Preparation of small-area Al/AlOx/Al tunnel junctions in a self-aligned in-line technology and observation of the Coulomb blockade

We have demonstrated the suitability of a self-aligned in-line (SAIL) technique for the preparation of ultra-small high-ohmic tunnel junctions as required for the investigation of singlecharge tunneling phenomena. The Coulomb blockade has been observed at 14mK by means of a series array of five AI/AIO,/AI tunnel junctions operated in the normal-conducting state. We have applied this conception to the fabrication of single junctions in a Nb/NbO,/PbAuIn system as well. At 4.2K these samples show the typical I-V behaviour of Josephson tunnel junctions as expected. The compatibility of this process with several thin film deposition techniques, evaporation as well as sputtering, extremely small parasitic capacitances and excellent integrability promise interesting applications in both single-charge,electronics and Josephson physics.