Fabricating WSi based superconducting microwire single photon detectors with laser lithography

To measure light down to the single photon level, superconducting nanowire single photon detectors (SNSPDs) have become the go-to devices, due to their near unity detection efficiency [1] , high-speed and low noise. An important figure of merit is the internal detection efficiency (IDE). To achieve a saturated IDE in the infrared, wire widths of the order 100 nm are typically required. Nevertheless, recent experiments have shown that functional detectors can be fabricated with wire widths up to 3 µm [2] – [4] . A higher silicon content of the films combined with a smaller film thickness enables wider wires. Increasing the wire width allows for bigger fabrication tolerances which enables the fabrication with optical lithography.