Evidence for Controllable Reduction of Critical Temperature in Titanium TESs by Baking in Air

We report on the characteristics of Ti superconducting transition-edge sensors (TES) baked in air at different temperatures from 100 °C to 140 °C. The critical temperature (T _C ) of Ti bare films is decreased by about 40% after baking at 140 °C for 30 hours, which might be due to the oxidation, lowering its effective thickness. Ti TES device, baked at 120 °C for 10 hours, exhibits a T _C of 257 mK, lowered by ∼100 mK, while its temperature sensitivity nearly keeps constant. The measured thermal conductance is ∼500 pW/K, more than 3 times lower than its original value. We demonstrate that baking in air is a simple way to get the required performance by depressing T _C of superconducting Ti TESs.