1. A programmable element comprising: a base having a transition-metal oxide with mobile ions for drifting under an applied electric field; a source electrode; and a drain electrode; wherein the source electrode and the drain electrode are in physical contact with the base; wherein the base is electrically contacted by a reference voltage contact that is not connected to the source or drain electrodes; wherein the source electrode, the drain electrode, and the base are made of materials such that an interface of the source electrode material and/or the drain electrode material with the transition metal oxide base material forms an energy barrier for electron injection from the source electrode and the drain electrode into the base material; and wherein the energy barrier has a height that depends on a concentration of the mobile ions of the base material.