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.