A Schottky-to-Ohmic Transition in Epitaxial Ferroelectric Hafnia Devices
type: CreativeWork
description: The development of analog resistive non-volatile memory elements is of great interest for future information storage technology. These devices can be used to emulate the electronic behaviour of biological synapses and neurons for neuromorphic computing or sensing applications. Hafnia is a promising material to use in resistive memory systems due to its high industrial compatibility. Both the migration of oxygen ions and ferroelectricity are two mechanisms actively being explored to drive resistance change in hafnia based devices. This thesis explores the interplay between interfacial redox chemistry and ferroelectricity and how these influence the resistance switching behaviour in epitaxial hafnia films. A device stack is engineered to elicit large resistance changes through both ferroelectricity and interfacial redox reactions. Ultra-thin epitaxial Y doped HfO2 (YHO) is grown with a controlled oxygen stoichiometry. To stabilise the polar phase in YHO and provide a resistance-tuneable bottom interface, YHO is grown on La0.66Sr0.33MnO3 (LSMO) buffered Nb doped SrTiO3 substrates. In-depth X-Ray diffraction based structural analysis identified the polar nature of the film and a strain induced rhombohedral distortion. Ferroelectricity in the film was confirmed by piezoresponse force microscopy. In device configuration, using an Au top electrode with an ultra-thin Ti adhesion layer, a resistance switching mode with large on-off ratio was observed. The pristine device was stabilised in an intermediate resistance state and did not need an electro-forming process. The mode reversibly switched between a purely capacitive (Schottky) and resistive (Ohmic) state, a Schottky-to-Ohmic transition (SOT). A series of voltage pulse trains were used to explore the intermediate resistance states of the system. Both analog and integration behaviour was demonstrated, depending on the pulse profile. The SOT may therefore find application as both a synapse and a neuron respectively in neur…
abstract: The development of analog resistive non-volatile memory elements is of great interest for future information storage technology. These devices can be used to emulate the electronic behaviour of biological synapses and neurons for neuromorphic computing or sensing applications. Hafnia is a promising material to use in resistive memory systems due to its high industrial compatibility. Both the migration of oxygen ions and ferroelectricity are two mechanisms actively being explored to drive resistance change in hafnia based devices. This thesis explores the interplay between interfacial redox chemistry and ferroelectricity and how these influence the resistance switching behaviour in epitaxial hafnia films. A device stack is engineered to elicit large resistance changes through both ferroelectricity and interfacial redox reactions. Ultra-thin epitaxial Y doped HfO2 (YHO) is grown with a controlled oxygen stoichiometry. To stabilise the polar phase in YHO and provide a resistance-tuneable bottom interface, YHO is grown on La0.66Sr0.33MnO3 (LSMO) buffered Nb doped SrTiO3 substrates. In-depth X-Ray diffraction based structural analysis identified the polar nature of the film and a strain induced rhombohedral distortion. Ferroelectricity in the film was confirmed by piezoresponse force microscopy. In device configuration, using an Au top electrode with an ultra-thin Ti adhesion layer, a resistance switching mode with large on-off ratio was observed. The pristine device was stabilised in an intermediate resistance state and did not need an electro-forming process. The mode reversibly switched between a purely capacitive (Schottky) and resistive (Ohmic) state, a Schottky-to-Ohmic transition (SOT). A series of voltage pulse trains were used to explore the intermediate resistance states of the system. Both analog and integration behaviour was demonstrated, depending on the pulse profile. The SOT may therefore find application as both a synapse and a neuron respectively in neur…
author: Müller, Moritz
language: eng
keywords: Ferroelectricity, Epitaxy, Memristor
license: https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/1557085f-9d36-4a1c-870c-a349a71af969/download
license: http://purl.org/NET/rdflicense/allrightsreserved
date published: 2024-08-30
date modified: 2026-07-22T22:23:59Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.117408