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Title: Chalcogenide thin films for probe-based data storage
Author: Cork, R. F.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2009
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This work focuses on use of the chalcogenide alloy Ge2Sb2Te5 (GST225) in phase-change memories, specifically in possible probe-based devices. The atomic-force microscope (AFM) has been extensively used here to recreate conditions in a probe-based memory device, with conductive AFM being used in read/write studies. Metal-coated AFM probes were used to make an electrical contact to the upper layer of a media stack, allowing an electrical current to be passed through the thickness of an amorphous GST225 film resulting in crystallisation due to Joule heating. The media stack used in the read/write studies consisted of a silicon substrate with an amorphous-carbon bottom electrode (BE) layer, followed by a GST225 active layer and finally an amorphous-carbon capping layer. The amorphous-carbon layers were deposited by DC sputtering of a graphite target, with resistivity control being achieved by varying the thicknesses of the deposited layers along with presputter times. During writing studies using CAFM it was possible to regularly create crystalline marks 30 nm in diameter, and resolve individual crystallites with diameters as small as 5 nm. Arrays of marks have been written at separations of 100 nm, corresponding to an areal density of 65 Gb in-2. Additionally, during preliminary studies on the chalcogenide layers from optical disks, an unexpected effect was observed following coating of the phase-change layer with a thin silver layer. This resulted in topographic contrast of ~8 nm between the amorphous and crystalline regions, allowing data marks to be accurately resolved in standard topographic-mode AFM.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available