Heat Transfer Regimes in Microstructures

Submicron dimensions are the hallmark of integrated electronic circuits, photovoltaic cells, sensors, and actuators. The design of these devices requires heat transfer analysis. Often it is not known to the designer whether a given microstructure can be analyzed using macroscale heat transfer theory, i.e., a method not considering the size dependence of a transport property such as thermal conductivity. This study develops regime maps showing the boundary between the macroscale and microscale heat transfer regimes. The maps relate the geometric dimension separating the two regimes to temperature for conduction in solids, to temperature, pressure, and Reynolds number for convection in gases, and to the temperature of the emitting medium for radiative transfer. The material purity and defect structure strongly influence the regime boundaries. Microstructures pertaining to a given technology are marked on these maps to determine whether macroscale heat transfer theory is applicable. By marking regions on the maps for the expected future development of microtechnologies, research needs in microscale heat transfer can be anticipated.