Enhanced Sensitivity of THz NbN Hot Electron Bolometer Mixers

TL;DR

This study demonstrates improved sensitivity of NbN hot electron bolometer mixers at THz frequencies, achieving lower noise temperatures and potential for faster measurements in space missions.

Contribution

The paper presents enhanced NbN HEB mixers with lower noise temperatures and improved performance at multiple THz frequencies, advancing their application in space-based heterodyne detection.

Findings

Achieved low T_mixer_DSB of 240 K at 1.6 THz

Demonstrated ~30% better performance than previous NbN HEB mixers

Limited improvement at 5.3 THz due to antenna geometry issues

Abstract

We studied the effect of the NbN/Au contact on the sensitivities of a NbN hot electron bolometer (HEB) mixer by measuring the double sideband (DSB) receiver noise temperature (T_rec_DSB) at three local oscillator frequencies of 1.6, 2.5 and 5.3 THz. The HEB has cleaned contact structures with a thick Au layer. We demonstrated low mixer noise temperatures (T_mixer_DSB) of 240 K and 290 K at 1.6 and 2.5 THz, respectively. The latter reach roughly 3 times the quantum noise at their frequencies. The mixer is developed for the proposed OASIS and SALTUS (concept) missions. The enhanced T_mixer_DSB are more than 30 % better in comparison with published NbN HEB mixers. The improvement can reduce the integration time of a heterodyne instrument roughly by a factor of 2. The T_mixer^DSB of the same HEB has shown limited improvement at 5.3 THz, which is partly due to non-optimized antenna geometry. Besides, the results also help to understand device physics of a wide HEB (4 um) at high frequencies.