Establishing a process for the fabrication of high-quality HTc SQUIDs

Rottier, P. A. (Pieter Adriaan)
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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: High-temperature (HTc) SQUID magnetometers are used in the biomedical field of magnetocardiography (MCG). The use of MCG enables a much earlier diagnosis of potentially dangerous conditions than the use of electrocardiography (EeG). For the use of MCG, high-quality HTc SQUIDs are necessary. These SQUIDs can only be realised if the design and fabrication processes are well defined and understood. In this thesis an extensive literature review on the design process explains all the concepts necessary to understand and design a high-quality HTc SQUID. Then the fabrication process is redefined and characterised. The SQUIDs are fabricated with YBCO thin films on MgO substrates. The relevant steps in the process are the pulsed laser deposition (PLD), UV lithography and argon ion milling. The characterisation of the fabrication process is based on a statistical method called Design of Experiment (DOE). This enables more information to be obtained about the fabrication process than before. For the PLO process the important parameters are determined and an initial optimisation is done. During the characterisation process it is proven that the use of ozone during PLO has a positive effect on the quality of the YBCO thin film. On the PLD apparatus the substrate heater and laser-beam profile is improved. The UV lithography process is analysed and a DOE is proposed for optimisation. A temperature bath is added to the process to enable better reproducibility. An rf multicusp ion mill is built for argon-ion milling, this device is tested and shown to provide the required etching capability.
AFRIKAANSE OPSOMMING: Hoë-temperatuur (HTc) SQUID magnetometers word in die biomediese rigting vir magnetokardiografie (MKG) gebruik. Met MKG kan 'n mens potensieel gevaarlike toestande heelwat vroeër diagnoseer as wat moontlik is met elektrokardiografie (EKG). HTc SQUIDs van hoë kwaliteit word benodig vir MKG. Sulke SQUIDs kan slegs vervaardig word as die vervaardiging en ontwerpsprosesse goed gedefinieer en verstaan word. In hierdie tesis verduidelik 'n omvattende literatuurstudie oor die ontwerpsproses al die konsepte wat nodig is om 'n SQUID van hoë kwaliteit te verstaan en te ontwerp. Verder word die vervaardigingsproses geherdefinieer en gekarakteriseer. Die SQUIDs word vervaardig met YBCO-dunfilm op MgO-substrate. Die relevante stappe tydens die vervaardiging is: gepulseerde laser deposisie (PLO), UV-litografie en argon-ioonstraling. Die karakterisering van die vervaardigingsproses is gebaseer op 'n statistiese metode genaamd "Design of Experiment" (DOE). Hierdie metode laat 'n mens toe om meer inligting oor die proses te verkry as wat voorheen moontlik was. Gedurende die karakterisering word bewys dat die gebruik van osoon gedurende die PLO-proses 'n positiewe invloed op die kwaliteit van die YBCO-dunfilm het. Die PLO-apparaat se substraatverwarmer en laserstraalprofiel word verbeter. Die UV-litografieproses word geanaliseer en 'n DOE word voorgestel vir die optimisering daarvan. Daar word 'n temperatuurbad by die proses gevoeg om die herhaalbaarheid te verbeter. 'n "Rf multicusp ion mill" word gebou, die toestel word getoets en daar word aangetoon dat dit die nodige etsvermoë het.
Thesis (MScEng)--University of Stellenbosch, 2002.
Superconducting quantum interference devices, Magnetometer, Superconductivity, Josephson effect, Dissertations -- Electronic engineering, Theses -- Electronic engineering