IeMRC – CAFMAD Workshop on Novel Electronic Materials

Citation

Goosey, M. (2010), "IeMRC – CAFMAD Workshop on Novel Electronic Materials", Circuit World, Vol. 36 No. 2. https://doi.org/10.1108/cw.2010.21736bac.004

IeMRC – CAFMAD Workshop on Novel Electronic Materials

Article Type: Exhibitions and conferences From: Circuit World, Volume 36, Issue 2

Technium CAST, Bangor, 24 November 2009

The Innovative Electronics Manufacturing Research Centre’s (IeMRC) final event in 2009 was held in collaboration with the Centre for Advanced Materials and Devices (CAFMaD) at Technium CAST in Bangor on the 24 November and the subject matter broadly covered the area of Novel Electronic Materials. The workshop was opened by Gary Reed who introduced CAFMAD, which was one of the four key research centres set up in Wales and which was based jointly in Aberystwyth and Bangor. Research areas covered by CAFMaD included organic conductors and molecular electronics, sensors and devices, extreme materials and characterisation and modelling.

Martin Goosey, Industrial Director of the Innovative Electronics Manufacturing Centre, then gave an introduction to the IeMRC and its current status. The IeMRC was currently preparing for the start of its second five-year period of funding and it was in the middle of reviewing and selecting projects that would be funded from March 2010. The IeMRC’s Vision Statement was presented and its engagement with the UK’s electronics industry highlighted. Examples of materials-related research that had been supported during the first five years of activity were highlighted. These were the project based at Birmingham University on high resolution, high sensitivity chemically amplified e-beam resists and the work carried out at Brunel University on printed electronic interconnects, devices and battery structures. Martin concluded by inviting attendees to engage with the IeMRC and highlighted the ways in which this could be possible.

The first technical presentation was given by Geoff Ashwell from CAFMaD, Bangor and it was entitled “Single Molecule Electronics”. In this presentation, Geoff detailed work on the synthesis of molecular wires and the control of their electrical properties via modification of molecular structure. The structure of the molecular wires was detailed and their synthesis could require a 11-stage process. The synthesis had been monitored using quartz microbalance and X-ray photoelectron spectroscopy techniques. The electrical properties of the molecules could be controlled by modifying their actual structures during their synthesis. Individual molecules could, for example, be changed from rectifying to non-rectifying by changing the end group terminations. Examples of the synthesis of a rectifying molecule were then described. Having synthesised the appropriate molecules, they could then be inserted into various device structures and one such example was described which was essentially a molecular necklace around a silicon nitride insulator layer. Work had been carried out in collaboration with QinetiQ, which had also developed various device structures where the molecules were deposited between silicon electrodes that were separated by a 7-nm silicon dioxide insulating layer. The molecule used in this later work had been synthesised by Durham University. Theoretical calculations of currents aligned well with the measured results. This in situ synthesis method for molecular wires had given the highest recorded rectification ratio from a molecular wire and the research had enabled the first examples of molecules inserted into nano-gap silicon devices. Future work would be undertaken to develop the first single molecule devices.

Marc Desmullliez of Heriot Watt University then gave a talk entitled “Enhanced Electrodeposition using Megasonic Agitation”. Marc began by describing the PCB market in Europe and discussed the current distribution of fabricators in different countries. Most of these were now smaller companies that did not have significant resources to support research and development. He then described the use of microvias in PCBs and the different approaches that were available for manufacturing them. The challenge was to be able to electroplate high-aspect ratio blind microvias and the difficulties of depositing metal in blind vias were described. The equations governing the deposition process were then detailed and some examples of the modelling data covering the deposition process were shown. The motivation for using acoustic streaming was then explained; the key objective was to decrease the thickness of the diffusion layer in order to increase the ionic concentration at the microvia surface. The acoustic streaming process was also illustrated; this had been built into a standard industrial plating line and had used Schloetter pulse-plating chemistry. A range of designed experiments had been undertaken and the results were shown. Pulse plating with or without megasonic agitation delivered good results in terms of uniformity, even up to a 6:1 aspect ratio. However, the use of megasonics allowed greater plating efficiencies and plating times could be reduced by up to 50 per cent. Future work would be carried out to investigate the potential of megasonics for etching various types of substrates including silicon.

Martin Taylor of CAFMaD then gave a talk on “Characterising Electronic Materials for Organic Electronics”. He began by discussing the motivation for moving to the use of organic electronic circuits and giving examples of MISFET and MIS capacitor structures and their use for characterising materials. A combination of AC and DC measurements was essential if the behaviour of organic electronic devices was to be fully understood. The characterisation method known as admittance spectroscopy was described. Results obtained were shown and the effects of temperature on AC response were detailed. Examples of C-V plots for doping density in MIS capacitors were also shown and the information they gave described. The presentation concluded with a description of a TSB supported project that was investigating the use of this technology to provide smart substrates for use in RFID applications. There was also a proposal under review with the IeMRC for a flagship project to take this work forward.

Following lunch, David Whalley from Loughborough University gave a presentation on his work related to “Polymer Ball Interconnect Technology”. This work had a focus on sub-millimetre sized balls that could be used as solder ball replacements for ball grid array (BGA) applications. This was somewhat different for their more conventional applications in anisotropically conductive adhesives, where the particles were much smaller. The use of polymer balls in BGA applications could provide compliance that could extend the thermal fatigue life and give improved shock resistance. They also helped to control stand-off height and the concept was extendable to smaller device geometries. The approach was said to have been in the public domain since 1997 and there was a commercial product available from Sekisui called MicroPearl. Conpart in Norway were also working in this area. Conpart had a unique technique for giving exceptionally uniform particle size (Cv ∼3 per cent), which was know as the Ugelstad process. The major performance characteristics that needed to be considered were then discussed. Thermal conductivity of polymer cores was much lower than that of typical metals and thus the thermal resistance was significantly worse. The polymers used were also not electrically conductive and thus attention had to be paid to the metallic coating. This had been studied using 2D FEA modelling. High-frequency performance had also been studied and this had not been found to be significantly adversely affected. Soft solders were known to be subject to electromigration, particularly at high temperatures and modelling work had been carried out on current densities likely to be encountered when using the polymer ball approach. The results suggested that the maximum currents allowable would be smaller for polymer balls compared to solder balls. However, by optimising the design of the pad and ball interfaces, significant improvements could be achieved. Data were also shown which confirmed positive improvements in thermo-mechanical fatigue performance. Impact and drop performance should also be enhanced by 30 to 50 per cent, especially compared to the typical performance achieved with lead-free solders. There were still some questions to be answered, such as the optimum metallisation and how thick it should be on the polymer ball. It was also not yet clear whether there was a need to use underfill with the polymer balls. Further work involving the whole supply chain was required to take the work forward towards industrial implementation but the results to date had been extremely positive.

Andrew Evans from CAFMaD, Aberystwyth, then gave a presentation on “Spectroscopy and Imaging of Optoelectronic Materials”. A unique facility had been established for monitoring and characterising organic molecular films. There were four areas of organic electronics research underway and these included organic photovoltaics and polymer films. There was also work on diamond electronics which was investigating high-temperature diodes and transfer-doped FETs. Andrew then discussed approaches to the optimisation of device structures via a better understanding of the fundamental science. An example was then given of the use of X-rays to provide information about the properties of deposited films via the collection of emitted electrons, IR-UV and X-rays. Work was also reported on the properties of diamond organic interfaces, which included the deposition of fullerenes onto diamond. The work had resulted in the development of new transfer dopants for diamond transistors.

Mike Lebby, CEO of the Optoelectronics Industry Development Association (USA), gave the final presentation of the workshop and this was called “Is this the era of green photonics?” Mike began by giving an overview of the use of optoelectronics in green technology such as renewable energy sources. Interestingly, Asia had 81 per cent of the $356 billion global market in 2008 and the market was predicted to grow significantly in the future, with green applications taking an increasing share. Mike introduced the concept of moving from local area networks to personal area networks or even body area networks. Another big issue was the energy consumption of networks and this was something that was not really considered seriously today. As the networks grow, energy consumption would become increasingly important. Data were also shown to highlight the growth in use of photonic lighting and there were significant energy savings that could be made as this transition took place. Solar cells would continue to become more efficient and they would become greener to produce. Mike then went on to give a comprehensive review of new and evolving applications for photonics devices. There was also a growing need, therefore, for new foundries to produce the devices that would be needed to satisfy these applications.

The presentations from this workshop are available at the IeMRC web site: www.iemrc.org. Further information on the activities of the IeMRC and CaFMAD can be found at the following addresses: www.iemrc.org and www.cafmad.ac.uk, respectively.

Martin Goosey