Simulation of Heat Transfer in Bridge-Based Micro Calorimeters

Previous studies of bridge-based micro calorimeters have shown that these devices can measure heat capacity and melting point of ultra thin films with pulse scan calorimetry. The bridge-based micro calorimeters consist of a sample region and several beams that connecting the sample region with silicon substrate. Both the sample region and the beams are suspending on the silicon substrate for thermal isolation. The temperature distribution of the micro calorimeter during a heating pulse depends on the joule-heating of the heating resistor, the heat absorption and heat conduct of the bridge. The heat transfer through the beams during a pulse scan measurement is complex because there is heat generation on some beams and the temperature distribution along the beams is not uniform. Using three dimensional finite element analyses (FEA), the thermal-electrical simulations of the heat transfer in the bridge-based micro calorimeters have been performed. The heat consumption and temperature distribution at steady state analyses, the temperature response of the bridge and the heat generation of the heater at transient analyses have been calculated for the bridge-based micro calorimeter with different sample thermal conductivities and heat capacities. The simulation results indicate that for the bridge-based microcalorimeter using pulse calorimetry, when the heat capacity of the sample film is close to or larger than the heat capacity of an empty calorimeter, the differential method of getting the sample heat capacity from the difference between a micro calorimeter with and without the sample is no longer suitable because the heat transfer and temperature distributions of the two calorimeters are no longer comparable to each other.