Fabrication and optical characterization of the normal metal hot-electron microbolometer with Andreev mirrors

Abstract

The normal metal hot-electron microbolometer (NHEB) is a direct detector for mm and sub-mm wavelengths. Theoretical estimations indicate that such a device should be able to achieve a sensitivity of around 10 −17 W/(Hz) 1/2 at 0.3 K and a time constant less than 1 μs. The temperature of the electron gas is monitored using superconductor–insulator–normal metal (SIN/NIS) tunnel junctions. We have fabricated such an NHEB where the normal metal strip is coupled to a double slot antenna for optical qualification (normal metal strip size (5.6×0.25×0.03) μm 3). The antenna is designed for 300 GHz and has an impedance of 30 Ω at the center frequency. The actual optical responsitivity and the response time of our NHEB has been measured at 0.5 K using a hot/cold load (black body radiation at room temperature and at liquid nitrogen temperature). DC-current measurements performed on other samples earlier indicate that our NHEB can achieve an electrical noise equivalent power (NEP) of at least 3×10 −16 W/(Hz) 1/2. We conclude that the optical responsitivity value obtained in the measurement is consistent with the electrical NEP value at the same temperature and in agreement with the estimated efficiency of the quasioptical coupling.