1. A memory storage and retrieval device, comprising: (a) an electrically conductive first electrode; (b) an electrically conductive second electrode; and (c) a layer stack intermediate said first and second electrodes, said layer stack comprising: (d) at least one active layer with variable electrical conductivity; and (e) at least one passive layer comprised of a source material for varying said electrical conductivity of said at least one active layer upon application of an electrical potential difference between said first and second electrodes.