An Integrated Liquid Metal Thermal Switch for Active Thermal Management of Electronics

Heat dissipation is a key obstacle to achieving reliable, high-power-density electronic systems. Thermal devices capable of actively managing heat transfer are desired to enable heat dissipation optimization and enhanced reliability through device isothermalization. Here, we develop a millimeter-scale liquid metal droplet thermal switch capable of controlling heat transfer spatially and temporally. We demonstrate the thermal switch by integrating it with gallium nitride (GaN) devices mounted on a printed circuit board (PCB) and measure heat transfer and temperature of each device for a variety of switch positions and heat dissipation levels. When integrated with a single GaN device (2.6 mm $\times4.6$ mm face area) dissipating 1.8 W, the thermal switch shows the ability to actively control heat transfer by conducting 1.3 W in the ON mode with the GaN device at 51 °C ± 1 °C, and 0.5 W in the OFF mode with the GaN device at 95 °C ± 1 °C. To elucidate the heat transfer physics, we developed a 1-D system thermal resistance model in conjunction with an independent 3-D finite-element method (FEM) simulation, showing excellent agreement with our experimental data. Finally, we demonstrated that when the switch is integrated with two GaN devices, the switch can balance the device heat transfer rate and enhance junction temperature uniformity and system reliability by lowering the device-to-device temperature difference from > 10 °C (no switch) to 0 °C.