i.e., active electrode) 2195. Conventional element 2100 can be programmed between different resistance states by application of a potential between the electrodes (2199 and 2195). Application of a programming potential can cause metal atoms to ionize and ion conduct within ion conducting layer 2197 to form conductive regions, e.g., a “filament” 2193. The presence or absence of such a filament 2193 can determine a data value stored by the memory element 2100. Anode 2195 can be a source of a metal that can ion conduct within ion conducting layer 2197. In the conventional CBRAM type element 2100, ion conducting layer 2197 has a large contact area with the anode 2195 and the cathode 2199, being in contact with a bottom surface of the anode 2195 and a top surface of the cathode 2199. In addition, a filament 2193 remains unconstrained in a direction transverse to filament creation. That is, a filament 2193 can generally grow in the vertical direction of FIG. 21A, and be relatively unconstrained in a horizontal direction (as well as in a direction directed into cross sectional view shown).
A drawback to some conventional CBRAM type elements can be a tendency for a filament to agglomerate back into an electrode and/or within ion conducting layer 2197 in a fashion detrimental to a conductive path between the electrodes (2199 and 2195). A representation of undesirable agglomeration is shown in FIG. 21B. FIG. 21B shows element 2100 after the passage of time and/or after temperature cycles. Agglomeration of atoms of the filament 2193′ can result in an undesirable change in resistance of element 2100 from a low resistance to a higher resistance. This can present limits to data retention and/or thermal stability of the memory element 2100.
Another drawback to some conventional CBRAM type elements can be insufficient thermal stability. In particular, if subject to sufficiently high temperatures, or sufficient durations at elevated temperatures, the anode 2195 can agglomerate in an amount large enough to create an electrical short between the electrodes (e.g., 2199 and 2195) through the ion conducting layer (e.g., 2197). A representation of undesirable agglomeration of the anode 2195 is shown in FIG. 21C. Grain 2196 of agglomerated anode 2195′ can contact electrode 2199. Such a contact can be detrimental to the ability of a memory element 2100 to be programmed to a high-resistance state. This can present limitations on the ability of a memory cell 2100 to store data based on changes in impedance.
USPTO Backgrounds
USPTO Backgrounds