(514a) A Nanofluidic Memristor Based on Anodic Oxide Formation on Silicon Microelectrode

We present a fast and robust fluid-based nonlinear ion memristor, based on a non-equilibrium anodic oxidation reaction of a silicon microelectrode in an aqueous solution, that can be used to synthesize nanofluidic logic circuits and fluid-based memory arrays with on-off logic components. The core components, with confined silicon microelectrodes and metal contacts, can be mass manufactured by simple silicon microfabrication method.  Versatile dynamic scaling yields devices at different scales, with predictable performance features from simple geometric scaling, including nanodevices for nanofluidic operations with high on/off resistance ratios and high switching speeds. The memory of ions transporting across the silicon/solution interface is recorded by a continuous formation of discrete oxide layers, which produces a history dependent resistance. During this anodic oxide film formation, high field at the solid/solution interface (> 10⁶~10⁷ V/cm) is shown to split water after a few layers, giving rise to a large current signature, with a ½ diffusive scaling with respect to time, that originates from the diffusive advance of the hydroxyl ion front across the nanoscale oxide film. The enhanced hydroxyl ion flux from this Faradaic source rapidly oxidizes the silicon film until the entire silicon microelectrode is covered by the oxide layer. Under cathodic bias, hydroxyl ions are extracted from the oxide film and hydride formation decomposes the layer. This rectification phenomenon at different polarization and the memory effect due to continuous oxide film formation under anodic conditions are the key mechanisms behind this robust memristor with distinct on-off current states. The non-equilibrium hydroxyl ion transport in the oxide layer under anodic bias and its contribution to resistance switching is studied by X-ray photoelectron spectroscopy. The nanofluidic memristor is then designed based on this mechanism to achieve a high on/off resistance ratio larger than 10, and a short resistive state switching time of less than 100ms. We will report the use of this memristor in a nonlinear ion circuit, consisting of ionic NAND/NOR gates and latches, that can activate (code) and read (decode) multiple sensors with a binary sequence in a single-input-single-output design. Excitable, bistable and oscillatory ionic circuits that mimick neurons will also be reported.