Big MEMS for Thermal Measurement

Abstract The rapid development of various micro-electro-mechanical 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. 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 approaches. Considering 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 techniques. For demonstration, we present a novel process that enables silicon-based suspended 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 ~20 µK, 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 µm and lengths up to 3.5 mm are measured. Moreover, intriguing transport phenomena such as divergent thermal conductivity 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.