Microfluidics based on silicon, polymer and all-polymer technologies as an alternative to silicon, glass: a case study for TopSpot printheads

Hochschulschrift

Zusammenfassung: The sample volumes handled in microfluidic devices are typically in the range of micro- to millilitres. This leads to spatially extended structures, which often cannot be manufactured in a cost-effective way by using established silicon/glass technologies. Therefore, microfluidic devices for cost-sensitive diagnostic applications are already realised solely on the basis of polymer materials. So far, there is no established alternative to silicon/glass technologies for the production of large-scale fluidic components with high aspect ratio microstructures and with high demands in terms of mechanical stability.An interesting example of combining such requirements is given by TopSpot printheads for printing of microarrays. The storage of up to 96 different biological samples in reservoirs with a capacity of typically 1 μl to 6 μl requires spatially extended microfluidic structures. At the same time, the 500 μm pitched microarray grid and the requirement to connect each nozzle to the corresponding reservoir by an individual supply channel demand for high integration density. Therefore, the fluidic channels have typical widths of 70 μm to 80 μm, depths of 80 μm to 300 μm – i.e. an aspect ratio of up to 4.3 – and the distance between two neighbouring channels in the nozzle array is only 55 μm to 180 μm. Currently, the fabrication process for TopSpot printheads is based on 100mm wafers and utilises deep reactive ion etching (DRIE) of silicon and anodic bonding of the silicon to semi-finished glass wafers with fluidic inlets and outlets. These established technologies enable outstanding printing performance and long lifetime of the printheads but are related to high manufacturing costs, long lead times and are only little responsive in terms of application specific designs.The scientific challenge of this work is therefore to explore alternative material combinations and processes for realisation of the TopSpot printheads. A starting point is the analysis of the current fabrication process with respect to a set of criteria. The focus of the thesis is the reduction of the manufacturing costs and production lead time without any compromise in terms of performance and lifetime compared to the established silicon/glass printheads.A common way to reduce manufacturing costs is the reduction of the device dimensions and the transition to a larger wafer size. The underlying principle is that most fabrication processes take a fixed amount of time and do not depend on the size of the wafer or the number of devices on it. It was found that for production volumes of 10 to 100 printheads, the reduction of the printhead size from 655 mm2 to 310 mm2 and the transition to 150mm wafers leads to a cost reduction of 20 to 50 % (depending on the production volume and considering a higher cost fraction due to size dependent processes and material purchasing). The expected lead time is not affected by the scaling and remains 42 days, with 7 days due to rework-related activities and a relatively high uncertainty of 24 days.The present work describes improvements that go beyond optimisation by scaling the established technology. Two alternative fabrication approaches were investigated and are described in more detail below. Both approaches were quantitatively evaluated with the analytic hierarchy process (AHP), a multi-criteria decision-making method. The AHP was used to measure the significance of the criteria performance, lead time, lifetime and costs and to identify the most appropriate technology with respect to these criteria.The first approach involves hybrid printheads where the semi-finished glass wa-fers are replaced by polymer layers. The hybrid printheads consist of a silicon layer with microfluidic structures, a layer of dry film resist allowing for selective microchannel sealing and a conventionally machined polymer layer with fluidic reservoirs as an interface to laboratory equipment such as pipettes and dispensing robots. The functionality of the hybrid printheads was determined experimentally and found to be well comparable to the silicon/glass printheads. For production volumes of 10 to 100 printheads, the cost reduction was calculated to be close to 60 % without changing the printhead or wafer size. The major contributors to this improvement are the lower material costs (up to 43 % reduction) and shorter process times (up to 52 % reduction) as well as the increase of the manufacturing yield from 60 % to 70 %. With the hybrid printheads, the expected lead time can be reduced from 42 to 28 days and the lead time for rework from 7 to 4 days. The uncertainty in lead time prediction is only 6 days, thus by a factor of 4 smaller compared to the silicon/glass printheads.The second approach enables the production of all-polymer printheads by means of repeated lamination-exposure-development cycles of a dry film resist on a semi-finished polymer substrate with fluidic access holes. In this way, all microfluidic components are patterned directly on the printhead interface, thus eliminating the need of assembling discrete components such as channels, nozzles and reservoirs. Major advantages of the all-polymer printheads are the non-use of glass and respectively the short-term availability of all semi-finished components (as long as silicon-based processes are considered available) as well as their lower manufacturing costs and short lead times. This second technological approach allows for a cost reduction close to 80 % and lead time reduction from 42 to 8 days. The manufacturing feasibility and functionality of the all-polymer printheads were demonstrated by experimental results, however, the printing performance was insufficient to compete with the silicon/glass and the hybrid printheads. Major drawbacks are inferior printing accuracy, short lifetime and higher risk of cross-talk and carryover contamination

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Albert-Ludwigs-Universität Freiburg, Dissertation, 2015

Klassifikation und Themen

• Klassifikation: Industrielle und handwerkliche Fertigung
• Schlagwort: Mikrofluidik ; MEMS ; Bio-MEMS

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2015
• Urheber: Kalkandjiev, Kiril
• Beteiligte Personen und Organisationen: Zengerle, Roland

Weitere Informationen

• DOI: 10.6094/UNIFR/10125
• URN: urn:nbn:de:bsz:25-freidok-101257
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 14.08.2025, 10:58 MESZ