Sputtering mode diagram for the precise growth of NbN superconductor films

The sputtering mode diagram (SMD) provides a powerful tool for comprehensive structure engineering of functional films in developing advanced electronic devices, but has not reported due to the complexity of dynamic process and multi-parameters. Here, we report the SMD of superconductor niobium nitride (NbN) films with reactive magnetron sputtering. Poisoned mode, competing mode and metallic mode are drawn by the boundaries identified by the current‒voltage curves of the sputtering system in the SMD, by which the phase structures and electronic properties of the NbN films can be precisely engineered. Typically, 9-nm-thick NbN films grown in the optimal poisoned and competing modes are applied for superconducting nanowire single-photon detectors (SNSPDs). The as-fabricated SNSPDs have flexible performances with saturated quantum efficiency and small kinetic inductance, which enables precise manipulation of the sensitivity and speed from the SMD. This work is also providing guidance for the research of other functional films and electronic devices, which can undoubtedly promote its practical application such as dark matter detection and high-speed quantum communication.