Fabrication and Characterization of Superconducting Bilayer (Al/Ti) Transition-Edge Sensor Bolometer Array

A four-by-four transition-edge sensor (TES) bolometer array based on an Al/Ti bilayer on an Si3N4 substrate for thermal connection, showing an unbiased transition temperature of 1.2K, was fabricated and characterized. Formation of the Al/Ti bilayer with tetragonal structure was confirmed by x-ray diffraction analysis. The surface roughness of 3.11nm calculated by atomic force microscopy was found to be negligible compared with the particle size (19.66nm), indicating a smooth surface. The smoothness of the resistance-temperature (R-T) curve corresponds to the smoothness of the surface of the bilayer sensor, and the superconducting transition curve of the suspended bilayer TES was designed with a biased T-c of 0.45K and T-c=2mK. Such TES bolometer arrays are suitable for astrophysical observations and are extensively used in cosmic microwave background polarization detection.