Soft image sensors are expected to take vital roles in our future daily life. They can monitor the physiological information of our body to provide real-time, noninvasive medical diagnostics, as well as capture and share photos, videos via wireless communications. However, current image sensing electronics cannot be integrated easily into humans, because they are made of rigid semiconductor photodetectors and integrated with optical filters for colour discrimination. In addition, the use of filter creates additional requirements on the optical path difference, which confines the foldability and limits the resolution of the detector array. To overcome these technological limitations, filterless foldable photodetectors which only detect light within a specific wavelength have emerged as critical elements for building soft image sensors. Colloidal quantum dots, metal halide perovskite and organic photodetectors have shown excellent flexibility and detectivity. However, their broad light absorption means filters need to be added to make them specific to a certain colour of light. So far, the most successful filterless model is based on charge collection narrowing (CCN) photodiodes, which are semiconductor devices that convert the specific colour of light into an electrical current. However, since the narrowband response is delivered by controlling photogenerated charge collection efficiency, micrometres thickness junction is often required, which results in an array with a greater likelihood of interpixel cross-talk and frequency bandwidth limitations. It has been demonstrated that the junction thickness can be reduced by using high reflectivity cavities, but a number of challenges still remain. In this research, we aim to tackle these challenges to help find suitable semiconductors that use non-toxic elements and are able to efficiently detect light within a specific wavelength of interest at thicknesses as little as few hundred nanometres. If successful, we would be moving a step closer to an eco-friendly soft image sensor with the potential for many applications. Among all incarnations of solution-processed semiconductors, the recently discovered two-dimensionally (2D) Colloidal Quantum Wells (CQWs) are highly promising for soft image sensor applications, not only do they offer high colour purity with ultranarrow full-width at half-maximum (FWHM) but they also exhibit excellent compatibility with flexible electronics, such as unique stretching enhanced optical polarisation. Unlike colloidal quantum dots, CQW ensembles have no inhomogeneous broadening due to an atomically-precise definition of the short axis and is the reason why CQWs exhibit the narrowest ensemble absorption and emission spectrum of any solution-processed material reported to date. However, looming over much of this success is the fact that all the reported CQWs include toxic heavy metals (e.g., cadmium and lead), and little progress has been made on the fabrication of non-toxic CQWs or CQW narrowband photodetectors. This proposal is therefore designed to substantially address this challenge by using non-toxic mechanically stretchable 2D solution-processed CQWs for the fabrication of soft image sensors. This proposal starts from the growth and surface functionalisation of non-toxic CQWs followed by predictions of the new cavity and charge transport layers for fast CCN. The proposed work will consider the key factors limiting frequency bandwidth, and will demonstrate the inkjet printing of multi-coloured CCN-based photodiodes in a soft image sensor scenario. The high impact objective of this project is the demonstration of a CQWs image sensor which is stretchable and mechanically conformable. This proposal will be underpinned from the established compound semiconductor research expertise at Cardiff University, in close collaboration with Oxford, Cambridge and Bristol University, TCL Corporate Research, Huawei UK, Glaia, 99P Recycling and Hamamatsu UK.

TOPIC: "Semiconductors" are often 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 technologies 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 5G wireless, ultra-high speed optical fibre connectivity, LIDAR for autonomous vehicles, high voltage switching for electric vehicles, the IoT and high capacity data storage. To date CSs are made in relatively small quantities using fairly bespoke manufacturing and manufacturers have had to put together functions by assembling discrete devices. But this is expensive and for many of the new applications integration is needed along the lines of the Silicon Integrated Chip. CDT research will involve: the science of large scale CS manufacturing (e.g. materials combinations to minimise wafer bow, new fabrication processes for non-flat surfaces); manufacturing integrated CS on Silicon and in applying the manufacturing approaches of Silicon to CS. The latter includes using generic processes and generic building blocks and applying statistical process control. By applying these approaches students will address and invent new ways to exploit the highly advantageous electronic, magnetic, optical and power handling properties of CSs and generate novel integrated functionality for sensing, data processing and communication. NEED: This CDT is a critical part of the strategic development of a CS Cluster supporting activity throughout the UK. It is part of the development of a wider training portfolio including apprenticeships and CPD activities, to train and upskill the CS workforce. Evidence of the critical need for a CDT, has been identified in a survey and analysis conducted by UK Electronics Skills Foundation highlighting the specific skills required in this rapidly growing high technology industrial sector. "We are looking for PhD level skills plus industry experience. We don't have the time to train up new staff." "There are no 'perfect employees' for CS companies, as this is effectively a new area. Staff, including those with PhDs, either have silicon skills and need CS-specific training, or have CS skills and need training in volume tools and processes, either in the cleanroom or in packaging." - quotes from CS Skills Survey - Report UKESF July 2018. We have worked with the CSA Catapult utilising the skills need they have identified as well as companies across the spectrum of CS activities and are confident of the absorptive capacity: the expected PhD level jobs increase for the existing cluster companies alone would employ all the students and the CDT will support many more companies and academic institutions. APPROACH: a 1+3 programme where Year 1 is based in Cardiff, with provision via taught lectures using university approved level 7 modules and transferable skills training, hands on and in-depth practical training and workshop material supplied by University and Industry Partner staff. A dedicated nursery clean room to allow rapid practical progress, learning from peer group activity and then an industry facing environment with co-location with industry staff and manufacturing scale equipment, where they will learn the future CS manufacturing skills. This will maximise cross fertilisation of ideas, techniques and approach and maximise the potential for exploitation. 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 communication, responsible innovation, entrepreneurship, co-innovation techniques and innovative outreach.

Photonics is one of six EU "Key Enabling Technologies. The US recently announced a $200M programme for Integrated Photonics Manufacturing to improve its competiveness. As a UK response, the research proposed here will advance the pervasive technologies for future manufacturing identified in the UK Foresight report on the Future of Manufacturing, improving the manufacturability of optical sensors, functional materials, and energy-efficient growth in the transmission, manipulation and storage of data. Integration is the key to low-cost components and systems. The Hub will address the grand challenge of optimising multiple cross-disciplinary photonic platform technologies to enable integration through developing low-cost fabrication processes. This dominant theme unites the requirements of the UK photonics (and photonics enabled) industry, as confirmed by our consultation with over 40 companies, Catapults, and existing CIMs. Uniquely, following strong UK investment in photonics, we include most of the core photonic platforms available today in our Hub proposal that exploits clean room facilities valued at £200M. Research will focus on both emerging technologies having greatest potential impact on industry, and long-standing challenges in existing photonics technology where current manufacturing processes have hindered industrial uptake. Platforms will include: Metamaterials: One of the challenges in metamaterials is to develop processes for low-cost and high-throughput manufacturing. Advanced metamaterials produced in laboratories depend on slow, expensive production processes such as electron beam writing and are difficult to produce in large sizes or quantities. To secure industrial take up across a wide variety of practical applications, manufacturing methods that allow nanostructure patterning across large areas are required. Southampton hosts a leading metamaterials group led by Prof Zheludev and is well positioned to leverage current/future EPSRC research investments, as well as its leading intellectual property position in metamaterials. High-performance special optical fibres: Although fibres in the UV and mid-IR spectral range have been made, few are currently commercial owing to issues with reliability, performance, integration and manufacturability. This platform will address the manufacturing scalability of special fibres for UV, mid-IR and for ultrahigh power sources, as requested by current industrial partners. Integration with III-V sources and packaging issues will also be addressed, as requested by companies exploiting special fibres in laser-based applications. In the more conventional near-infrared wavelength regime, we will focus on designs and processes to make lasers and systems cheaper, more efficient and more reliable. Integrated Silicon Photonics: has made major advances in the functionality that has been demonstrated at the chip level. Arguably, it is the only platform that potentially offers full integration of all the key components required for optical circuit functionality at low cost, which is no doubt why the manufacturing giant, Intel, has invested so much. The key challenge remains to integrate silicon with optical fibre devices, III-V light sources and the key components of wafer-level manufacture such as on line test and measurement. The Hub includes the leading UK group in silicon photonics led by Prof Graham Reed. III-V devices: Significant advances have been made in extending the range of III-V light sources to the mid-IR wavelength region, but key to maximise their impact is to enable their integration with optical fibres and other photonics platforms, by simultaneous optimisation of the III-V and surrounding technologies. A preliminary mapping of industrial needs has shown that integration with metamaterial components optimised for mid-IR would be highly desirable. Sheffield hosts the EPSRC III-V Centre and adds a powerful light emitting dimension to the Hub.

This proposal targets the development of a compact high power planar Gunn diode suitable for Tera-Hertz (THz) imaging. THz imaging is seen as new opportunity for enhanced security screening at airports, train stations, and other security sensitive places to counter terrorist threats. To achieve high-power THz Gunn diodes, novel heat-sink technologies will need to be developed, which is the key aim of this proposal. This proposal focuses on a novel Gunn diode design, planar Gunn diodes, which enables output frequencies much higher than possible with the traditional commercially available vertical Gunn diode design. We will develop innovative integrated cooling approaches using a combination of thermoelectric (TE) and gas micro-refrigeration for planar Gunn diodes to achieve the goal of a compact and high power Gunn diode suitable as source for THz imaging. With the UK being technology industry leader on Gunn diodes (e.g. e2v technologies Ltd.), the development of compact and high-power THz Gunn diodes is of strategic importance for UK science, engineering and technology, to gain an international lead in the THz field. Developments on integrated active device cooling achieved in this work, however, will be transferable to other device systems. This is important as active cooling to remove heat from electronic and opto-electronic devices is becoming increasingly important as devices shrink in size, packing densities increase, and as higher output powers are demanded in many applications. The proposal brings together internationally leading UK groups on Gunn diodes and their design, cooling technologies, thermal characterization and device thermal management.

The rapidly developing technique of transfer printing on the micro and nanoscales allows the manufacture of high quality, high performance devices on a wide range of substrates in almost any location. This highly versatile capability features a high-precision mechanical pick-and-place assembly technique that utilises the adhesive properties of soft stamps, and the technology has only recently broken into the field of electronics and photonics. Placing this exciting and highly important development into context, in the 1990s Whitesides (Harvard University Chemistry Dept.), a pioneer in microfabrication and nanotechnology, established the ground-breaking concept of patterning self-assembled monolayers for lithographic, sensing, medical and pharmaceutical applications and termed this micro-contact printing. From this foundation, the technique has evolved into much higher levels of complexity in which micro-transfer printing has recently delivered micro- LED arrays that, for example, feature in flexible displays and provide inorganic analogues of flexible organic light-emitting diodes (OLEDs) - something that was previously thought to be extremely challenging if not impossible. In this programme, 'Hetero-print', we aim to rapidly push this exciting field further by establishing, for the first time and ahead of the international competition, new routes towards the manufacture of heterogeneous devices, consisting of integrated systems made from pure and/or hybrid inorganic/organic materials. The demand for these hybrid approaches is extremely high, because it opens up the prospect of multifunctional devices that organic materials can deliver in tandem with inorganic semiconductor technology. The ambition of Hetero-print is to deliver micro- and nano-transfer printing as the technology for the versatile and scalable manufacture of heterogeneous materials, structures and devices. In achieving this, we will introduce significant new capabilities for the manufacture of electronic, photonic, and other systems, which complement and are synergistic with those of established semiconductor mass-manufacturing methods including vacuum deposition and solution processing. In this respect, transfer printing is a highly scalable technique and perfectly suited to high volume manufacture, allowing >10,000 micro-sized integrated circuits to be processed in a single run. An issue with many photonic devices is cost, but micro-transfer printing can be economical with the number of print cycles from a single stamp running into the tens of thousands; the technique is also economical in terms of materials waste, providing a methodology to manufacture multiple-array devices in very high yield.