In this research, first a modular polymer-based (PMMA) injection micromixer prototype has been designed, fabricated and tested. This micromixer is easy to be integrated into biochemical microfluidic systems under development for BioMagnetICs DARPA funded project at CAMD. To improve the mixing efficiency, layout of micronozzles of the
mixer was optimized according to the simulation results. Also because SU-8, an epoxy-based negative photoresist, has high chemical resistance, an SU-8 injection mixer was designed and fabricated to run some biochemical sample liquids. Internal stress in patterned SU-8 structures has been reduced and multi-layer SU-8 processing has been successfully developed to fabricate SU-8 injection mixer.
This paper describes a novel fabrication method for the manufacture of multi-level microfluidic structures using SU-8. The fabrication method is based on wafer bonding of SU-8 layers and multilayer lithography in SU-8 to form microchannels and other structures at different levels. In our method, non-UV-exposed SU-8 layers are transferred to SU-8 structured wafers at desirably low temperatures. This technique is particularly useful for building multi-level fluidic structures, because non-UV-exposed SU-8 can be used as cover for microchannels and the cover can then be lithographically structured, i.e., to form interconnects, after which subsequent transferring of non-UV-exposed SU-8 onto the wafer allows for the fabrication of interconnected multi-level channels and other structures. Examples of interconnected multi-level microchannels were realized using this newly developed method. Liquid has been introduced into the microchannels at different levels to reveal the desirable functionality of the interconnected multi-level channels. The method described here is easily implementable using standard photolithography and requires no expensive bonding equipment. More importantly, the fabrication procedure is CMOS compatible, offering the potential to integrate electronic devices and MEMS sensors into microfluidic systems.
A series of polymer-based Polydimethylsiloxanes (PDMS) ball valves with different opening pressures have been developed for biomedical applications. By tuning different weight ratios of the two components (the base and the curing agent) of PDMS, the valves will have different opening pressures because of different stiffness of the PDMS materials. The curing conditions and mechanical properties of the PDMS material with different ratios have been thoroughly studied. The compressive Young's modulus of the material can be tuned from 310 KPa to 2.0 MPa. Such kind valves can be fabricated by injection molding, one of the cheapest fabrication techniques. Also such kind valve has no dead volume and easily to be integrated into micro-total analysis systems (μTAS).
SU-8 has been used directly as structural material for MEMS/BioMEMS components as well as optical MEMS components. Although the applications of SU-8 photoresist have widely been presented, the material properties and behavior at elevated temperature have rarely been reported. In this paper, the thermal stability of the SU-8 structures as the function of exposure doses and photo initiator concentration changes has been studied. Differential Scanning Calorimeter (DSC), Thermogravimetric Analyzer (TGA) and Dynamic mechanical analysis (DMA) are employed to study the thermal stabilities of exposed SU-8 microstructures. Mass loss as the function of exposure doses and post-baking time were studied by TGA. The results show that the relative mass loss is inversely proportional to the exposure dose as well as the post-baking time, which also directly affect the thermal stability of SU-8 components. The DSC results reveal that there is a phase change reaction occurs around the temperature of 150°C and is directly related to the photo initiator. The effects of this phase change on the tensile strength and creep behavior of SU-8 fabricated microstructures were also explored using DMA. These results will provide the MEMS researchers and engineers with the usable information in SU-8 applications. At the end, how to optimize SU-8 processing parameters to increase its thermal stability is discussed.