Christopher Carron and Dr. Aaron Hawkins, Electrical Engineering Dept.
There are currently two basic ways to make microfluidic devices: sacrificial etching and wafer bonding. Each method has both advantages and disadvantages. Sacrificial etching is more consistent than wafer bonding and results in finer and more uniform microfluidic devices, but it is also much slower than wafer bonding and can take weeks or months to complete devices that wafer bonding can typically produce in just a few days. Figure 1 shows the differences between these two methods.
The goal of this project was to develop a method that could combine the advantages of both approaches. That is, we wanted a way to create microfluidic devices with the advantages of sacrificial etching (i.e. device uniformity and channel accessibility) but without the slow process time.
To accomplish this we began testing various photosensitive polymers, called photoresists, to find a pair that would not dissolve each other when one was coated over the other. We eventually found a combination that would work as long as the bottom layer was irradiated with Deep Ultra-Violet (DUV) light. The DUV irradiation basically “cooks” the skin of the polymer, forming a thin, hardened shell that protects it from being dissolved by the top layer. We then found a solvent, acetone, is used to remove only the bottom layer polymer, leaving a hollow microfluidic tube. This is very similar to the sacrificial etching method but with a very significant advantage—the acetone attacks the bottom polymer from its exposed ends (like traditional sacrificial etching) but also penetrates through the top polymer until it reaches the bottom polymer and begins dissolving it from above. In this way the bottom polymer can be dissolved and removed much more quickly than is possible with traditional sacrificial etch approaches.
After developing the process, we made many different types of microtubes and tested their integrity when filled with aqueous solutions. We found the tubes to be leak-proof and capable of being integrated into microfluidic chips. This research was presented at a conference (UCUR-2008) and was recently accepted for publication in a peer-reviewed journal (Microfluidics and Nanofluidics). I have progressed both as a student and as an independent researcher, and have thoroughly enjoyed my time and research at BYU. Also, I would like to thank ORCA for promoting undergraduate research.