GaN HEMT with superconducting Nb gates for low noise cryogenic applications

We report on the successful integration of superconducting Nb gate electrodes to AlGaN/GaN heterostructures and HEMTs for low noise cryogenic applications. First, a specific Nb-gate process was developed and implemented on stand-alone gate test structures. The latter were tested at cryogenic temperatures down to 4 K, using DC end-to-end measurements. The results show a clear transition to a superconducting state at Tc ~ 9.2 K. The superconducting nature of the Nb gates further verified on actual HEMTs, featuring 2 fingers design with gate length of 0.2 μm, through their S-parameters measurements at Tc. Finally, we demonstrate a significant reduction of the gate resistance with superconducting Nb compared to Au-gated transistor with the identical dimensions. The results confirm the potential of the GaN HEMTs with superconducting Nb-gate for low noise operation at cryogenic temperatures.