${\rm MgB}_{2}/{\rm insulator/Pb}$ Josephson Junctions With Different Tunnel Barriers

High quality MgB
₂
/insulator/Pb Josephson tunnel junctions with two different barriers were studied. The junctions were fabricated using MgB
₂
films grown by hybrid physical-chemical vapor deposition and the barriers were formed at different temperature regions. Both kinds of junctions show clear tunneling characteristics with clear Josephson supercurrent, high I
_c
R
_N
products, and the expected I
_c
(B) pattern. The junctions with barriers formed at 200 to 450degC have higher I
_c
R
_N
, larger MgB
₂
pi gap values, thinner barriers and higher barrier heights than the junctions with barriers formed over 700degC. In addition, some intermediate temperature barrier junctions show features due to the sigma gap of MgB
₂
, which were not observed in the high temperature barrier junctions. High device yield indicates that the approaches to form tunnel barriers are promising for device fabrications.