Modeling and Fabrication of a Microthermocouple Array
Cryobiology is the study of how living cells and tissues respond to freezing and exposure to subzero temperatures. Studies in this field are aimed toward improving methods of cryosurgery as well as the storage of cells and tissues. For example, one area of research is to link the biophysical cellular dehydration and intracellular ice formation in cells during tissue freezing to cell viability and mechanical properties after thawing. There is currently a method for measuring dehydration in cells as part of a tissue, but not an adequate method for measuring intracellular ice formation in tissues.
A prototype device that would allow measurement of intracellular ice formation by measuring the heat release of individual cells during freezing with an array of type-T microthermocouples was fabricated and tested. The device was designed to consist of a microfabricated wiring layer with an intermediate post layer to improve thermal insulation, and a rectangular junction layer to connect the two metals of the thermocouple.
Modeling was used to determine the most suitable geometries for the device. Posts of 3 ?m and 5 ?m in diameter were modeled, with heights of 20 ?m and 50 ?m, as well as a wiring layer without posts. For both heights tested, the 3 ?m posts improved the thermocouple response over a no post case, while 5 ?m posts gave inferior results. Interference between adjacent thermocouples was found to be negligible as long as a cell was in contact with a thermocouple junction.
A multilayer UV-LIGA process on a silicon wafer substrate with an E-beam deposited seed layer was used to fabricate the device. Electrodeposition was used to fabricate the wiring, posts, and junctions for the thermocouples. The seed layer was then etched away to provide electrical insulation between individual thermocouples.
The microfabricated device was connected to a custom made PC board with multiplexing, amplifying and filtering circuitry. In initial tests, the thermocouple array showed a trend of voltage variation with temperature, indicating a working thermocouple array. Future work to more adequately characterize the performance is presented.
Advisor:Michael Murphy; Ram Devireddy; Elizabeth Podlaha-Murphy; Srinath Ekkad
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:03/24/2006