Ramp-type YBa2Cu3O7−δ Josephson junctions with high characteristic voltage, fabricated by a new, completely in situ, growth technique

Abstract

We have fabricated YBa2Cu3O7−δ/PrBa2Cu3O7−δ/YBa2Cu3O7−δ ramp-type Josephson junctions with high characteristic voltage Vc=IcRn at a temperature of 77 K. A microshadow mask technique was used to grow completely in situ a ramp-type multilayer structure. Junctions with barrier thicknesses of about 13 and 45 nm were characterized. Junctions with a thicker barrier exhibited supercurrent up to 80 K and showed a resistively shunted-junction-like current voltage characteristics with a Vc as high as ∼1.5 mV at 77 K and 16 mV at 15 K. Junctions with a thinner barrier worked up to 90 K and exhibited the ac Josephson effect at 77 K under 8.9 GHz microwave radiation.