A diode structure includes a rectangular first doping region, and a second doping region surrounds the first doping region wherein the first doping region and the second doping region are separated by a first isolation structure. A third doping region surrounds the second doping region wherein the second doping region and the third doping region are separated by a second isolation structure. The first isolation structure, the second doping region, the second isolation structure and the third doping region are arranged in a quadruple concentric rectangular ring surrounding the first doping region.

A conjugated polymer layer with a built-in diode is formed by providing a first metal-chalcogenide layer over a bottom electrode. Subsequently, a second metal-chalcogenide layer is provided over and in contact with the first metal-chalcogenide layer. The first metal-chalcogenide layer has a first conductivity type and the second metal-chalcogenide layer has a second conductivity type. The plane of contact between the first and second metal-chalcogenide layers creates the p-n junction of the built-in diode. Then a polymer layer is selectively deposited on the second metal-chalcogenide layer. The second metal-chalcogenide layer provides ions to the polymer layer to change its resistivity. A top electrode is then provided over the polymer layer. An exemplary memory cell may have the following stacked structure: first electrode/n-type semiconductor/p-type semiconductor/conjugated polymer/second electrode.