Fluidic Microsystems Fabricated in Epoxy

Sealing of the fluidic structure was realized through wafer-scale bonding to glass with an additional coating of SU-8 as adhesive, while the need for precision alignment during bonding was eliminated through design. Fluidic feedthrough ports and access to electrical bond pads were formed by a low-cost, batch KOH-etch process from the backside of the silicon substrate. Fluidic and electrical interconnections were completed by the attachment of tubing and ultrasonic wirebonding.

Demonstrating the versatility of the SU-8 process, a thermal bubble valve was implemented which featured a silicon nitride membrane for thermal isolation. N-doped polysilicon electrodes were designed as thermistors and resistive heaters for generating thermal bubbles. The nitride membrane allows power savings in generating thermal bubbles and enables the monolithic integration of thermal flow rate measurement designs by reducing thermal cross talk.

Extending the basic process further, a streamlined package-and-release design was explored to produce SU-8 flexural structure as fluidic check valve. By releasing the moving parts after packaging, the process becomes much more robust and would be more suitable for large-scale production.

In addition to fabricating the basic fluidic structures through CMOS-compatible processes, packaging issues include sealing and interconnection requirements for both fluidic and electrical input must be resolved for the proper operation of microfluidic MEMS. On the other hand, low-cost design and large-scale manufacturing are central to a successful product. The application of SU-8 epoxy in fluidic microsystems is discussed in this context.