Twin-slot antenna coupled NbN hot electron bolometer mixers for space applications

摘要

We report record performance in spiral antenna coupled NbN phonon-cooled hot electron bolometer mixers: receiver noise temperatures of 950 K at 2.5 THz and 750 K at 1.9 THz. We also obtain a comparable noise temperature, 700 K at 1.6 THz, using a twin slot antenna mixer with a reduced HEB size. The absorbed LO power is 30 nW in the smallest HEB of 1μm in width and 0.15 μm in length. The LO power required to pump the mixer in front of the lens is expected to be about 100 nW. The improvement is achieved by changing the contact structures between the bolometer and the contact pads. The surface of the NbN film is sputter cleaned prior to the deposition of the contact pads to remove the contact resistance, while an additional superconducting NbTiN layer is in-situ added between the Au and the NbN to preserve superconductivity under the pads. Apart from the superior noise temperatures, we also observe a good reproducibility. Our approach opens a route towards further improvement of the performance.