In this paper, soft-lithographic methods for the fabrication of 3D-DEP devices equipped with high- aspect-ratio pillars, combined with a PDMS micro-fluidic channel replicated from a SU-8 mold fabricated by PBW Introduction
Experiments PBW of SU-8 layer on silica for patterning pillar arrays and a mold for a micro-fluidic channel
Soft ithography of micro-fluidic channel by the SU-8 mold
Sealing the pillar arrays on silica with the PDMS, where the silica substrate with pillar arrays is bonded to PDMS with a micro-fluidic channel
Results and discussion Fig. 3a shows a SEM image of the part of pillar arrays with an area of 1.0 mm 80 µ m by PBW onto a 15 µ m thick SU- 8 on a silica substrate High-aspect-ratio pillars (rectangular of 2.5x6.8 µ m in shape and 13 µ m in height) were observed with smooth and vertical surface, as shown in Fig. 3b.
Fig. 4a shows the SEM image of a SU-8 mold with 200 µ m in width and 2.0 mm in length and 20 µ m in height. Following the process illustrated in Fig. 1b, the pattern of the SU-8 mold was successfully transferred to PDMS, as shown in Fig. 4b.
From an optical microscope image in Fig. 5a Fig. 5b shows a photograph of the DEP device with tubing at inlet and outlet ports. Thanks to the plasma treatment, the tight sealing was achieved and no leakage was observed.
Fig. 6a shows a SEM image of a SU-8 mold with arrays of holes with rectangle of 7.0 X 5.3 µm^ 2 in shape and 12 µm in depth. As shown in Fig. 6b, the holes were successfully replicated to PDMS as arrays of pillars.
important to lower the adhesion force between the SU-8 mold and PDMS and alignment of vertical direction during separation to avoid fracture of PDMS replica,
Conclusions A soft lithography technique combined with PBW was successfully applied to the fabrication of the 3D-DEP device equipped with high- aspect-ratio pillar arrays in micro-fluidic channel.
The most critical part of the process is pattern transfer of the high-aspect pillar from the SU-8 mold to PDMS. Replication of relatively low-aspect-ratio pillar arrays was successful. Trials of successful replication of both pillar arrays and a micro-fluidic channel are underway for DEP devices with more complex structures.