AVS 51st International Symposium
    Materials Solutions for Cooling Technology Topical Conference Monday Sessions
       Session CT+TF-MoM

Paper CT+TF-MoM2
Thin Film SiGe Superlattice Micro Refrigerators Flip-Chip Bonded with IC Chips

Monday, November 15, 2004, 8:40 am, Room 303B

Session: Thermal Transport in Thin Films and Nanostructured Materials
Presenter: Y. Zhang, University of California, Santa Cruz
Authors: Y. Zhang, University of California, Santa Cruz
A. Shakouri, University of California, Santa Cruz
G. Zeng, University of California, Santa Barbara
P. Wang, University of Maryland
A. Bar-cohen, University of Maryland
Correspondent: Click to Email
Thin film SiGe-based superlattice micro refrigerators, with device sizes ranging from 40-150 micron in diameter, have demonstrated cooling by 4.5C at ambient temperature and cooling power density exceeding 500W/cm2. In this talk we present theoretical and experimental study of these thin film refrigerators flip-chip bonded underneath 50 micron thick silicon substrate. The idea is to evaluate the effectiveness of these refrigerators to eliminate hot spots in IC chips without modifying the IC processing steps. Even though the 50 micron thick silicon has relatively high thermal conductivity and the cooling of micro refrigerators is spread over larger areas, theoretical studies show that localized cooling by 1-2C with cooling power density exceeding 100W/cm2 should be possible. Experimentally three micron thick gold-to-gold bonding is used to attach the two wafers. Cooling on top of the silicon heat load wafer is measured using microthermocouples. Thin film resistor heaters are used to evaluate the cooling power density. We have achieved cooling power density ~40W/cm2. It is interesting to note that even though bare microrefrigerators have an optimum size for maximum cooling on the order of 70 microns in diameter and largest cooling power density is obtained with the smallest devices, in the two-chip bonded configuration, the biggest coolers have the largest cooling and the cooling power density is not a strong function of the size. 3D electrothermal simualtions are used to explain the measured results and to evaluate maximum cooling performance under various ideal and non-ideal conditions.