Transition edge sensors for X-ray astronomy

Investigations are underway for new detector technologies for the next generation of X-ray observatories. Several groups around the world are concentrating on superconducting transition edge sensors as a technology which may deliver the spectral performance required for these future missions. The rapid development of the TES indicates that the desired 2 eV FWHM resolution at 1 keV may be achievable. However, the technology is still in its infancy and substantial technical challenges lie ahead. Our current emphasis is on the reliability and longevity of the films comprising the sensor, while the same time demonstrating, and improving, spectral resolution. Here we demonstrate Al–Ag films with tunable transition temperature accurate to 5 mK, with transition width of <2 mK, and α∼400. We discuss the reliability of films and both diffusion and oxidation mechanisms are present which lead to ageing of both the normal resistance and the transition temperature.