Electron-Phonon Decoupling NbSi CMB Bolometers

Abstract

Precise measurements of the cosmic microwave background (CMB) is crucial to cosmology, since any proposed model of the Universe must account for the features of this radiation. E_cient very large bolometer arrays (>10,000 pixels) constitute an important challenge for CMB observations and are actually developed by many groups worldwide. We present here an explorative new bolometer design based on a structure that simplifies the fabrication process and exhibits high sensitivity. This innovative device replaces delicate membrane-based structures and eliminates the mediation of phonons: the incoming energy is directly captured and measured in the electron bath of an appropriate sensor and the thermal decoupling is achieved via the intrinsic electron-phonon decoupling of the sensor at very low temperature. Reported results come from a 204-pixel matrix of Nb _x Si_1−x transition edge sensors with a meander structure fabricated on a 2-inch silicon wafer using electron-beam co-evaporation and standard lithography process. To validate the application to CMB measurements, we have realized an optical calibration of our sample in the focal plane of a dilution cryostat test bench.