Since the discovery of superconductivity in MgB 2 1 considerable progress has been made in determining the physical properties of the material, which are promising for bulk conductors 2-5 . Tunneling studies [6][7][8][9] show that the material is reasonably isotropic and has a well-developed s-wave energy gap (∆), implying that electronic devices based on MgB 2 could operate close to 30K. Although a number of groups have reported the formation of thin films by post-reaction of precursors 10-14 , heterostructure growth is likely to require considerable technological development, making single-layer device structures of most immediate interest. MgB 2 is unlike the cuprate superconductors in that grain boundaries do not form good Josephson junctions, and although a SQUID based on MgB 2 nanobridges has been fabricated 15 , the nanobridges themselves do not show junction-like properties. Here we report the successful creation of planar MgB 2 junctions by localised ion damage in thin films. The critical current (I C ) of these devices is strongly modulated by applied microwave radiation and magnetic field. The product of the critical current and normal state resistance (I C R N ) is remarkably high, implying a potential for very high frequency applications.Our film deposition technique has been described elsewhere. 12 Briefly, B films were deposited at room temperature on to (0001) sapphire substrates by electron beam evaporation and then ex-situ annealed in a Mg vapour at 850°C for 30 minutes to produce MgB 2 films with a final thickness of 100nm and a critical temperature (T C ) of 36K. We deposited a 20nm Au film onto the films by dc magnetron sputtering in order to protect the MgB 2 from contact with water during subsequent processing. Tracks and contact pads were patterned in the bilayer film using standard photolithography and broad beam Ar-ion milling. The T C of the patterned tracks was approximately 35K. In order to fabricate the junctions, the film was then transferred to a focused ion beam system (FIB) (Philips-FEI Inc. FIB 200). Chips were wirebonded to enable the resistance of the tracks to be monitored during the FIB milling process. 16 The barrier was defined by writing 50nm wide cuts across the width of tracks using a 4pA 30kV Ga ion beam. The depth of the cut was calibrated by comparing the cut time to that required to completely sever a track; since the Au mills more than order of magnitude faster than the MgB 2 it could be ignored in calibrating the cut depth. Compared to other materials used to fabricate SNS junctions using this technique, 17 MgB 2 offers the advantage of a relatively low milling rate and hence excellent depth control due to the low atomic mass of its constituents and high melting point.The devices were measured in dip probes placed in 4 He storage dewars. The probes are equipped with coils to provide a magnetic field perpendicular to the substrate plane, and with a microwave antenna. The inset to Fig. 1 shows the resistance against temperature for two tracks on the same substrate,...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.