High-performance of Superconducting Tunnel Junction for Terahertz Imaging

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A Nb/Al-AlOx-Al/Nb superconducting tunnel junction is expected as a highly sensitive detector for Terahertz imaging. In the use of a highly sensitive detector, it is necessary to reduce the sub-gap leakage current to the limit indicated in the BCS theory. For obtaining the junction with small sub-gap leakage current, we take a new approach, that is, a electron-beam excited sputtering technique, for fabricating the junction consisted of Nb layer, Al layer and tunneling barrier. We studied the deposition conditions for both Nb and Al layers, and the etching condition for Al layer using this system. The transition temperature of the Nb layer and the residual resistance ratio have indicated 9.3 K and more than 3. Fabricated Nb/AlOx-Al/Nb Josephson junction has exhibited SIS characteristics with the gap structure.