Electrolytes are generally thought of as molten or liquid substances that conduct electricity. Solid electrolytes are also possible and have a property that makes them useful for memory devices: the conducting and nonconducting states are nonvolatile. Creating or dissolving conduction paths in a solid electrolyte that bridge a memory cell's source and drain electrodes could build a nonvolatile memory. But high operating voltages and currents are needed if the controlling gate lies in the conduction path.
A novel nanoscale three-terminal device from NEC researchers gets around the problem. The solid electrolyte consists of a 40-nm spin-coated layer of Cu2S; the source and gate electrodes are copper; and the drain electrode is made from platinum. Applying a positive voltage to the gate causes both the gate and source electrode to inject positive copper ions into the electrolyte. When that happens, a copper bridge grows within the electrolyte and electrically connects the source and drain. The bridge disappears when a negative voltage is applied. More work needs to be done to improve cycling endurance and to reduce switching speeds at lower voltages, but the work is a promising first step.
