Big-MEMS for high thermal conductivity measurement

Macroscopic materials of high thermal conductivity are crucial for thermal management applications and also for the exploration of fundamental transport mechanisms. However, accurate thermal measurement of such materials poses several challenges associated particularly with the high contact thermal resistance as compared to that of the sample and also the small temperature difference that has to be resolved. In this study, we address these challenges by building upon the recently proposed concept of big-MEMS for thermal measurement. At the core of our approach is a suite of suspended devices fabricated from low-stress silicon nitride (SiNx) nanofilms with integrated platinum resistive heater/thermometers, in conjunction with a multiprobe experimental scheme. The SiNx suspension beams feature an ultralow thermal conductance, which ensures picowatt heat-flow resolution and reduces unwanted conductive heat loss to a negligible level. Meanwhile, the impact of contact thermal resistance on temperature sensing is also minimized (<3%). For demonstration, we measure the thermal conductivity of four representative materials with different sample geometries (all are a few millimeters long), including three types of metal wires (platinum, gold, and silver) and two silicon bars (doped and intrinsic). The thermal conductivity values we obtain reach beyond 1000 W m-1 K-1 at low temperatures and agree remarkably well with textbook recommendations and previous measurements. Our multiprobe big-MEMS approach based on SiNx devices offers a reliable and convenient avenue for identifying and understanding high thermal conductivity materials.