Comparative studies of noise limitations in superconducting thin-film radiation detectors

We report measurements on the noise limitations of superconducting thin films operating as thermal detectors (bolometers) and as current-dependent detectors. By making measurements in each mode on the same film it is possible to make a comparative study of the noise limitations for both detection mechanisms in the same device. Thin tin films with normal state sheet resistances on the order of 100 Ω per square have been studied. The devices were scribed to produce total normal state resistances on the order of 10 kΩ and were mounted in the vacuum chamber of a demountable tail Dewar so that they were not in direct contact with liquid helium. The resulting bolometers have response times and sensitivities similar to those of Martin and Bloor. The dominant noise mechanisms we have observed appear to be Johnson noise in the thermal mode and 1/f noise in the current mode. These results confirm previous conclusions regarding the sensitivity of these films as radiation detectors.