Magnesium diboride nanobridges fabricated by electron-beam lithography

MgB2 nanobridges were fabricated by e-beam lithography and Ar-ion beam milling. Nanobridges of widths ranging from 60 nm to 1 μm and 3 μm in length were realized by Ar-ion beam milling using amorphous carbon as etching mask. The processing did not harm the superconducting properties appreciably. High values of the critical current density, more than 10 MA cm2, were measured for bridges with widths down to 60 nm. Current-voltage (I-V) characteristics showed a behavior typical of a bridge going normal, after the critical current is exceeded, and remaining normal as the current is decreased to a lower switch back value due to Joule heating. We could also observe switching behavior in some bridges indicating formation of normal hotspots in the bridges before they returned to their superconducting state. Alternative explanations may include natural grain boundaries in the film or the movement of Abrikosov vortices. The current-voltage (I-V) characteristics showing critical current densities up to 5× 107 A/cm2 indicates excellent film properties in the nanobridges.

[1]  J. Nagamatsu,et al.  Superconductivity at 39 K in magnesium diboride , 2001, Nature.

[2]  K. N. Sood,et al.  SEM, STM/STS and heavy ion irradiation studies on magnesium diboride superconductor , 2002 .

[3]  Z. Ivanov,et al.  Submicron YBa2Cu3Ox ramp Josephson junctions , 2002 .

[4]  M. Naito,et al.  In situ growth of superconducting MgB2 thin films by molecular-beam epitaxy , 2002, cond-mat/0210259.

[5]  T. H. Kim,et al.  Highly crystallized as-grown smooth and superconducting MgB2 films by molecular-beam epitaxy , 2002 .

[6]  M. Naito,et al.  MgB2 thin films for superconducting electronics , 2004 .

[7]  M. Naito,et al.  As-grown superconducting MgB2 thin films prepared by molecular beam epitaxy , 2001 .

[8]  Z. Ivanov,et al.  Mesoscopic Josephson Junctions of high-Tc Superconductors , 2003 .

[9]  Direct observation of nanometer-scale Mg- and B-oxide phases at grain boundaries in MgB2 , 2001, cond-mat/0107324.

[10]  Sung-Ik Lee,et al.  MgB2 Superconducting Thin Films with a Transition Temperature of 39 Kelvin , 2001, Science.

[11]  Zi-kui Liu,et al.  Superconducting MgB2 thin films on silicon carbide substrates by hybrid physical–chemical vapor deposition , 2003 .

[12]  H. Rogalla,et al.  Superconducting Mg–B films by pulsed-laser deposition in an in situ two-step process using multicomponent targets , 2001 .

[13]  Qi Li,et al.  Thermodynamics of the Mg–B system: Implications for the deposition of MgB2 thin films , 2001 .

[14]  J. Rowell.  The widely variable resistivity of MgB2 samples , 2003 .

[15]  H. Rogalla,et al.  Superconducting quantum interference device based on MgB2 nanobridges , 2001 .

[16]  Synthesis and photoemission study of as-grown superconducting MgB2 thin films , 2001, cond-mat/0111404.

[17]  Berkeley,et al.  Penetration depth and anisotropy in MgB 2 , 2001, cond-mat/0103029.

[18]  The road to magnesium-diboride thin films, Josephson junctions and SQUIDs , 2003 .

[19]  Michael Tinkham,et al.  Self‐heating hotspots in superconducting thin‐film microbridges , 1974 .

[20]  Ren Zhi-An,et al.  Structural Properties of MgB 2 Superconductors with a Critical Current Density Greater than 10 5 A/cm 2 , 2001 .