Nanomanufacturing of High-temperature Superconductor Circuits Using Focused Ion Beams

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The research objective is to investigate high-throughput, large-area nanomanufacturing of high-temperature ceramic oxide superconductor electronics. At liquid nitrogen temperature, ceramic oxide materials superconduct, i.e., they conduct electricity without offering resistance. These superconductors are anisotropic and the conductivity varies in different crystallographic directions, which complicates the manufacturing of Josephson junctions, the building-blocks of these circuits. Recent advances in focused ion beam technology has opened up a new resistless direct-write nanomanufacturing method for high-temperature superconductor electronics that has the potential to improve performance and reduce cost. This research involves several disciplines in science and engineering including nanofabrication, superconductor electronics, and cryogenics. The project will develop knowledge and skills in film growth, nanofabrication, mathematical modeling, advanced low noise electron transport measurement techniques as well as critical thinking to prepare students for careers in Science Technology Engineering and Mathematics. The Institute's Faculty Mentor Program will be utilized to create opportunities for women and underrepresented minority students. The superconductor electronics industry will be impacted in areas from high performance cryogenic computing to high temperature semiconductor amplifiers.The challenges to fabricating high transition temperature (high-Tc) ceramic oxide superconductor circuits are several. Its anisotropic crystal structure complicates the manufacture of Josephson junctions. The figure of merit for Josephson junctions scales exponentially with the circuit critical dimension. High performance devices require feature sizes in the sub-10 nanometer regime. Variation of even 1 nm can result in large fluctuations in the figure of merit. Despite these challenges many high-Tc junction manufacturing techniques have emerged over the last three decades but none is able to generate large numbers of Josephson junctions with high-yield and predictable properties. This award utilizes a finely focused 0.5 nm helium ion beam to directly modify the superconducting material for the precise fabrication of nanowires for Josephson junctions. The key to this method is that the material is very sensitive to the oxygen ordering in the crystal lattice which can be altered by light ion irradiation. Restricting this altered region to the nanoscale allows for the creation of in-plane tunneling barriers directly in the material with no resists or etching. The method is compatible with commercially available high-TC superconductor films on relatively inexpensive large area sapphire wafers. There are a number of variables in the parameter space for this process, such as beam current, dose, film thickness, and spatial Josephson junction dimensions. The goal is to study the impact of these parameters throughput, yield, and figure of merit uniformity.