4. Josephson and SQUID junctions: technological aspects

The technology of low-critical-temperature Josephson junctions, known as LT _c junctions, is now well established. These are essentially junctions corresponding to the Nb-AlO _x -Nb stack, and are therefore of the superconductor-insulator-superconductor type (figure 9 ). They are shunted by a resistor to achieve non-hysteretic behavior. Their characteristics are stable under thermal cycling, reproducible, well matched to theory, and exhibit excess noise only at very low frequencies (f ≤ 10 Hz). Excess noise depends on the quality of the various interfaces, so it varies from one realization to another. For this reason, the energy resolution ε of a SQUID is specified at high frequency...