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Title: Materials and methods for microstereolithography
Author: Purssell, C. P.
ISNI:       0000 0004 2739 7642
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2012
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There is an increasing requirement to fabricate ever smaller components and microdevices and incorporate them within all aspects of our lives. From a Wii controller to a car airbag, micro-technology is employed in a huge spectrum of applications. Within process control and sample analysis, micro-components are making a significant impact, driven by the desire to use smaller volumes, lower concentrations, less reagent, or simply to make the process quicker or cheaper. Currently, methods of fabrication for such devices are based predominantly on silicon processing techniques. While these techniques are suitable for mass manufacture / high volume applications, there are a number of disadvantages for situations requiring lower volumes or where the end system is continually evolving – such as for research applications. The primary drawbacks are cost, turnaround time and the requirement for expensive processing facilities. However, for these situations, additive layer manufacture presents huge promise as an alternative fabrication technology. The field of additive layer manufacture has advanced greatly since its inception 25 years ago. While such technologies are still primarily focused on the field of rapid prototyping of purely mechanical structures, it is clear that their full potential is yet to be realised. This is particularly the case for stereolithography and microstereolithography, the latter of which provides the capability to create complex, true 3D structures (as opposed to pseudo 3D/extruded 2D of silicon techniques), measureable on the micron scale. This thesis shows that microstereolithography has the potential to become an alternative fabrication method for functional micro-devices and structures. This is due to the simplicity of its single-step fabrication process and the significant time/cost savings it presents. Therefore, making it an affordable technique for low volume production where a fast turnaround is required. However, the lack of functional materials compatible with microstereolithography, and hence the lack of examples of the technology being used to produce active components, currently limits it in this respect. This project therefore focused on exploring the possibilities of using microstereolithography as an alternative to traditional silicon based techniques for the direct fabrication of functional micro-devices and sensors. This was achieved through the development of a number of microstereolithography compatible, novel materials, methods and applications. Here, presented for the first time are both conductive and magnetic composite photopolymers compatible with microstereolithography technology. The materials were developed with the use of a custom built, constrained surface system using a parallel projection method. The system used LED technology as a novel exposure source, tuned to the developed materials in an attempt to gain extra control over the curing process and hence achieve higher quality components. These materials were characterised and then used to fabricate exemplar sensing devices using microstereolithography – a method not previously used for creating such devices. Microfluidic flow sensing devices were used to demonstrate the practical application of the magnetic material. One of which, a lab-on-chip type device, was demonstrated to have a working range of 5 to 70 ml/min when tested with a liquid medium. Similarly, a practical application of the conductive material was shown through the fabrication of MSL-printed conductometirc vapour sensors. The sensors showed favourable characteristics working in range of humidites (up to 50% RH) and temperatures (up to 70°C). The sensors also demonstrated a degree of selectivity to different analyte vapours. Finally, the technology was demonstrated as a feasible method of fabricating ultrasonic beam forming apparatus. Acoustic testing of a range of materials also suggested that the composite metal materials could be used to further improve performance. The novel materials and techniques investigated, along with the exemplar devices produced, demonstrate further abilities and a wider range of applications than has been demonstrated with this technology to date. It is hoped that this research will lead to wider use of the technology and encourage further advances in the field of microstereolithography.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering