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.

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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
Funder's Name: UNSPECIFIED
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: http://theses.gla.ac.uk/id/eprint/6877

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