Investigation of Electronic Mechanisms in Sputtered Thin-Film Oxides for Next Generation Computational Devices

Author

Matthew I. Flynn-Hepford, University of Tennessee, KnoxvilleFollow

Orcid ID

https://orcid.org/0009-0007-7318-3919

Date of Award

8-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Philip D. Rack

Committee Members

Olga S. Ovchinnikova, Sergei V. Kalinin, Dustin A. Gilbert

Abstract

The increasing demand for data processing, alongside the tapering of Moore’s Law, poses a critical challenge for the continued advancement of computing technologies. As energy consumption by information technology rises rapidly, there is an urgent need to develop new materials and device architectures that enable energy-efficient, high-density, and scalable memory and logic solutions. This dissertation investigates the mechanisms underlying resistive and ferroelectric switching in metal-oxide thin films, with a focus on tantalum oxide (Ta₂O₅), zirconium oxide (ZrO₂), and hafnium-zirconium oxide (Hf_xZr_1-xO_₂) systems.

A combined conductive atomic force microscopy (C-AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) workflow was used to directly observe field-driven ion migration in Ta₂O₅/Ta memristive devices. The study reveals three dominant mechanisms: charge trapping, oxygen vacancy migration, and irreversible breakdown. Each of these mechanisms is associated with distinct voltage and current regimes. This understanding provides a foundation for tuning operational windows to promote reversible switching behavior.

A combinatorial approach is employed to synthesize and characterize Zr_xTa_1-xO_y thin films across a range of compositions. This enables high-throughput exploration of how cation chemistry affects electronic trap depth, ionic motion, and switching performance. The results demonstrate that optimal switching behavior occurs near 30% Zr content, where hysteresis and current levels are maximized. These findings are supported by ab initio molecular dynamics simulations, which reveal enhanced ionic mobility at this composition.

Ferroelectric switching was investigated in sputtered Hf_xZr_1-xO₂ thin films. Structural analysis reveals a reduction in the monoclinic phase and emergence of orthorhombic and tetragonal phases with increasing Zr content. Electrical measurements indicate that charge trapping and interface effects contribute to the observed switching behavior, with phase composition and electrode-induced stress playing critical roles.

This work advances fundamental understanding of the structure-property relationships governing oxide-based resistive switching and ferroelectric devices. The insights gained provide principles for designing and fabricating the next-generation, energy-efficient computing systems based on tunable oxide thin films.

Recommended Citation

Flynn-Hepford, Matthew I., "Investigation of Electronic Mechanisms in Sputtered Thin-Film Oxides for Next Generation Computational Devices. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/12706