Purssell, C. P. (2012) Materials and methods for microstereolithography. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Microlithography, Microelectromechanical systems, Microfabrication
Official Date:	June 2012
Dates:	Date Event June 2012 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Covington, James A., 1973- ; Billson, D. R.
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC)
Extent:	xxi, 273 leaves : illustrations, charts.
Language:	eng

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