Superconductor–normal–superconductor Josephson junctions fabricated by oxygen implantation into YBa2Cu3O7−δ

Abstract

We report Josephson junctions in YBa2Cu3O7−δ films, fabricated by oxygen irradiation through a 50 nm wide slit in an implantation mask. After annealing the irradiated microbridges at 500 °C in an oxygen atmosphere, this process creates a homogeneous barrier region with a reduced but finite transition temperature, allowing Josephson coupling in a temperature window of ⩽15 K. Over the entire temperature range of Josephson coupling these junctions show resistively shunted junction behavior. The exponential dependence of the critical current on temperature is in good agreement with conventional superconductor–normal–superconductor proximity effect theory.

High-quality planar high-Tc Josephson junctions

“…Such an ideal behavior has not been reported in previous studies 4,5 . The period of the modulation corresponds to one flux quantum in the junction provided λ L is taken to be typical of thin films 11 (400 nm at 72K).…”

Nanometer scale masked ion damage barriers in YBa/sub 2/Cu/sub 3/O/sub 7-δ/

“…The steep R(T) curve exhibited by the higher T c junction is typical for a barrier whose effective resistive length changes rapidly as a function of temperature: scattering of ions causes the barrier to have a graded distribution of T c s both along the length and thickness of the track [1,5]. Since they were on the same chip, both these devices received an identical implantation dose.…”

“…However the FEBI technique is realistically limited to circuits consisting of fewer than 100 junctions and so alternative techniques will be required for large-scale circuit fabrication. Several groups have recently demonstrated junction formation by masked ion damage (MID) in which ions from a broad beam ion source locally damage regions of superconductor to form the junction barriers, while the remainder of the circuit is protected by a mask which absorbs the implanted ions [4][5][6]. Although MID has the advantage that junction barriers are formed by a parallel, rather than a serial technique (as is the case for FEBI), the difficulties of preparing successful mask structures have meant the progress to date has been relatively slow.…”

Optimisation of masked ion irradiation damage profiles in YBCO thin films by Monte Carlo simulation

“…Experimental results reported so far include O þ , Ne þ and H þ ion irradiation with various masks [2][3][4]. The preliminary experimental results are promising, but the device performances are not satisfactory in general, and differ from one group to another.…”