Large area electronics: addressing the applications challenge

Citation

Goosey, M. (2013), "Large area electronics: addressing the applications challenge", Circuit World, Vol. 39 No. 2. https://doi.org/10.1108/cw.2013.21739baa.016

Large area electronics: addressing the applications challenge

Article Type: Conferences and exhibitions From: Circuit World, Volume 39, Issue 2

The Hauser Forum, Cambridge, UK18 December 2012

The Cambridge Integrated Knowledge Centre (CIKC) held its large area electronics event at the Hauser Centre, Cambridge on the 18 December 2012, with the objective of providing a showcase of recent progress towards the commercial application of large area electronics. With leading experts from both industry and academia, the event covered the opportunities and challenges for new low temperature manufacturing techniques in photonics and electronics as they made the transition from laboratory to market place.

The meeting was opened by Chris Rider, Director of the CIKC, who welcomed the attendees to the Hauser Centre and who said that large area electronics was at last beginning to take off, with companies now at the stage where they were producing large quantities of prototype materials and devices. He also gave an overview of the CIKC, its structure and activities. The CIKC was interested in electronics and photonics that incorporated new materials and related areas where there were multi-billion pound opportunities. Its mission was to facilitate the commercial exploitation of early stage university technology, especially where there were challenges of bringing disparate technologies together. Example technology areas included printed organic photovoltaics, transparent microelectronics, polymer waveguides and colour displays on plastic.

The first formal technical presentation was then given by Scott White of PragmatIC Printing Ltd, who discussed the high-value manufacturing of low cost electronics. He began by explaining why there was an interest in printing electronics and dispelling some of the myths around low cost printing. In many cases improving printing processes sufficiently for electronics deposition made it expensive, and controlling quality and consistency of functional inks was also very challenging. Sometimes, subtractive processes could be more efficient and lower cost than additive approaches. For example, high-speed roll to roll printing offered economies of scale, but starting and stopping a roll to roll process wasted material. Each application needed to be considered on an individual basis. A big benefit of printed electronics was its ability to be automated, thereby maximising the utilisation of equipment and minimising labour costs. PragmatIC Printing produced printed logic circuits on plastic substrates, i.e. that were thin, flexible, transparent, robust and disposable. By using an imprint process, it was possible to integrate large numbers of transistors in a small area. Feature sizes were typically 50 nm to 5 μmmicrons and they built thin film transistors with novel architectures using a two dimensional approach. Scott concluded by outlining the company’s business model and their pilot production activities, which were being undertaken in collaboration with CPI in Sedgefield.

Felice Torrisi from the Department of Engineering at Cambridge University then covered the inkjet printing of graphene and 2D materials which could provide a new platform for cheap, flexible and transparent electronics. He began by introducing the various methods that could be used for making graphene. An approach called liquid phase exfoliation had been employed in this work to produce graphene inks and these had been characterised using Raman spectroscopy. A centrifuge-based process was employed to separate the graphene monolayers and the subsequently produced inks had been utilised for a number of electronics applications. The deposition characteristics of the inks had been optimised and the properties of the deposited inks studied in ink jet printed devices. Films had good optical transparency and the mechanical flexibility was superior to indium tin oxide, which had allowed flexible smart windows to be fabricated.

The final presentation of the first session was then given by Damian Gardiner from the Inkjet Research Centre, which was part of the Centre for Molecular Materials for Photonics and Electronics at Cambridge University and he covered printable liquid crystal lasers. Current tuneable lasers were typically large, complex and expensive and this had tended to restrict their application. A potential alternative was to use liquid crystals and, in particular, to exploit photonic band gaps in chiral nematic liquid crystals. High efficiency band edge lasing could be achieved over continuously tuneable wavelengths from 450 to 850 nm. Inkjetting and bar coating could be used to produce these lasers on a variety of substrates and the deposition processes were described. Portable printable laser demonstrators had been produced and some of the large number of potential applications for these low cost tuneable lasers were discussed.

Following a networking break there were three more presentations before lunch. Guillame Fichet of Plastic Logic gave a presentation on new applications of flexible displays. He began by presenting an overview of Plastic Logic and its operations. R&D was undertaken in the UK with production being in their Dresden facility, which was now producing thousands of displays per week and operated on a true optimised industrial scale. Examples of the qualification tests required for organic thin film transistors and display modules were described. The company produced the lightest and most durable backplane technology that was currently available. Displays up to 10.7 in (diagonal) size with 16 grey scale levels were available with a pixel density of 225 ppi and thicknesses down to 400 μm. A colour display architecture was also described and this had 640 by 480 pixels. Plastic Logic had developed a method for dealing with overlay distortion and the process had been qualified in their production facility. An example was also shown of a colour display with 1280 by 960 pixels in a 10.7 in (diagonal) display. Flexible displays could easily be cut and bonded together to make larger displays. The company was interested in working with partners to help develop markets and applications for their display technology.

Richard Penty from the Department of Engineering a Cambridge University then gave a presentation on high performance polymer waveguide interconnects. The work reported in his presentation had used a proprietary Dow Corning siloxane-based material. He explained the recent evolution of optical interconnects and the need for very short-distance optical interconnects. Optical interconnects enabled the shortcomings of electrical interconnects to be overcome as data rates increased. Advantages were reduced losses and crosstalk, power savings and reduced size possibilities. The crossover point to optical interconnects varied with distance and data rates but, as the cost of optical interconnects was coming down, the crossover points were changing. The use of optical interconnects allowed the power consumption to be significantly reduced over conventional copper interconnects. Board level optical interconnect approaches were described and the three key approaches used free space interconnects, waveguides and embedded fibres. A board design based on low cost FR4 substrates was shown in which the optical layers were sequentially built on the bottom layer of the board. This board integrated 10 Gb/s optical functionality and subsequent work had concentrated on a 40 Gb/s design. Other work had focussed on a waveguide-based regenerative optical architecture that allowed connection of multiple bus segments and which was compatible with VCSEL/PD arrays. A proof of principle four channel, three card bus module had been produced and data was shown to confirm that error-free transmission had been achieved at 40 Gb/s. This work had been carried out in collaboration with Dow Corning and Xyratex and a proposal (PHLARE) was currently under consideration by the European Commission for a project that would help to build the supply chain.

The final presentation of the session was by Tom Taylor of CPI Ltd and he detailed work undertaken at the CPI National Printable Electronics Centre in Sedgefield to take industrial innovation to market in printed electronics. It was part of the first UK Technology Innovation Centre which had almost 250 employees and had received £75 million in funding to date. CPI covered a range of technology areas around printed electronics and it had two clean rooms for prototyping, fabrication and testing. One of these was used for scale up and yield improvement, i.e. for companies to get proof of manufacture before getting further investment. CPI owned a multi-functional printing pilot line which offered unique combinations of print processes and it could be used for novel types of integration. This was combined with a component pick and place facility. Thin film transistor arrays and OLED lighting tiles could be produced. The example of a tuneable OLEDs for low cost medical applications was described and this had progressed towards production on the millions per year scale. The CPI had wide experience across formulation, coating, encapsulation, testing and process engineering and it was available as a UK resource to help take new technology forward to production.

The afternoon session began with a talk on the development of organic photovoltaic modules for off-grid applications. This was given by Michael Niggemann from Eight19 Ltd, which was a spin out company that came out of the Cavendish Laboratories. The company developed technology for the manufacturing of organic photovoltaics. Organic PVs had shown a rapid increase in attainable efficiency over the last ten years and they were now well above 10 per cent. However, the high efficiencies had largely been achieved on non-scaleable devices. New materials and advanced device architectures were needed to get the efficiency above 10 per cent, e.g. such as by stacking cells on top of each other. The current costs for thin film PVs were around $0.62 per Watt peak compared to $0.78 for silicon-based PVs. OPV would be adopted in off grid applications before they were used in on grid ones. Roll to roll production of organic solar cells had been around for some time and typical traditional device architectures were compared with those for OPVs in terms of cost. Eigth19 were focussing on cell/module architectures that could be transferred to a roll to roll process and hence these were typically on flexible substrates. The designs had been iterated to be chlorine-free and also not to use indium tin oxide. Further technology challenges would continue to be around efficiency and lifetime, coupled with the need to utilize large areas, to reduce costs to below $40/square metre and to be fully roll to roll processable. The company had a model for providing solar lighting at low cost to people that currently did not have access to conventional electricity supplies.

Henning Sirringhaus then gave a talk on the CIKC’s high performance printed organic transistor circuits programme. He began by giving an overview of the fundamental aspects of organic transistors. They were typically made from abundant, low temperature processable materials and there had been significant improvements made in their mobilities in recent years. They also exhibited excellent mechanical properties which enabled them to be bent and rolled, etc. The project had integrated high performance OFETs with sensors and displays. Circuit applications of OTFT technology included RFIDs and in integrated device driver circuits. An 8 bit microprocessor similar to an Intel 4004 device had been demonstrated. For many applications it was necessary to integrate both n and p type devices into a CMOS format and this was a challenge with organic transistors. However, some devices were ambipolar ie they were capable of n and p type operation and a key development had been the development of new ambipolar materials with high mobilities. Example gate structures were shown and capacitance reduction had been achieved by using self-aligned gates. Ring oscillators had been produced that could operate in the 300 kHz range. An overall objective of the project had been to produce silicon-free integrated smart label displays that incorporated a sensor, battery, logic and display. Demonstrator circuits had been produced in collaboration with Plastic Logic.

The third paper of this session was on laminated electroactive foils for the built environment and it was given by Daping Chu from the Centre for Advanced Photonics and Electronics (CAPE) in the Department of Engineering at Cambridge University. He began by outlining the needs for radiation control and sustainability in the built environment. Smectic liquid crystals could be used to provide dynamic light scattering in buildings. They were switchable between the clear and scattering states and were stable in these switched states without the need to apply a continuous field. Switching was achieved by applying varying frequency AC fields. Customised formulations had been switched many millions of times and there had been no change in the switching voltages required. The devices were normally white in the scattering state but the use of colourants had also been investigated and these had shown no degradation in colour over several years of testing. 64-by-64 element switchable displays had also been fabricated. The ultimate aim was to have the displays used in the windows of buildings.

The penultimate talk was given by Andrew Flewitt from the Electrical Engineering division of Cambridge University and it was called “how to detect a single virus”. The presentation was on a collaborative project with the Universities of Bolton and Manchester to develop new biosensors. There was growing interest in the use of “lab on chip” devices for early diagnosis of diseases. These devices typically needed to be very sensitive, easy to use low cost, robust and disposable and there were a range of potential detection methods. The approach used in this work was based on acoustic biosensing but traditionally this had been limited in sensitivity. However, surface acoustic wave devices operating with a resonant frequency of 200 MHz had a sensitivity of 10⁻¹¹ grammes, however the target sensitivity was 1,000 times lower at 10⁻¹⁴ g. A method for increasing the sensitivity was to increase the device resonant frequency even further ie into the GHz range. Zinc oxide was one of the preferred materials for this type of sensor application and it could be sputtered to give suitable low stress, piezoelectric films. Devices had been fabricated and shown to be capable of detecting species of interest. If the electrodes were fabricated using carbon nanotubes, the sensitivity increased even further via a much larger frequency shift. The result was that the mass sensitivity that been achieved was now down to 10⁻¹⁵ to 10⁻¹⁶ g. Interestingly, the surface acoustic wave feature might also be used to move the sample liquids around the sensor devices if required.

The final presentation was given by Chris Jones of Novalia and he talked about printed electronics for print, packaging and point of sale applications. Novalia was a small Cambridge-based company whose aim was to seamlessly integrate print with electronics. Examples of their work were shown and these included a tissue box with a piano keyboard on the side for entertaining children, a music playing poster and an interactive pharma package which reminded the user when to take medication. The print processes used by Novalia were those that were already used in volume in the printing industry and based on conventional printing equipment.

Ian White of the CIKC closed the event with words of thanks to the speakers who had taken time to give presentations at the event, as well as to all of the staff and researchers that had undertaken the work that had been presented during the day.

This meeting provided a valuable update on some of the excellent work that has been undertaken in the UK to take large area electronics from research forward towards commercialisation. The potential areas of use are broad and disparate, but it seems that in many of these there is beginning to be more of an application specific pull because traditional routes are unable to provide the performance required. This is an exciting area that seems, at last, to be on the verge of significant application and commercialisation and it will be interesting to see how things progress in the coming years. Overall, this was an excellent and well organised event that was attended by a large number of delegates from industry and academia. The CIKC is to be congratulated for organising such a successful event. The presentations from the event were to be made available on the CIKC web site (www-cikc.eng.cam.ac.uk) in due course.

Martin Goosey

18 December 2012