Stability and uniformity of planar high temperature Josephson junctions fabricated using nanolithography and ion damage

We have investigated the room temperature stability and the critical current uniformity of planar thin film YBa2Cu3O7-delta Josephson junctions. The junctions were fabricated using electron-beam lithography to define a stencil structure followed by ion damage from a conventional 200 keV ion implanter. Using this technique, we have fabricated junctions with weak link lengths of 20 - 100 nm that showed classical de and ac Josephson effects at 77 K. By a suitable choice of damage and stencil width, these devices may be tuned to operate at any temperature between 1 K and the bulk transition temperature, and they may be placed anywhere on a wafer, providing a high degree of flexibility for circuit applications. Results obtained over several months showed a high level of room temperature stability, and the uniformity of the junctions was maintained.