Fabrication and Characterization of an MgB2 bolometer

In this work, we present the experimental results obtained in the fabrication and characterization of a superconducting MgB2 bolometer. The device was made from an MgB2 meander-like structure suspended on a 500 nm thick SiN membrane. The MgB2 meander line was 50 μm wide and 7.6 mm long and it was defined by optical lithography and dry etching. The SiN membrane had an area of 1.3 mm× 1.3 mm and it was obtained by a silicon micromachining technique. The electrical and thermal properties of the device were measured at low temperature in a closed-cycle cryocooler. The resulting Tc of the meander was unchanged with respect to the unprocessed film and the transport properties, measured in voltage-biased mode, indicated a value for Jc of the order of 105 A cm−2 at 27 K. The logarithmic sensitivity of the bolometer turned out to be higher than 150. The study of the thermal properties of the bolometer on the membrane showed a thermal conductance of the order 10−5 WK−1 at a working temperature of 32 K. The bolometer, irradiated by a chopped laser beam, showed a cut-off frequency of 94 Hz. The maximum experimental responsivity was estimated to be 2.3 × 103 VW−1.