Polymerization optimization of SU-8 photoresist and its applications in microfluidic systems and MEMS

Abstract

In this paper, SU-8 EPON-based photoresist (PR) polymerization optimization and its possible microfluidic and MEMS applications are reported. First, the optimization results of SU-8 under UV lithography are reported. The parameters which could have an influence on the lithography quality were chosen and optimized by a three-level, L9 orthogonal array of the Taguchi method. By optimization, the optimal parameter range and the weighted per cent of a parameter on the final results were determined. For SU-8-5 and SU-8-50, many microstructures with thicknesses of more than 100 and 500 µm and aspect ratios of more than 20 and 50 were obtained with high resolution. The optimization results show that the prebake time plays the key role in the quality, which is different from the previously published results. With the optimization results obtained, some possible applications of SU-8 were developed and demonstrated. These applications included using SU-8 as a structural material for a microfluidic system, as a micromold for electroplating, as a master for plastic hot-embossing, and even as a mask for some wet-etching processes.

Direct hot embossing of microelements by means of photostructurable polyimide

“…By means of nanoindentation experiments at room temperature, we have obtained a young's modulus of 4.19 GPa and a surface nanohardness of 415.06 MPa for the polyimide material used in this work that is maintained up to glass transition of the polyimide (300°C). In comparison, SU-8 photoresists that were used for direct hot embossing, 7,8 have a lower glass transition temperature (200°C) and young's modulus (2.0 GPa) as reported by the SU-8 suppliers. Compared to SU-8, polyimide possesses longer polymer chains, which explains its higher thermomechanical stability and compromises, however, the quality of patterning (straightness and smoothness of side walls of patterns) with photolithography.…”

“…On the other hand, further processing after photoresist patterning adds to the complexity of the manufacturing process in large-scale productions. There have been few, if any, thriving attempts to directly emboss polymers by means of bare photoresists, 7,8 and in particular polyimidebased photoresists. Here, we completely eliminate the silicone replications, and reinvent the use of photostructurable polyimide for direct hot embossing.…”

Integrated Lithographic Molding for Microneedle-Based Devices

“…Chuang et al further developed the technique to generate stacked microfluidic components [26]. Among other recent publications, Jackman et al [27], who demonstrated on-line UV detection within a microfluidic system employing SU-8, confirm the importance of SU-8 processes for integrated microfluidic analytical devices [28], [29]. These examples show a strong trend toward the manufacture of devices of complex integrated functionality applying established technological routes of MEMS fabrication instead of moving to alternative routes, for example, polymer injection molding in combination with laser ablation, which was demonstrated for the fabrication of conical hollow microneedles by Trichur et al [30].…”

Flexible free-standing SU-8 microfluidic impedance spectroscopy sensor for 3-D molded interconnect devices application

“…A variety of wafer-based SU-8 microfluidic structures have already been published (Lin et al, 2002;Zhang et al, 2001), but completely free-standing SU-8 microfluidic structures are rarely declared due to the complex structuring process of metal layers on SU-8 and the releasing step technology for centimeter-scale structures.…”