| This dissertation introduces the design, fabrication, and application of a copper-oxide-based memristor for the passive sensing of oxygen and other gases. The device design was as follows: Deposition of copper (Cu) bottom electrodes, (oxygen) vacancy-rich copper oxide (CuxO) switching layers, and tungsten (W) top electrodes in a crossbar array structure. The CuxO layer was deposited via reactive sputtering of a Cu target with an argon-oxygen (Ar/O2) mixture. A portion of this layer was extended from each array cell to be exposed for sensing. Memristive devices of different switching layer thicknesses were initially explored for irreversible sensing of oxygen in ambient air. Results of this first experiment demonstrated an increase in resistance states upon prolonged exposure to ambient air. For the second experiment, memristive devices were fabricated with sub-micron holes that were etched into the W top electrode to better reveal the switching layer surface. The devices were also subjected to ambient oxygen at 180 deg C to induce passive sensing in minutes. Resistance results were consistent with the first experiment but also revealed a dependence on the surface area of the exposed oxide. Finally, memristive devices were investigated in a third experiment for reversible sensing of an oxidizing gas and reducing gas at room temperature. This time, changes were not only observed in resistance but also in hysteresis (current versus voltage) depending on the type of gas introduced. Overall, this work demonstrates a step towards the use of the memristor as a gas sensor, which we have named "memsensors", by taking advantage of the device's ability to memorize (or record) historical information. |
