Three Dimensional Thermal Effects in MEMS Devices
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Three Dimensional Thermal Effects in MEMS Devices Edward Van Keuren1, John Currie1, Matthew Nelson3, Makarand Paranjape1, Thomas Schneider1, 2, Ryan Smith3, Pat Treado3, John Ward2 and Robert White1, 2 1 Georgetown University, Dept. of Physics, Washington, DC 2 Science Applications International Corporation, McLean, VA. 3 ChemIcon, Inc., Pittsburgh, PA ABSTRACT A three dimensional thermal imaging system is being developed for measuring temperature profiles in MEMS-biomedical devices. These devices rely on a thermal microablation of the dead-skin layer in order to sample transdermal fluids. This is accomplished using microheaters embedded into a PDMS microchannel device. In order to determine the proper functioning as well as long-term safety of the devices, a temperature profile of the device and the skin in contact with the heaters is needed. The results of simple analytical models are used to optimize a prototype device. Using a three-dimensional chemical imaging microscope and temperature-dependent fluorophores, the temperature profile in a sample can be determined quantitatively as well. We demonstrate the technique on a model sample, and discuss extension to other applications such as thermal imaging in biological systems.
INTRODUCTION Thermal phenomena play an important role in both biological processes and device fabrication. In biological systems, temperature has the roles of an environmental parameter to which organisms must adapt, both macroscopically, as in an animal’s regulation of body temperature, and microscopically, as in temperature dependence of gene expression. Thermal effects are also critical in bio-MEMS devices, in particular those employing resistive heating elements. The effect of heat generation by active devices on the biological system it interacts with must be considered. Thermal phenomena may also play a critical role in the device functionality. One such device is the Bio-Fluidic Integrable Transdermal (B-FIT) Microsystem [1] currently being developed at the Georgetown Advanced Electronics Lab (GAEL), and funded by DARPA [2], to detect and assess glucose levels as a physiological indicator of health. The basic concept and operation of the B-FIT is illustrated in Figure 1. A micro-fluidic sampling system coupled with thermal micro-ablation elements enables body analyte sampling at the Stratum Corneum (SC)/Viable Epidermis (VE) interface without invasive extraction of interstitial fluid. The thermal micro-heaters create micro-pore openings in the dead skin layer (SC), then a physiological fluid, which has been encapsulated in individual B-FIT reservoirs, is released using electrolytic gas bubble formation that acts as the fluidic driving mechanism. The physiological fluid bathes the micro-pore region and the biomolecules contained within the bubble-driven fluid, in conjunction with capillary action, allows for fluidic mobility towards the glucose detection subsystem. Up to 2000 individually addressable analysis systems can be fabricated in a 1 cm2 area. It also incorporates colorimetric
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