From high-speed superconducting devices to nanosensors

Perold, Willem (2017-03)

Thesis (DEng)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: In this dissertation the story of a research career spanning 34 years is told. It started in microelectronics in the early 1980’s and focused on aspects of design and optimization of high-voltage diodes. Advanced simulation tools, such as Monte Carlo particle simulation algorithms, was also implemented, specifically for the design of microwave diodes. During a sabbatical at GEC Hirst Research Centre in 1988, shortly after the discovery of high-temperature superconductors, an opportunity arose to work on superconducting devices. The research was focused on understanding and modeling the mechanisms of single particle (quasiparticle) tunnelling in NIS or SIS junctions. The ultimate goal was, as was the case for semiconductor electronics, to have a three-terminal switching device that can be utilized as a binary switch. Back at Stellenbosch, the superconductivity laboratory was established, with the primary focus on the manufacture of high-temperature superconducting (YBCO) devices, including thin film deposition, photolithography and etching of micron-sized patterns. In 1995 a sabbatical was spent at the University of California at Berkeley, in the research group of Professor Ted Van Duzer, one of the pioneers of superconducting technology. During this sabbatical the fastest superconducting voltage-state logic family, Complementary Output Switching Logic (COSL) was designed and successfully tested at a clock speed of 1 GHz. Towards the end of 1996 these devices were successfully tested at clock speeds up to 18 GHz, making it the fastest voltage-state logic family to this day. An alternative method to predict the circuit yield of superconducting circuits, incorporating all the imperfections of the manufacturing process, was also introduced. This method was based on a Monte Carlo analysis approach, and was extensively used to optimize the COSL circuits for maximum yield. In 1996, back from Berkeley, the research focus of the group was extended (from the emphasis on the fabrication of high-temperature YBCO devices) to include the design of ultra-fast low-temperature superconducting devices, specifically COSL and Rapid Single Flux Quantum (RSFQ) circuits. The unique contributions in the low-Tc field included the conceptualization of the first Superconducting Programmable Gate Array and the design of such a circuit using a hybrid approach, mixing RSFQ and COSL gates. A major contribution was the advances made in the 3D-extraction of circuit parameters from the circuit layout, which incorporated the imperfections due to the fabrication processes. This effort led to the establishment of a spin-off company, NioCAD, which focussed on advanced software for the layout of superconducting circuits. An important component of the software was the circuit extraction capabilities. Due to the capabilities available in the superconductivity research laboratory, where submicron devices could be fabricated and also inspected, using the AFM and the tabletop SEM, the research focus gradually evolved to incorporate non-superconducting devices, with specific emphasis on nanosensors. An important aspect of the work on nanosensors is that it is, by nature, multidisciplinary. Very fruitful collaboration was thus established with researchers in microbiology, amongst others. Some of the unique contributions here were the successful design and testing of a piezoelectric nanogenerator (based on ZnO nanowires), and the incorporation of pathogens on the nanogenerator, using a protein scaffolding system, to form a biosensor. The successful testing of the biosensor proved that, by attaching antibodies on the piezoelectric nanogenerator, a specific pathogen (e.g. TB, E. coli, etc.) would attach to the antibody, thus generating a voltage that would confirm the presence of the specific pathogen. Significant advances have been made on alternative transducers, and electrospun microfibers, and also paper, have been successfully tested for the detection of bacteria. Biosensor research is currently the main focus area of the research group.

AFRIKAANSE OPSOMMING: In hierdie proefskrif word die storie vertel van ’n navorsingsloopbaan wat oor 34 jaar strek. Dit het alles in mikroëlektronika in die vroeë 1980’s begin, met die fokus op aspekte van die ontwerp en optimisasie van hoogspanningsdiodes. Gevorderde simulasiegereedskap, soos Monte Carlo partikelsimulasie algoritmes, is geïmplementeer, spesifiek vir die ontwerp van mikrogolfdiodes. Kort na die ontdekking van hoë-temperatuur supergeleiers, gedurende studieverlof by GEC Hirst Research Centre in 1988, het die geleentheid hom voorgedoen om oor supergeleidende komponente navorsing te doen. Die fokus was om begrip te ontwikkel van die meganismes van enkelpartikel (kwasipartikel) tonnelling in NIS- en SIS vlakke, en ook om dit te modelleer. Die doel was om, soos die geval is by halfgeleier komponente, ’n drieterminaal komponent te vind wat as ’n binêre skakelaar kan optree. Terug op Stellenbosch is die supergeleier navorsingslaboratorium gevestig. Die primëre doel was om hoë-temperatuur supergeleier (YBCO) komponente te vervaardig, en ook om dunfilm neerslag, fotolitografie en etsing te doen vir mikron-grootte komponente. ’n Studieverlofperiode is in 1995 by die Universiteit van Kalifornië in Berkeley, in die navorsingsgroep van die legendariese prof. Theodore Van Duzer, deurgebring. Gedurende hierdie tydperk is die vinnigste spanningstoestand logiese familie, Complementary Output Switching Logic (COSL), ontwerp en getoets by ’n klokspoed van 1 GHz. Teen die einde van 1996 is die komponente suksesvol getoets by ’n klokspoed van 18 GHz, wat dit, tot vandag toe nog, die vinnigste spanningstoestand logiese familie maak. ’n Alternatiewe metode om die opbrengs van vervaardigde supergeleidende bane, met al die imperfeksies van die vervaardigingsproses in ag geneem, te voorspel, is ook ontwikkel. Hierdie metode is gebaseer op die Monte Carlo analisemetode, en is ekstensief gebruik om die COSL bane se opbrengs te optimiseer. In 1996, terug van die besoek aan Berkeley, is daar besluit om die navorsingsfokus van die groep te verbreed vanaf die enger klem op die vervaardiging van hoë-temperatuur YBCO komponente, en om ook te konsentreer op ultra-hoëspoed lae-temperatuur supergeleidende komponente, soos COSL en RSFQ bane. Unieke bydraes op die gebied van laetemperatuur supergeleidende komponente gedurende hierdie tyd sluit die eerste ’Superconducting Programmable Gate Array’ (SPGA) in, waar gebruik gemaak is van ’n hibriede benadering, wat beide COSL en RSFQ komponente ingesluit het. ’n Verdere wesenlike bydrae was die vordering wat gemaak is in die drie-dimensionele onttrekking van baanparameters uit die uitleg van die baan, met inbegrip van die imperfeksies van die vervaardigingsproses. Hierdie navorsing het gelei tot die stigting van ’n afwentelmaatskappy, NioCAD, waar die fokus op gevorderde programmatuur vir die uitlê van supergeleierbane was. ’n Belangrike kompnoent van die programmatuur was uiteraard die vermoë om baanparameters te onttrek. Die bestaande vermöe in die supergeleier navorsingslaboratorium om sub-mikron komponente te vervaardig en met die hulp van AFM en die kompakte SEM te inspekteer, het daartoe gelei dat die navorsingsfokus mettertyd verskuif het om ook nie-supergeleidende komponente, spesifiek nanosensors, in te sluit. ’n Belangrike aspek van die werk op nanosensors is dat dit uiteraard multidissiplinêr van aard is. Baie vrugbare samewerking het dus tot stand gekom met navorsers van, onder andere, mikrobiologie. Sommige van die unieke bydraes op hierdie gebied was die suksesvolle ontwerp en implementering van die ZnO nanodraad piesoëlektriese nanogenerator, en die suksesvolle integrering daarvan met patogene, deur gebruik te maak van ’n proteïenstellasie om ’n biosensor te vorm. Die sukses van die sensor het bewys dat, deur teenliggaampies aan die piesoëlektriese nanogenerator te koppel, ’n spesifieke patogeen (bv. TB, E. coli, ens.) kan koppel aan die teenliggaampie, om sodoende ’n elektriese spanning op te wek om die teenwoordigheid van die sepsifieke patogeen te verklik. Beduidende vordering is ook gemaak om alternatiewe omskakelaars te vind, en elektrostaties-geweefde mikrovesels, asook papier, is suksesvol gebruik om bakterieë op te spoor. Biosensornavorsing is tans die hooffokus van die navorsingsgroep.

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