Windows for Defining the Action Area of Nb Tunnel Junctions
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Many applications of Josephson tunnel junctions require the area of the junction to be defined by a "window" in a relatively thick insulator placed over the base electrode, as shown in Fig. 1. An essential step in obtaining good tunneling characteristics with Nb base electrodeg is sputter etching of the surface in a high energy, low pressure Ar plasma, before growth of the tunneling oxide. However, in a clean system and with extended cleaning time, a conducting film of back-sputtered Nb is deposited on the side walls of the window. Being nearly vertical at the lower edge, this film oxidizes much more slowly than the base electrode, forming effectively a shunt resistance across the tunnel barrier of the completed junction which contributes a high leakage current.