Nanogram calorimetry using microscale suspended SiN_x platforms fabricated via focused ion beam patterning

Comprehensive characterization of thermal properties in nanoscale heterostructures requires microscale thermally isolated platforms combined with sensitive thermometry in order to measure small heat accumulations. Amorphous SiN_x membranes are often used for these measurements due to their low thermal conductivity and compatibility with standard fabrication techniques. The total thermal conductance of such SiN_x membranes is typically microwatts per kelvin or higher. Here, we further reduce this thermal coupling to 120 nW/K by using a focused ion beam (FIB) to remove large portions of commercially available amorphous SiN_x membranes, leaving a 100 μm × 100 μm square platform suspended by 10 μm wide by 325 μm long support legs. We demonstrate the capability of these platforms by measuring the heat capacity of a 6.2 ng Au sample and show that it matches well with established specific heat of bulk Au.