Nanocharacterisation of zirconia based RRAM devices deposited via PLD

Parreira, Pedro Miguel Raimundo (2015) Nanocharacterisation of zirconia based RRAM devices deposited via PLD. PhD thesis, University of Glasgow.

Abstract

With CMOS technology reaching fundamental scaling limitations, innovative data storage technologies have been a topic of great academic and industrial interest. Emerging
technologies, not all based in semiconductors, that exploit new variables like spin, polarisation, phase and resistance, are being investigated for their feasibility as data storage
devices. One very promising technology is resistive switching random-access memory
(RRAM). In RRAM devices memory operation relies on the change in resistance of a
metal-insulator-metal structure, typically induced by ion migration combined with redox
processes. Here, RRAM devices based on amorphous and crystalline zirconia have been
prepared by means of pulsed laser deposition (PLD). The thesis starts with an overview
of the commissioning of a new PLD system, with a focus on characterisation of the laser
ablation plume, reduction of the density of “droplets” and development of the optimal
system parameters, like temperature, oxygen pressure and laser fluence, for the preparation
of zirconia based RRAM devices. For both amorphous and crystalline devices, titanium
was used as an active electrode as it promotes the introduction of oxygen vacancies which
are responsible for inducing resistive switching. In addition, growth of epitaxial Nb doped
strontium titanate (Nb:STO) via PLD was achieved, as the high temperatures used during
growth hinder the use of metallic bottom electrodes. Both types of RRAM devices have
good performance figures, with ON/OFF ratios of 1000 and 10000 and endurance of more
than 10000 cycles. Conduction mechanisms point to two different types of resistive switching:
insulator-to-metal transition and trapping and de-trapping at the metal-oxide interfaces.
Surprisingly, both conduction mechanisms were found to coexists on amorphous devices.
Scanning transmission electron microscopy and electron energy loss spectroscopy were
used to investigate how interfaces can influence resistive switching. Results indicate that
titanium, in addition to introducing oxygen vacancies, creates an ohmic interface with
zirconia which forces the resistive switching to take place on the inert metal-oxide Schottky
interface, which was not described so far.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: MacLaren, Dr. Donald and McVitie, Dr. Stephen
• Date of Award: 2015
• Depositing User: Dr Pedro Parreira
• Unique ID: glathesis:2015-6877
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 25 Nov 2015 11:48
• Last Modified: 10 Dec 2015 10:17
• URI: https://theses.gla.ac.uk/id/eprint/6877