CHARACTERIZATION OF DIFFERENT TYPES OF Nb-AIO, BASED JOSEPHSON TUNNEL JUNCTIONS

The Nb/Al,AlO,(/Al)/Nb trilayer is deposited in a turbo pumped vacuum system. Nb and A1 films were deposited by two DC magnetron sputter guns at a rate of 200 nm/min and 22 nm/min, respectively. During sputtering the oxygen pressure was in the low lo-' mbar range. The water pressure was 10-7-10-8 mbar. The T, of the Nb films is 9.2 K. The trilayer configuration of the junctions is listed in table 1. The thickness of the Nb base electrodes is 300 nm. The A1 overlayers were thermally oxidized in pure 0, at 10 'C, during 1 hour. The double oxide layer of the SNIIS type junction has been formed in two steps. The A1 layer was oxidized in 0.04 mbar 0, for 15 minutes. Then a second Al layer of 10 A was deposited and completely oxidized in 27 mbar 02. The junction areas (20x20, 10x10, and 5x5 pm2 on one thermally oxidized Si wafer) were defined by SNAP (Selective Niobium Anodization Process) [5]. To complete the junctions 300 nm Nb was deposited and structured by lift-off, to form contacts with the counter electrodes.