# Experimental Investigation of Ultra-Thin Microchannel Oscillating Heat Pipes with Submillimeter-Scale Thickness

## Abstract

As the heat flux generated by semiconductor devices is ever-increasing, one promising thermal management approach is to directly integrate microchannels into the package for embedded liquid cooling that can effectively spread or extract heat. Oscillating heat pipes (OHPs) have gained significant attention owing to their completely passive operation and highly effective heat transport capacities. However, the millimeter-scale channel diameters of conventional OHPs disallow their integration into typical electronic chips. In this paper, we study the downscaling of the OHPs to submillimeter-scale thicknesses and report the successful operation of microchannel OHPs with a channel height of mathbf{100} boldsymbol{mu}mathbf{m}. The OHPs are fabricated by etching into a silicon substrate with channel depths of mathbf{500} boldsymbol{mu}mathbf{m}, mathbf{200} boldsymbol{mu} mathbf{m}, and mathbf{100} boldsymbol{mu}mathbf{m} and charging with HFE-7100 to a filling ratio of simmathbf{50}%. We observe the flow oscillation behavior to explain the thermal performance of these OHPs with channel heights on the scale of sim mathbf{100}mathbf{s} boldsymbol{mu}mathbf{m}. A mathbf{100} boldsymbol{mu}mathbf{m}-mathbf{thick} microchannel OHP is shown to start up and sustain stable bulk circulation modes while dissipating heat fluxes at sim mathbf{70} mathbf{W}/mathbf{cm}{mathbf{2}}. These results reveal new opportunities for dissipating high heat fluxes using ultrathin microchannel OHPs in semiconductor packaging.