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。这一突破性创新现在被半导体行业的路线图所指(ITRS 2007)。提出的研究计划将使用这种新的制造技术来实现纳米级超导约瑟夫森结(JJ)。低温超导体JJ的制备方法主要有两种：影子蒸发(如Al基量子计算)和平面金属-势垒-金属(如Nb基快速单磁通量子电子学)。这项新技术将是过去20年来约瑟夫森结制造方法的第一次重大变化。这项新技术有望带来两个重大成果：在量子比特设计(量子计算比特)中，可以实现更小面积的Nb结，从而获得更大的平衡电荷和约瑟夫森能量的自由；RSFQ路线图所期望的更高的工作频率(~500 GHz)和更高的RSFQ大规模电路集成密度。此外，这项技术将允许隧道屏障工程，即使在超小面积的交界处，这是传统方法很难做到的。该计划的第一阶段是探索与制造和所产生的JJ的超导性质有关的材料问题。Nb将是候选材料，但将考虑其他材料。第二阶段将实施屏障工程，并研究其对结性能的影响。第三阶段的目标是在已开发的技术基础上制造小型超导电路。讨论了它在量子计算、量子比特设计和RSFQ中的应用。这项研究计划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可用并且得到了很好的支持。该计划还将极大地受益于我在超导纳米结构方面的广泛专业知识，以及我在该领域扩大的本地和国际网络。

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.