High Quality Superconducting Thin Films And Fabrication Of Quantum Electronic Devices

Since Onnes discovered the phenomenon of superconductivity in 1911,people have never stopped exploring the nature and laws of superconducting electricity.With the rapid development of cryogenic technology in recent years,the practical application of superconductivity becomes possible.In these applications,superconducting quantum devices have attracted more and more attentions as a strong contender for quantum computing.Among them,the preparation of high quality superconducting films and devices is a key step to determine the performance of quantum bits.In this thesis,the growth of high quality superconducting thin films,the preparation and properties of superconducting quantum devices are systematically studied.The conclusions are as follows:We have obtained a series of high quality superconducting films of different thickness that grew by optimizing the parameters such as background vacuum,sputtering pressure,Ar,N2 ratio and sputtering power.The Tc of 300 nm thick Nb Ti N film reached 15.5 k,the surface roughness was 0.2 nm,and the superconducting transition width was 0.03 k.The extremely low surface roughness and extremely narrow transition width indicate that the film has good uniformity,which provides a good basis for the preparation of quantum devices such as superconducting tunneling junction.The 5 nm ultra-thin Nb Ti N film grew on the high-resistance Si substrate at room temperature sputtering,Tc up to 7.63 k,has laid a good foundation for the preparation of single-photon detection devices.In order to study the thermal stability of the thin film and improve its superconductivity,we treate Nb Ti N thin films by rapid thermal annealing in the atmosphere of pure nitrogen and nitrogen hydrogen mixture respectively.Experimental results show that the superconducting transition temperature can be increased by rapid thermal annealing in both gases.It is better to heat annealing in the mixture of nitrogen and hydrogen.The 10 nm-thick Nb Ti N thin film superconducting transition temperature increased from 9.6 k to 10.3 k in a mixture of 85% N2 and 15% H2 at 450 ? for 10 minutes of rapid thermal annealing.We have fabricated High quality superconducting coplanar waveguide resonator devices by laser direct writing and inductively coupled plasma etching.The main factors affecting the intrinsic quality factors of the superconducting resonator were studied by comparing the different substrate processing techniques,changing the development exposure parameters,and comparing the preparation parameters of different substrate etching depths.It is found that the two-level system at the interface between substrate and film has a great influence on the quality factor of the resonator.The treatment of passivation and degassing for surface of Si substrate before depositing the film will greatly improve the film quality factor.At present,through substrate surface treatment and substrate depth etching and other technologies,the intrinsic quality factor of the superconducting Nb film coplanar waveguide resonantor prepared by us can reach up to 800,000 and up to 1 million orders of magnitude at 20 m K and nearly single photon level.The quality factor of superconducting Nb Ti N thin film coplanar waveguide resonator can reach 150,000.We have investigated the fabrication process and precautions of Josephson parametric amplifier on Si substrates by using magnetron sputtering superconducting Nb films.Compared with the preparation of devices using Al film on sapphire substrate,the preparation process of superconducting quantum bits using Nb film on Si substrate is simplified due to the fact that there is no need to prepare a layer of gold film as a nesting location.The array Josephson parametric amplifier replaces the plate capacitance with the interdigital capacitance,and obtains large inductance through the series connection of several SQUID,thus realizing parametric amplification and simplifying the preparation process of parametric amplifier.At present,the preparation technology of SQUID series junction on Si substrate is basically mature,and its properties are preliminarily tested.We prepared a planar Josephson tunnel junction by wet etching.First we prepared In Ga Zn O amorphous insulating film with certain thickness in the substrate.Then there will be a concave through the Micro-nano processing technology and wet etching method.Finall we grow the superconducting thin film plating on both sides of steps.We can obtain the steps on nanometer level through the methods such as control bench height,film thickness and concave depth.We may fill in the gap to study nanoparticles on the tunneling properties.High quality superconducting thin films and quantum devices are the key and foundation of quantum computing.In this paper,the parameters affecting the film quality and device performance are studied,and the key steps and main factors affecting the device index are discussed.By optimizing the sputtering parameters and improving the preparation process,high quality superconducting films and superconducting quantum devices were obtained,which laid a good foundation for the preparation of high quality qubit devices.