Terahertz Direct Detectors Based on Superconducting Hot Electron Bolometers with Microwave Biasing

Terahertz (THz) direct detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) with microwave (MW) biasing are studied. The MW is used to bias the HEB to the optimum point and to readout the impedance changes caused by the incident THz signals. Compared with the thermal biasing method, this method would be more promising in large scale array with simple readout. The used NbN HEB has an excellent performance as heterodyne detector with the double sideband noise temperature (T_\rm N) of 403 K working at 4.2 K and 0.65 THz. As a result, the noise equivalent power of 1.5 pW/Hz^1/2 and the response time of 64 ps are obtained for the direct detectors based on the NbN HEBs and working at 4.2 K and 0.65 THz.