On-Chip Thermoelectric Hotspot Cooling

Abstract

Increased power density and non-uniform heat dissipation present a thermal management challenge in modern electronic devices. The non-homogeneous heating in chips results in areas of elevated temperature, which even if small and localized, limit overall device performance and reliability. In power electronics, hotspot heat fluxes can be in excess of 1kW/cm2. Although novel package-level and chip-level cooling systems capable of removing the large amounts of dissipated heat are under development, such “global” cooling systems typically reduce the chip temperature uniformly, leaving the temperature non-uniformity unaddressed. Thus, advanced hotspot cooling techniques, which provide localized cooling to areas of elevated heat flux, are required to supplement the new “global” cooling systems and unlock the full potential of cutting-edge power devices. Thermoelectric coolers have previously been demonstrated as an effective method of producing on-demand, localized cooling for semiconductor photonic and logic devices. The growing need for the removal of localized hotspots has turned renewed attention to on-chip thermoelectric cooling, seeking to raise the maximum allowable heat flux of thermoelectrically-cooled semiconductor device hotspots. This dissertation focused on the numerical and empirical determination of the operational characteristics and performance limits of two specific thermoelectric methods for high heat flux hotspot cooling: monolithic thermoelectric hotspot cooling and micro-contact enhanced thermoelectric hotspot cooling. The monolithic cooling configuration uses the underlying electronic substrate as the thermoelectric material, eliminating the need for a discrete cooler and its associated thermal interface resistance. Micro-contact enhanced cooling uses a contact structure to concentrate the cooling produced by the thermoelectric module, enabling the direct removal of kW/cm2 level heat fluxes from on-chip hotspots. To facilitate empirical validation of on-chip thermoelectric coolers and characterization of advanced thin film thermoelectric coolers, it was found necessary to develop a novel laser heating system, using a high power laser and short-focal length optics. The design and use of this illumination system, capable of creating kW/cm2-level, mm-sized hotspots, will also be described.