Development of superconducting tunnel junction photon detector on SOI preamplifier board to search for radiative decays of cosmic background neutrino

We present a development of a novel photon detector based on superconducting tunnel junction (STJ) and silicon-on-Insulator (SOI) technology for application to an experiment to search for radiative decays of cosmic background neutrinos using photon energy spectrum in the cosmic infrared background region. The requirement of the detector for the experiment is a capability of photon-by-photon detection in the far-infrared region. In principle, a Nb/Al-STJ is expected to be able to detect a single far-infrared photon, however, it has not succeeded yet even with the STJ since the signal from the single far-infrared photon is much smaller than the readout noise level currently achieved. To solve this problem, we employ a preamplifier that can be operated at a cryogenic temperature below 1K to improve the signal-to-noise ratio in STJ readout signal. SOI preamplifier is a promising candidate as it was reproved to function at 4K by a JAXA and KEK group. We process a STJ directly on the SOI wafer with the preamplifier circuit to make the detector simple and compact. First we tested a STJ on a SOI board only with SOI-MOSFETs to verify the electrical contact between the STJ and the SOIFET electrodes as well as the STJ being processed without causing any damage on SOI-FET. We have confirmed that the SOI-FET shows an excellent performance below 1K and the STJ on the SOI can operate normally. Then we designed a more practical version of the SOI-STJ photon detector with a preamplifier circuit in the SOI wafer.