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

TLDR

The paper presents a method for fabricating 3‑D micro‑channels in PDMS elastomer. The technique stacks sub‑100‑µm patterned PDMS layers using a sandwich‑molding process with silicon masters, reactive‑ion‑etched surface activation, methanol bonding, and surface‑tension self‑alignment to achieve sub‑15‑µm layer registration and coring for off‑chip connections. Instant bonding is optimized by low RF power and short treatment times.

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.