Thermal management in GaN-devices for increased power density

The increasing demand for higher power density is a major trend for almost all electronic applications spanning from power to RF electronics. Gallium Nitride HEMT technology is a frontrunner in both power and RF application, due to its remarkable material properties that offer high-frequency operation simultaneously with higher power. However, we are still far from experiencing the full potential of GaN HEMT in power densities, for which thermal management is necessary. At the desired power densities, GaN HEMTs suffer from severe Joule heating that results in performance degradation and premature failure. A potential solution for increasing the efficiency in GaN HEMTs has been recognized in its integration with diamond, known for its excellent thermal properties. GaN-on-Diamond has been an attractive area of research, that was surveyed under major programs like DARPA ICECool and NJTT. On the other hand, diamond growth on GaN, although explored, did not have much
success due to difficulties with diamond-centric processing. Recently our group has demonstrated several key results suitable for Diamond-on-GaN integration.
Our integration technique has demonstrated the growth of diamond films at low temperature (down to 400℃) near the hot spot in the GaN channel. High-quality diamond is mainly grown at high temperatures >700°C which constrains its application to materials with a high thermal budget. The ability to reduce the CVD (diamond’s) growth temperature to <400℃ while maintaining its
excellent sp3-like properties was crucial. At 400℃, a phase purity of ~97% was achieved which resulted in a remarkably low thermal boundary resistance of ~5
m2K/GW with a relatively high thermal conductivity of ~300 W/m/K for a 800-nm thick layer. Furthermore, the diamond film when integrated to N-polar GaN HEMT devices measured a 70℃ lower temperature in the channel at a DC power of 25 W/mm.