Nicolas Fahrni

Bio: Nicolas Fahrni is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Resist & Photoresist. The author has an hindex of 4, co-authored 4 publications receiving 1796 citations.

SU-8: a low-cost negative resist for MEMS

Abstract: This paper describes the characterization of a home-made negative photoresist developed by IBM. This resist, called SU-8, can be produced with commercially available materials. Three blends were prepared for this article and some of its optical and mechanical properties are presented. One of its numerous advantages is the broad range of thicknesses which can be obtained in one spin: from 750 nm to with a conventional spin coater. The resist is exposed with a standard UV aligner and has an outstanding aspect ratio near 15 for lines and 10 for trenches. These ratios combined with the electroplating of copper allow the fabrication of highly integrated electromagnetic coils.

High-aspect-ratio, ultrathick, negative-tone near-UV photoresist and its applications for MEMS

Abstract: Detailed investigations of the limits of a new negative-tone near-UV resist (IBM SU-8) have been performed. SU-8 is an epoxy-based resist designed specifically for ultrathick, high-aspect-ratio MEMS-type applications. We have demonstrated that with single-layer coatings, thicknesses of more than 500 μm can be achieved reproducibly. Thicker resist layers can be made by applying multiple coatings, and we have achieved exposures in 1200 μm thick, double-coated SU-8 resist layers. We have found that the aspect ratio for near-UV (400 nm) exposed and developed structures can be greater than 18 and remains constant in the thickness range between 80 and 1200 μm. Vertical sidewall profiles result in good dimensional control over the entire resist thickness. To our knowledge, this is the highest aspect ratio reported for near-UV exposures and the given range of resist thicknesses. These results will open up new possibilities for low-cost LIGA-type processes for MEMS applications. The application potential of SU-8 is demonstrated by several examples of devices and structures fabricated by electroplating and photoplastic techniques. The latter is especially interesting as SU-8 has attractive mechanical properties.

High-aspect-ratio, ultrathick, negative-tone near-uv photoresist for MEMS applications

Abstract: Detailed investigations of the limits of a new negative-tone near-UV resist (IBM SU-8) have been performed. SU-8 is an epoxy-based resist designed specifically for ultrathick, high-aspect-ratio MEMS-type applications. We have demonstrated that with single-layer coatings, thicknesses of more than 500 /spl mu/m can be achieved reproducibly. Thicker resist layers can be made by multiple coatings, and we have achieved exposures in 1200-/spl mu/m-thick, double coated SU-8 resist layers. We have found that the aspect ratio for near-UV (400 nm) exposed and developed structures can be greater than 18 and remains constant in the thickness range between 80 and 1200 /spl mu/m. Vertical sidewall profiles result in good dimensional control over the entire resist thickness. To our knowledge, this is the highest aspect ratio reported for near-UV exposures and resist thicknesses. These results will open up new possibilities for low-cost LIGA-type processes for MEMS applications. In addition, the SU-8 material has interesting mechanical properties which also makes it attractive for photoplastic device fabrication.

Process for fabricating and marking micromechanical components using photolithography and electrodeposition

Abstract: Production of a metal component bearing an imprint comprises: (a) providing a substrate covered with a conductive layer and coated with a photoresist; (b) irradiating the photoresist through a mask, polymerizing it and removing nonirradiated material; (c) applying a thicker layer of photoresist and repeating step (b); (d) depositing a metal layer with a thickness corresponding to the target component by electroforming on the substrate; and (e) separating the metal part from the substrate and removing the photoresist. An Independent claim is also included for production of a metal component bearing an imprint by: (a) a) providing a substrate covered with a conductive layer and coated with a photoresist; (b) irradiating the photoresist through a mask that defines the contours of the component and the trace of a mechanical signature; (c) polymerizing the photoresist and removing nonirradiated material; (d) depositing a metal layer (7) with a thickness corresponding to the target component by electroforming on the substrate; and (e) separating the metal part from the substrate and removing the photoresist.

Micro Total Analysis Systems. 1. Introduction, Theory, and Technology

Abstract: Review

Three-dimensional micro-channel fabrication in polydimethylsiloxane (PDMS) elastomer

Abstract: This paper describes a fabrication technique for building three-dimensional (3-D) micro-channels in polydimethylsiloxane (PDMS) elastomer. The process allows for the stacking of many thin (less than 100-/spl mu/m thick) patterned PDMS layers to realize complex 3-D channel paths. The master for each layer is formed on a silicon wafer using an epoxy-based photoresist (SU 8). PDMS is cast against the master producing molded layers containing channels and openings. To realize thin layers with openings, a sandwich molding configuration was developed that allows precise control of the PDMS thickness. The master wafer is clamped within a sandwich that includes flat aluminum plates, a flexible polyester film layer, a rigid Pyrex wafer, and a rubber sheet. A parametric study is performed on PDMS surface activation in a reactive-ion-etching system and the subsequent methanol treatment for bonding and aligning very thin individual components to a substrate. Low RF power and short treatment times are better than high RF power and long treatment times, respectively, for instant bonding. Layer-to-layer alignment of less then 15 /spl mu/m is achieved with manual alignment techniques that utilize surface tension driven self-alignment methods. A coring procedure is used to realize off-chip fluidic connections via the bottom PDMS layer, allowing the top layer to remain smooth and flat for complete optical access.

Polymer microfabrication methods for microfluidic analytical applications

Abstract: A growing number of microsystem technology (MST) applications, particularly in the field of microfluidics with its applications in the life sciences, have a need for novel fabrication methods which account for substrates other than silicon or glass. We present in this paper an overview of existing polymer microfabrication technologies for microfluidic applications, namely replication methods such as hot embossing, injection molding and casting, and the technologies necessary to fabricate the molding masters. In addition, techniques such as laser ablation and layering techniques are examined. Methods for bonding and dicing of polymer materials, which are necessary for complete systems, are evaluated.

Microneedle devices and methods of manufacture and use thereof

Abstract: Microneedle devices are provided for transport of therapeutic and biological molecules across tissue barriers and for use as microflameholders. In a preferred embodiment for transport across tissue, the microneedles are formed of a biodegradable polymer. Methods of making these devices, which can include hollow and/or porous microneedles, are also provided. A preferred method for making a microneedle includes forming a micromold having sidewalls which define the outer surface of the microneedle, electroplating the sidewalls to form the hollow microneedle, and then removing the micromold from the microneedle. In a preferred method of use, the microneedle device is used to deliver fluid material into or across a biological barrier from one or more chambers in fluid connection with at least one of the microneedles. The device preferably further includes a means for controlling the flow of material through the microneedles. Representative examples of these means include the use of permeable membranes, fracturable impermeable membranes, valves, and pumps.