A process route for fabricating microstrip-coupled Superconducting Transition Edge Sensors giving well-controlled device characteristics

Current and future astronomical instruments require large arrays of Superconducting Transition Edge Sensors (TESs). Of particular importance are microstrip-coupled TESs, where the incoming signal is delivered onto a silicon nitride membrane by means of a superconducting microstrip transmission line. This transmission line is then terminated with a thin-film load. We report on a wafer-based fabrication route for Molybdenum/Copper microstrip-coupled TESs that gives highly reproducible superconducting transition temperatures, and electrical and thermal parameters. Although a large array of voltage-biased TESs will operate satisfactorily with widely varying individual pixel characteristics, uniformity of the characteristics is clearly advantageous from an operational point of view in terms pixel to pixel variations in responsivity, power handling and noise. An overall device yield of 65% has been achieved for our first multi-wafer production run.