| The thermal performance of Microelectromechanical Systems (MEMS) as well as Integrated Circuits (ICs) depends critically on the thermophysical properties of constituent thin film materials. This work develops a method for thermophysical characterization of free-standing thin films based on the thermal response of the thin film to a sinusoidal heating current. MEMS-based microheater structures with silicon nitride and NiTi membranes are fabricated and thermally characterized using the method. Measured values of thermal conductivity and heat capacity for silicon nitride are found to agree well with previous measurements. Thermal conductivity measurements for thin film NiTi indicate a 40% reduction in thermal conductivity compared to the well known bulk value. Heat capacity of thin film NiTi increases with temperature in the low temperature phase, and saturates in the high-temperature phase. Theoretical modeling and measurements presented in this work are expected to aid in improved thermal modeling of microsystems comprising of thin film membranes, particularly those employing the shape memory effect.; This work also uses MEMS-based membrane microheaters to study the interaction of cells with their thermal microenvironment. While cellular response to physiochemical factors like chemical gradients, electric fields, fluid flows, etc. has been well studied, thermal interactions have not been studied in detail. This work develops an equilibrium biochemistry based model for predicting the effect of spatial temperature gradients on cells. This model is based on the temperature dependence of ligand-receptor interactions on the cell membrane. Using the limited data available in literature, a temperature difference of around 1-2°C across the cell is predicted to be sufficient to elicit thermotactic response. Thin-film microheaters are designed and microfabricated in order to experimentally study thermotaxis in a variety of cell types. The control of cell life/death using heat generation in the microheater device is demonstrated. A large parameter space is explored by varying the magnitude of temperature gradient, exposure time, ambient temperature, etc. However, no thermotactic activity is observed in any the cell types investigated in this work. This observation is most likely because of the weak temperature dependence of ligand binding interactions, about which very little data is available in the literature. |
