Performance and mass optimization of thermoelectric microcoolers

Abstract

We report a scalable and parametric analysis of thermoelectric (TE) microcoolers for hotspot cooling based on analytic formulations. Design for minimizing cooling power and least mass or cost of TE material is an ultimate goal for electronic devices that require spot cooling beyond that provided by passive heat transport to the thermal ground. Performance of thermoelectric hotspot cooling on electronic devices depends on external thermal resistances, physical dimension (thickness) of the thermoelectric element, and the applied drive current. Active cooling located at the hotspot minimizes the cooling power and the internal heat generation from the TE element and also minimizes the additional driving power used for heat rejection with a preexisting air-cooling fan or a liquid-cooling pump. Electronic devices are required to operate below a specific temperature for functionality and high reliability. The hotspot cooler must be designed to deal with the amount of heat generated from the heat source with this temperature constraint. We investigate two design cases: 1) the maximum cooling and 2) the minimum drive current for a given hotspot temperature to obtain an improved coefficient-of-performance (COP). The study explores the impact of individual thermoelectric material properties, i.e. Seebeck coefficient, electrical conductivity, and thermal conductivity to find the direction that should be taken with engineered materials. We show that COP up to 8 is possible for hotspot heat fluxes of about 80 W/cm2, if TE leg thickness is optimized to ∼20–30 microns with today's Bi2Te3 material. Model shows that COP > 2–3 is possible for hotspot heat fluxes bigger than 200–300 W/cm2. We find that lowering the thermal conductivity have the greatest impact, resulting in a thinner element (and therefore lower cost) while maintaining the same figure-of-merit (ZT).