Challenges and Potential of N-polar GaN HEMT for beyond 5G Wireless Network

This paper describes the advantages of N-polar GaN HEMT by comparing device characteristics with those of Ga-polar HEMT. The N-polar GaN HEMT epi-structure, which was designed for RF devices, was grown on 4-inch semi-insulating SiC substrate by MOCVD with smooth surface morphology and low sheet resistance non-uniformity of 1.2%. This paper reports, for the first time, N-polar HEMTs which were fabricated using the same 4-inch wafer process facilities and our manufacturing expertise for commercial Ga-polar GaN HEMTs. The reported N-polar GaN HEMT achieved drain current density of 1.74 A/mm and drain conductance of less than 40 mS/mm. Both of these are superior to Ga-polar GaN HEMT. Using hafnium oxide-based dielectrics, high-k gate insulators were developed and achieved a relative permittivity of 17. N-polar GaN HEMTs with these high-k gate insulators were fabricated and these devices reached a sufficient level to be used for high frequency RF power amplifiers. These results indicate that N-polar GaN HEMTs will be the key technology for next generation high power and high frequency power amplifiers.