LARGE-AREA FABRICATION OF SUB-μm PDMS THROUGH-HOLE
MEMBRANES
H. Le-The
1, M.A. Palma do Carmo
1, M.W. van der Helm
1, J.G. Bomer
1, L.I. Segerink
1,
A. van den Berg
1, and J.C.T. Eijkel
11
BIOS Lab on a Chip, MESA+ Institute for Nanotechnology, University of Twente,
THE NETHERLANDS
ABSTRACT
We report and demonstrate a robust and high-yield fabrication method that allows to pattern ultrathin (sub-μm) and free-standing polydimethylsiloxane (PDMS) membranes with through-holes over large-areas. KEYWORDS: Through-hole PDMS Membrane, Free-standing PDMS Nanomembrane
INTRODUCTION
Free-standing PDMS through-hole membranes have been studied extensively in biomedical applications including biomolecular filters, and organs-on-chips [1,2]. However, fabrication of such membranes at an ultrathin thickness (sub-μm) over large-footprints is still challenging. Recently, Kang et al. reported a compelling technique that allows large-scale patterning of ultrathin and free-standing PDMS nanomembranes [3]. Further improving this technique using two photoresist layers (one patterned layer on another sacrificial layer) and plasma-etching technique, we demonstrate an enabling method for high-yield fabrication of ultrathin and free-standing PDMS through-hole membranes over large-areas.
EXPERIMENTAL
Figure 1 shows the process for fabricating free-standing PDMS through-hole membranes. The sputtered Titanium (Ti) layer was used to prevent the intermixing of the first positive photoresist (PR) layer with the second PR layer. Moreover, at this sputtered thickness a discontinuous Ti layer was obtained, allowing dissolution of the first PR-layer in acetone by diffusion.
Figure 1: Fabrication process of free-standing PDMS through-hole membranes. (a) A PR layer (~1.7 μm) was spin-coated on a silicon (Si) wafer, and a Ti layer (~3 nm) was sputtered on the coated PR layer, using a DC sputtering system (in-house built T’COathy system, NanoLab) at a pressure of 6.6×10-3 mbar, and 200 W. (b-c) An array of microcolumns (~1.5 μm diameter) was patterned into the second PR layer (~1.7 μm), using conventional photolithography processes (see Figure 2a). (d) A solution of PDMS prepolymer with curing agent (10:1) was diluted with hexane at a 1:10 (PDMS:hexane) ratio, and then spin-coated on the fabricated PR microcolumn array at 6000 rpm for 3 min (see Figure 2b). (e) After baking the Si-wafer on a hot-plate at 80℃ for at least 3 h, a plasma-etching process of the PDMS membrane (~1.6 μm thickness) was conducted in a reactive-ion etching system (in-house built TEtske system) at 47 sccm SF6, 17 sccm O2, 50 mTorr, and 100 W to open the through-holes (see Figures 3a and 3b). (f) A PDMS ring (~6 cm diameter) as a support was glued onto the top-surface of the membrane using PDMS solution, and followed by baking on a hot-plate at 80℃ for at least 2 h. Acetone was spread over the membrane surface to partially dissolve the photoresist structures, enabling the smooth detachment of the membrane with the PDMS ring in methanol (see Figure 4).
RESULTS AND DISCUSSION
Figure 5 shows top-view SEM and optical images of a free-standing PDMS membrane with through-holes (~1.5 μm diameter), indicating a nice release of the membrane without breaking. The black holes in the close-up SEM image, and the bright spots in the close-up optical image due to the light transmission again indicate a through-hole membrane.
978-0-692-94183-6/µTAS 2017/$20©17CBMS-0001 375 21st International Conference on Miniaturized Systems for Chemistry and Life Sciences October 22-26, 2017, Savannah, Georgia, USA
Figure 2: SEM images of (a) photoresist columns (PR2) supported on another photoresist layer (PR1), and (b) PDMS-coated resist columns. Scale bars represent 5 μm.
Figure 3: SEM image of (a) a peel off PDMS membrane (970 nm thickness) after plasma etching for 30 s, and (b) a PDMS membrane (706 nm thickness) after plasma etching for 1 min. The plasma etching was conducted in 47 sccm SF6, 17 sccm O2,
50 mTorr, and 100 W. Scale bar represents 10 μm.
Figure 4: Optical image of a free-standing PDMS through-hole membrane supported on a PDMS ring with an inner diameter of approximately 6 cm.
Figure 5: Top-view (a) SEM and (b) optical images (scale bar: 50 μm) with inserted close-up images (scale bar: 5 μm) of a free-standing PDMS membrane (~1 μm thickness) with through-holes (~1.5 μm diameter). The black holes in the SEM image, and the bright spots in the optical image due to the light transmission indicated a through-hole membrane. Scale bars represent 5 μm.
CONCLUSION
In summary, we report and demonstrate a robust method for fabricating sub-μm and free-standing PDMS through-hole membranes over large-areas. Moreover, this method is suitable for high-yield production at low-cost. Next, we will test this membrane for organ-on-chip applications [4].
ACKNOWLEDGEMENTS
This work was supported by the Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC), and the Netherlands Organisation for Scientific Research (NWO) Gravitation programme funded by the Ministry of Education, Culture and Science of the government of the Netherlands.
REFERENCES
[1] D. Huh, H. J. Kim, J. P. Fraser, D. E. Shea, M. Khan, A. Bahinski, G. A. Hamilton, D. E. Ingber, Nat.
Protoc., 8, 2135 (2013).
[2] H. J. Kim, D. Huh, G. Hamilton, D. E. Ingber, Lab Chip, 12, 2165 (2012).
[3] E. Kang, J. Ryoo, G. S. Jeong, Y. Y. Choi, S. M. Jeong, J. Ju, S. Chung, S. Takayama, S. H. Lee, Adv.
Mater., 25, 2167 (2013).
[4] M. W. van der Helm, M. Odijk, J. P. Frimat, A. D. van der Meer, J. C. T. Eijkel, A. van den Berg, L. I. Segerink, Biosens. Bioelectron., 85, 924 (2016).
CONTACT
* H. Le-The; phone: +31-620-310-132; h.lethe@utwente.nl (a)
(b)
