Dependence of Excess Noise on the Partial Derivatives of Resistance in Superconducting Transition Edge Sensors.

We have measured the relation between sensor noise and the steepness (α = <FRACTION><NUM>T</NUM><DEN>R</DEN></FRACTION>· and β = <FRACTION><NUM>I</NUM><DEN>R</DEN></FRACTION>·<FRACTION><NUM>dR</NUM><DEN>dI</DEN></FRACTION>) of the superconducting transition for various superconducting transition edge sensors. The measurements are performed on square Mo/Cu bilayer thermistors of three sizes (125 μm, 250 μm and 400 μm), which are fabricated for X-ray detection. We have identified the devices in two regimes: a) α>100 and b) α<100. The devices with α smaller than 100 strictly follow non-linear bolometer and micro-calorimeter noise theory while in most devices with α greater than 100, we see an unexplained noise contribution. [ABSTRACT FROM AUTHOR]