Study On Superconductivity In Niobium Nitride Thin-film And Nanowire

Superconducting nanowire-based single-photon detector?SNSPD?is a potential and revolutionary single-photon detecting technology,which possesses all the breakthrough of key parameters for single-photon detecting.The material currently used in SNSPD is mainly niobium nitride?NbN?since it has a suitable coherence length and penetration depth.Therefore,it is important to find a way to grow high-quality niobium nitride superconducting films.Polymer assisted deposition?PAD?,which is an aqueous chemical solution route developed has been developed to growth epitaxial thin films of complex metal oxides,nitrides and carbides.Those PAD-synthesized thin films with merits of large-area smooth,uniform and dense provides a new cognitive platform for growing high-quality thin films.With ultra-thin superconducting thin film grown by PAD and magnetron sputtering method as the starting point and micromaching superconducting nanowires as the research object,this thesis focuses on the fundamental research of SNSPD.The key scientific problems to solve are to analyze the growth mechanism of the ultra-thin superconducting thin films and study the effects of micromaching technology on the performance of superconducting nanowires.The main subjects of the work are concluded as follows:1.Soluble polymer-assisted deposition is developed and high-quality superconducting NbN thin film is grown with homogeneous precursor solutions.Here we develop a chemical method of PAD to grow large lattice matched superconducting NbN thin film.The precursor solution is prepared by niobium chloride and polyethyleneimine?PEI?.The uniform precursor solution is spin-coated onto suitable substrate and then annealed in NH₃atmosphere,after which the NbN thin film is finally obtained.At the same time,we also use PAD to grow the transparent conductive high-quality carbon film on the quartize substrate and study its electrical properties.2.The ultra-thin superconducting NbN thin film is also grown by physical method-magnetron sputtering.The effects of pressure,atmosphere ratio,sputtering power,substrate,sputtering time on the NbN thin film are carefully investigated.So far,the synthetic problems of high-performance ultra-thin?<10 nm?NbN thin film has been solved.The as-prepared thin films have reached the requirements of superconducting single-photon detecting.3.The etching methods including inductively coupled plasma etching and reactive ion-beam etching are explored in depth to obtain superconducting circuitous NbN nanowires.With the assistance of mask plate,nanowires with different line width and circuity can be efficiently etched.Moreover,different circuitous nanowire patterns with excellent critical transition temperature and critical current density have been successfully etched.