Experimental development of a near junction microchannel heat spreader

This paper describes a convection-based alternative to conduction heat spreaders that uses liquid microchannels to remove heat directly from the transistors. The concept connects microchannels etched directly into the die with a hydraulic circuit that includes a piezo-diaphragm pump, thermally-regulated autonomous flow control valves, and a high-efficiency heat exchanger to create a stand-alone, hermetically-sealed cooling module. The first part of the paper reviews the experiments performed to develop the key components in the cooling package. It describes the flow tests that measured the pressure drop characteristics of different microchannel designs, reviews the bench tests used to design the piezo-diaphragm pump, and discusses the process followed to train the shape-memory alloy used for the autonomous flow control valves. The second part presents micro Raman spectroscopy experiments that measured gate temperatures in energized GaN-on-SiC dies cooled by different microchannel designs. These measurements show that the microchannels enable up to a 50% increase in device input power over conventional conduction cooling with no increase in gate temperature. They also quantify how cooling effectiveness varies with channel geometry and show how thermal performance plateaus with increasing coolant flow rate.