Anodized niobium as barrier for Josephson tunnel junctions

We have fabricated Nb-NbOx-Pb Josephson tunnel junctions in which the barrier is formed by anodization of the niobium electrode. The anodized barrier is made thick (>100 Å) to then be sputter etched to the desired thickness. The geometry of the niobium electrode is defined by a selective anodization process and the lead electrode is patterned by chemical etching. The I-V characteristics of 10−6-cm2 rectangular junctions have been measured at 4 K. Our junctions exhibit large leakage current and low ICRN product, making them less attractive for practical applications than junctions made by other techniques. However, the ease of fabrication and reasonable reproducibility of the electrical characteristics of our junctions make our method of fabrication quite useful when high quality of the barrier is not a stringent requirement. Noise measurements in our junctions and electron diffraction analysis of niobium-oxide films grown by anodization confirm the presence of a large number of defects in the barrier.