Phase Separation in Tungsten Transition Edge Sensors

To optimize the signal efficiency in detectors utilizing Transition Edge Sensor (TES) technology we have fabricated and characterized test devices which approximate the electrical and thermal properties of the tungsten TES parallel arrays used for the Cryogenic Dark Matter Search (CDMS) phonon sensors. We measure the equilibrium power as a function of bias voltage by sweeping the bias current through the TES array and measuring the resulting current through the sensor. Our results are in agreement with previous estimates of the critical length for a TES to separate into superconducting and normal phases. However, we found that the presence of the tungsten sections, which connect the TES to the aluminum fins, significantly shortens the critical length for the onset of phase separation, and indicate that many CDMS phonon sensors have operated with phase separated TESs. We have also improved the determination of the electron‐phonon coupling in our tungsten films to be (0.32±0.02)×109W/m3K5. Finally, we also found that the thermal conductance between the tungsten electron and phonon systems does not scale linearly with added fin connector volume, instead ∼75% of added volume contributes