In October 2014 the UK energy surplus during winter months dropped to below 5% overcapacity. In the future, this emergency overcapacity may be further diminished and actually become devastatingly insufficient, necessitating the national grid to divert large power demands to areas at opposite ends of the country or face serious and harmful disruption to energy supply. A viable solution to this supply problem is to build new national high voltage DC (HVDC) energy network connections in addition to more international connections to the super grid. To implement HVDC effectively, companies are considering two options: 1) to implement mature Si 300 MW HVDC technologies (circa 2009) requiring large overhead, land requirements, maintenance costs and cooling systems by scaling with the number of converters per line. Or 2) to invest in technologies which upscale the blocking voltage and the current capacity of individual power devices in a converter where fewer line converters and greater efficiency can be achieved for 2 GW MMC HVDC. Even by reducing the series chain effect in power transmission across the UK and conversion a 3% saving can equate to three 500 MW coal power stations from the current UK power usage of approximately 37 GW. This fellowship seeks to develop revolutionary Silicon Carbide (SiC) material for ultra-high voltage (UHV) >30 kV power devices with large current ratings, up to 150A, with the intention of pushing the current rating as far as possible. The current rating of UHV vertical devices depends on availability of large surface areas (> 1 cm2) and is presently limited due to defects from excess material deposits forming on the wafer during the material growth. This is a problem which I believe will be a critical roadblock to such technology and receives little attention as the proposed power ratings are currently off the 5-10 year power electronics roadmap. Problematically, many in the field trust it will be solved at that point, however, no major research drive is currently underway to solve this essential problem. Chemical vapour deposition (CVD) is the industry gold-standard technique for creating the semiconductor materials used in these UHV devices due to its excellent uniformity, scalability and reproducibility and so must be developed for quick uptake of any power device technology. For UHV devices the material choice and quality is key, where a defect free, thick (~100 um) layer with a large surface area is needed. Chlorinated chemistry is a recent development in SiC CVD and helps push growth rates up to 100 um/hr for thick layers and can be used to better achieve low background doping densities which are both required for high power technology. Here, thick high quality material will be achieved by state of the art epitaxial growth in the UK's only industrial SiC CVD at Warwick. In tandem to improving the material, its superiority will be shown by fabrication of vertical UHV devices: Schottky Diodes, PiN Diodes and MOSFETS, whilst developing IGBT processing, to show their potential for future modular multi-level converter (MMC) HVDC networks. Bipolar devices such as Si thyristors and Si PiN diodes will be used in rail traction and grid level HVDC applications due to the high quality of Si material which allows large current ratings. In 2014, Yole predicted that these sectors would boost the >3.3 kV SiC market and in 2015 Mitsubishi showed an all SiC 3.3 kV traction inverter system. I further predict that SiC devices will only completely replace Si IGBTs in the > 10 kV range when the current-limiting surface defects are minimised and device reliability due to minor material defects is better understood. Only then will large current ratings be achieved, which will allow the technology to surpass current HVDC technology. This fellowship directly studies these limiting mechanisms and will develop the material and associated technology to underpin this step change in power technology

Internet and telecoms are facing an explosive growth in data traffic, increasing at 50% per year. This requires the development of monolithic on-chip integration of electronics and photonics, which offers a massive reduction in both footprint and processing costs. Such a compact system will require a high power density and excellent high temperature tolerance. Monolithically integrating III-nitride based electronics and photonics on silicon on a single chip will represent the most promising approach to meeting the requirements in the telecoms regime. The photonic parts include active (laser diodes) and passive (photodetectors) components linked by waveguides, where the laser diodes are controlled by high electron mobility transistors. The electronic and photonic parts both need to meet the requirements for high power, high frequency and high temperature operation, as well as excellent temperature stability and robust mechanical properties. Conventional III-V semiconductors (GaAs or InP) suffer a number of fundamental limitations such as intolerance to high-temperatures, temperature sensitivity, limited power density capacity and fragility. They also exhibit high losses due to scattering (high refractive index) and multiphoton absorption. III-nitride semiconductors all have direct bandgaps and cover a vast spectral region from deep ultraviolet to infrared. Compared with conventional III-V materials, the III-nitrides exhibit major advantages in the fabrication of high power, high frequency and high temperature devices due to their intrinsically high breakdown voltage, high saturation electron velocity and excellent mechanical hardness. III-nitrides exhibit low free carrier absorption, negligible multiphoton absorption, low refractive index (2.3 for GaN compared with 3.5 for GaAs) and superior temperature stability of the refractive index (one order of magnitude higher than that of InP). Therefore, III-nitrides offer great potential to revolutionise current internet and telecoms and enable ultra-fast speed and ultra-broad bandwidths, going far beyond that so-far achieved in the telecoms regime (1.3-1.55 um). Up to now research on III-nitrides has mainly been confined to the visible spectral range but this is not a limit. III-nitrides based devices exhibit superior properties in terms of delivering the power/efficiency required for next-generation telecoms. This is important to the communications industry, which is expected to use 20% of the global electricity by 2025, where a large proportion (>30%) is consumed by the data centre cooling systems. Monolithically integrating III-nitride electronics and photonics on silicon on a single chip by direct epitaxy in the telecoms regime would therefore offer transformative performance. Our ambitious vision is to employ the two major leading epitaxial growth techniques (MOVPE and MBE) for III-nitrides, combining the leading-expertise established at Sheffield, Cardiff and Strathclyde along with a world-leading research team at Michigan in USA in order to demonstrate the first monolithic on-chip integration of III-nitride based electronics and photonics on silicon with operation in the telecoms regime. This is expected to revolutionise current internet and telecoms.

This project develops new sensing technology for use in power electronic systems, helping the UK to better compete with global leaders in power electronics. Power electronics is a key electrification technology: it is needed in electric vehicles, renewable energy generation, our electricity grid, and anywhere where the flow of power needs to be accurately dosed. This dosing is carried out by rapidly switching currents on and off to create the desired average. This technology reduces our carbon footprint and contributes nearly £50bn per year to the UK economy and supports 82,000 skilled jobs in over 400 UK-based companies (2016 data). The power electronics industry is undergoing significant change, as ultra-fast transistors made from silicon carbide (SiC) or gallium nitride (GaN) have recently emerged, to replace silicon transistors. These new transistors switch 10x faster, which results in 75% less energy being lost in power converters, and enables converters to be shrunk to less than half their previous size. This makes it much easier to build them into other systems, e.g. electric vehicles, resulting in lighter cars with more space for batteries. This project is about helping to maximise the potential of the new transistors. Many companies are struggling to adopt them, because whilst the very fast switching provides the benefits of improved efficiency and radically smaller system size, it also creates problems with electromagnetic interference, and device and system reliability. The transistors switch current on or off so fast (in less than ten nanoseconds, the time it takes light to travel 3 meters), that engineers cannot accurately measure how the voltages and currents change during this time, even with their best equipment, which means it is difficult to fix problems such as interference. Because of this, even the leading companies are slowing down these new transistors, and losing some of their efficiency potential. Our project develops small, low-cost sensors, that make these nanosecond-scale changes visible. They will allow engineers to see exactly how the transistors are switching, helping them develop better, smaller, lighter, and more reliable power electronics. They will allow computer-controlled SiC and GaN power converters to sense when they are creating too much electromagnetic noise, and reduce this by switching more intelligently. It will allow power circuits to detect external short circuits and isolate these before they damage the power converter. We are also developing sensors that provide engineers, or control systems, directly with information that they need (e.g. device temperature), rather than having to infer this indirectly from volts and amps, making the measurements faster and more efficient. The sensors work by detecting electric or magnetic fields via coils, conductive plates, or antennas. The received signal is fed into a chip inside the sensor that computes the required parameter. These new SiC and GaN transistors have made small field sensors on circuit boards viable for the first time, because as signal speeds increase, the wavelengths of these signals become shorter (cm-scale), meaning that their fields can be picked up with millimetre-size coils or antennas. In order to ensure that we develop what industry needs, we are working with 12 partners across automotive, renewable energy, semiconductors, commercial R&D organisations with deep sector experience, and we are accepting new collaborators on request. Our project provides partners and other UK companies and universities with sample sensors. Their feedback, and discussions with partners helps us prioritise our research, and ensures that we are using our research funds to solve the most important problems. We are providing workshops to help keep engineers up-to-date with advanced measurement techniques, and keeping our results online (publications and a dedicated website) for companies to use as desired.

Over the next twenty years, the automotive and aerospace sector will undergo a fundamental revolution in propulsion technology. The automotive sector will rapidly move away from petrol and diesel engine powered cars towards fully electric propelled vehicles whilst planes will move away from pure kerosene powered jet engines to hybrid-electric propulsion. The automotive and aerospace industry has worked for the last two decades on developing electric propulsion research but development investment from industry and governments was low until recently, due to lag of legislation to significantly reduce greenhouse gases. Since the ratification of the 2016 Paris Agreement, which aims to keep global temperature rise this century well below 2 degrees Celsius, governments of industrial developed nations have now legislated to ban new combustion powered vehicles (by 2040 in the UK and France, by 2030 in Germany and similar legislation is expected soon in China). The implementation of this ban will see a sharp rise of the global electric vehicle market to 7.5 million by 2020 with exponential growth. In the aerospace sector, Airbus, Siemens and Rolls-Royce have announced a 100-seater hybrid-electric aircraft to be launched by 2030 following successful tests of 2 seater electric powered planes. Other American and European aerospace industries such as Boeing and General Electric must also prepare for this fundamental shift in propulsion technology. Every electric car and every hybrid-electric plane needs an electric drive (propulsion) system, which typically comprises a motor and the electronics that controls the flow of energy to the motor. In order to make this a cost-effective reality, the cost of electric drives must be halved and their size and weight must be reduced by up to 500% compared to today's drive systems. These targets can only be achieved by radical integration of these two sub-systems that form an electric drive: the electric motor and the power electronics (capacitors, inductors and semiconductor switches). These are currently built as two independent systems and the fusion of both creates new interactions and physical phenomena between power electronics components and the electric motor. For example, all power electronics components would experience lots of mechanical vibrations and heat from the electric motor. Other challenges are in the assembly of connecting millimetre thin power electronics semiconductors onto a large hundred times bigger aluminium block that houses the electric motor for mechanical strength. To achieve this type of integration, industry recognises that future professional engineers need skills beyond the classical multi-disciplinary approach where individual experts work together in a team. Future propulsion engineers must adopt cross-disciplinary and creative thinking in order to understand the requirements of other disciplines. In addition, they will need an understanding of non-traditional engineering subjects such as business thinking, use of big data, environmental issues and ethical impact. Future propulsion engineers will need to experience a training environment that emphasises both deep subject knowledge and cross-disciplinary thinking. This EPSRC CDT in Power Electronics for Sustainable Electric Propulsion is formed by two of UK's largest and most forward thinking research groups in this field (at Newcastle and Nottingham Universities) and includes 16 leading industrial partners (Cummins, Dyson, CRRC, Protean, to name a few). All of them sharing one vision: To create a new generation of UK power electronics specialists, needed to meet the societal and industrial demand for clean, electric propulsion systems in future automotive and aerospace transport infrastructures.

There is an increasing demand for electronics that can operate at temperatures in excess of 200 degrees C, well above the maximum operating temperature of traditional silicon microelectronics. Key application areas are in the power, automotive, aerospace and defence industries. Electronic devices capable of operating at such high temperatures are now available. However, new methods are also needed for integrating these devices into circuits and systems, and in particular for attaching them, both mechanically and electrically, to circuit boards and heatsinks. At present high-temperature devices are typically attached by soldering using high-melting-point, lead-rich solders. However, there is a strong environmental imperative to reduce the use of lead in all electronics, so this cannot be accepted as a long-term solution. Alternative solutions employing gold-rich solders or sintered nano-silver pastes can be used, but these are expensive and can suffer from reliability issues. Low-cost, lead-free high-temperature solder alloys are also available; however, these tend to require significantly higher soldering temperatures and longer processing times, leading to slower production and higher thermal load on the devices during soldering. This project will explore the use of quasi-ambient bonding (QAB) with reactive nanofoils as a route to lowering the process time and thermal load during packaging of high-temperature electronic devices. Reactive nanofoils are multilayer materials comprising alternating layers of two elements (typically nickel and aluminium) that react exothermically i.e. with the release of heat. Once the reaction is triggered, it is self-propagating and spreads throughout the foil. If the foil is sandwiched between two parts that are pre-coated with solder, the heat generated can be used to melt the adjacent solder layers momentarily and form a permanent bond. The heating is intense, but occurs over a short timescale, so that while the local temperature can reach up to 1500 degrees C, heating is confined to a narrow region around the foil, with negligible temperature rise occurring elsewhere. Up to now, quasi-ambient bonding applications have used traditional lower-temperature solders. In this project we will extend the application of QAB to a range of low-cost, lead-free high-temperature alloys. The primary aim will be to develop bonding processes tailored for applications in high-temperature power electronics and optoelectronics. We will also explore the use of QAB for sealing of hermetic packages which is another key area where low cost and low thermal load can be an advantage. The processes developed will be evaluated in terms of bonding strength and in-service reliability, and benchmarked against alternative processes based on lead- and gold-based solders. Alongside the process development and evaluation, we will carry out extensive modelling and characterisation aimed at gaining an improved understanding of the QAB process. Developments to date have been mainly empirical, and fundamental aspects of the process remain poorly understood. QAB is fundamentally different from traditional soldering because of the very short timescale over which the process takes place. In order for it to become established in mainstream electronics manufacturing, the potential detrimental effects of residual stresses and microstructural defects incorporated into QAB bonds need to be fully understood. The proposed research has the potential to provide a low-cost, sustainable joining technology for electronics manufacturing that can continue to meet the operating temperature requirements of high-temperature electronics for many years to come. At the same time it will yield new fundamental insights into processes involving rapid solidification of complex alloys that will be of wide interest to the materials science and manufacturing research communities.