Manipulating Connectivity and Electrical Conductivity in Metallic Nanowire Networks

When: Friday, September 20, 2013 at 11:00 am
Where: DA 114
Speaker: Dr. Jessamyn Fairfield
Organization: Trinity College, Dublin
Sponsor: Physics Seminar

Nonvolatile memory can be demonstrated by tuning the connectivity and conductivity of metallic nanowire networks. The conductivity of interwire resistive junctions is manipulated by applying an electric field to create materials with tunable electrical conductivity. Spray deposited nanowires create dense, two-dimensional films of randomly oriented nanowires that are addressable using shadow mask electrodes. The junctions between nanowires initially act as capacitors with a random distribution of electrical properties, but can be activated to become conductive. The connectivity between individual nanowires determines what path is most favorable for charge traversing the network, and the sheet resistance of the material. Devices are made using metal nanowires that have either a polymer coating, which can break down irreversibly under an electric field, or an oxide passivation layer, which can undergo reversible electromigration to create a conduction path. In both cases, an electric field can be used to modify the connectivity and conductivity of the nanowire network. The network self-selects the lowest resistance paths to be activated first. Subsequent voltage cycling can activate additional conduction paths. Passive voltage contrast imaging, in scanning electron and helium ion microscopes, is used to visualize the activation and evolution of connectivity within these networks.  This imaging is correlated with I-V measurements to match changes in connectivity to changes in device resistance. Nanowire networks are simulated as leaky resistor-capacitor networks with a random distribution of junction activation voltages, revealing a universal scaling behavior relating the size of the connected cell of nanowires to the applied voltage. Local connectivity within these networks can be programmed to create materials whose properties evolve and adapt in response to external stimuli.

Host: Assistant Professor Meni Wanunu