Quantum-limited detection and noise in superconducting tunnel-junction mixers
High-quality Superconductor-Insulator-Superconductor (SIS) tunnel junctions with small subgap leakage currents and a sharp current rise at the sum-gap voltage were produced for studying strong quantum mixing effects at 36 GHz.These junctions employ a Ta or Nb base electrode and a PbBi counter electrode. The novel step-defined process used to fabricate these junctions yields functions with small areas (1-6 ..mu..m/sup 2/), high critical current densities (10/sup 2/-10/sup 4/ A/cm/sup 2/), low subgap leakage currents (<1%), and a sharp current rise of width ..delta.. V approx. 30 ..mu..V at the sum-gap voltage. These junction properties are required for the experimental observation of strong quantum-mixing effects at 36 GHz which are discussed in this thesis. The relatively new technique of ion-beam sputter deposition is also described. This technique was used for preparing high-quality Nb and Ta refractory superconducting films on room-temperature substrates. These films were used in the fabrication of SIS mixers discussed above. The transport and electrical properties of these films were characterized and found to approach those of the bulk material.
- Research Organization:
- Yale Univ., New Haven, CT (USA)
- OSTI ID:
- 6476137
- Country of Publication:
- United States
- Language:
- English
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