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Journal of Applied Physics

Constricted junction based superconducting quantum interference devices via nano-laser direct writing

Yicong Huang, Songling Xiao, Wenzhi HuangHaifeng ChengChaoyang Zhang, Wenqian Liu, Enhua Chen, Chaoyun Zhang, Shangqing Li, Daqian Liu, Xiaoliang Wang, Xiuyan Peng Xiuyan Peng, Huachuan Wang, Jianxin Lin

Published Dec 23, 2025• 2 citations
Publisher

Abstract

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.

DOI
10.1063/5.0279330

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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.
Abstract We propose the fabrication of micro-superconducting quantum interference devices via nano laser direct writing (NLDW). A 20 nm thick Nb film with a critical transition temperature of 9.2 K was deposited on a silicon substrate by sputtering, and nanopatterning was performed with NLDW. After optimizing parameters such as the laser pulse width and power, we investigated the electrical performance of SQUIDs by varying the laser power between 245 mW and 270 mW in 5 mW steps. Experimentally, the voltage–flux (V–Φ) characteristics of micro SQUIDs exhibited typical periodic modulation, confirming the Josephson effect and magnetic flux quantization effect based on the NLDW process. The noise spectral density measurements of SQUID fabricated with laser power of 265 mW achieved a white noise level of 3 μ Φ 0 /Hz 1 / 2 , demonstrating comparable flux noise sensitivity compared to electron beam and ion beam fabrication processes. Furthermore, the devices retained stable superconducting and electrical performance after 101 days, illustrating excellent long-term stability. To some extent, the NLDW shows the potential to perform micro-nanopatterning of superconducting devices efficiently and cost-effectively, as well as an avenue for conducting nanoscale thermal engineering on superconducting devices for basic science research.
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.
In this work, we demonstrate the ability to fabricate superconducting quantum interference devices (SQUIDs) by directly writing Josephson junctions into the plane of YBa2Cu3O7−δ thin films with a focused helium ion beam. This technique allows for the control of the Josephson barrier transport properties through the single parameter, ion dose. SQUIDs written with a dose of 4 × 1016 ions/cm2 had metallic barrier junctions that exhibited nearly ideal electrical transport characteristics at 50 K and a flux noise of 20 μΦ0/Hz at 10 Hz. At higher irradiation doses, the SQUIDs had insulating barrier Josephson junctions with a quasi particle energy gap edge at 20 meV.
Abstract Superconducting flux memory devices fabricated with nanoscale junctions and high-inductance materials can maintain high-speed access performance while significantly reducing the area required for superconducting loops. In this work, we present a method for preparing nanoscale NbN-based superconductor/normal-metal/superconductor (SNS) Josephson junctions that combines electron beam lithography with chemical mechanical planarization process. Scanning electron microscope images reveal that the junction has a very round shape, while cross-sectional transmission electron microscopy shows that it has a truncated cone structure, characterized by a narrow top and a wide bottom. The minimum diameter of the junction is 51 nm, with the diameter at the interface between the wiring layer and the top electrode being just 27 nm. These nanoscale junctions exhibit excellent Josephson properties with a critical current density J c of 673 ± 64 kA cm −2 and a characteristic voltage V c of 1.63 ± 0.45 mV at 4.2 K. Furthermore, we designed the superconducting memory cell based on the simulated inductance values of the NbN loop and the nanoscale NbN-based SNS junctions. The cell has a total area of 12.6 μ m × 6.5 μ m and contains a radio-frequency superconducting quantum interference device with one junction in the storage loop and a direct-current superconducting quantum interference device with two junctions in the readout loop. Using the flux-locked and feedback measurement method, a clear flux hysteresis curve can be obtained to verify the read-write functions of the device.
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.
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.