Near-junction microfluidic cooling for GaN HEMT with capped diamond heat spreader

With a constant push to shrink size and elevate power density, the heat flux in GaN-based devices is drastically intensified, requiring effective cooling to control junction temperature. This work presents an embedded manifold microchannel cooling (EMMC) arrangement targeted at mitigating junction temperature, in which microchannels are directly etched in the GaN substrate to extract heat generated due to self-heating. The single-phase laminar flow of deionized water through near-junction microchannels has been investigated in a unit-cell mimicking a recently reported GaN power converter with EMMC arrangement. The effects of geometrical parameters of the manifold and microchannel, heat flux and flow rate on the thermal-hydraulic performance of the unit-cell model are thoroughly studied. High heat transfer coefficients in the order of 105 W/(m2·K) associated with the near-junction microfluidic single-phase flow are acquired, which demonstrates the excellent heat extraction capability of EMMC applied to GaN-based devices. The unit-cell model in the prediction of the thermal performance of a large-scale EMMC multifinger GaN device is in good agreement with experiment and capable of providing detailed fluid flow and temperature distributions for design optimization. Furthermore, a capped diamond heat spreader is integrated with the EMMC GaN device to reduce junction thermal spreading resistance. It is shown that high die heat flux in the range 0.86‒3.01 kW/cm2 can be effectively removed for the 10-µm-thick diamond capped GaN-on-SiC EMMC device within a junction temperature range 48‒110°C. This new EMMC arrangement complemented with capped diamond holds promise as an ultimate near-junction cooling solution that facilitates the implementation and development of high-power compact GaN-based devices.