A programmable metallization device, comprises a first electrode; a memory layer electrically coupled to the first electrode and adapted for electrolytic formation and destruction of a conducting bridge therethrough; an ion-supplying layer containing a source of ions of a first metal element capable of diffusion into and out of the memory layer; a conductive ion buffer layer between the ion-supplying layer and the memory layer, and which allows diffusion therethrough of said ions; and a second electrode electrically coupled to the ion-supplying layer. Circuitry is coupled to the device to apply bias voltages to the first and second electrodes to induce creation and destruction of conducting bridges including the first metal element in the memory layer. The ion buffer layer can improve retention of the conducting bridge by reducing the likelihood that the first metallic element will be absorbed into the ion supplying layer.