Wireless connectivity is becoming increasingly important in modern society with a forecast of several hundreds of millions of connected devices in the UK alone by 2022, carrying out more than a billion daily data transactions. A large part of these connections will be machine-to-machine (M2M) communications through the rapidly increasing Internet of Things (IoT) that will connect a large number of sensing devices for a wide range of applications. Depending on the application, these wireless connections will span a large area of the radio frequency (RF) and microwave spectrum, from low UHF to mm-wave bands. Compact wireless devices and sensors for IoT with enhanced capabilities and multiple functionalities are required in order to meet the demands of the envisaged systems. The development of new communication and sensing systems for aircrafts (including unmanned air vehicles - UAVs) and automotive vehicles is also becoming crucial for the successful deployment of the next generations of these platforms, such as autonomous air vehicles and driverless cars. Military and civilian aircrafts as well as automotive vehicles are required to cope with an increasing demand for radio frequency communication and sensing capability. With the current trend of increasing wireless connectivity functionalities both in air/automotive vehicles and in compact IoT devices, the size and number of antennas may end up defining the overall size, cost and/or power requirements (e.g. battery life in the case of IoT sensors) of the system. A promising solution to the challenges outlined above is the developing science of RF/microwave metamaterials. Metamaterials and metasurfaces are artificial structures capable of achieving electromagnetic properties and behaviours that are not available from natural materials. This proposal aims to develop new paradigms of multi-functional and tunable metamaterials that will enable the development of novel multi-functional antennas for the two major applications sectors mentioned above, namely IoT wireless devices and autonomous air/automotive vehicles. The outcomes of this work would place the UK at the centre of developments in this transformative area. Importantly, this proposal brings together a leading academic research group with key industrial partners who will help to shape the programme and shorten the lag between fundamental research and product development thus further increasing impact generation.

EPSRC have a delivery plan to align their portfolio to areas of UK strengths and national importance and have designated a number of 'Grow' areas. This application addresses two of these areas: 'RF and microwave communications' and 'RF and microwave devices', specifically matching the terahertz technology aspect of the latter. Why has EPSRC highlighted these areas? The answer is that society is evolving with a continuously increasing demand for the exchange of digital information. There is an expectation that everyone will be permanently connected to the Internet, no matter where they are. People are expecting that more information of a higher quality is delivered immediately: therefore newer services are requiring higher and higher data volumes and transfer rates. On demand video is an excellent example, with in-home delivery with standard definition now common place and demonstrations of new 4k on demand video now taking place. The data rates expected for these services are vast and the infrastructure needs adapt to cope. One way to achieve this is to move to higher frequencies for wireless links. We propose to demonstrate new building block components for such a communications system, designing and building these on an entirely new basis. A frequency of 300 GHz is chosen as it is at the cusp of technology; systems are now being deployed at frequencies below about 100 GHz where as systems approaching 1000 GHz are some years away because of the lack of active circuits. The components will also be applicable in radar and sensing scenarios. Once the individual components have been demonstrated, a full communications system will be designed, built and tested. There are very few demonstrations of communication systems at 300 GHz and the unique design methodology will provide a world-class demonstration. Three groups are collaborating in this project: the Fraunhofer Institute in Freiburg, Germany (IAF), and it the UK the Rutherford Appleton Laboratory (RAL) and Birmingham University. All partners have substantial design and measurement capabilities at these very high frequencies. IAF are world leaders in the production of submillimetre wave integrated circuits and will be supplying transistors for the amplifiers. RAL will deliver world class Schottky barrier and the University of Birmingham has advanced micromachining capabilities. At Birmingham a new interconnect principle has been developed to link the Schottky diodes and transistors. Instead of using wires and their analogues, hollow waveguide tube based resonant cavities will be used. Currently 300 GHz components are mounting in conventionally milled gold pated blocks. The required waveguide dimensions are about 0.8 mm by 0.4 mm. Although conventional milling machines can machine this, once internal structures for resonators are required, milling becomes difficult or impossible. A technology that can be used for the waveguide cavities, and for smaller resonators at higher frequencies, is micromachining. Birmingham University have demonstrated micromachined waveguides, filters, diplexers and antennas at and above 300 GHz. This technology is now ready for the next step, which is the inclusion of active and non-linear devices. The micromachining work at Birmingham has been done by a number of techniques, the primarily technique is by etching an ultraviolet sensitive photoresist called SU8. This allows a pattern to be defined photolithographically by a mask and then etching sections produces the waveguide. The final structure is made by bonding a number of SU8 etched layers together and then metal coating them. The performance of the SU8 waveguides has been shown to be as good as metal. Other techniques for micromachining circuits will be investigated in order to find the optimum solution.

Three-dimensional (3D) printing, also known as additive manufacturing, is now common place in many industries and is used widely. Some types of 3D printers are available for home use at modest cost. However, detailed work, together with demonstrator devices, is still in the very early stages in relation to the manufacture of microwave and terahertz circuits. These requires a level of precision and materials very different from the consumer products. This proposal is to evaluate and improve the performance of 3D printing for microwave and terahertz passive and diode circuits through measurement, design and demonstration. These high frequencies, from 10 GHz to 1000 GHz, are used for free space communications, security sensing and remote monitoring of the Earth's atmosphere. The focus will be on evaluation of 3D printed circuits at frequencies above about 50 GHz, the small feature sizes required for these frequencies allows only the best printing process to compete; enabling the project to evaluate the most advanced 3D printing approaches. This exciting project will be the most comprehensive academic study worldwide to date. A strong, experienced, national team, at the University of Birmingham and the STFC Rutherford Appleton Laboratory (RAL) will conduct the research in collaboration with several UK and international industry partners. The Communications and Sensing research group at Birmingham University have already demonstrated significant research in this area, with 3D printed devices published covering the frequency range 0.5 GHz to 100 GHz. The importance of this work has been recognised externally through prizes, invited international presentations and refereed academic publications. Birmingham's partners, the Millimetre Wave Technology Group in the RAL Space department, bring extensive expertise in precision manufacturing of conventional devices for these high frequencies, and knowledge of the demanding space and other requirements that the new 3D circuits must fulfil. RAL staff will conduct post processing of the 3D printed circuits and perform accelerated lifetime measurements under conditions of elevated temperature and humidity. 3D printed microwave and terahertz circuits will have an important beneficial economic impact on UK industry, not only because complex circuits become possible at low cost, but because new design approaches emerge because of the unique manufacturing. The applicants will both work on their own ideas, and closely with industrial partners, during the project. There are a number of hurdles to overcome before the technology becomes mainstream: this proposal tackles these challenges. The advantages of 3D printing include the availability to rapidly generate novel circuits with complex shapes and multiple functions using low material volumes in a lightweight form. This enables reliable, low cost, superior performance circuits with less waste and reductions in lead time. Considerations to be addressed include the metal coating of polymer circuits which adds an extra step in the production, as well as potentially lower thermal stability and power handling of such circuits. If the polymer is used as a microwave dielectric, power loss may be a problem. For metal 3D printed circuits, power handling and thermal stability is good, but surface roughness may reduce device performance. These problems and others are addressed in the proposal with a methodical investigation based on the measurement of resonant waveguide cavities, the microwave equivalent of a tuning fork. Changes to the frequency and decay time indicate the quality of manufacture. The project will inform industry and academia through a widely distributed technology development roadmap and external collaborative projects, as well as the provision of advice and guidance. Our finding will also be communicated to national and international colleagues through academic publications, and presentations at relevant conferences.

"Semiconductors" are synonymous with "Silicon Chips". After all Silicon supported computing technologies in the 20th century. But Silicon is reaching fundamental limits and already many of the technologies we now take for granted are only possible because of Compound Semiconductors (CS). These include The Internet, Smart Phones, GPS and Energy efficient LED lighting! CSs are also at the heart of most of the new technologies expected in the next few years including 6G wireless, ultra-high speed optical fibre connectivity, LIDAR for autonomous vehicles, high voltage switching for electric vehicles, the IoT and high capacity data storage. CSs also offer huge opportunities for energy efficiency and net zero. CSs are often made in small quantities and using bespoke techniques and manufacturers have had to put together functions by assembling discrete devices. But this is expensive and for many of the new applications scale-up and integration, along the lines of the Silicon Chip, are needed CDT research will involve the science of large scale CS manufacturing, manufacturing integrated CS on Silicon and applying the manufacturing approaches of Silicon to CS; it will generate novel integrated functionality and all with an emphasis on finding environmentally sustainable manufacturing methods. CIVIC PRIORITY: This CDT is a fundamental part of the strategic development of the CS Cluster centred in South Wales, and in linking it to activity across the UK. It is part of a wider training strategy including apprenticeships, MScs and CPD, to train and upskill the entire workforce. The latest skills requirements have been identified by partner companies and through working with Welsh Government, CSconnected and the CS Applications Catapult The partners support the CDT financially and with their time. This is because the limiting factor to rapid cluster growth is skilled people. The expected PhD level jobs increase for the existing cluster companies alone would mop up all the students trained by this CDT. We provide a £2k stipend top-up to maximise recruitment from all backgrounds. However, the CDT does more - clusters are about cross-fertilisation of people and ideas and the CDT combines academics from 4 universities with leading and complementary expertise in CS. We form teams of two academics from different universities, one industry supervisor and the PhD student to create and carry out each PhD. The CDT also ensures the whole cohort regularly works together to exchange new knowledge and ideas and maintain breadth for each student. The UK and Welsh administrations see CS as an opportunity to boost the economy with high technology jobs and the UK government uses the CDT as part of its pitch to overseas companies to locate here. APPROACH and OUTCOMES: a 1+3 program where Year 1 (Y1) is based in Cardiff, with provision via taught lectures and transferable skills training, hands on and in-depth practical training and workshops led by University and Industry Partner staff. Following requests from Y2-4 students the industry workshops are presented in hybrid format so all Y2-4 students can further benefit from this program and where we now cycle presenters, companies and specific topics over 3 years. A dedicated training clean room allows rapid practical progress in a supportive environment, learning from doing, experts and the rest of the cohort and then an industry facing cleanroom, co-located with industry staff and manufacturing scale equipment, where students learn the future CS manufacturing skills. This maximises exchange of ideas, techniques and approach and the potential for exploitation. Both students and industry partners have praised the practical skills this produces. Y2-Y4 consist of an in depth PhD project, co-created with industry and hosted at one of the 4 universities, and specialised whole cohort training and events, including energy audit, research ethics and innovative outreach

"Semiconductors" are synonymous with "Silicon chips". After all Silicon supported computing technologies in the 20th century. But Silicon is reaching fundamental limits and already many of the technologies we take for granted are only possible because of Compound Semiconductors (CS). These include: the internet, smart phones and energy-efficient LED lighting! CSs are also at the heart of most of the new technologies envisaged, including 6G wireless, ultra-high speed optical fibre connectivity, LIDAR for autonomous vehicles, high voltage switching for electric vehicles, the IoT and high-capacity data storage. CSs also offer huge opportunities for energy efficiency and net zero. The CS Hub will contribute to "Engineering Net Zero", through products, such as energy-efficient electronics, and by introducing new environmentally-friendly manufacturing processes; to "Quantum Technologies", by creating practical implementations that can be manufactured at scale; to the "Physical and Mathematical Sciences Powerhouse" and "Frontiers in Engineering and Technology", through e.g. cutting-edge materials science and manufacturing-process innovation. CS materials are grown atom-by-atom on slices of crystalline material, known as substrates, which provide mechanical support for the resulting "wafer" during the next stage of fabrication. CSs are often made on relatively small substrates. Manufacturers have had to combine functions by assembling discrete devices but this is expensive. New approaches to integration in epitaxy and fabrication are required along with wafer-size scale-up for the new applications. Applications such as in quantum technology (QT) are pushing requirements for more accurate and highly reproducible manufacturing-processes. With such improvements CS will underpin the UK quantum industry and enable impact for the existing QT investments. We will create designs that are more tolerant to typical variations that occur during manufacturing; develop manufacturing processes that are more uniform and repeatable; create techniques to characterise performance part-way through manufacturing, create techniques to combine materials (e.g. CS grown atom-by-atom on Silicon) and combine functions on chip. We will study and implement ways to make CS manufacturing more environmentally friendly. We will make it easier to compare the environmental foot-print of different CS research and manufacturing-processes by making available relevant, high quality data in the form of accessible libraries of the resource and energy usage of the feedstocks and processes used in CS manufacturing. We aim to change the mind-set of UK academics. Our vision is that researchers think about the translation of their research from the beginning of the innovation process and about the requirements that next generation product manufacturers will face. As a critical factor in all future manufacturing, we aim to embed the philosophy of resource efficiency of the research itself, resource efficiency of the manufacturing process, as well as of the application it supports. We aim to repatriate and connect CS manufacturing supply chains to re-shore production and facilitate innovation, enabling development of holistic solutions. We will address the current staffing shortages of the CS industry by: providing leadership in improving career structure and enhancing training for Hub research and technical staff; putting in place the very best ED&I practice to create the most positive and inclusive working environment and promulgating this across the industry; inspiring the next generation of the CS workforce as well as spreading the news about the fantastic career opportunities currently available. By working closely with industry partners on all these aspects we will attract and retain staff in this critical UK manufacturing industry.