Monolithic Si-Micropillar Loop Heat Pipe with 250 µm Thickness for High-Heat-Flux Semiconductor Cooling

An ultra-thin and all-silicon micropillar loop heat pipe (Si-LHP) was designed and fabricated as a passive two phase cooling device fully compatible with MEMS processing. The device employs Si-Si wafer level bonding to realize a monolithic silicon architecture, which has been difficult to achieve due to the strict flatness and stress requirements of ultra-thin Si-Si bonding. A one-dimensional steady-state model was developed to evaluate conductive heat leakage through the silicon substrate. Using water as the working fluid, the Si-LHP integrates periodic arrays with micropillars and grooves in the evaporator, and a branched microchannel network in the condenser, achieving a total thickness of 250 µm and a theoretical heat transport capacity of 15 W. Experiments demonstrated stable operation up to 10 W (10 W cm⁻²), with a 34°C temperature reduction at 9 W. These results demonstrate the feasibility of monolithic Si-based two-phase cooling devices for thermal management in future semiconductor chips and 3D integrated systems.