Fabrication Of Superconducting Al/Al₂O₃/Al Josephson Junctions And Superconducting Nb Air-bridges

Compared with classical computers,quantum computers have greatly improved the speed of computation.Therefore,quantum computing has become a hot topic in international research.Quantum computation can be achieved through a number of different physical systems.Among them,the superconducting qubits based on Joseph junction have attracted much attention because of their advantages of low loss,easy control,easy to scale,and compatibility with traditional microelectronic processing technology.The superconducting qubit is not perfect,because it is easily coupled with the outside world,which leads to a shorter time to degenerate from the superposition state to a single state.And that is,the time of the decoherence is short.Researchers have studied this difficult point and made great progress from the first few nanoseconds to few hundred microseconds.The study shows that the decoherence time is closely related to material,device structure and fabrication technology.In this paper,the fabrication technology of some important devices in the superconducting qubit circuit and some key technology are mainly studied.The fabrication of aluminum/alumina/aluminum(Al/Al2O3/Al)structure of Josephson tunnel junction was studied with aluminum as a superconducting material.And the fabrication technology of the Nb air-bridges was also studied in the superconducting quantum bit circuit.In addition,the fabrication process of the aluminum tunnel junction was used in the preparation of the Joseph parametric amplifier.The main research is in the following aspects:1.Study on the fabrication of Al/Al2O3/Al Josephson junctionThe structure of the suspended shadow mask was fabricated by deep UV lithography(DUV),and the aluminum film and the alumina barrier layer were grown by the method of electron beam angle evaporation.The AI/Al2O3/Al tunnel junction was prepared by this technique in one time,which greatly improved the characteristics of the tunnel junction.At the same time,the problems in the process of preparing suspended shadow mask and electron beam evaporating Al thin film were also explored and solved.2.Fabrication process and characteristics of superconducting Nb air-bridgesUsing the photoresist as a supporting layer and many micromachining methods such as direct current(DC)sputter,reactive ion etching(RIE)and lithography fabricate air-bridge structure connecting different ground planes of complex microwave circuits.A air-bridge with strong mechanical stability can be fabricated by controlling the thickness of supporting layer and the edge shape of the supporting layer.Different sizes of superconducting air-bridges were successfully fabricated and the low temperature superconducting electrical properties of the air-bridges were measured.The method is simple and stable,and the fabrication of air-bridges can becompleted by using the commonly micromachining process.The fabrication process can be used in the fabrication of complicated superconducting qubits circuits containing microwave components.3.Fabrication of Superconducting Josephson parametric amplifierBecause of the excellent low noise and high efficiency reading characteristics,the Josephson parametric amplifier plays an important role in the quantum bit measurement,and is a key device in the quantum bit research work.Based on the fabrication process of the perfect Al/Al2O3/Al Josephson junction,we successfully completed the fabrication of the superconducting Josephson parametric amplifier.