Normal Metal Hot-Electron Microbolometer with Superconducting Andreev Mirrors

Abstract: This thesis concerns development of the Normal metal hot-electron microbolometer (NHEB). The NHEB is an antenna-coupled direct detector of sub-millimeter wave electromagnetic radiation. The input signal power is delivered to the electron subsystem in a microscopic metal strip, which results in elevation of the electron temperature above the lattice temperature. The electron temperature is measured by means of normal-metal/insulator/superconductor (NIS) tunnel junctions. Andreev reflection is used to thermally isolate the electron subsystem of the strip from the antenna electrodes.

The NHEB is suggested for future applications in astrophysics as an alternative to the presently used blackbody bolometers. The NHEB has a comparable sensitivity (Noise Equivalent Power) on the order of 1e-17 W/sqrt(Hz), but it offers a much higher detection speed, and it is fully compatible with planar microfabrication technology, which is necessary for creating of large multipixel bolometer arrays.

In the course of this work NHEB detectors have been fabricated using electron-beam lithography and shadow evaporation of metals. The detectors have been initially characterized electrically by applying constant heating current through the sensor and measuring the detector response. A sensitivity NEP = 5e-18 W/sqrt(Hz) at 0.1 Kelvin has been measured for the NHEB in these experiments. A cryogenic measurement setup with quasioptical coupling has been built to characterize the bolometers with an external electromagnetic signal. In this setup the NHEB has been successfully operated as a receiver at 300 GHz. Its optical power responsivity has been measured using the hot/cold load method.