THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Thursday, May 21, 2020

10:00 AM

via

BlueJeans Video Conferencing

https://bluejeans.com/664057658

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Matthew West

"Fundamental Investigation of the Thermal Field on the Analog Response in Filamentary Adaptive Oxides for Neuromorphic Computing"

Committee Members:

Prof. Eric Vogel, Advisor, MSE

Prof. Meilin Liu,  MSE

Prof. Matthew McDowell, ME/MSE

Prof. William Alan Doolittle, ECE

Prof. Samuel Graham, ME

Abstract:

As we near the scaling limit for silicon-based transistors, developing new materials that can be used for non-traditional computing becomes increasingly important. Today’s computer architecture suffers from the Von Neumann bottleneck, which is due to computational instructions sharing the same pathway as data writes. This is a fundamental drawback of binary computing and it significantly limits system performance. Adaptive oxide devices, commonly referred to as memristors, are a promising new technology that can allow for analog, neuromorphic computing and allow for computation to occur in memory. The realization of adaptive oxides for neuromorphic computing hinges on repeatable and predicable changes of electrical resistance.

The focus of this proposal is on filamentary memristors which exhibit a non-volatile change in resistance by modulating the concentration of oxygen vacancies within a small (filamentary) region of an otherwise insulating oxide layer in a metal-insulator-metal (M-I-M) stack. During operation, these devices experience localized temperatures over 1000 K on picosecond timescales, with drift, diffusion, and thermophoresis causing the migration of oxygen ions and oxygen vacancies. All three of these mechanisms have a strong dependence on temperature. Therefore, the management of the thermal field will be crucial to successful implementation of these materials and devices.

A study to independently understand the role of the thermal environment on the analog temporal response of these devices has been completed in Aim 1. Identical device structures were fabricated on different substrates with two orders of magnitude difference in thermal conductivity. It was determined that lower thermal conductivity substrates have a larger change in resistance due to an increase in the local temperature of the filament. The second aim of this proposal will focus on engineering the thermal field for a more repeatable analog response. By encapsulating the device with a low thermal conductivity material, it is hypothesized that the temperature gradient within the device will be reduced. This will lessen the effect of thermophoresis and cause drift to become the dominate vacancy migration mechanism. Since the electric field is controlled by the applied voltage, the resistance change should be more predictable. The third aim will provide understanding of the effect of the thermal field within the nanoscale filament. Ex-situ studies using STEM/TEM to image the filament and EELS/EDX to map the oxygen concentration of filament operated in varying thermal environments will provide a fundamental understanding of the thermal field. Completion of this work will contribute fundamental knowledge of the effect of the thermal environment on the nanoscale filament and provide new insight on how to engineer the materials used in neuromorphic circuits with filamentary adaptive oxides.PhD