Large-Area Niobium Titanium Nitride Superconducting Microstrip Single-Photon Detector Fabricated Using a Photolithography Process

In this paper, we present a large-area niobium titanium nitride (NbTiN) superconducting microstrip single-photon detector (SMSPD) fabricated using a photolithography process. We fabricated a 1-μm-wide NbTiN-SMSPD covering 420 × 420 μm
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active area with a filling factor of 20% using an i-line stepper. The detector is cooled down to approximately 2.2 K, and its performance is evaluated at the wavelengths from visible to near-infrared. The detector operates stably without a shunt resistor and shows single-photon sensitivity for photons with a wavelength of 1550 nm. The bias current dependence of the detection count rate is measured at the wavelengths from 406 to 1550 nm. The saturation of the detection count rate with increasing the bias current was successfully observed at wavelengths below 850 nm, suggesting an internal detection efficiency approaching 100%. Furthermore, we evaluated the timing jitter performance using the femtosecond pulse laser with a wavelength of 1550 nm. Consequently, we achieved a system timing jitter of 85 ps for a light spot diameter of 100 μm.