Characterization of an Iridium Based TES Light Detector for Neutrinoless Double Beta Decay Search

Reading out both the heat and light signals from the cryogenic calorimeters used in neutrinoless double beta decay search and direct dark matter detection is a powerful way to reject the background events on an event-by-event basis. For this purpose, we are developing a superconducting transition edge sensor (TES) based light detector targeting O(10) eV energy threshold and O(100) $\mu$s response time, to measure the scintillation or Cherenkov light produced in the target material by particle interactions. The light detector is fabricated by patterning an iridium/platinum bilayer TES at room temperature at the center of a two-inch silicon wafer. The superconducting transition temperature of the TES is tuned to achieve the target energy resolution and response time using the proximity effect. We will present the design, fabrication, and static characterization of such detectors, including the measured dependence of the transition temperature on normal metal thickness, electrical and thermal parameters of the TES, and their calorimetric performance.