Synthesis and characterization of photodefinable polycarbonates for use as sacrificial materials in the fabrication of microfluidic devices

Abstract

A fabrication technique recently developed at Georgia Institute of Technology involving thermally sacrificial polymeric materials allows for fabrication of microfluidic devices with greater degrees of functionality (i.e., fully integrated, complex, multi-level fluidic systems with functional valves, pumping systems, and other micro- electromechanical system [MEMS] components). In this method, thermally sacrificial polymers are coated onto a substrate and patterned into the shape of the desired channels and devices. These polymeric structures are then over-coated with a permanent structural material such as an inorganic glass or polymer. These steps can be repeated to produce complex, three-dimensional systems. Once the device build-up is complete, the structure is heated to a temperature at which the sacrificial polymer slowly decomposes, thus leaving behind the desired open-channeled structures. This process was first developed using functionalized polynorbornenes that decompose at temperatures in the range of 425 degree(s)C. In order to make this approach compatible with a wider range of substrates and structural materials, polymers with lower decomposition temperatures were desired. Polycarbonates were identified as a class of polymers with the desired lower decomposition temperatures (200- 300 degree(s)C). A disadvantage of commercially available polycarbonates, like poly (propylene carbonate), is that they have low glass transition temperatures (T g approximately equals 40 degree(s)C). This introduces several problems, including pattern deformation at elevated processing temperatures. Also, a significant number of process steps are required to pattern the channel structures using simple polymer materials. Therefore, this paper will describe recent results of work on photodefinable polycarbonates with improved thermal properties. Utilizing a polymer that can be patterned directly by conventional lithography greatly simplifies the fabrication process and eliminates the need for the plasma etch steps required in the original process. Results of the synthesis and characterization of polycarbonates patterned with the use of a photoacid generator, thus exploiting the acid-catalyzed thermolysis of polycarbonates, will be presented.