| Single photon is the smallest basic unit of light,detecting a single photon is the most important breakthrough in the field of detection technology.At present,single-photon detection technology has been widely used in various fields such as fluorspar spectroscopy,nuclear investigation and quantum communication.Among them,the superconducting nanowire single photon detector(SNSPD)has gradually become a mainstream detection technology due to its high efficiency,low noise and small time jitter.Niobium nitride(NbN)is widely used in SNSPD because of its high transition temperature and good stability.For SNSPD devices,the quality of the superconducting thin film is one of the key factors that determine the performance of the device.Therefore,growth of NbN thin films with high quality is particularly important to fabricate SNSPD devices.In this paper,magnetron sputtering and polymer-assisted deposition(PAD)are used to grow ultrathin superconducting NbN thin films.The quality and performance of the films grown under different processes and conditions were studied.After that,e-beam lithography and reaction ion etching have been used to fabricate superconducting meander-line nanowires and their single photon detector devices.Finally,a set of electron beam direct writing patterning technology was developed based on the PAD method,which provides the basic research for the fabrication of new superconducting nanowires and the potential applications of their single photon detectors.The specific content is divided into the following four parts:1.Growth of ultra-thin superconducting NbN films by magnetron sputtering method.The magnetron sputtering is used to grow NbN thin film on magnesium oxide(MgO)substrate.And the effects of different sputtering conditions on the properties of thin film were specifically studied.After obtaining the optimal conditions,a superconducting epitaxial NbN film with about 5 nm thickness and 12.5 K superconducting critical temperature has been grown on MgO substrate.Base on this research,ultra-thin superconducting NbN film grown on different substrates has been achieved2.PAD to achieve ultra-thin superconducting niobium nitride film growth.PAD is the thin deposition method that combines atomic layer deposition and chemical vapor deposition.This method mainly uses water-soluble polymer to coordinate with metal ions to form a stable precursor solution.Subsequently,the precursor is spin coated on various substrate and annealed at high temperature in an ammonia atmosphere.At this time,the polymer will be decomposed at high temperatures,and the metal ions will be rearranged on the substrate surface.Thereby,the controllable growth of the ultra-thin NbN film can be precisely achieved at the molecular level,which with 7±2 nm thickness and 10.8 K superconducting critical temperature.3.Fabrication of NbN-SNSPD devices.After the previous ultra-thin film growth,the superconducting meander-nanowires were obtained through ultraviolet exposure,electron beam lithography and reactive ion beam etching.At the same time,a SNSPD test system consisting of low-temperature system,circuit system and light path system was built.Finally,75%(1550 nm)detection efficiency of the devices is obtained through the test system,and the performance parameters of the devices are analyzed in detail.4.Research on direct-write electron beam lithography for superconducting nanowires and semiconductor micro/nano devices.Based on the PAD method,a precursor solution capable of coordinate metal ions and having photolithographic/electron beam properties has been developed.By acting of the electron beam,semiconductor patterns of different sizes and structures can be achievedIn summary,this research provided experimental support for the fabrication of SNSPD devices.Combined with direct-write electron beam lithography,it can provide a feasible solution for the realization of circuit devices in the post-Moore era. |
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