Realization and properties of MgB2 metal-masked ion damage junctions

Abstract

Ion beam damage combined with nanoscale focused-ion-beam direct milling was used to create manufacturable superconductor–normal–superconductor type (SNS) Josephson junctions in 100-nm-thick MgB2 with TC of 38 K. The junctions show nonhysteretic current–voltage characteristics between 36 and 4.2 K. Experimental evidence for the dc and ac Josephson effects in MgB2 metal-masked ion damage junctions are presented. This technique is particularly useful for prototyping devices due to its simplicity and flexibility of fabrication and has a great potential for high-density integration.

MgB2thin films

“…For example, Brinkman et al used a focused ion beam to produce nanobridges with a width of about 70 nm, a height of 150 nm, and a length of 150 nm [144,148], and made SQUIDs using these weak link junctions which work well over 20 K [148]. Local ion damage is another way to produce weak links in MgB 2 films [149,150]. Ion implantation suppresses T c in the weak link region such that resistively shunted junction characteristics can be observed in a certain temperature range.…”

Multiple-barrier and nanoscale superconducting devices

“…However, the technology and geometry of these types of devices limit the minimum separation of the junctions and it is in any case much larger than is possible in a heterostructure stack. The development of irradiation damage junctions in which either electrons [23,24], or ions [25][26][27][28][29] locally suppress the superconductivity (see figure 2) enabled the creation of arrays of junctions in which the junction position could be arbitrarily controlled lithographically. Using a focused ion beam to locally remove the upper superconducting layer to divert the current into an underlying normal metal layer provided a method of creating junctions with the same geometry in low T c metallic superconductors [30,31].…”

Mechanism of operation of Josephson junctions made from HTc materials by ion modification

“…Other kinds of ions were also successfully used: argon [10], neon [11][12][13] and hydrogen [14,16]. Moreover, after the recent discovery of superconductivity in MgB 2 this technology was applied also to create excellent Josephson junctions from this new material [15,17,18].…”