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There is a need for a high voltage, capacitance voltage (HV, CV) measurement system for the measurement and characterization of silicon carbide (SiC) power MOSFETs. The following study discusses the circuit layout and automation software for a measurement system that can perform CV measurements for all three MOSFET capacitances, CGS, CDS, and CGD. This measurement system can perform low voltage (0–40V) and high voltage (40–5kV) measurements. Accuracy of the measurement system can be safely and effectively adjusted based on the magnitude of the MOSFET capacitance. An IRF1010N power MOSFET, a CoolMos, and a prototype SiC power MOSFET are all measured and their results are included in this study. All of the results for the IRF1010N and the CoolMos can be verified with established characteristics of power MOSFET capacitance. Results for the SiC power MOSFET prove that more testing and further development of SiC MOSFET fabrication is needed. / Master of Science

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This research presents the first use of side-polished Panda fiber in the fabrication of slab-coupled optical sensors (SCOS). It is determined that the Panda SCOS provides a sensor that is comparable to the D-fiber SCOS in cases of electric field sensing. It exhibits greater power transfer and higher bandwidth than a typical D-SCOS. The Panda SCOS is also less costly and easier to splice than the D-fiber alternative. This comes at a cost of slightly decreased sensitivity and a more fragile fabrication process. This research also demonstrates the use of the Panda-SCOS as means of voltage characterization across both the spark gap of an ignition coil circuit along with the spark gap of an automobile. This paper demonstrates the use of a Panda SCOS to measure the voltages and time delays across the spark gaps at different stages of a Marx generator setup .

This work highlights slab coupled optical sensors (SCOS) and their ability to measure high voltages. Although other high voltage measurement techniques exist, most of these techniques are electrical devices and are therefore more susceptible to stray ground currents and other electromagnetic interferences (EMI), which may cause signal distortion. Optical sensors are less susceptible to such interferences and these sensors, such as the Pockels cell, have been used in measuring high voltage. SCOS offer an alternative method of measuring high voltage optically. Consisting of an optical fiber and an electro-optic slab waveguide, SCOS have the advantage of being very small in size (0.2 mm x 0.3 mm cross-section), simpler composition, and potentially less coupling losses. Issues associated with high voltage measurements are addressed such as unwanted corona, arcing, and EMI. Solutions are also explored which include insolating materials, electrode geometries, Faraday cages, and using optical sensors such as SCOS. Although the SCOS has been traditionally used to measure electric field, the SCOS is able to measure high voltage through the use of an electrode structure. The SCOS' ability to measure high voltage is showcase through the construction and output measurements of several high voltage systems: an ignition coil-based circuit, a dual ignition coil circuit, a Marx generator, and a 200 kV generator used in a capacitor discharge configuration. These measurements show the SCOS' ability to measure at least 111 kV capacitor discharges with 6.6 ns rise times and other various high voltage waveforms.

Iron Silicide (FeSi) films deposited on silicon substrates with the native SiO2 layer have shown a Metal-to-Insulator Transition (MIT) of more than four order of magnitude change in resistance. Modification of the SiO2/Si interface due to Fe diffusion has been attributed to the formation of this effect. In this research a systematic experimental investigation has been carried out to study the effect of the growth parameters and substrate doping type in the transition. In addition, transport properties of continuous and discontinuous films have been investigated to understand the mechanism of this metal-to-insulator transition.Four probe measurements of films deposited in p- and n-type doped Si substrates with resistivity in the range of 1-10 Omega cm showed similar temperature dependent resistance behavior with transition onsets at 250 K and 300 K respectively. These results indicate that the current transport takes place via tunneling through the SiO2 layer into the Si substrate up to the transition temperature. Current appears to switch to the film after the transition point due to the development of high interface resistance. Discontinuous FeSi films on silicon substrates showed similar resistance behavior ruling out possibility of current transport through inversion layer at the SiO2/Si interface. To investigate the role of the magnetic ion Fe, transport measurements of FeSi films were compared with those of non-magnetic metals such as Platinum (Pt) and Aluminum (Al). Absence of Metal-to-insulator transition on Pt and Al films show that the presence of magnetic moment is required for this transition.Temperature dependent Hall voltage measurements were carried out to identify the carrier type through the substrate for FeSi films deposited on p- and n-type Si substrates. Results of Hall voltage measurements proved that the type of conductivity flips from majority carriers to minority after the transition.Metal-to-insulating transition behavior of FeSi films depending on different laser fluences has been also investigated. Our results revealed as laser fluence is increased observed transition of the FeSi films reduces rapidly showing a highest magnitude of transition of about 1 M Omega for the films deposited with lowest laser fluence (0.64 J/cm2) and a lowest of about 10 Omega for the films deposited with highest laser fluence (3.83 J/cm2). Ion probe measurements indicated that the average kinetic energy of the ablated ion in the plume is considerably increased with the increase of the laser fluence. Consequently, magnitude drop in the transition can be considered due to the deeper penetration on Fe ion through the SiO2 layer. Thickness dependence study carried out for FeSi films deposited with high and low laser fluencies indicated transition slightly drops as thickness is increased, concluding the current transportation through the film becomes dominant after the transition temperature.

Fault location detection plays a crucial role in power transmission network, especially on security, stabilization and economic aspects. Accurate fault location detection in transmission network helps to speed up the restoration time, therefore, reduce the outage time and improve the system reliability [1]. With the development of Wide Area Measurement System (WAMS) and Phasor Measurement Unit (PMU), various fault location algorithms have been proposed. The purpose of this work is to determine, modify and test the most appropriate fault location method which can be implemented with a PMU only linear state estimator. The thesis reviews several proposed fault location methods, such as, one-terminal [2], multi-terminal [3]-[11] and travelling wavelets methods [12]-[13]. A Two-stage fault location algorithm using PMU voltage measurements proposed by Q. Jiang [14] is identified as the best option for adaption to operate with a linear state estimator. The algorithm is discussed in details and several case studies are made to evaluate its effectiveness. The algorithm is shown to be easy to implement and adapt for operation with a linear state estimator. It only requires a limited number of PMU measurements, which makes it more practical than other existing methods. The algorithm is adapted and successfully tested on a real linear state estimator monitored high voltage transmission network. / Master of Science

In the past decade, DNA origami self-assembly has been widely applied for creating customised nanostructures with base-pair precision. In this technique, the unique chemical addressability of DNA can be harnessed to create programmable architectures, using components ranging from dye or protein molecules to metallic nanoparticles. In this thesis, we apply DNA nanotechnology for developing novel light-harvesting and optical voltage sensing nano-devices. We use the programmable positioning of dye molecules on a DNA origami plate as a mimic of a light-harvesting antenna complex required for photosynthesis. Such a structure allows us to systematically analyse optimal design concepts using different dye arrangements. Complementary to this, we use the resistive-pulse sensing technique in a range of electrolytes to characterise the mechanical responses of DNA origami structures to the electric field applied. Based on this knowledge, we assemble voltage responsive DNA origami structures labelled with a FRET pair. These undergo controlled structural changes upon application of an electric field that can be detected through a change in FRET efficiency. Such a DNA-based device could ultimately be used as a sensitive voltage sensor for live-cell imaging of transmembrane potentials.

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The electrical properties of ZnO and contacts to ZnO have been investigated using different techniques. Temperature dependent Hall (TDH) effect measurements have been used to characterize the as-received melt grown ZnO samples in the 20 – 330 K temperature range. The effect of argon annealing on hydrogen peroxide treated ZnO samples has been investigated in the 200 – 800oC temperature range by the TDH effect measurement technique. The experimental data has been analysed by fitting a theoretical model written in Matlab to the data. Donor concentrations and acceptor concentrations together with the associated energy levels have been extracted by fitting the models to the experimentally obtained carrier concentration data by assuming a multi-donor and single charged acceptor in solving the charge balance equation. TDH measurements have revealed the dominance of surface conduction in melt grown ZnO in the 20 – 40 K temperature range. Surface conduction effects have proved to increase with the increase in annealing temperature. Surface donor volume concentrations have been determined in the 200 – 800oC by use of theory developed by D. C. Look. Good rectifying Schottky contacts have been fabricated on ZnO after treating the samples with boiling hydrogen peroxide. Electrical properties of these Schottky contacts have been investigated using current-voltage (IV) and capacitance-voltage (CV) measurements in the 60 – 300 K temperature range. The Schottky contacts have revealed the dominance of predominantly thermionic emission at room temperature and the existence of other current transport mechanisms at temperatures below room temperature. Polarity effects on the Schottky contacts deposited on the O-polar and Zn-polar faces of ZnO have been demonstrated by the IV technique on the Pd and Au Schottky contacts at room temperature. Results obtained indicate a strong dependence of the Schottky contact quality on the polarity of the samples at room temperature. The quality of the Schottky contacts have also indicated their dependence on the type of metal used with the Pd producing contacts with the better quality as compared to the Au. Schottky barrier heights determined using temperature dependent IV measurements have been observed to increase with increasing temperature and this has been explained as an effect of barrier inhomogeneities, while the ones obtained from CV measurements have proved to follow the negative temperature coefficient of the II – VI semiconductor material, i.e. a decrease in barrier height with increasing temperature. However, the values have proved to be larger than the energy gap of ZnO, an effect that has been explained as caused by an inversion layer. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Physics / unrestricted