Big Micro-Electromechanical Systems for Thermal Measurement

The rapid development of various micro-electromechanical systems (MEMS) over the past few decades has served as a cornerstone for precisely probing thermal transport in a rich variety of nanomaterials and nanostructures, all the way down to single-walled carbon nanotubes and monolayer graphene. However, numerous materials that are macroscopic (millimeter scale and above) at least in one dimension, such as metal wires, carbon fibers, and polymer fibers/films, have remained largely inaccessible by MEMS-based experimental approaches. In light of the great fundamental and technological value of these materials, we propose the concept of "big-MEMS" here as an effort to fill this notable gap. The idea is to create macroscopic measurement devices through standard MEMS design and fabrication techniques. For demonstration, we present a novel process that enables silicon-based suspended heater/calorimeter devices of millimeter to centimeter dimensions to be fabricated reliably, reconfigurably, and at low cost. In particular, the beam thermal conductance of our big-MEMS devices can be tuned from around 1.1 to 0.2 mW/K. Combined with a temperature resolution down to about 20 lK, these devices are suitable for characterizing materials spanning a broad range of thermal conductivity. As an example, the thermal conductivity of platinum wires with a diameter of 20 lm and lengths up to 3.5 mm are measured. Moreover, intriguing transport phenomena such as divergent thermal conductivity in low-dimensional materials and heat flow mediated by surface polaritons can be explored considering their inherent need for multiscale analysis. In principle, our concept of big-MEMS can also be applied to the study of thermal diffusivity, heat capacity, charge transport, and beyond.