Abstract In this Perspective article, we evaluate the current state of research on the use of focused electron and ion beams to directly fabricate nanoscale superconducting devices with application in quantum technologies. First, the article introduces the main superconducting devices and their fabrication by means of standard lithography techniques such as optical lithography and electron beam lithography. Then, focused ion beam patterning of superconductors through milling or irradiation is shown, as well as the growth of superconducting devices by means of focused electron and ion beam induced deposition. We suggest that the key benefits of these resist-free direct-growth techniques for quantum technologies include the ability to make electrical nanocontacts and circuit edit, fabrication of high-resolution superconducting resonators, creation of Josephson junctions and superconducting quantum interference device (SQUIDs) for on-tip sensors, patterning of high-Tc SQUIDs and other superconducting circuits, and the exploration of fluxtronics and topological superconductivity.
Abstract In this Perspective article, we evaluate the current state of research on the use of focused electron and ion beams to directly fabricate nanoscale superconducting devices with application in quantum technologies. First, the article introduces the main superconducting devices and their fabrication by means of standard lithography techniques such as optical lithography and electron beam lithography. Then, focused ion beam patterning of superconductors through milling or irradiation is shown, as well as the growth of superconducting devices by means of focused electron and ion beam induced deposition. We suggest that the key benefits of these resist-free direct-growth techniques for quantum technologies include the ability to make electrical nanocontacts and circuit edit, fabrication of high-resolution superconducting resonators, creation of Josephson junctions and superconducting quantum interference device (SQUIDs) for on-tip sensors, patterning of high-Tc SQUIDs and other superconducting circuits, and the exploration of fluxtronics and topological superconductivity.
This article reviews recent progress in superconducting nanodevices, with particular emphasis on fabrication methods developed for superconducting nanowires and nanoscale Josephson junctions based on different barrier materials. It evaluates the future potential of superconducting nanodevices, including nano-superconducting quantum interference devices (nanoSQUIDs), in light of improvements in nanoscale fabrication and manipulation techniques, along with their likely impacts on future quantum technology and measurement. The article first considers efforts to realize devices at the physical scale of 100 nm and below before discussing different types of Josephson junction such as trilayer junctions. It also describes the use of focused ion beam milling and electron beam lithography techniques for junction fabrication at the nanoscale and the improved energy sensitivity detectable with a nanoSQUID. Finally, it looks at a range of applications for nanoSQUIDs, superconducting single photon detectors, and other superconducting nanodevices.
Researches on the fabrication of ~ 0.1 × 0.1 μ m 2 superconductor–insulator–superconductor (SIS) Josephson junctions are reviewed. Today, a typical dimension is 1–10 μm for Josephson junctions in superconducting integrated circuits. These Josephson junctions are defined by well-established photolithographic technology with reactive ion etching (RIE), and for the superconductor, Nb is almost always used. The merits of Nb include the facts that the superconducting transition temperature Tc of Nb (9.2 K ) is higher than the boiling point of He (4.2 K ), and that Nb has excellent stability against thermal cycling between room temperature and liquid- He temperature. For the fabrication of ~ 0.1 × 0.1 μ m 2 junctions, on the other hand, there is a standard process with electron-beam lithography, shadow evaporation, and lift-off. This process works well for Al (Tc = 1.2 K ), however, it is not ideal for Nb . The scope of this brief review is the nanoscale junction with Nb electrodes. We will look at the efforts of optimizing the standard lift-off process for Nb , electron-beam-lithographic versions of the Nb Josephson-junction technology, focused-ion-beam (FIB) etching as a convenient alternative to electron-beam lithography and RIE, etc. In order to characterize nanoscale tunnel junctions, the single-charge transistor has been often fabricated. Therefore, a summary of its theoretical transport properties is also included.
The requirements of quantum metrology and nanoscience are driving the need for single-particle detection capability across a wide variety of physics areas, including quantum information processing, single-photon detection, nanoelectromechanical systems, nanomagnetism and spintronics. The single particles to be detected include atoms, molecules, photons, spins and even phonons, in the future. Nanoscale superconducting quantum interference devices (nanoSQUIDs) represent a new manifestation of an old but exciting superconducting technology which addresses some of these requirements. In this paper we describe a straightforward approach to fabricating Nb microbridge weak links using combined optical lithography and focused ion beams which may be used to fabricate nanoSQUIDs. The devices show non-hysteretic current?voltage characteristics and demonstrate very low noise, even at operating temperatures above 4.2?K. To improve our understanding of the superconducting properties of the Josephson microbridge/nanobridge junctions which have proved very successful in realizing low noise nanoSQUIDs we have carried out a combination of investigations. These include cryogenic resistance versus temperature (R(T)) and current?voltage characteristic measurements, atomic force microscope scans, controlled gallium (Ga) ion milling and implantation, and ion beam track modelling of these Josephson devices and Nb thin films.
Thermal effects serve as universal stimuli for material transformation, capable of inducing processes, such as crystallization, evaporation, and melting in various materials. In this paper, we propose an efficient and cost-effective fabrication method based on nano-laser direct writing (NLDW) technology for the fabrication of Nb constricted junctions and superconducting quantum interference devices induced by thermal effects. By narrowing the spacing between laser paths step by step, the I–V characteristics of constricted junctions can be continuously adjusted from collective Cooper pair transport to Josephson junction behavior. Additionally, the heat-affected zones induced by laser irradiation were characterized by heat transfer simulations and electrical transport behavior. Furthermore, the flux noise spectral density of a patterned superconducting quantum interference device based on NLDW is 2.8μΦ0/Hz1/2 in the white noise range, which exhibits comparable performance to devices based on traditional ion beam or electron beam etching processes. In this case, this technique could provide a reliable and reproducible pathway for scaling up the fabrication of superconducting quantum circuits, as well as an avenue to conduct nanoscale thermal engineering in superconducting materials research for basic science.
We present a fabrication technology for nanoscale superconducting quantum interference devices (SQUIDs) with overdamped superconductor-normal metal-superconductor (SNS) trilayer Nb/HfTi/Nb Josephson junctions. A combination of electron-beam lithography with chemical-mechanical polishing and magnetron sputtering on thermally oxidized Si wafers is used to produce direct current SQUIDs with 100-nm-lateral dimensions for Nb lines and junctions. We extended the process from originally two to three independent Nb layers. This extension offers the possibility to realize superconducting vias to all Nb layers without the HfTi barrier, and hence to increase the density and complexity of circuit structures. We present results on the yield of this process and measurements of SQUID characteristics.
Abstract In this paper a nanofabrication process, based on a focused ion beam (FIB) nanosculpting technique, for high sensitivity three-dimensional nanoscale superconducting quantum interference devices (nanoSQUIDs) is reported. The crucial steps of the fabrication process are described, as are some peculiar features of the superconductor–normal metal–insulator–superconductor (SNIS) Josephson junctions, which may useful for applications in cryocooler systems. This fabrication procedure is employed to fabricate sandwich nanojunctions and high sensitivity nanoSQUIDs. Specifically, the superconductive nanosensors have a rectangular loop of 1 × 0.2–0.4 μ m 2 interrupted by two square Nb/Al–AlO x /Nb SNIS Josephson junctions with side lengths of 0.3 μ m. The characterization of a typical nanoSQUID has been carried out and a spectral density of magnetic flux noise as low as 0.8 μ Φ 0 Hz –1/2 has been measured.