Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / Dissertation presented for the degree of
Doctor of Philosophy in Engineering at the
University of Stellenbosch / ENGLISH ABSTRACT: Planar weak link structures, such as micro-bridges, variable thickness bridges and nanobridges,
have always attracted a lot of attention. Their potential to behave as real Josephson
elements make them useful devices, with numerous applications.
Powerful techniques, such as focused ion-beam and electron-beam lithography, were successfully
used and are well understood in planar weak link structure fabrication. In this
dissertation the results of an experimental study on planar weak link structures are presented.
For the first time these structures have been successfully fabricated using AFM
nanolithography on hard high-temperature superconducting YBCO tracks, where diamond
coated silicon tips were used as a ploughing tool.
Superconducting YBCO thin films were deposited on different substrates, using inverted
cylindrical magnetron sputtering. The films were used to fabricate micro-bridges, variable
thickness bridges and nano-bridges, by using conventional photolithography, argon ion-beam
milling and AFM nanolithography.
The measured I-V characteristics of the fabricated micro-bridges (width down to 1.9 µm),
variable thickness bridges (thickness down to 15 nm) and nano-bridge (width down to 490
nm) showed well defined DC and AC Josephson effect characteristics.
For better understanding of the behaviour of these types of weak links, critical current versus
temperature measurements, and magnetic field modulation of the critical current measurements,
were also performed, with the results and discussions given inside the chapters.
The major challenges that were experienced in the laboratory during the fabrication processes
and the operation of the fabricated devices are also discussed, with the solutions given
where appropriate. / AFRIKAANSE OPSOMMING: Swak-skakel vlakstrukture, soos mikrobr.ue, br.ue met veranderlike dikte en nanobr.ue, het
nog altyd baie aandag getrek. Hul het die potensiaal om soos werklike Josephson-elemente
te kan funksioneer en is, as gevolg hiervan, nuttige toestelle met veelvuldige toepassings.
Kragtige tegnieke, soos gefokuste ioonstraal- en elektronstraal litografie, is suksesvol gebruik
en word goed verstaan in die vervaardiging van swak-skakel vlakstrukture. In hierdie
proefskrif word die resultate van ¡¦n eksperimentele studie van swak-skakel vlakstrukture
voorgel.e.
Vir die eerste keer is hierdie strukture suksesvol vervaardig, deur gebruik te maak AFMnanolitografie
op harde, ho¡Le-temperatuur supergeleier YBCO (Yttrium Barium Koperoksied)
spore, waar diamantbedekte silikonpunte gebruik is as ploeginstrument.
¡¦n Dun lagie van supergeleidende YBCO is op verskillende substrate gedeponeer, deur gebruik
te maak van omgekeerde silindriese magnetron verstuiwing. Die dun lagies is gebruik
in die vervaardiging van mikrobr.ue, br.ue met veranderlike dikte en nanobr.ue, deur die
gebruik van gewone fotolitografie, argon-ioonstraal frees en AFM nanolitografie.
Die gemete I-V eienskappe van die vervaardigde mikrobr.ue (met breedte so laag as 1.9 µm),
veranderlike-dikte br.ue (dikte tot 15 nm) en nanobr.ue (breedte so min as 490 nm) toon
goed gedefinieerde GS en WS eienskappe van die Josephson-effek.
Ten einde die gedrag van hierdie tipes swak-skakels beter te kan verstaan, is metings gedoen
van kritieke stroom teenoor temperatuur, asook magnetiese veld modulasie van die kritieke
stroom. Hierdie resultate en besprekings daarvan word binne die toepaslike hoofstukke
aangebied.
Die grootste uitdagings wat in die laboratorium, sowel as met die toetsing van die vervaardigde
toestelle ondervind is, word ook bespreek. Waar moontlik, word toepaslike oplossings
voorgestel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5421 |
| Date | 12 1900 |
| Creators | Elkaseh, Akram Abdulsalam |
| Contributors | Perold, W. J., Srinivasu, V. V., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 116 p. : ill. |
| Rights | University of Stellenbosch |
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