Preparation And Performance Study Of AlN Insulating Layer Of NbN Superconducting SIS Junction For LCT Telescope

Based on the upgrade of the LCT submillimeter-wave telescope led by the China-Chile International Joint Laboratory for Submillimeter Astronomy,this paper uses the high-energy gap Nb N based superconducting SIS junction to transform the original Nb based superconducting receiver,so that the LCT can meet the requirements of sky survey observation with large sky area,high resolution and high sensitivity.Since the Nb N superconducting coherence length is much smaller than Nb,the thickness of the Al N insulation layer of the Nb N superconducting SIS junction is required to be?2 nm,and on this basis,low leakage current and small dielectric constant are realized to obtain superconducting SIS junction with high current density.Therefore,this paper studies the preparation of the Al N insulating layer,the key technology in Nb N superconducting SIS junction,and establishes the relationship between the preparation process and the structure and electrical properties of Al N films,in order to finally realize the preparation of high current density Nb N based superconducting SIS junction.The main research contents and results of this paper are as follows:1.By changing the sputtering pressure and sputtering power,the morphology and structure evolution of Al N films were explored,and the relationship between sputtering conditions and the structure and physical properties of Al N films was established.The results show that Al N films sputtered with different parameters are wurtzite hexagonal structure with highly preferred orientation along(002)direction in pure N₂atmosphere and surface roughness is between 0.26 and 0.58 nm.Al N films prepared at low sputtering pressure have residual compressive stress and good adhesion,which provides a reference for the subsequent study of the electrical properties of Al N films.2.Change the sputtering pressure,sputtering power and film thickness,study the change law of the conductivity and dielectric properties of Al N film,explore the causal relationship between the electrical properties and the material structure morphology,and get the corresponding law.The preparation of a large-area Nb N superconducting SIS junction is a preliminary exploration for the preparation of high current density superconducting SIS junction.By changing the sputtering pressure,sputtering power and film thickness to study the change law of the conductive and dielectric properties of Al N films,explore the causal relationship between the electrical properties and the material structure and morphology,and obtain the corresponding law.Prepare large-area Nb N superconducting SIS junction,and carry out preliminary exploration for the preparation of high current density superconducting SIS junction.The results show that when the sputtering pressure is 2 mtorr and the sputtering power is 100 W,the average resistivity of Al N films is 7.76×10⁹?·cm,the relative dielectric constant is 3.47,which meets the electrical performance requirements of SIS junction of Nb N superconducting receiver.The I-V test curves of the large area Nb N superconducting SIS junction have obvious nonlinear step characteristics of the superconducting SIS junction current.The Al N films prepared in this paper have good insulation properties and small roughness,which can meet the preparation requirements of barrier layer films of superconducting SIS junction.It provides a reference for the preparation of 1?m²superconducting SIS junction in the next step.