High quality tantalum superconducting tunnel junctions for microwave mixing in the quantum limit
We report on a novel step-defined process used to produce small area (1--6 ..mu..m/sup 2/), high critical current density (10/sup 2/--10/sup 4/ A/cm/sup 2/) superconducting tunnel junctions with Ta base electrodes and Pb/sub 0.9/Bi/sub 0.1/ counterelectrodes. These junctions have extremely small subgap leakage currents, a ''sharp'' current rise of width ..delta..Vapprox.30 ..mu..V at the sum-gap voltage, and show strong quantum effects when used as microwave mixers. Accurate measurements at 34.5 GHz with a 1.5 GHz intermediate frequency (IF) give single sideband mixer gains up to G = 1.1 +- 0.1 and mixer noise temperatures as low as T/sub M/ = 3.8 +- 1.0 K. This value of T/sub M/ is close to the quantum limit T/sub Q/ = h..omega../k ln 2 = 2.5 K. The lowest receiver noise temperature measured at the 1.3 K input to the mixer block, T/sub R/ = 24 +- 1 K, is the best value reported for any heterodyne receiver. Infinite available gain is obtained for a low (25 MHz) IF and a coupled gain as large as 1.6 +- 0.4 is observed.
- Research Organization:
- Section of Applied Physics, Yale University, P. O. Box 2157, New Haven, Connecticut 06520
- OSTI ID:
- 5899391
- Journal Information:
- Appl. Phys. Lett.; (United States), Journal Name: Appl. Phys. Lett.; (United States) Vol. 48:16; ISSN APPLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMPLIFICATION
CURRENT DENSITY
CURRENTS
DATA
ELECTRIC CURRENTS
ELECTRODES
ELECTROMAGNETIC RADIATION
ELEMENTS
EXPERIMENTAL DATA
GAIN
INFORMATION
JUNCTIONS
LEAKAGE CURRENT
METALS
MICROWAVE RADIATION
MIXERS
NOISE
NUMERICAL DATA
RADIATIONS
SUPERCONDUCTING JUNCTIONS
TANTALUM
TRANSITION ELEMENTS
TUNNEL EFFECT