Study of superconducting Josephson junctions fabricated using a novel nanodamascene process for quantum computing and RSFQ application

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In 2007, a Université de Sherbrooke team reported an innovative new tunnel barrier fabrication method that allows greater dimensional control on metallic single electron transistor (SET). This breakthrough innovation is now referred to by the semiconductor industry's roadmap (ITRS 2007). The proposed research program will use this novel fabrication technique to realize nanoscale superconducting Josephson junctions (JJ). Low temperature superconductor JJs have been made using mainly 2 methods: shadow evaporation (e.g. Al based quantum computing); planar metal-barrier-metal (e.g. Nb based rapid single flux quanta electronics, RSFQ). This novel technique will be the first major change in Josephson junction fabrication methods in the last 2 decades. Two significant outcomes are expected from this new technique: smaller area junctions could be achieved in niobium thus giving a greater freedom to balance charging and josephson energy in qubit designs (quantum computing bit); higher operation frequency (~500GHz) and integration density for RSFQ large scale circuits as expected by the RSFQ roadmap. Furthermore, this technique will allow tunnel barrier engineering even at ultra small area junctions, which is hardly possible with the conventional methods. The 1st phase of the program is to explore material issues related to fabrication and to superconducting properties of the resulting JJs. Niobium will be a candidate of choice but other materials will be considered. The 2nd phase will be to implement barrier engineering and study its effect on junction properties. The 3rd phase will aim at fabrication small scale superconducting circuits based on the developed technology. Applications to quantum computing qubit designs and RSFQ are considered. This research program has a unique potential for innovation by challenging the conventional fabrication methods. The required nanofabrication environment is already available and well supported. The program will also greatly benefit from my extensive expertise in superconducting nanostructures and from my extended local and international network in the field.