High-quality planar high-Tc Josephson junctions

Abstract

Reproducible high-T c Josephson junctions have been made in a rather simple two-step process using ion irradiation. A microbridge (1 to 5 µm wide) is firstly designed by ion irradiating a c-axis-oriented YBa 2 Cu 3 O 7-δ film through a gold mask such as the non-protected part becomes insulating. A lower T c part is then defined within the bridge by irradiating with a much lower fluence through a narrow slit (20 nm) opened in a standard electronic photoresist. These planar junctions, whose settings can be finely tuned, exhibit reproducible and nearly ideal Josephson characteristics. This process can be used to produce complex Josephson circuits. a) Electronic

Comment on “High Tc superconducting quantum interference devices made by ion irradiation” [Appl. Phys. Lett. 89, 112515 (2006)]

“…After some skepticism some other groups also have successfully fabricated and investigated such weak links in Jena University, 11 KFA Julich, 12 RWTH ͑Germany͒, 13 University of Cambridge ͑UK͒, 14 University of California ͑USA͒, 15 and, recently, CNRS ͑France͒. 16 Here, I would like to point out that the ion irradiated high T c weak links have a great potential to be used not only in SQUIDs but also in other applications such as Josephson arrays for voltage standards and rapid single flux quantum ͑RSFQ͒ circuits because they can be fabricated reproducibly using only standard microelectronic methods and can be put everywhere on the film surface. Of course, they have some drawbacks.…”

High-Temperature-Superconducting Weak Link Defined by the Ferroelectric Field Effect

“…That type of disorder locally depresses T C , which allows "patterning" the superconducting properties of the film [9,10]. Both S/N/S weak-links [7,8] and S/I/S tunnel junctions [11] can be defined in this way. Besides yielding very reproducible Josephson characteristics [12], the key advantage of this approach is that the planar geometry allows for very large junction arrays [13], thus opening the door to a variety of superconductor electronics applications [14] .…”

“…A versatile approach, developed during the last decade, exploits a nanoscale spatial modulation of T C in a superconducting film [7,8]. This is accomplished by controllably introducing structural disorder (mostly oxygen interstitials and vacancies) on a local scale, via masked ion irradiation or focused ion beams.…”

Response to “Comment on ‘High Tc superconducting quantum interference devices made by ion irradiation’ ” [Appl. Phys. Lett. 90, 136101 (2007)]

“…No further annealing is needed to get the predictable and reproducible results described in our letters. 4,12 In conclusion, HTSc IJJs have been made for many years, but not widely used in real applications. We have developed a new and rather simple process at a nanoscale ͑20 nm͒ to make them reproducible enough to open perspectives again for this technology.…”