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

2007年，舍布鲁克大学的一个团队报告了一种创新的隧道势垒制造方法，该方法可以对金属单电子晶体管（SET）进行更大的尺寸控制。这一突破性的创新现在被半导体行业的路线图（ITRS 2007）所提及。提出的研究计划将使用这种新颖的制造技术来实现纳米级超导约瑟夫森结（JJ）。低温超导体JJs主要采用两种方法制备：阴影蒸发（如基于人工智能的量子计算）；平面金属-势垒金属（如Nb基快速单通量量子电子学，RSFQ）。这种新技术将是约瑟夫森结制造方法在过去二十年中的第一个重大变化。这项新技术有望取得两个重要成果：在铌中可以实现更小的面积结，从而在量子比特设计（量子计算位）中提供更大的自由来平衡充电和约瑟夫森能量；RSFQ路线图所期望的RSFQ大规模电路更高的工作频率（~500GHz）和集成密度。此外，这项技术将允许隧道屏障工程甚至在超小面积的交汇处，这是传统方法几乎不可能做到的。该计划的第一阶段是探索与制造相关的材料问题以及由此产生的JJs的超导特性。铌将是一个候选选择，但其他材料将被考虑。第二阶段将进行势垒工程，研究其对结性质的影响。第三阶段的目标是在现有技术的基础上制造小规模超导电路。考虑了量子计算中量子比特设计和RSFQ的应用。该研究项目通过挑战传统的制造方法，具有独特的创新潜力。所需的纳米制造环境已经存在并且得到了很好的支持。我在超导纳米结构方面的广泛专业知识以及我在该领域扩展的本地和国际网络也将极大地受益于该项目。

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.