Design, microfabrication and thermal characterization of a hotspot cooler testbed for convective boiling experiments in extreme-microgap with integrated micropin-fins

In this work, we designed, fabricated and characterized a novel hotspot testbed to dissipate ultra-high power density by two-phase convective boiling of refrigerant in a microgap with integrated micropin-fins and isolation air trenches around resistance heaters. The 300 µm long, 200 µm wide, and 10 µm tall microgap with 4 µm diameter micropin-fins was batch micro-fabricated in silicon. The 40 µm wide and 180 µm deep isolation air trenches around the heater and a SiO2 passivation layer were used to provide thermal isolation. The testbed dissipates a power density of up to 4.75 kW/cm2 using R134a refrigerant as the coolant. Thermal resistance and pumping power were compared between the micropin-fin device of interest and a reference ‘empty microgap’ device to assess tradeoffs in performance. Micropin-fins were found to slightly reduce thermal resistance at the cost of a large increase in pumping power. In addition to experimental work, thermomechanical simulations were implemented to analyze the reliability of the device for high pressure conditions.