Terahertz Direct Detection Behavior of a Superconducting NbN bolometer by Noise Thermometry

In this paper, we report the investigation of direct detection behavior of a superconducting niobium nitride (NbN) hot electron bolometer (HEB) based on noise thermometry. The HEB consists of a microbridge made from 5.5 nm thick NbN film and a twin slot antenna for radiation coupling. In the microbridge, hot electron system is generated after radiation pumping and it creates extra noise at RF frequencies. We measured the response of the noise at 0.5-1.8 GHz and the noise equivalent power (NEP) of the superconducting NbN HEB at different bias voltages. The measurement result shows that the superconducting NbN HEB has a noise equivalent power of 1.24×10-12 W/Hz1/2 at its optimal bias point. We also compared the noise equivalent power measured by noise thermometry at two different readout bandwidths. The measured results are found to be in good agreement with the theoretical one.