Exploration of Thin Films for Neuromorphic, Electrofluidic, and Magneto-Plasmonic Applications

Author

Walker L. Boldman, University of Tennessee, KnoxvilleFollow

Date of Award

8-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Philip Rack

Committee Members

Philip D. Rack, Jason Fowlkes, Thomas Ward, David Mandrus

Abstract

Due to the limit in computing power arising from the Von Neumann bottleneck, computational devices are being developed that mimic neuro-biological processing in the brain by correlating the device characteristics with the synaptic weight of neurons. We demonstrate a platform that combines ionic liquid gating of amorphous indium gallium zinc oxide (aIGZO) thin film transistors and electrowetting for programmable placement/connectivity of the of the ionic liquid. In this platform, both short term potentiation (STP) and long-term potentiation (LTP) are realized via electrostatic and electrochemical doping of the aIGZO, respectively, and pulsed bias measurements are demonstrated for low power considerations. Using a lithium-based ionic liquid, we demonstrate both potentiation (decrease in device resistance) and depression (increase in device resistance), and propose a 2D platform array that would enable a much higher pixel count via Active Matrix electrowetting. Fabrication and optimization of the aIGZO thin film transistors are then studied and optimized for integration into a 16x16 Active Matrix platform. Poly-silicon transistors are also explored as an alternative to aIGZO, and the behavior of these transistors are compared and contrasted with the aIGZO results.

Bimetallic alloys with large discrepancies in atomic radii and crystal structure typically yield systems that are highly immiscible, even at high temperatures. The Ag_xFe_1-x [silver iron] binary system has limited solid and liquid solubility and thus phase separated silver + iron alloys should result. Furthermore, silver has interesting plasmonic properties and iron is a strong ferromagnet, thus magneto-plasmonic nanoparticles/films should result due to their phase separation. We have leveraged a combinatorial sputter deposition to synthesize thin films with a large Ag_xFe_1-x (0.19 < x < 0.84) phase space to correlate the composition and structure to the optical and magnetic properties for both as-deposited and annealed compositions.

Recommended Citation

Boldman, Walker L., "Exploration of Thin Films for Neuromorphic, Electrofluidic, and Magneto-Plasmonic Applications. " PhD diss., University of Tennessee, 2020.
https://trace.tennessee.edu/utk_graddiss/6942