Investigation of an anti-reflection silicon nitride layer on a superconducting NbxSi1-xfilm absorber for inductive superconducting transition edge detectors

Abstract

We report research on superconducting transition temperature (Tc) tuning and the antireflective layer of NbxSi1-x films that were used as the absorbing layer in inductive superconducting transition edge detectors (ISTED). The Tc of NbxSi1-x film absorber should be tuned to be to the operating temperature range of the readout nano superconducting quantum interference devices. The composition ratio of Nb/Si was controlled by the co-sputtering powers of the Nb and Si target to adjust the Tc. To improve the detection efficiency, a 30 nm Nb95.7Si4.3 film with Tc 6.3 K was chosen to demonstrate the effect of the antireflective layer SiNx made by low temperature plasma enhanced chemical vapor deposition (LT-PECVD). According to the spectral refractive indexes and extinction coefficients of the Nb95.7Si4.3 and SiNx films, the structure parameters for 633 nm incident light were designed and the optical properties were calculated. The reflectivity measurements showed that the reflectivity was effectively reduced, which was consistent with the calculation.