Double-barrier Nb/Al2O3/Al/Al2O3/Nb tunnel junctions are used as mixing elements in a 345 GHz waveguide mixer. Noise temperatures (double side band) down to 720 K at 3.0 K are obtained without the need to apply a magnetic field to suppress the Josephson current. It is shown that the composite barrier acts as a single barrier for photon-assisted tunneling. Surprisingly, at these frequencies the capacitance of two stacked tunnel barriers is only determined by one barrier.
|Number of pages||3|
|Journal||Applied Physics Letters|
|Publication status||Published - 14-Feb-1994|