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.

Today, innovation of novel reconfigurable materials, which can be integrated on Si chip and used for engineering devices, is the key driver for realization of future chip-scale multi-functional systems for applications impacting almost every aspect of life, from energy saving systems and high-speed internet to small consumer devices. This project proposes the novel concept for on-chip architecting of the dynamically reconfigurable systems on Si chip for many advanced optoelectronics device applications. This will be achieved using novel reconfigurable nanocomposites, based on nematic liquid crystals doped with graphene. For the first time, we propose the optofluidic technology for the infiltration of developed in this project nanocomposites into Si photonic platform and for their direct low-power controllable self-assembling into defined micro-structures and micro-devices. The approach to realize this ambitiouse aim in 24 motnhs of this project is (A) to develop novel nanocomosite material platform for integration on Si chip; (B) to demosntrate the first electrically/themrally driven reconfigurable device integrated into micro-photonic circuit on Si chip, i.e. an active metamaterial structure with an ability to filter, split, and switch polarized light in the plane of chip.

The optical fibre core network underpins the internet and the digital economy, with the present capacity of today's core networks being limited to ~ 1Tbit/s per fibre. While in current networks, the limited broadband data rates afforded by the copper based access network prevents the optical core network from being stretched to capacity, as optical fibre permeates the access network, the bottleneck will move from the access network to the core network. To overcome these limitations and to maximise the opportunities afforded by a fibre optic access network will require the capacity of the installed core network to be increased, either by increasing the number of wavelengths used or by increasing the data rate per wavelength. The proposed research aims to combine both techniques simultaneously - transmitting 100 gigabit Ethernet (GbE) on each wavelength, while employing wavelength division multiplexing (WDM) to increase the capacity of the core network to beyond 10Tbit/s.Using conventional intensity modulation schemes, much of the installed fibre base is unable to support data rates faster than 10Gbit/s due to imperfections in the installed fibre which causes pulse spreading. Current research at UCL, led by the principal investigator (PI), has recently experimentally demonstrated the potential of digital signal processing (DSP) combined with coherent detection of spectrally efficient modulation formats to overcome these limitations for 40Gbit/s transmission systems, with the same principles being equally applicable to 100GbE systems. In a digital coherent receiver the four components of the optical field, the in-phase and quadrature components of the two polarisations, are mapped into the electrical domain. This allows digital compensation of transmission impairments and the use of spectrally efficient four-dimensional modulation formats. Given the huge investment which has been made into installing the fibre base infrastructure, the ultimate aim of the research is to determine how this four-dimensional modulation space can be used in conjunction with DSP to maximise the capacity of the installed fibre.The proposed research combines fundamental theoretical research with a determinedly experimental research program into the nonlinear transmission of four-dimensional modulation formats at 100Gbit/s+ and beyond. The initial workpackage will investigate both experimentally and theoretically quadrature amplitude modulation, in combination with polarisation division multiplexing as a four dimensional modulation scheme for 100GbE transmission systems. Within this first workpackage, the system under investigation will be receiver centric, such that all of the DSP, both linear and nonlinear, is based at the receiver. In the second workpackage this assumption will be relaxed and combined transmitter and receiver DSP will be investigated, both experimentally and through simulation. The third and final workpackage which is a theoretical study, will draw on the conclusions of the previous workpackages, and will aim to answer the question Given the optical fibre is dispersive and nonlinear, what is the optimal modulation scheme which enables the capacity of the core network to be maximised assuming we are able to employ appropriate digital signal processing?

This is a proposal for advanced crystal growth equipment to enable the UK to take a lead in important areas of Quantum Technologies. It will enable the growth of nanometre-scale semiconductor quantum dots with world-leading properties. These properties include emission limited only by fundamental properties of the dots unaffected by the surrounding environment, and ordered arrays of dots, critical to enable scale-up and to translate the much excellent science of quantum dots to highly competitive Quantum Technologies. The Quantum Technology applications rely on purely quantum mechanical principles such as superposition, where a system can be in two states at the same time, and entanglement where an operation at one spatial location influences another remotely, without there being any direct connection between them. Quantum dots are extremely well suited to exploiting these quantum mechanical effects (sometimes termed 'Quantum 2'). The favourable properties of III-V semiconductor quantum dots include on-demand single and entangled photon emission, ready incorporation in cavities, very long coherence and compatibility with well-developed III-V semiconductor processing technology. III-V semiconductors are familiar in everyday life as the basis of light emitting diodes, internet data transmission, and laser disk storage to name just a few. Here we turn the favourable III-V properties to enable new applications in Quantum Technologies, including as sources for secure Quantum Cryptography, quantum relays for Quantum Communications, integrated entangled sources for Quantum Cryptography and sensing, and longer-term opportunities for memories and spin chains for Quantum Networks. The crystal growth equipment, an Epitaxy Cluster Tool, is comprised of two principal chambers, one dedicated solely to the growth of highest quality quantum dots, and the second to the advanced processing of structured templates for growth of arrays of dots with pre-determined location, enabling the realisation of very high brightness sources of single photons and of arrays essential for scale-up. The two principal chambers will be connected together by an automated loading, transfer and analysis chamber, enabling high throughput of the system, and furthermore ensuring that only highest cleanliness wafers are transferred to the ultrahigh purity chamber. The Cluster Tool constitutes an integrated suite of growth, analysis and processing features. It will provide the UK with unique experimental infrastructure to take a leading position in the translation of quantum-dot-based science into Quantum Technologies.

The coherent oscillations of mobile charge carriers near the surface of good conductors-surface plasmons- have amazing properties. Light can be coupled to these surface plasmons and trapped by them near the interface between a metal and an adjacent material. This leads to the nanoscale confinement of light, impossible by any other means, and a related electromagnetic field enhancement. The associated effects and applications include high sensitivity to the refractive index of surroundings used in biosensors, enhancement of Raman scattering near the metal surfaces used in chemical sensing and detection, enhanced nonlinear optical effects, localised light sources for imaging, and many others. At the same time the influence of the electrons which participate in the formation of surface plasmons on the surroundings of the metal nanostructures is virtually unexplored. Microscopic electron dynamic effects associated with surface plasmons are capable of significantly influencing physical and chemical processes near the metal surface, not (only) as a result of the high electric fields, but also from the transfer of energetic electrons to the adjacent molecules or materials. We propose to develop a comprehensive research programme in order to understand the physics and harness applications associated with such electronic processes, induced by plasmonic excitations, in designer nanostructures. This will open up new paradigms in ultrafast control over nanoscale chemical reactions switchable with light, optically controlled catalysis, optical and electric processes in semiconductor devices induced by plasmonic hot-electrons, as well as nanoscale and ultrafast temperature control, and many other technologies of tomorrow.