This work has as main objective the integration of planar Gunn diodes and high electron mobility transistors (HEMTs) on the same chip for the realisation of high-power oscillators in the millimeter-wave regime. By integrating the two devices, we can reinforce the high frequency oscillations generated by the diode using a transistor-based amplifier. The integration of the planar Gunn diode and the pseudomorphic HEMT was initially attempted on a combined gallium arsenide (GaAs) wafer. In this approach, the active layers of the two devices were separated by a thick buffer layer. A second technique was examined afterwards where both devices were fabricated on the same wafer that included AlGaAs/InGaAs/GaAs heterostructures optimised for the fabrication of pHEMTs. The second approach demonstrated the successful implementation of both devices on the same substrate. Planar Gunn diodes with 1.3 μm anode-to-cathode separation (Lac) presented oscillations up to 87.6 GHz with a maximum power equal to -40 dBm. A new technique was developed for the fabrication of 70 nm long T-gates, improving the gain and the high frequency performance of the transistor. The pHEMT presented cut-off frequency (fT) equal to 90 GHz and 200 GHz maximum frequency of oscillation (fmax). The same side-by-side approach was applied afterwards for the implementation of both devices on an indium phosphide (InP) HEMT wafer for the first time. Planar Gunn diodes with Lac equal to 1 μm generated oscillations up to 204 GHz with -7.1 dBm maximum power. The developed 70 nm T-gate technology was applied for the fabrication of HEMTs with fT equal to 220 GHz and fmax equal to 330 GHz. In the end of this work, the two devices were combined in the same monolithic microwave integrated circuit (MMIC), where the diode was connected to the transistor based amplifier. The amplifier demonstrated a very promising performance with 10 dB of stable gain at 43 GHz. However, imperfections of the material caused large variations at the current density of the devices. As a consequence, no signals were detected at the output of the complete MMIC oscillators.

The core of this thesis is a thorough investigation of the scaling properties of conventional nano-CMOS MOSFETs, their physical and operational limitations and intrinsic parameter fluctuations. To support this investigation a well calibrated 35 nm physical gate length real MOSFET fabricated by Toshiba was used as a reference transistor. Prior to the start of scaling to shorter channel lengths, the simulators were calibrated against the experimentally measured characteristics of the reference device. Comprehensive numerical simulators were then used for designing the next five generations of transistors that correspond to the technology nodes of the latest International Technology Roadmap for Semiconductors (lTRS). The scaling of field effect transistors is one of the most widely studied concepts in semiconductor technology. The emphases of such studies have varied over the years, being dictated by the dominant issues faced by the microelectronics industry. The research presented in this thesis is focused on the present state of the scaling of conventional MOSFETs and its projections during the next 15 years. The electrical properties of conventional MOSFETs; threshold voltage (VT), subthreshold slope (S) and on-off currents (lon, Ioffi ), which are scaled to channel lengths of 35, 25, 18, 13, and 9 nm have been investigated. In addition, the channel doping profile and the corresponding carrier mobility in each generation of transistors have also been studied and compared. The concern of limited solid solubility of dopants in silicon is also addressed along with the problem of high channel doping concentrations in scaled devices. The other important issue associated with the scaling of conventional MOSFETs are the intrinsic parameter fluctuations (IPF) due to discrete random dopants in the inversion layer and the effects of gate Line Edge Roughness (LER). The variations of the three important MOSFET parameters (loff, VT and Ion), induced by random discrete dopants and LER have been comprehensively studied in the thesis. Finally, one of the promising emerging CMOS transistor architectures, the Ultra Thin Body (UTB) SOl MOSFET, which is expected to replace the conventional MOSFET, has been investigated from the scaling point of view.

The project is concerned with the development of methods for the fabrication of magnetic sensor devices on Atomic Force Microscopy (AFM) probes and their characterization. The devices use the principle of the Hall effect (based on the Lorentz force) to sense the magnetic properties of a magnetized specimen. In the past Hall bar sensors have been fabricated using semimetals such as Bismuth, or using 2-d electron gas material based on heterojunctions in III-V material. The former probes are limited by low sensitivity. The latter are limited by the difficulty encountered when trying to integrate the device with a force-sensing cantilever. The highest spatial resolution reported for a Hall bar operating at room temperature is 50 nm. Due to quantum effects (long mean free path), scaling down devices based on high mobility material results in a drop in sensitivity. For magnetic material studies of current interest higher resolutions are required. To achieve this goal in a material system which is compatible with micromachining the proposed approach utilises silicon as the sensing material. Silicon Hall bars have already been reported to work for large scale devices. This thesis presents the development of p-type enhancement mode MOSFET transistor fabrication process on a tip of Atomic Force Microscope (AFM) probe. The active device fabrication process was developed in order to allow fabrication of a magnetic sensor for Scanning Hall Probe Microscope (SHPM). The Hall bar was constructed on the apex of the AFM tip of attractive mode probes. The fabrication is performed in batches by using common semiconductor techniques leading to micromachining of the Si substrate, formation of the active device and cantilever release step. The transistor characteristics are presented, compared with expected performance of the modelled device and the reasons for differences are discussed. In this work, a method for application of spin-on-dopant on highly topographic structures is developed. Other encountered process incompatibilities are dealt with to finally present a full process for p-type enhancement mode MOSFET transistor on AFM tip fabrication.

In order to meet greenhouse gas emissions targets, the Great Britain (GB) future electricity supply will include a higher fraction of non-dispatchable generation, increasing opportunities for demand side management (DSM) to maintain a supply/demand balance. Domestic electricity demand is approximately a third of total GB demand and has the potential to provide a significant demand side resource. An optimization model of UK electricity generation has been developed with an objective function to minimize total system cost (£m/year). The models show that dispatchable output falls from 77% of total output in 2012 to 69% in 2020, 41% in 2030 and 28% in 2050, supporting the need for increased levels of future DSM. Domestic demand has been categorised to identify flexible loads (electric space and water heating, cold appliances and wet appliances), and projected to 2030. Annual flexible demand in 2030 amounts to 64.3TWh though the amount of practically available demand varies significantly on a diurnal, weekly and seasonal basis. Daily load profiles show practically available demand on two sample days at three sample time points (05:00, 08:00 and 17:30) varies between 838MW and 6,150MW. Access to flexible demand for DSM purposes is dependent on the active involvement of domestic consumers and/or their acceptance of appliance automation. Analysis of a major quantitative survey and qualitative workshop dataset shows that 49% of respondents don’t think very much or not at all about their electricity use. This has implications for the effectiveness of DSM measures which rely on consumers to actively modify behaviour in response to a signal. Whilst appliance automation can be a practical solution to realising demand side potential, many consumers are reluctant to allow remote access. Consumers are motivated by financial incentives though the low value of individual appliance consumption limits the effectiveness of solely financial incentives. A range of incentives would be required to encourage a wide cross-section of consumers to engage with their electricity consumption.

The main aim of this project is to investigate the influence of the inter-laminar short circuit faults on the performance of magnetic cores and develop a non-destructive method to detect these kinds of defects. The eddy current path in magnetic laminations which is magnetised by time varying magnetic field was modelled by an equivalent resistor network to calculate and predict the eddy current power losses in magnetic laminations. The model was validated over a wide range of magnetisation conditions. Based on the developed model, the influence of a wide range of magnetising frequency and peak flux density on the magnetic properties of electrical steels was studied. An experimental-analytical technique was developed to separate magnetic loss components over a wide range of magnetisation. Two electrical steel laminations, Conventional Grain Oriented (CGO) and Non-Oriented (NO), were used in the experimental work of the relevant studies. 2-D FE based modelling was performed to simulate inter-laminar faults on stacks of laminations and visualise the distribution of eddy currents in the faulted laminations. The influence of inter-laminar faults on the eddy current power loss was experimentally investigated by introducing artificial short circuits of different configurations on stacks of Epstein size laminations of GO steel. A non-destructive test method was developed to detect inter-laminar fault between the laminations of the magnetic cores by means of Flux Injection Probe (FIP). A prototype model of a FIP was developed and its application to quality assessment of transformer core laminations was investigated. The research presented here can be utilised by electrical steel manufacturers and electrical machine designers to survey the effect of inter-laminar faults on the magnetic properties of magnetic cores and their quality assessment, to reduce the risk of core damage or machine failure caused by the inter-laminar faults.

Solar energy has been extensively used in the renewable technology field, especially for domestic applications, either for heating, electrical generation or for a combination of heat and power (CHP) in one system. For CHP system solar photoelectric/thermal (PV/T) is the most commonly used technology for roof top applications. However, combination between solar hot water and thermoelectric generators has become an attractive for CHP system, this is due to its simplicity of construction and its high reliability. Moreover, this technology does not rely simply on sunlight and it can work with any other heat source, such as waste heat. However, its main drawback is its low efficiency. Recent publications by Kraemer et al (2011) and Arturo (2013) have shown that the efficiency of solar thermoelectric systems has improved dramatically, especially when combined with a solar concentrator system, as well as within a vacuum environment. The project recorded in this thesis focused on the design, construction and investigation of an experimental solar thermoelectric system based on a flat plate solar absorber. The aim was to study the technical feasibility and economical viability of generating heat and electric power using a solar thermoelectric hot water system. The design procedure involved on determining the heat absorbed and emitted, as well as the electrical power that was generated by the system. It began by obtaining the efficiency of the solar absorber, including selecting its paint, this was done through an experimental technique to determine the heat absorbed by the absorber, and the results obtained were verified by direct measurements of the light intensity. xvi An intensity meter was used, and results from both the experimental and theoretical models showed good agreement. The process also included calculating the heat from the system that was gained, lost and generated, as well as the electrical power provided. This was done to provide the system optimal size optimization to obtain the best and most economical system. Further improvement was made to the system by assembling a vacuum cavity, to improve the system’s efficiency. Although the maximum electrical efficiency obtained was relatively low (0.9%), compared to results recorded in the literature (Kraemer et al ,2011 and Arturo, 2013). However, the results of the electrical power output, under a vacuum level of 5 x 10-2mbar, increased approximately three times compared to the results obtained under normal (atmospheric) conditions. Additionally, the thermal power increased by 37% at this level of vacuum. The process involved determining the best thermoelectric geometries to achieve the optimum power outcome under different environmental conditions. The results showed that the system, which included the Thermoelectric device (TEG) with a larger geometric size, produced the best thermal power among other sizes. It was concluded that the system with the smallest TEG geometric size provided the best electrical power output.

This thesis, addresses some aspects of the well-known, problem, experienced by designer of radio frequency power amplifiers (RFPA): the efficiency/linearity trade-off. The thesis is focused on finding and documenting solution to linearity problem than can be used to advance the performance of radio frequency (RF) and microwave systems used by the wireless communication industry. The research work, this was undertaken by performing a detailed investigation of the behaviour of transistors, under complex modulation, when subjected to time varying baseband signals at their output terminal: This is what in this thesis will be referred to as “baseband injection”. To undertake this study a new approach to the characterisation of non-linear devices (NLD) in the radio frequency (RF) region, such as transistors, designated as device-under-test (DUT), subjected to time varying baseband signals at its output terminal, was implemented. The study was focused on transistors that are used in implementing RF power amplifiers (RFPA) for base station applications. The nonlinear device under test (NL-DUT) is a generalisation to include transistors and other nonlinear devices under test. Throughout this thesis, transistors will be referred to as ‘device’ or ‘radio frequency power amplifier (RFPA) device’. During baseband injection investigations the device is perturbed by multi-tone modulated RF signals of different complexities. The wireless communication industry is very familiar with these kinds of devices and signals. Also familiar to the industry are the effects that arise when these kind of signal perturb these devices, such as inter-modulation distortion and linearity, power consumption/dissipation and efficiency, spectral re-growth and spectral efficiency, memory effects and trapping effects. While the concept of using baseband injection to linearize RFPAs is not new the mathematical framework introduced and applied in this work is novel. This novel approach NOVEL POWER AMPLIFIER DESIGN USING NON-LINEAR MICROWAVE CHARACTERISATION AND MEASUREMENT TECHNIQUES CARDIFF UNIVERISTY - UK ABSTRACT vi has provided new insight to this very complex problem and highlighted solutions to how it could be a usable technique in practical amplifiers. In this thesis a very rigorous and complex investigative mathematical and measurement analysis on RFPA response to applied complex stimulus in a special domain called the envelope domain was conducted. A novel generic formulation that can ‘engineer’ signal waveforms by using special control keys with which to provide solution to some of the problems highlighted above is presented. The formulation is based on specific background principles, identified from the result of both mathematical theoretical analysis and detailed experimental device characterisation.

Composite strengthening was attempted to improve the mechanical strength and toughness of the brittle near equiatomic Fe-Co alloy. The matrix alloy chosen for this research falls in the Fe-(30-50) Co group, which are known for their highest saturation induction (B-sat) and Curie temperature among the commercial soft magnetic alloys. The reinforcements, which exhibited a wide range of aspect ratios, included SiC particulates, SiC whiskers and carbon nanotubes (CNTs). In order to minimize the interfacial reaction between the reinforcements and the Fe-50Co alloy (matrix) and to realise higher compact density, spark plasma sintering (SPS) was selected for rapid compaction of materials. Reinforcements were coated using electroless deposition with Ni-P, copper and cobalt to modify the interfacial chemistry and thickness, and hence the final properties of the composites. A comprehensive study on the sintering variables found, within the range of examination and under constant heating and cooling rates, the optimum maximum temperature, soaking time and mechanical pressure of 900oC, 2-5 minutes and 80 MPa to rapidly consolidate the Fe- 50Co alloy to near-theoretical density. The volume fraction and size of the ordered regions in the monolithic alloy and hence the magnetic properties, were sensitive to the heating rate, cooling rate, temperature at which the mechanical pressure was applied and removed and post heat treatments. The influence of reinforcement coatings on the wetting characteristics, and in turn the properties, was compared using SiC particulate Fe-50Co composites. The introduction of bare and coarse (20 μm) SiC particulates negatively affected both magnetic and mechanical properties. Electroless Co coating of particulates improved both the flexural properties and magnetic characteristics such as permeability and coercivity by promoting the formation of narrower interfaces and better bonding. The addition of bare and coated whiskers in Fe-Co alloys enhanced densification and grain growth of the matrix. Copper coating over whiskers was found to be not helpful in realising uniform dispersion, whereas Co and Ni-P coating aided to achieve uniform dispersion of whiskers in the matrix. The amorphous Ni-P coating on whiskers was nanocrystallised during the rapid sintering process and resulted in a material with highly improved mechanical strength and ductility in comparison to the monolithic and other whisker reinforced composite materials. A novel attempt to prepare bulk Fe based alloy composites reinforced with CNTs was also undertaken. Both soft magnetic and mechanical property enhancements were observed in composites with lower vol% of CNTs (i.e. < 1.5%, in the range of examination up to 10%) due to the improvement of compact density by CNTs. An increase in the CNT vol% produced a negative effect on saturation induction and mechanical properties due to the agglomeration of CNTs and reduction in compact density. SPS helped to retain the structural integrity of CNTs during processing. Electroless Ni-P coating over the CNTs helped to reduce the structural damage of CNTs during processing and to improve the mechanical strength and ductility at a marginal cost of saturation induction, in comparison to the monolithic compacts and bare CNT reinforced composites. To date accurate temperature assessment of the compact in the SPS die has been difficult due to the remote position of the pyrometer within the body of the die. It has been found that the ferromagnetic Curie transition can be successfully employed to calibrate SPS pyrometer during processing.

This thesis is primarily concerned with experimental tests and computer simulations to determine the high frequency and transient performance of earth electrode systems. The work has involved an extensive review of published literature, theoretical and analytical investigations of earth electrode systems. The experimental investigations on earth electrodes were carried out an outdoor site prior to electrode testing the test site soil resistivity were undertaken. Specifically, the soil resistivity was obtained at the location of the vertical test rod. In order to obtain better understanding of the soil stratification, fourteen profiles of soil resistivity were measured at the field site. From the measurements 2D soil models were constructed to visualise both horizontal and vertical resistivity variation. High frequency and impulse characteristics of vertical test rods up to 6m length and horizontal electrodes up to 88m buried in a non-uniform soil outdoor test site were tested. DC, AC and impulse test results show that increasing the length of electrode reduces the earthing resistance but not impedance. It was shown that, the earth resistance/impedance is constant over a low frequency range, while higher or lower impedance values are observed in the high-frequency range due to inductive or capacitive effects, depending on the length of earth electrode. Improved high- frequency and transient response of earth rods was determined experimentally by connecting horizontal electrode enhancements in star or cross formation at the top of vertical rods. Using these additional enhancements, a reduction in both resistance and impedance has been demonstrated. The addition of horizontal enhancements to the vertical rod can reduce the earth potential rise (EPR) by approximately 70% and 48% for 1.2m and 6m rods respectively. Voltage and current distributions of earth electrode systems under low/high frequency and impulse conditions, for different lengths of vertical rods with horizontal electrode enhancements and along a horizontal electrode with and without insulated conductor, were investigated experimentally and verified by computer simulation. In the case of the of the rods with an added ‘4-cross’ horizontal conductor enhancement, it was shown that the rods carry the majority of the current at low frequency, but this proportion decreases significantly as frequency increases The field test results show that current distribution in earth conductor systems is significantly different under high-frequency and impulse energisation compared with power frequency conditions. Close agreement was obtained between the measured and computed current and voltage High voltage tests in the ground around the vertical electrodes were investigated experimentally. It was observed that when a sufficiently high current magnitude is injected through vertical electrodes, a significant reduction in the impulse resistance by increase in current with a sudden fall of voltage is observed which is called soil ionisation. Such phenomenon does not occur when the vertical electrodes with horizontal enhancements is tested, where the current through all earth electrodes is small.

The evolution of high power transistors has ultimately increased the complexity of their design, interaction and incorporation within microwave frequency power amplifiers. The requirement for high efficiency and high linearity for a wide band frequency by the consumer has put pressure on designers. Due to unexpected and unpredictable failures, device characterisation of the transistor in operational conditions is a highly valuable advantage. The proposed work will describe a non-intrusive, ultra-miniaturised, high resolution electric field probe system; with the capability of measuring relative voltage and waveforms distribution of complex active devices within their operating conditions. The design, construction and evolution of the probing system will be described displaying a resolution of better than 100μm, with a flat frequency response of up to 8GHz. Due to the miniaturised size and the flexibility in positioning, the probe has the ability to measure on-chip, at the device plane, across the device periphery. Results will show direct observation of device plane voltages in high power RFPAs, where the device can exhibit variation in the voltage distribution across the periphery. Such variation will be a function of the internal behaviour and not evident in the output characteristics of the device. This work will also describe a novel method for absolute calibration of the probing system which can be implemented with every movement of the measurement plane. Therefore presenting a successful and calibrated EFP system capable of device characterisation and diagnostics.