Si-N membrane-based microcalorimetry: Heat capacity and thermal conductivity of thin films

We have used silicon micromachining techniques to fabricate devices for measuring specific heat or other calorimetric signals from microgram-quantity samples over a temperature range from 1.7 to at least 525 K in magnetic fields to date up to 8 T. The devices are based on a robust silicon-nitride membrane with thin film heaters and thermometers. Different types of thermometers are used for different purposes and in different temperature ranges. These devices are particularly useful for thin film samples (typically 100-400 nm thick at present) deposited directly onto the membrane through a Si micromachined evaporation mask. They have also been used for small bulk samples attached by conducting grease, Ga or In, and for powder samples dissolved in a solvent and dropped onto devices. The measurement technique used (relaxation method) is particularly suited to high field measurements because the thermal conductance can be measured once in zero field and is field independent, while the time constant of the relaxation does not depend on thermometer calibration.