Ces travaux s’intègrent dans le projet de recherche SUPERSWITCH dans lequel des solutions alternatives à l’IGBT, utilisées dans les convertisseurs de puissance dans la gamme des tenues en tension 600-1200 V, sont envisagées. Les nouvelles structures du transistor MOS basées sur le principe de Super-Jonction tel que le transistor DT-SJMOSFET et sa terminaison originale, la « Deep Trench Termination » se propose comme alternative aux IGBT. Dans ce contexte, cette thèse se focalise sur la caractérisation de la robustesse de la terminaison DT2 adapté à une diode plane. Après avoir effectué un état de l’art sur les composants de puissances à semi-conducteur unidirectionnels en tension, les terminaisons des composants de puissance et la fiabilité des modules de puissance, un véhicule de test a été conçu en vue de réaliser les différents essais de vieillissement accéléré et suivi électrique. La fiabilité de la terminaison DT2 a été évaluée par des essais expérimentaux et des simulations numériques, dont une méthodologie innovante a été proposée. Au final de nouvelles structures ont été proposées pour limiter les problèmes de délaminage et de charges aux interfaces mis en avant dans notre étude. / This work is a part of the research project SUPERSWITCH in which alternatives solutions to the IGBT, are investigated. This solution was used IGBT in power converters in the 600-1200 V breakdown voltage range. The new MOSFET structures based on the super-junction, such as the DT-SJMOSFET and its "Deep Trench Termination", is proposed as an alternative to IGBT. In this context, this thesis focuses on the robustness characterization of the DT2 termination adapted to a planar diode. After a state of the art on unidirectional voltage power components, the power components termination, and power modules reliability, a test vehicle has been designed in order to carry out different accelerated ageing tests and electrical monitoring. The reliability of DT2 termination was evaluated by experimental tests and numerical simulations. An innovative modeling methodology has been proposed. Finally, new structures have been proposed to limit the delamination failure mechanisms and interface charges problems highlighted in this thesis.

Le développement de l’énergie renouvelable loin des zones urbaines demande le transport d'une grande quantité d’énergie sur de longues distances. Le transport d’électricité en courant continu haute tension (HVDC) présente beaucoup d’avantages par rapport à celui en courant alternatif. Dans ce contexte il est nécessaire de développer des convertisseurs de puissance constitués par des composants électroniques très haute tension, 10 à 30 kV. Si les composants en silicium ne peuvent pas atteindre ces objectifs, le carbure de silicium (SiC) se positionne comme un matériau semiconducteur alternatif prometteur. Pour supporter des tensions élevées, une région de "drift", relativement large et peu dopée constitue le cœur du composant de puissance. En pratique l’obtention d’une tension de blocage effective dépend de plusieurs facteurs et surtout de la conception d'une terminaison de jonction adaptée. Cette thèse présente une méthode pour améliorer la tenue en tension des composants en SiC basée sur l’utilisation des terminaisons de jonctions : Deep Trench Termination. Cette méthode utilise une tranchée gravée profonde en périphérie du composant, remplie avec un matériau diélectrique pour supporter l'étalement des lignes équipotentielles. La conception de la diode avec cette terminaison a été faite par simulation TCAD, avec deux niveaux de tension 3 et 20 kV. Les travaux ont pris en compte les caractéristiques du matériau, les charges à l’interface de la tranchée et les limites technologiques pour la fabrication. Ce travail a abouti sur la fabrication de démonstrateurs et leur caractérisation pour valider notre conception. Lors de la réalisation de ces structures, la gravure plasma du SiC a été optimisée dans un bâti ICP de manière à obtenir une vitesse de gravure élevée et en conservant une qualité électronique de l'état des surfaces gravées. Cette qualité est confirmée par les résultats de caractérisation obtenus avec des tenues en tension proches de celle idéale. / The development of renewable energy away from urban areas requires the transmission of a large amount of energy over long distances. High Voltage Direct Current (HVDC) power transmission has many advantages over AC power transmission. In this context, it is necessary to develop power converters based on high voltage power electronic components, 10 to 30 kV. If silicon components cannot achieve these objectives, silicon carbide (SiC) is positioned as a promising alternative semiconductor material. To support high voltages, a drift region, relatively wide and lightly doped is the heart of the power component. In practice obtaining an effective blocking voltage depends on several factors and especially the design of a suitable junction termination. This thesis presents a method to improve the voltage withstand of SiC components based on the use of junction terminations: Deep Trench Termination. This method uses a trench deep etching around the periphery of the component, filled with a dielectric material to support the spreading of the equipotential lines. The design of the diode with this termination was done by TCAD simulation, with two voltage levels 3 and 20 kV. The work took into account the characteristics of the material, the interface charge of the trench and the technological limits for the fabrication. This work resulted in the fabrication of demonstrators and their characterization to validate the design. During the production of these structures, plasma etching of SiC has been optimized in an ICP reactor so as to obtain a high etching rate and maintaining an electronic quality of the state of etched surfaces. This quality is confirmed by the results of characterization obtained with blocking voltage close to the ideal one.

<p> Over the past decade, the development of surface-initiated living polymerization methods has brought a breakthrough to surface modification owing to their control ability. Surface-initiated atom transfer radical polymerization (si-ATRP), as the most popular one, has been widely employed to give novel polymer structures and functionalities to various surfaces for the purposes of tailoring surface properties, introducing new functions, or preparing so-called "smart surfaces", which can respond to external stimuli such as solvent type, pH, temperature, electric and magnetic fields etc. In this thesis, the mechanistic study of the si-ATRP was first carried out through modeling to gain good understanding of si-ATRP. Si-ATRP was then employed to prepare different types of polymer brushes to produce "smart surfaces". </p> <p> The kinetic model was developed using the method of moment. Combined with experimental data, a quantitative analysis was carried out for the si-ATRP mechanism. All information of grafted polymer chains, including active chain concentration, radical concentration, chain length, polydispersity, was illustrated. A new radical termination mechanism, termed as migration-termination, was proposed for si-ATRP. </p> <p> Si-ATRP was then employed to graft poly(oligo(ethylene glycol) methacrylate) (POEGMA) block poly(methyl methacrylate) (PMMA) brushes on silicon wafer surfaces. Simple solvent treatment gave nanoscale patterns via the phase segregation of POEGMA and PMMA segments. Various patterns including spherical aggregates, wormlike aggregates, stripe patterns, perforated layers and complete overlayers, were obtained by adjusting the upper block layer thickness. Furthermore, these nanopatterns had a unique stimuli-responsive property, i.e., switching between different morphologies reversibly after being treated with selective solvents. </p> <p> POEGMA-block-poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC) brushes, having two hydrophilic segments, were synthesized by si-ATRP method. A variety of nanopatterns and their stimuli-responsive ability were observed. The adsorption behaviors of fibrinogen on these patterns were thoroughly studied by ellipsometry, water contact angel measurement, AFM and radio labelling method. </p> <p> A novel thermo-responsive copolymer, poly(2-(2-methoxyethoxy)ethyl methacrylate -co-oligo(ethylene glycol) methacrylate) (P(ME02MA-co-OEGMA)), was also grafted onto silicon wafers. Its thermo-responsive behavior and chain conformation in aqueous solution were studied by neutron reflectometry (NR). Both extended and collapsed brushes exhibited good protein adsorption resistance. </p> / Thesis / Doctor of Philosophy (PhD)

Text in Afrikaans / Summaries in Afrikaans and English / In Afrikaans, soos in NederJands en Duits, word saamgestelde woorde aanmekaar geskryf. Nuwe woorde word dus voortdurend geskep deur woorde aanmekaar te haak Dit bemoeilik die proses van woordafkapping tydens teksprosessering, wat deesdae deur rekenaars gedoen word, aangesien die verwysingsbron gedurig verander. Daar bestaan verskeie afkappingsalgoritmes en tegnieke, maar die resultate is onbevredigend. Afrikaanse woorde met korrekte lettergreepverdeling is net die elektroniese weergawe van die handwoordeboek van die Afrikaanse Taal (HAT) onttrek. 'n Neutrale netwerk ( vorentoevoer-terugpropagering) is met sowat. 5 000 van hierdie woorde afgerig. Die neurale netwerk is verfyn deur 'n gcskikte afrigtingsalgoritme en oorfragfunksie vir die probleem asook die optimale aantal verborge lae en aantal neurone in elke laag te bepaal. Die neurale netwerk is met 5 000 nuwe woorde getoets en dit het 97,56% van moontlike posisies korrek as of geldige of ongeldige afkappingsposisies geklassifiseer. Verder is 510 woorde uit tydskrifartikels met die neurale netwerk getoets en 98,75% van moontlike posisies is korrek geklassifiseer. / In Afrikaans, like in Dutch and German, compound words are written as one word. New words are therefore created by simply joining words. Word hyphenation during typesetting by computer is a problem, because the source of reference changes all the time. Several algorithms and techniques for hyphenation exist, but results are not satisfactory. Afrikaans words with correct syllabification were extracted from the electronic version of the Handwoordeboek van die Afrikaans Taal (HAT). A neural network (feedforward backpropagation) was trained with about 5 000 of these words. The neural network was refined by heuristically finding a suitable training algorithm and transfer function for the problem as well as determining the optimal number of layers and number of neurons in each layer. The neural network was tested with 5 000 words not the training data. It classified 97,56% of possible points in these words correctly as either valid or invalid hyphenation points. Furthermore, 510 words from articles in a magazine were tested with the neural network and 98,75% of possible positions were classified correctly. / Computing / M.Sc. (Operasionele Navorsing)

This study explored knowledge, perceptions and attitudes regarding contraception and contraceptive practices among secondary school learners in the Limpopo Province. Self-administered questionnaires were completed by 612 Grade 8 and 332 Grade 12 learners from 24 randomly selected secondary schools. The study found that permissive attitudes prevailed towards sex, characterised by casual sexual activities commencing at 12 years of age. The availability of contraceptive and termination of pregnancy (TOP) services did not enable learners to utilise them, because of social, cultural, financial and service barriers. Most learners were sexually active without being knowledgeable about contraceptives, emergency contraceptives and TOP services. Two workshops conducted with learners produced similar results to those obtained from the completed questionnaires. Semi-structured interviews conducted with nurses, providing contraceptive and TOP services in the Limpopo Province, also substantiated the findings from the questionnaires. Secondary school learners in the Limpopo Province require more knowledge about and ready access to contraceptives to enable them to delay child bearing until they are emotionally, financially and physically ready for these responsibilities. Nurses and teachers in this province can enhance the learners' contraceptive knowledge and utilisation to help learners make better informed decisions about their own and their future children's lives. / Health Studies / D. Litt. et Phil. (Health Studies)

Exploration of factors that lead to early termination of therapeutic services to sexually abused children at TygerBear Unit. Some children referred to TygerBear Unit because of sexual abuse did not complete their therapeutic intervention programmes and possibly did not receive sufficient time to work through the trauma of sexual abuse. The purpose of this qualitative study was to explore and describe the factors that result in the early termination of sexually abused children’s therapeutic services at TygerBear Unit. Applied research that is exploratory and descriptive in nature, with the case study method as strategy, was followed. Data were collected through telephonic and/or one-on-one semi-structured interviews, in addition to the use of notes in personal records. Respondents included parents and/or caregivers of children whose therapy was terminated early, as well as social workers involved with play therapeutic service delivery to these children. Information was analysed with reference to the Field Theory, Ecological Theory and the relevant literature. Several factors that influenced parents and/or caregivers to terminate therapeutic services early were identified. / Die verkenning van faktore wat lei tot voortydige terminering van terapeutiese dienslewering aan seksueel-mishandelde kinders by TygerBeer Eenheid. Sommige kinders wat na TygerBeer Eenheid verwys word weens seksuele mishandeling, voltooi nie hul terapeutiese intervensieprogramme nie. Die kinders is moontlik nie genoeg tyd gegun om deur die trauma van seksuele mishandeling te werk nie. Die doel van hierdie kwalitatiewe studie was om faktore te verken en te beskryf wat lei tot die voortydige terminering van terapeutiese dienslewering aan seksueel-mishandelde kinders by die TygerBeer Eenheid. Toegepaste navorsing van 'n verkennende en beskrywende aard is gebruik, met die gevallestudiemetode as strategie. Data is versamel deur middel van telefoniese en/of een-tot-een semi-gestruktureerde onderhoude en persoonlike rekords. Respondente het bestaan uit ouers en/of versorgers wat hul kinders of voogde se terapie voortydig termineer het, asook maatskaplike werkers betrokke by spelterapeutiese dienslewering aan kinders. lnligting is ontleed met verwysing na die Veldteorie en Ekologiese Teorie, asook die relevante literatuur. Verskeie faktore is geidentifiseer wat ouers en/of versorgers noodsaak om terapeutiese dienste voortydig te termineer. / Social Work / M. Diac. (Play Therapy)

The aim of this study was to investigate sexual activity as well as contraceptive knowledge and use among termination of pregnancy (TOP) clients at Prince Mshiyeni Memorial Hospital’s TOP clinic in the province of KwaZulu-Natal (KZN). This was a non-experimental quantitative study in the form of a cross sectional study. Self-administered questionnaires were used for collecting data from 61 respondents selected non-randomly. The majority of the respondents were single young women between 18 and 27 years of age. Sexual intercourse frequency was mostly once a month (91.8%). Most were unemployed and dependent on government grants and had heard of both contraception in general and emergency contraception. Only 44 (78.6%) had used contraceptives before and the most frequently used method of contraception was the injection (36.6%). Despite the respondents having heard of contraception, the median score of the knowledge of contraception was only 16%. The distribution of knowledge was very wide, but on the whole the level of knowledge of contraception was very low / Health Studies / M.A. (Public Health)

The goal of the research was to explore the ongoing problem of Baptist Pastors leaving the ministry and to attempt to discover the impact of this problem upon Baptist Churches by means of "focus group" interviews. The dissertation links the problem with a Baptist ecclesiology and seeks to understand the Baptist belief in the autonomy of the Local Church and the praxis of accreditation for pastoral ministry, plus the existence of so-called "subterranean Pastors" which has contributed toward pastoral termination. / Practical theology / M.Th. (Practical Theology)

The aim of this study was to explore the psychological effects of termination of pregnancy by choice amongst adolescents within the ages of 18 to 21 years. Exploratory, contextual, qualitative design was used to determine the psychological effects of termination of pregnancy by choice amongst adolescents. Purposive sampling method as well as snowballing were used to select participants for the study. Data collection was done through in-depth, one-on-one, face-to-face interviews, using a semi-structured interview guide. The study highlighted that adolescents who seek abortion are unmarried and mostly still studying. The results revealed that adolescents experience mental ill health after termination of pregnancy due to feelings of guilt. All participants stated that abortion is murder of a life person and that it is a bad thing to do. The study revealed that counselling that is done before TOP focuses on the procedure of TOP. There is need for a holistic approach to counselling. As a guide, policy makers need to specify the mandatory counselling in the Choice on Termination of Pregnancy Act (Act No 92 of 1996). / Health Studies / M.A. (Nursing Science)

Thesis (MA (Philosophy))--University of Stellenbosch, 2008. / The practice of abortion continues to provoke controversy and disagreement. However, within the context of this wider debate, a greater level of consensus appears to have been reached as to the moral acceptability of the practice of prenatal screening, and selective abortion following the detection of foetal abnormality. This study seeks to interrogate whether justifications of this practice lend credence to the moral permissibility of selective abortion. In particular, it considers whether justifications for this practice amount to, or perpetuate, discrimination on the basis of the characteristic of disability, as selective abortion entails choosing against a particular foetus because of its characteristics. This study poses this question in two contexts – where the moral permissibility of selective abortion is regarded as an exception to the general moral impermissibility of abortion, and where selective abortion is regarded as one distinct justification within the context of the general moral permissibility of abortion. This study attempts to show that while justifications of selective abortion are directly discriminatory in the former case, they are not necessarily discriminatory in the latter case. This latter conclusion, however, recommends maintaining vigilance against the possibility that such justifications could rely upon or perpetuate prejudice, or restrict reproductive autonomy. These conclusions are considered within the South African context; in particular, with regard to their application to the Choice on Termination of Pregnancy Act of 1996.