Development of a superconducting X-ray microcalorimeter with a titanium/gold thin film as a thermometer

By applying a transition edge sensor (TES) as the thermometer in an X-ray m icrocalorimeter, the intrinsic energy resolution is expected to be signific antly improved. The extremely low intrinsic noise allows us to operate the calorimeter at temperatures as high as one can obtain by pumping liquid He- 3 ( similar to 0.3 K) and still achieve an energy resolution comparable to conventional semiconducting microcalorimeters operating at similar to 60 mK (Delta E similar to 10 eV FWHM). Taking this advantage into account, we ar e developing a titanium/gold bilayer TES calorimeter fabricated on a silico n wafer. The transition temperature is about 0.5 K. We have succeeded in de tecting X-ray photons from 3 to 25 keV, which proves that this TES calorime ter works in a wide energy range. The energy resolution is, however, still much worse than we expected - 550 eV (FWHM) at 5.9 keV. This is because the design parameters are not optimized. Several approaches to improve the per formance are described. (C) 2000 Elsevier Science B.V. All rights reserved.