Current dependence of performance of TES microcalorimeters and characteristics of excess noise

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2004-03, Vol.520 (1-3), p.340-343
• Main Authors: Takei, Y, Fujimoto, R, Ishisaki, Y, Morita, U, Tanaka, K, Koga, T, Mitsuda, K, Ohashi, T, Yamasaki, N.Y, Iyomoto, N, Ichitsubo, T, Sato, K, Fujimori, T, Oshima, T, Futamoto, K, Shinozaki, K, Morooka, T, Nakayama, S, Yoshida, K, Takai, N, Chinone, K
• Format: Article
• Language: English
• Subjects: Microcalorimeter; Transition-edge sensor (TES); X-rays
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2003.11.262

We are developing transition edge sensor (TES) microcalorimeter arrays for future Japanese astronomy missions. Although 6.6eV energy resolution for 5.9keV and 74μs decay time are achieved, our energy resolution was limited by the excess noise of unknown origin. The dominant noise showed 1/R dependence and it only appeared when the current through the TES, I, is larger than 10μA. This is explained if we assume a constant voltage noise source with a level of ∼2(4kTCRn)1/2. We also investigated the influence of I on the TES performance and found the TES sensitivity α is reduced when the ratio of current to the critical current I/IC is large. It can explain the reduction of α observed when operated without a magnetic shield. We also found a strong correlation between IC and α or the baseline width. Thus, we conclude that IC is an essential parameter for the TES performance.