'Hetero-print': A holistic approach to transfer-printing for heterogeneous integration in manufacturing

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.

Hetero-print addresses the urgent need for heterogeneous integration in many forms of advanced manufacturing. Although rooted in semiconductor industry techniques, new applications lie in the fields of flexible electronics, new forms of displays, silicon photonics, photonic integrated circuits, sensors for medicine and healthcare, novel quantum-based sensors, smart labels, and photovoltaics. These emerging fields are all of critical importance to the future UK economy, and many of the example applications mentioned will be implemented in mass market products and/or wearables, having significant societal impact. The enormous economic potential for end products is backed by authoritative forecasts, eg. IDTechEx predicts a market for organic and flexible electronics of over 73 billion USD by 2027.

The investigators bring a range of existing UK-based company collaborators spanning the range of relevant industries, from materials supply, through advanced printing technologies, to end-product integrated systems. These partners involve 12 companies and 4 Centres and Hubs (see letters of support). We expect early adoption of technologies developed from Hetero-print by the companies mentioned, plus others engaged through our workshops and the work of our 0.5 FTE Impact Champion. Where appropriate to apply external technical expertise or specialist equipment to manufacturability issues (e.g. yield optimisation and scale-up), we will arrange sub-contracts with organisations such as CPI. The investigators also have previous spin-out experience through the foundation of companies including mLED and Sci-Tron, and will have strong institutional support for launching similar new ventures if judged to be the appropriate mechanism to exploit research findings. There are a number of relevant translational organisations and consortia which include Fraunhofer UK, the Compound Semiconductor Applications and High Value Manufacturing Catapults, the CIM in Large Area Electronics, the National Hub in High-Value Photonic Manufacturing, and the Future Compound Semiconductor Manufacturing Hub. The investigators are well connected already to these various organisations, and recognise the importance of further developing collaborative links. We will work with selected partners on definition of a Technology Roadmap from the mid-point of the programme. In this exercise, we will benchmark Technology Readiness Levels of our various strands of activity, and also capture and prioritise opportunities for further exploitation.

The outcomes of Hetero-print will be very suitable for exhibiting either as actual hardware demonstrators, which particularly is the case with Workpackage 4 (Interconnects and Systems Demonstrations'), or through videos of manufacturing processes or systems in operation. The Strathclyde IoP team, for example, has extensive and very positive recent experience of such demonstrations both through events targeted at professional audiences, and aligned with EPSRC projects (eg. UP-VLC project Open Day, Quantum Showcases), and in wider public engagement activity (e.g. Glasgow Explorathon). Within Hetero-print, the two workshops will provide a natural focus for preparation of demonstrators illustrating the breadth of achievement. These particular events will be targeted at professional audiences, addressing fellow academics, industrialists, trade association members, and government and funding body representatives. Once available, the same demonstrators will be suitable for public outreach events and/or permanent installations, and the Hetero-print Impact Champion will co-ordinate this important strand of activity.

Consistent with their past achievements, the investigator team will continue to prioritise publication in the highest impact academic journals, and dissemination through UK and international conferences.