MicroTech-2009 overview

Microelectronics International

ISSN: 1356-5362

Article publication date: 31 July 2009



Sinnadurai, N. (2009), "MicroTech-2009 overview", Microelectronics International, Vol. 26 No. 3. https://doi.org/10.1108/mi.2009.21826cac.002



Emerald Group Publishing Limited

Copyright © 2009, Emerald Group Publishing Limited

MicroTech-2009 overview

Article Type: Conferences and exhibitions From: Microelectronics International, Volume 26, Issue 3

MicroTech-2009, focused on BioSensors and MEMS packaging, was held on 2-3 March at the elegant Edinburgh Conference Centre of Heriot-Watt University. MicroTech-2009 was financially cosponsored by Heriot-Watt University and IeMRC and technically cosponsored by IEEE-CPMT UKRI, all of whom were strongly represented at the event. Some 75 delegates attended from around Europe (Figure 1).

The event was organised differently from previous MicroTech events in that the first day provided tutorials on the basics and applications of the enabling LTCC technologies and an information session on NEXUS – the pan-European micro and nano-systems network.

 Figure 1 Some of the delegates to the BioSensors and MEMS packaging seminar

Figure 1 Some of the delegates to the BioSensors and MEMS packaging seminar

The tutorials were very thorough, with Marc Desmulliez providing not only the capabilities and processes of LTCC but also providing an escorted tour of the labs to show actual processing of LTCC. Then, Franz Bechtold, the founder of Via Electronics, explaining the custom solutions that have been applied to achieve excellent performance in a range of applications for Microsystems.

Andrew Richardson, the Vice-Chairman of NEXUS gave an in-depth insight to the function, operation and opportunity for participation in NEXUS. He explained that NEXUS was set up to service the European microsystems component community – transferring research to industrial users – by organising networking events and publishing independent market studies and roadmaps to help plan future research and set industrial strategies as well as monitor effectiveness of current programmes within the EU. Membership of NEXUS for active players is free.

Socially, the delegates had a very pleasant break at dinner hosted by CoorsTek at Deacon Brodies Tavern in the heart of the Royal Mile in Edinburgh. This was the very palatable occasion to savour the traditional Haggis and sip the exotic golden liquor – the unbeatable malt whisky.

Erik Jung of Fraunhofer IZM, Berlin described comprehensively a very effective platform for cell-cell interaction investigation employing biocompatible/non-cytotoxic material multi-layer structures. He elaborated the process flow to create PCB-like multi-layer structures with biocompatible/non-cytotoxic material been defined by using vacuum lamination, structured Al etching and laser direct structuring. Both small structures (50 μm holes, 15 μm insulative cuts as well as 350 μm holes, 150 μm pitched routing structures) had been created by combining the used processes to a defined flow. The stack lamination process was controlled to realize 1:1 aspect ratio metal:dielectric structures down to 15 μm layer:layer thickness. Hydrophobizing/hydrophilizing surfactants had been evaluated to selectively modify the exposed surfaces of the structure. A membrane attachment process had been realized, allowing the nourishment of cells confined in the microwells and simultaneously removing their metabolites.

Research and development of accelerometers in heart bypass surgery was undertaken by collaboration between Institute of Microsystems Technology, Tonsberg, Norway, Microsystems Engineering Centre, Edinburgh, Scotland, of The Interventional Centre, Rikshospitalet, Oslo. Craig Lowrie described progress with the design, simulation, fabrication and packaging of some monolithic micro-machined three-axis accelerometers utilising silicon-on-insulator technology to realise Piezo-resistive sensing. The resultant designs incorporate wrapped masses to achieve theoretical matching in-plane and out-of-plane sensitivity, tapered beams to manipulate the stress distribution for out-of-plane acceleration, and tabs for packaging purposes. The packaging was achieved using low-temperature BCB-bonded glass caps. The sensors are to be used in the medical study of measuring heart wall motion to detect problems such as cardiac infarction which can be a complication following heart bypass surgery.

The INEX institute at the University of Newcastle has fabricated catheterised sensing integrated on flexible film. Tony Corless described microscale flexible circuits which offer new ways of thinking and fabrication directly on film which is advantageous for simple structures. For more complex structures wafer-based fabrication and release is the next step.

Kaiser of Reinhardt Microtech described flexible thin film multi-layer substrates for medical sensors and actuators. The Reinhardt materials had important benefits such as the use of different carrier/insulator polyimide material and a fine line patterning capability utilising a range of metallisation materials suited to biocompatibility. The technology was especially suitable for medical applications such as implants. Sophisticated products were illustrated including actual applications in retinal implants. The technology evidently has many additional applications such as electrodes or stimulation devices.

Bernassau and Demore of the Institute of Medical Science and Technology, Dundee spoke on the practicalities of progress towards wafer-scale fabrication of ultrasound arrays for real-time high-resolution biomedical imaging. Specifically, they described a novel approach for fabricating transducer arrays working at 50 MHz and above through the characterisation of an epoxy for elevated temperature curing and improved resistance to heating and acetone. Such properties of the epoxy allowed the patterning of the electrodes by photolithography. The optimised temperature was found to be 100°C. They also described the need for specific surface preparation, where smooth and planar surfaces of composites have been obtained by lapping with a glass plate combined with Al2O3 slurry. They then described how they achieved a photolithography solution for defining precisely high-frequency array elements directly on composites and obtained good electrode quality and electrical impedance.

A substitute speaker spoke on behalf of John Sweet of loadpoint on issues in manufacturing of wafer-scale three-dimensional (3D) piezoelectric-on-silicon structure, essentially giving a roadmap insight on what may be achieved in the future.

Production issues again featured in the commercialisation of microfluidic devices in the work undertaken by Patrick Webb and his team at the School of Manufacturing Engineering at Loughborough. They proved that low-frequency inductive heating was effective in bonding between polymer and metal/polymer. Thick layers (50-100 nm) reached temperatures above 50°C while small nickel foils reached temperatures above 220°C. Aluminium was found to be an effective susceptor material, which enabled the building up of layered microfluidic structures. Samples withstood 590 kPa without failure. These developments could be used for applications such as: medical point of care, consumer medical, companion animal health, environmental monitoring. Webb et al. painted the typical scenario for genesis of a diagnostic device that an SME wishing to exploit lab based assay IP by creating a device may not have expertise in microfluidics design or manufacture. Since the market is at an early stage, the capabilities are highly fragmented and there is no one stop shop for all implementation options.

Supporting the theme of manufacturing quality of wirebonding for MEMS was described as the PIQC by Graham Biddulph of Accelonix. Evidently the PiQC© detected: misplaced bonds on pads, scratches, extraneous material and over deformation. PIQC generated five significant parameters and the signals processed give the “Quality Index” which gave 100 per cent indication of failures The system built up its own learning data from which reference values gave metrics of bonding performance.

The latest developments technology and practical solutions by the Implanted Devices Group, UCL, following their outstanding work on enabling improvements in the disabled commenced over two decades ago was described by Anne Vanhoestenberghe. The challenges for long-term implantation in humans had to take account of the hostile chemical and climatic environment in which the electronics has to be contained. Vanhoestenberghe dealt with: biocompatibility such as tissue reaction and flexibility, electrical such as functional consistency and low-leakage currents and finally fitness for long life – typically 20 years – by avoidance of corrosion or degradation by the use of appropriate silicones or by hermeticity. We were shown impressive samples of silicone implants that had survived more than 12 years with no corrosion or degradation. Because of the long-term successes, the team has established “gold standards” of good products against their stress test survival. This enables straightforward reliability evaluation by comparison of new technologies against the gold standards.

Suzanne Millar had investigated leak-detection methods for MEMS packaging hermeticity. She dealt with some of the older MIL-Std-883. It is very surprising that some MEMS customers and manufacturers still cite this long-discredited defunct and very inaccurate method. Millar then went on to deal with the hermeticity requirements of MEMS packages at the very low detection level of 10−6 bar cm3 s−1. Millar described a number of alternatives such as Q-factor testing, FTIR, Raman Spectroscopy and in situ test structures. It became clear that because of the wide variety of device types, packaging materials and techniques used in MEMS manufacturing, a portfolio of hermeticity test methods is required. Greatest sensitivity was likely to be achieved using in situ testing although due to problems concerning space inside the cavity this may not always be a viable option. For that reason, further external test methods are necessary that are sensitive enough for MEMS applications.

Cavity encapsulation of MEMS was also explored by Changhai Wang packaging using polymer bonding rings with an embedded barrier for high hermeticity. The method is suitable for wafer level MEMS packaging. A micro cavity was produced between two substrates to house a MEMS device using a polymer bonding ring with an inserted barrier for hermetic packaging. The method retained the low cost, low temperature bonding advantages of the polymer materials but overcame the disadvantage of non-hermetic sealing associated with the purely polymer materials (Figure 2).

 Figure 2 Speakers at the MicroTech-2009 BioSensors and MEMS packaging

Figure 2 Speakers at the MicroTech-2009 BioSensors and MEMS packaging seminar

The poster papers maintained the high quality of the event.

Yufei Liu continued the theme of polymer bonding for MEMS packaging but this time using laser assistance. Fast bonding was achieved using localised laser heating effect to reduce the thermal load on the MEMS device and hence the thermally induced stress alleviating the effect of temperature on functional failure of the devices. Because of the localised nature of the temperature rise, it had been difficult to monitor the temperature change precisely during the bonding process using conventional methods. So Liu developed thin film miniature temperature sensor arrays for in situ process monitoring. Distributed temperature sensors were fabricated on both silicon and glass substrates and used successfully to monitor the temperature rise and distribution within the package assembly in the bonding process.

 Figure 3 Delegates checking out the poster presentations

Figure 3 Delegates checking out the poster presentations

Lopez-Villarroya et al. described a novel microfluidic sensing device based on waveguide cavity filters for the characterisation, detection of cells in solution and chemical substances in micro-litre volumes. The sensor consisted of an E-plane waveguide filter within a micromachined microfluidic channel and with the option to be designed for different frequency regimes to improve the sensitivity. The sensor was proposed for fabrication in different manufacturing platforms. An initial prototype with a 100μm micromachined channel embedded within an X-band E-plane waveguide had been fabricated and tested (Figure 3).

Nihal SinnaduraiGeneral ChairMicroTech-2009

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