Thermal properties of superconducting proximity‐effect bridges, fabricated from Nb, Ta, and Ti films, were measured by two experimental methods: (1) measurement of the low‐frequency (20–2000 Hz) noise‐fluctuation power spectrum in the bridge and (2) measurement of the Joule heating needed to elevate the bridge region to an easily identified fixed temperature above that of the helium bath. A comparison was made between the measurements and calculations based on a simple thermal boundary model in which the bridge volume alone is treated as elevated in temperature. Thermal effects were shown responsible for critical current hysteresis, high‐frequency Josephson step limitations, the low‐frequency 1/f2 noise power spectrum, and an unstable resistance regime of current bias. Methods for alleviating these limitations by correct bridge geometry were found. Thermal effects were found not to be responsible for the excess current which appears on the current‐voltage trace of the proximity‐effect bridge.
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