Limits of Heat Removal in Microelectronic Systems

Thermal management issues play an increasingly prominent role in microelectronic system design. The constraints on heat removal are a major factor limiting the performance of a microelectronic system. This work presents the thermodynamic limit of performance for a thermal solution utilizing air cooling to reject thermal energy as the inverse of its mass flow-heat capacity product. The minimum resistance to heat flow offered by a thermal solution is further refined by including the effects of thermal interface materials, substrate materials, and the impact of nonuniform device layer heating. Active cooling solutions may offer additional needed cooling for microelectronics systems, but the system thermal resistances limit its applicability. This work describes the minimum efficiency that an active cooling solution must provide to offer a thermal advantage over passive cooling. This minimum efficiency is dictated by the thermal resistances involved in drawing heat into the active cooler and expelling heat to the ambient environment. Knowledge of the fundamental limitations of thermal solutions gives system designers realistic expectations to set roadmaps, define architecture specifications, and evaluate the validity of thermal system performance claims