Investigations of High Heat Flux Cooling Using Carbon Nanotube Bi-Wick Structure and Integrated Platinum Thermometer/Heater

Abstract

With the increase of power consumption in compact electronic devices, passive heat transfer cooling technologies with high heat flux characteristics are highly desired in microelectronics industries. Carbon nanotube (CNT) cluster/forest has high effective thermal conductivity, nano pore size and large porosity, which can be used as wick structure in a heat pipe heatspreader and provides high capillary force for high heat flux thermal management. In this research, investigations of high heat flux cooling of the CNT bi-wick structure are associated with the development of a reliable thermometer and high performance/interface free heater. A 100nm thick and 600μm wide Z-shaped platinum wire resistor is fabricated on the backside of a CNT sample substrate to heat a 2×2mm2 wick area. As a heater, it provides direct heating effect without thermal interface and is capable of over 800°C high temperature operation. As a thermometer, reliable temperature measurement is achieved by calibrating the resistance variation with temperature after the annealing process is applied. The CNT sample substrate is silicon. The backside of the silicon substrate is thermally oxidized to create a 2μm thick and pinhole-free SiO2 layer so that the platinum heater and thermometer can survive from the server CNT growth environments and without any electrical leakage. For high heat flux cooling, the CNT bi-wick structure is composed of 250μm tall, 100μm wide stripe-like CNT clusters and 50μm empty space. Using 1×1cm2 CNT bi-wick samples, experiments are completed in both the open and saturated environments. Testing results of CNT bi-wick structure demonstrate 600W/cm2 heat transfer capacity and good thermal & mass transport characteristics in the nano level porous media.