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We studied and improved the performance of a terahertz (THz) direct detector based on the superconducting NbN hot electron bolometer (HEB) integrated with microwave readout for imaging arrays and other applications. A 6 nm thick NbN microbridge at the feed point of a twin-slot antenna is embedded into a high-Q quarter-wavelength coplanar waveguide (CPW) resonator made from a 350 nm thick NbN film which is weakly coupled to a CPW feedline. THz direct detection was performed at a signal frequency of 0.66 THz at a bath temperature of 4.2 K. When operating at a low input microwave power level, the device acting as a microwave kinetic inductance detector with a kinetic inductance fraction of 0.45 changes the surface impedance of the resonator in response to incident THz radiation. The estimated optical noise equivalent power (NEP) is ∼0.23 pW · Hz−0.5 which shows about one order of magnitude improvement compared to that of the traditional voltage-biased NbN HEBs. The improved performance of the THz direct detectors with lower NEP and easy readout makes them promising in imaging with a large number of the array pixels. [ABSTRACT FROM AUTHOR]

Superconducting receivers based on large hot electron bolometer (HEB) bridges were constructed and they show low noise temperatures. Their stability has been characterized by the Allan variance measurements with either far-infrared laser or Gunn oscillator plus multiplier chain as the local oscillator. An Allan time of about 1 s has been obtained. Also demonstrated is the effectiveness of a stabilization scheme in which a radiation at a frequency much lower than the gap frequency of niobium nitride is used for improvement. [ABSTRACT FROM AUTHOR]