Doug A. A. Ohlberg

Memristors based on an organic monolayer of molecules and a thin film of solid electrolytes

The memristor is a fundamental circuit element (along with capacitor, resistor and inductor) whose conductance is dependent on the previous functioning history. The concept was postulated almost four decades ago and was actually fabricated only recently. We report the fabrication of memristive junctions using an insulating film of a monolayer of cadmium stearate deposited using the Langmuir-Blodgett method in the gap of an inert electrode and a chalcogenide solid electrolyte. The thickness of the organic monolayer is about 2.8nm and its presence helps ensure a constant gap size between the electrodes. We used an energetic plasma process to create the chalcogenide solid electrolyte using sulfur (S) containing plasma for converting thin films of copper (Cu) into a mix of covelite phase CuS and chalcocite phase Cu2S.

A Novel Non-destructive Interfacing Technique for Molecular Scale Switching Junctions

Characterization of molecular scale electronic devices generally involves deposition of a metal top electrode onto an organic film. During the evaporation process, high-energy granules of metals may lead to unwanted reactions between the organic molecules and deposited top electrodes. This can cause, as commonly reported, lasting damage which leaves most junctions either shorted or an open circuit. To overcome this important issue of physical damage to the molecules, we developed a novel technique of interfacing molecules by laying a prefabricated metallic electrode on top of a monolayer of molecules which were deposited onto another set of electrodes. A monolayer of cadmium stearate ((C17H35COO)2Cd) was deposited, using the Langmuir-Blodgett technique, onto platinum (Pt) electrodes which further rested on 200nm of oxide used for isolation. A separate set of aluminum with native oxide (Al/AlOx) electrodes were fabricated on a different oxide free, highly p-doped substrate and was gently placed on the cadmium stearate monolayer. Electrical connection to the top electrode was accomplished by probing the backside of the highly doped wafer whereas the bottom electrodes were individually addressed. Pressure was applied to ensure firm contact between the molecules and the top electrodes. Preliminary results showed an observed switching voltage of 3V-4V. Most of the devices with Al as the top electrodes exhibited a gradual progression from switching on the positive side, closing or no longer switching, and then switching towards the negative side.