Robust Microfabrication of Highly Parallelized Three-Dimensional Microfluidics on Silicon

Area of Science:

• Microfluidics and Microsystems Engineering
• Materials Science and Engineering
• Chemical Engineering

Background:

• Increasing the throughput of microfluidic material synthesis requires parallelized microfluidic chips with dense arrays of Through Silicon Vias (TSVs).
• Existing fabrication methods face challenges in creating high-density TSV arrays needed for advanced 3D microfluidic devices, limiting scalability and performance.
• Challenges include achieving small TSV footprints, enabling bi-directional fluid flow, minimizing debris, and preventing wafer warping for reliable bonding.

Purpose of the Study:

• To present a novel, robust three-dimensional (3D) microfabrication method for highly parallel microfluidics.
• To enhance the throughput of on-chip material synthesis through simultaneous operation of numerous replicate devices on a single chip.
• To overcome limitations of previous approaches in fabricating 3D microfluidic chips with dense TSV arrays.

Main Methods:

• Developed a two-layer TSV design enabling small diameter vias (<20 µm) without compromising mechanical stability.
• Utilized a patterned silicon dioxide (SiO2) etch-stop layer to eliminate the need for carrier wafers during Deep Reactive Ion Etching (DRIE).
• Employed conventional semiconductor fabrication equipment for the microfabrication process.

Main Results:

• Successfully fabricated over 50,000 TSVs (15 µm diameter) on a single 4-inch wafer with 100% yield, a significant improvement over previous 30% yields.
• Engineered a microfluidic chip integrating 20,160 flow-focusing droplet generators, doubling the previously reported number on a single chip.
• Demonstrated high-throughput synthesis of 5-9 µm polycaprolactone particles (>60 g/hr, >1 trillion particles/hour) with low coefficient of variation (<5%).

Conclusions:

• The presented microfabrication strategy offers a robust and scalable solution for producing 3D microfluidic chips with dense TSV arrays.
• This method significantly enhances the throughput for on-chip material synthesis, particularly for applications like pharmaceutical microparticle formulation.
• The developed technology utilizes standard semiconductor equipment, making it accessible for industrial-scale production of advanced microfluidic devices.