Advancement of GaN HEMT Power Electronics on Diamond Substrate

Wide bandgap power electronics have been commercialized for many applications. Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) has superior performance in high frequency applications. The outstanding concerns are the self-heating and thermal dissipation due to high current density through the piezoelectric channel exhibiting as a two-dimensional electron gas (2DEG). Substrates, silicon or silicon carbide, support GaN epitaxial processing limit the thermal transport ability. Alternative substrate materials for device level heat spreader with high thermal conductivity have been considered for substrate transfer technology to extend the application ranges. Among them, diamond has the highest thermal conductivity but is challenged by high cost and fabrication difficulties. Although GaN HEMT on Diamond has been studied for many years, the challenges remain in many aspects for implementation. This study summarizes and analyzes the crucial factors of materials, processing, and integration schemes of diamond heat spreader technologies in recent advancement. The effective thermal boundary resistance between GaN and Diamond is chosen as a parameter for comparisons. Advantages and disadvantages of direct polycrystalline growth and direct bonding methods are also discussed. The impacts on device performances, sizes, costs, the preferable applications gaining benefits and momentum, the manufacturing challenges, and the desired future improvement are also highlighted.