This paper presents a novel fabrication process for a tapered hollow metallic microneedle array using backside exposure of SU-8, and analytic solutions of critical buckling of a tapered hollow microneedle. An SU-8 mesa was formed on a Pyrex glass substrate and another SU-8 layer, which was spun on top of the SU-8 mesa, was exposed through the backside of the glass substrate. An array of SU-8 tapered pillar structures, with angles in the range of 3.1 •-5 • , was formed on top of the SU-8 mesa. Conformal electrodeposition of metal was carried out followed by a mechanical polishing using a planarizing polymeric layer. All organic layers were then removed to create a metallic hollow microneedle array with a fluidic reservoir on the backside. Both 200 µm and 400 µm tall, 10 by 10 arrays of metallic microneedles with inner diameters of the tip in the range of 33.6-101 µm and wall thickness of 10-20 µm were fabricated. Analytic solutions of the critical buckling of arbitrary-angled truncated cone-shaped columns are also presented. It was found that a single 400 µm tall hollow cylindrical microneedle made of electroplated nickel with a wall thickness of 20 µm, a tapered angle of 3.08 • and a tip inner diameter of 33.6 µm has a critical buckling force of 1.8 N. This analytic solution can be used for square or rectangular cross-sectioned column structures with proper modifications.
We present a novel microfabrication method for a tapered hollow metallic microneedle array and its complete microfluidic packaging for drug delivery and body fluid sampling applications. Backside exposure of SU-8 through a UV transparent substrate was investigated as a means of fabricating a dense array of tall (up to 400 lm) uniformly tapered SU-8 pillar structures with angles in the range of 3.1-5°on top of the SU-8 mesa. Conformal electroplating of metals on top of the array of the tapered SU-8 pillars, lapping of the tip of the metallic microneedles with planarizing polymer, and removal of the SU-8 sacrificial layers resulted in an array of tapered hollow metallic microneedles with a fluidic reservoir on the backside. A microfluidic interconnector assembly was designed and fabricated using SU-8 and conventionally machined PMMA in a way that it has a male interconnector, which directly fits into the fluidic reservoir of the microneedle array at one end and the other male interconnector, which provides fluidic interconnection to external devices at the other end. The fluid flow rate was measured and it showed 0.69 lL/s. per microneedle when the pressure of 6.89 KPa (1 psi) was applied.
This paper presents a novel pattern transfer process of LIGA and UV-LIGA MEMS onto CMOS chips using polydimethylsiloxane (PDMS) replication and electroplating-based post-IC integration techniques. An array of cylindrical posts was fabricated by the standard LIGA process and an inverse replica was made using a PDMS replication technique. The replicated PDMS mold was used to transfer the LIGA MEMS onto a CMOS chip using electroplating. For the pattern transfer of UV-LIGA MEMS onto CMOS chips, double-layered circular spiral inductors were fabricated using the UV-LIGA technique as metallic master molds. Inverse replicas of the inductors were built in PDMS as double-layered PDMS electroplating mold (PEM). This PEM was aligned and attached onto the chips, and electroplating was performed to transfer the metallic UV-LIGA MEMS inductors onto the chips. The transferred inductors showed a self-resonant frequency of 7.5 GHz, an inductance of 2.11 nH, and a Q-factor of 78.9 at 0.6 GHz.
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