Characterization of NbSi TES on a 23-Pixel Array

Instrumental progress allowed the development of bolometric detectors adapted to submillimeter and millimeter wavelengths. Superconducting transition-edge sensors (TESs) are currently under heavy development to be used as ultra sensitive bolometers. In addition to good performance, the choice of material depends on long term stability (both physical and chemical) along with a good reproducibility and uniformity in fabrication. For this purpose we are investigating the properties of NbSi thin films and have already developed arrays of NbSi TES. NbSi is a well-known alloy for use in resistive thermometers. We present a low temperature characterization of the NbSi films on a 23-pixel array. In order to tune the critical temperature of the NbSi thermometers down to the desired range, we have to adjust the concentration of Niobium in the NbSi alloy. In this experiment, we set for a Niobium concentration of 15 percent, to be able to run tests at a convenient temperature larger than 300 miliKelvin. Tests are made using Helium4-cooled cryostats, 300 miliKelvin Helium3 mini-fridges, resistance bridge and a commercial SQUID with its readout circuit. Parameters being measured are: critical temperature, resistance, sharpness of the transition given by the alpha parameter and noise measurements. The multiplexing is also developed to prepare the final chain for noise measurements on 23 pixel bolometers array.