SU-8 On Pmma - A New Technology For Microfluidics

Abstract

Conventional SU-8 lithography process for fabricating microfluidic devices ofthe uses silicon or glass as wafer materials. Since silicon and glass are hard and brittle, drilling fluid access holes or dicing the wafers into individual devies are difficult. We investigated the use of polymethylmethacrylate (PMMA) as a new wafer material. PMMA, an amorphous thermoplastic, was chosen for being easy to drill or cut, biocompatible, transparent, and much cheaper than silicon or glass wafers. Moreover, is thermal expansion coefficient ideally matches that of SU-8. PMMA poorly resists solvents, and has low glass transition temperature (105°C). Thus, the conventional process needed to be modified. The wafer was only cleaned with isopropyl alcohol and deionized water. The baking temperature was lowered to 90°C. In addition, a "base layer" of SU-8, helping to achieve a high quality structural pattern, was coated before coating the actual structural SU-8 layer. A Tesla valve, a non-moving part microfluidic valve, was successfully fabricated in SU-8 using thr presented process,. However, the PMMA wafer bowed ue to the thermal residual during baking steps. Despite the bowing which can be solved by increasing wafer thickness, we conclude that PMMA is a promising wafer material for a SU-8 process.