Roadmap Review for Cooling High-Power GaN HEMT Devices

The state-of-the art technology for high power RF applications is based on GaN HEMT (High Electron Mobility Transistor) devices. Compared to GaAs technology it can reach 5-10 times higher power densities, higher operating channel temperatures and a higher efficiency at elevated power levels. Due to the extremely high power, GaN devices are susceptible to high increase in channel temperature which subsequently causes degradation both in performance and reliability. It is widely known that the self heating phenomenon is one of the main problems facing the GaN technology. In order to cope with the self heating effect, many measures have been taken to dissipate the heat and many more are planned. For example, one of the main considerations in growing GaN on SiC substrates has been the high thermal conductivity of SiC. However, applying current thermal management technology enables only partial utilization of the technology. The roadmap to employ GaN high power amplifiers in high frequency and CW mode consists of developing more sophisticated technology, which will ultimately evolve into near-junction active cooling. This paper presents various cooling strategies for GaN HEMTs and compares their ability to dissipate the thermal power. Solutions range from passive remote cooled stacks up to integrated active cooled dice.