Normal-metal hot-electron microbolometer with on-chip protection by tunnel junctions

We describe recent developments in a fully on-chip integrated antenna-coupled bolometer for astrophysical applications at millimetre and submillimetre wavelengths. We have developed a normal-metal hot-electron microbolometer with Andreev mirrors for thermal protection of the absorber and the coupling to the antenna. In previous experiments we could not operate the sensor at temperatures below 300 mK presumably because of the high external noise load. Our latest results with the absorber protected by tunnel junctions show how this problem can be solved experimentally. We have achieved noise performance mostly limited by the amplifier, which corresponds to expected detector NEP on the order of 1.5x10-17 W Hz1/2 at 100 mK. (author)