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 1.2 K, was fabricated and characterized. Formation of the Al/Ti bilayer with tetragonal structure was confirmed by x-ray diffraction analysis. The surface roughness of 3.11 nm calculated by atomic force microscopy was found to be negligible compared with the particle size (19.66 nm), 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 Tc of 0.45 K and ΔTc = 2 mK. Such TES bolometer arrays are suitable for astrophysical observations and are extensively used in cosmic microwave background polarization detection.