Dendritic flux avalanches in high-quality NbN superconducting films

Niobium nitride (NbN) thin films are extensively used in superconducting devices such as single-photon detectors, hot electron bolometers, microwave resonators and kinetic inductance detectors. The operation of these devices is strongly influenced by the quality of the films, especially by their resistivity and superconducting transition temperatures (Tc). NbN films have rather high Tc of ∼16.5 K and high resistivity of few hundreds micro-Ohm cm, which is perfect for operation of many superconducting devices. However, at low temperatures films are vulnerable to thermomagnetic instabilities in form of dendritic avalanches promoted by high resistivity in the normal state. Recently, new production route for NbN films has been established using high-temperature chemical vapor deposition (HTCVD). Transport measurements show low resistivity in normal state and suggest low level of lattice disorder. The highest for NbN Tc of 17.06 K was also reported in the films grown by HTCVD. According to previous study, these films should be thermo-magnetically stable. This work clarifies if it is the case and searches in one of them for dendritic flux avalanches. The nanoscale origin of avalanches is discussed.