Investigation of Ti/Au Transition-Edge Sensors for Single-Photon Detection

Transition-edge sensors (TES) are remarkable superconducting devices for a wide range of radiation detection with the ability of both energy resolution and counting photons. For the detection of single photons at telecom wavelength, optical Ti/Au bilayer TESs are fabricated and characterized. The superconducting transition temperature (T-c) of the Ti/Au films is effectively tuned from 162 to 72 mK by increasing the relative thickness ratio between the Au and Ti layer. The sensitive area is 20 mu m x 20 mu m, on which an SiO2/SiNx antireflection structure is coated by an ICP-PECVD process. The TES device shows an energy resolution of 0.19 eV and can discriminate up to 36 incident photons, with an effective time constant around 107 mu s at 95 mK.