Preparation And Properties Of Superconducting NbN Thin Films And Their Effects On SIS Junction Properties

In the 1980s,the technology in the terahertz frequency band broke through the bottleneck of terahertz sources and detectors.At the same time,the preparation process of superconducting tunnel junctions has been greatly improved.Scientists have begun to invest more in this field.Promote the development of superconducting electronics.High-sensitivity superconducting mixing technology is an important factor to promote astronomical observations in the terahertz band,and superconducting tunnel junctions are the core components of superconducting mixers.An important link in Hertzian astronomical observations.In this paper,according to the characteristics and application requirements of the core device superconducting mixer in LCT submillimeter-wave telescopes,NbN thin films and NbN/Al N/NbN films were prepared on single-crystal Mg O substrates at room temperature by magnetron sputtering technology.NbN three-layer film structure,specifically by changing nitrogen content and sputtering power,a superconducting NbN film with better quality is obtained,and it is applied to the three-layer film structure.Using probe profiler,XRD,SEM,AFM,EDS,XPS,PPMS and other modern measurement techniques to analyze the structure and properties of superconducting NbN thin films and trilayer films.The specific research contents are as follows:1.NbN thin films were prepared by magnetron sputtering,and the relationship between nitrogen content in the reaction gas and the structure,morphology,element valence and superconducting properties of the films was studied.The results show that when the partial pressure of N₂ reaches 10%(Ar:N₂=90:10),an obvious?-NbN diffraction peak can be observed,and the film grows preferentially along the(200)direction,with a narrow half-height width.The stoichiometric ratio of Nb/N is about1:1.The surface of the film is uniform and dense with low roughness.The superconducting performance is excellent,the superconducting transition width is narrow,the residual resistivity is greater than 1,and the highest superconducting transition temperature is 14.5 K.It shows that the film prepared under this condition is?-phase NbN,with high crystallization degree,good superconductivity and metal resistance properties.2.The nitrogen content was fixed(10%N₂)and the sputtering power was changed.The research results showed that the NbN film still showed good crystallinity at 350 W,400 W and 450 W,only the NbN(200)diffraction peak appeared,and the surface was smooth and flat with low roughness.In terms of superconducting properties,the superconducting transition temperature of the NbN films grown under the conditions of 400 W,450 W and 500 W are all above 14.5 K,the highest is 14.72 K,the superconducting transition width is narrow,and the residual resistivity is 1.05.3.Based on the above analysis,NbN films prepared under the conditions of power of 400 W and 450 W and nitrogen content of 10%were selected for the preparation of superconducting tunnel junction three-layer film structure.The NbN/Al N/NbN structure was grown under these conditions,with a high gap voltage up to 4.5 m V,a small gap voltage width of 0.24 m V,and a critical current density of1.36×10^-1 A/cm².After the definition of the superconducting SIS junction in the three-layer film structure is completed by photolithography,the reduction of the junction area is expected to greatly increase the critical current density.All the research work in this paper provides experimental reference for the subsequent photolithography and etching of superconducting tunnel junctions,lays a solid foundation for the further development of superconducting mixers,and facilitates the smooth development of the LCT submillimeter-wave telescope international cooperation project.It provides a guarantee and provides strong support for improving the detection capability of the telescope and realizing high-sensitivity and high-resolution detection...