The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Fabrication of SU-8 Microstructures for Analytical Microfluidic Applications

Santeri Tuomikoski

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Large Seminar Hall of Micronova at Helsinki University of Technology (Espoo, Finland) on the 2nd of February, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-8607-2)   [1130 KB]
Dissertation is also available in print (ISBN 978-951-22-8606-5)

Abstract

Miniaturization of analytical devices has been an ongoing trend to improve performance of analytical tools. These systems have been microfabricated originally of silicon and glass, but polymers have become increasingly popular as alternative materials. Polymers are mostly used because the material costs are lower and fabrication processes are easier. However, those facts depend heavily on the fabrication method and particular polymer. In this thesis the usability of epoxy-polymer SU-8 has been studied for analytical microfluidic applications. Lithographically defined SU-8 can provide simpler fabrication processes as comparison to silicon and glass fabrication. In this thesis processes for microdevice fabrication of SU-8 are studied and developed. For many devices the proper microchannel enclosure method becomes the most critical fabrication step. Therefore adhesive bonding using SU-8 has been studied extensively.

A widely applicable microchannel fabrication process has been developed as a combination of lithographic patterning of SU-8 and ultraviolet-cured adhesive bonding. This process enables high yield of microfluidic devices with wide range of channel dimensions both laterally and cross-sectionally. Furthermore, multilevel structures are possible, inlet fabrication is easy and alignment of inlets and other structures like electrodes can be done fully lithographically. Hence the SU-8 fabrication process avoids many limitations of the earlier fluidic chip fabrication processes.

SU-8 microchannels have been used for electrophoretic applications for the very first time. Electroosmotic flow (EOF) mobility was measured in the channels and also first electrophoretic separations were made. SU-8 promises good properties for such applications, because the EOF mobility was higher than with most other untreated polymers. Solid phase extraction was integrated to electrophoresis chips to enable sample purification or concentration before the electrophoretic separation. This was realized by applying high aspect ratio pillars and multilevel SU-8 structures. Detection from the chip can be done by fluorescence detection through the SU-8 cover. To improve detection sensitivity mass spectrometric detection was also studied from the chips using electrospray ionization (ESI) mass spectrometry. SU-8 provided good material properties for the ESI-analysis. Furthermore, SU-8 enables accurate tip fabrication that is difficult with most other microfabrication methods.

This thesis consists of an overview and of the following 7 publications:

  1. Tuomikoski, S., Franssila, S., Wafer-level bonding of MEMS structures with SU-8 epoxy photoresist, Physica Scripta, T114, (2004), 223-226.
  2. Tuomikoski, S., Franssila, S., Free-standing SU-8 microfluidic chips by adhesive bonding and release etching, Sensors and Actuators A, 120, (2005), 2, 408-415. © 2005 Elsevier Science. By permission.
  3. Sikanen, T., Tuomikoski, S., Ketola, R., Kostiainen, R., Franssila, S., Kotiaho, T., Characterization of SU-8 for electrokinetic microfluidic applications, Lab on a Chip, 5, (2005), 888-896.
  4. Sikanen, T., Korpisalo, I., Tuomikoski, S., Ketola, R., Kostiainen, R., Franssila, S., Kotiaho, T., Characterization of SU-8 microchannels for electrophoretic separations, 9th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2005), Boston, USA, 1349-1351.
  5. Tuomikoski, S., Virkkala, N., Rovio, S., Hokkanen, A., Sirén, H., Franssila, S., Design and fabrication of integrated solid-phase extraction-zone electrophoresis microchip, Journal of Chromatography A, 1111, (2006), 258-266. © 2006 Elsevier Science. By permission.
  6. Tuomikoski, S., Sikanen, T., Ketola, R., Kostiainen, R., Kotiaho, T., Franssila, S., Fabrication of enclosed SU-8 tips for electrospray ionization-mass spectrometry, Electrophoresis, 26, (2005), 4691-4702.
  7. Tuomikoski, S., Sikanen, T., Ketola, R., Kostiainen, R., Kotiaho, T., Franssila, S., Fabrication and optimization of enclosed SU-8 tip structures for electrospray ionization mass spectrometry, 9th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2005), Boston, USA, 982-984.

Keywords: SU-8, microfluidics, microfabrication, adhesive bonding, mass spectrometry, electrophoresis

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2007 Helsinki University of Technology

Last update 2011-05-26