Large Signal Amplitude and Bias Range of Cascade Switch Superconducting Nanowire Single Photon Detectors

Cascade switch superconducting nanowire single photon detectors has been fabricated of ultrathin NbN films deposited by DC-magnetron sputtering at room temperature on MgO substrates. Detectors using 4 to 24 nanowires in parallel, having an area coverage of 5x6 um^2 and a filling factor of 40%, have been investigated. Signal amplitudes increase with the number of parallel nanowires and reaches 12.3 mV with a signal noise of 20 uV. The range of bias currents where the detectors emit signal pulses also increase with the number of parallel nanowires and exceeds the nanowire critical current.