New manufacturing process Superconducting nanowire detectors for precise quantum communication

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Photonic sensors are the key to secure quantum communication and high-precision measurement technology. Researchers have developed a manufacturing process for superconducting nanowire single-photon detectors (SNSPD).

Light is the foundation for modern communication and sensing. Whether in quantum communication, optical metrology, or high-speed telecommunication, the detection of individual photons plays a central role.

An international research team has now made significant advances in the production of scalable superconducting nanowire single-photon detectors (SNSPDs), enabling extremely high sensitivity and fast signal processing. These detectors are relevant not only for secure quantum encryption but also for lidar systems in autonomous vehicles, biomedical imaging, and extremely low-light astrophysical measurements.

Complex manufacturing processes

Photon detectors like SNSPDs detect individual photons with high efficiency and speed. They are based on ultra-thin superconducting nanowires that transition from a superconducting to a normal conducting state when a photon impacts.

Arced-fractal SNSPDs (AF SNSPDs) are particularly powerful, as they detect photons independent of the angle of incidence and polarization due to their fractal structure. However, their production has so far involved considerable additional effort. In AF SNSPDs, the fractal structure ensures that the detection efficiency remains largely independent of these factors.

In a recent study published in the IEEE Journal of Selected Topics in Quantum Electronics, scientists from Tianjin University present an optimized manufacturing strategy for AF SNSPDs. The process involves several key steps:

• Optical microresonators: Coating a silicon wafer with alternating layers of silicon dioxide (SiO₂) and tantalum oxide (Ta₂O₅) using ion beam assisted deposition (IBD) to create a Bragg reflector structure.

• Superconducting layer: Applying a 9 nm (0.00035 inches) thin film of niobium titanium nitride (NbTiN) through reactive magnetron sputter deposition.

• Nanowire patterning: Structuring the nanowires with electron beam lithography and subsequent reactive ion etching.

• Chip finalization: Shaping the chips using lithographic methods and plasma etching for the integration of optical fibers.

Better manufacturing stability and outlook

The researchers recommend specific adjustments to optimize production. For example, a 5 nm (0.00020 inches) thick silicon or 3 nm (0.00012 inches) SiO₂ layer significantly improves the adhesion of the nanowire structure to the NbTiN layer. Additionally, extra nanowire patterns help calibrate the width of the wires and optimize the layout, minimizing variations in the structure. Precise exposure with accurate alignment masks also helps reduce structural distortions and improve the stability of etching processes, significantly enhancing the manufacturing precision of the detectors.

Through these process improvements, detectors with high sensitivity and system detection efficiency were realized. The results offer promising approaches for advanced photonic components, especially in quantum information and optical sensing. The continuous improvement of SNSPD technology could thus pave the way for new generations of highly sensitive and scalable detectors. (heh)