Fabrication of Granular Aluminum Microbolometers -- Solving the Contact Resistance Problem

The fabrication of granular aluminum superconducting bolometers with a $\sim $10 ns response time and an active area of 10 micron x 20 micron will be described. Photomask design, the photolithographic and sputtering processing steps will be discussed in detail. Reproducible bolometers with room temperature resistances of 10-Ohms are routinely obtained. In particular, the common problem of the oxidation of the granular aluminum prior to the deposition of the electrical contact pads has been solved by sputtering a thin ($\sim $50 angstroms) palladium protective layer over the aluminum prior to exposure to air.