Novel hot-electron microbolometer

We present measurements of a novel power detector which can be used as an ultra-sensitive detector of millimeter and sub-millimeter radiation. The absorbing element consists of a thin film resistor with submicroneter dimensions, which is connected to superconducting electrodes. This device exploits the Andree´v reflection of electrons, and the weak interaction between electrons and phonons at low temperatures, in order to produce a large temperature rise for a small input power (≈10 mK/fW). The temperature rise of the electrons is measured from the temperature dependence of the current-voltage characteristic of a superconductor-insulator-normal metal tunnel junction, where part of the resistor strip forms the normal electrode. We have measured a voltage responsivity ≈109 V/W, and an amplifier-limited electrical NEP≈3×10-18WHz-1/2 at an operating temperature of 100 mK. If infrared radiation were coupled to the absorbing element by using superconducting planar antennas, then the sensitivity of this detector would be at least a factor of 10 higher than the best available direct detectors and thus may become the detector of choice for important astrophysics investigations.