Controlling Tc of iridium films using the proximity effect

• Published in: Journal of applied physics 2020-10, Vol.128 (15)
• Main Authors: Hennings-Yeomans, R., Chang, C. L., Ding, J., Drobizhev, A., Fujikawa, B. K., Han, S., Karapetrov, G., Kolomensky, Yu. G., Novosad, V., O’Donnell, T., Ouellet, J. L., Pearson, J., Polakovic, T., Reggio, D., Schmidt, B., Sheff, B., Singh, V., Smith, R. J., Wang, G., Welliver, B., Yefremenko, V. G., Zhang, J.
• Format: Article
• Language: English
• Subjects: calorimetry; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; light detection; phase transitions; phonons; proximity effects; radioactive decay; superconductivity; superconductors; thermodynamic states and processes; thin films
• ISSN: 0021-8979; 1089-7550

A superconducting Transition-Edge Sensor (TES) with low- T c is essential in high resolution calorimetric detection. With the motivation of developing sensitive calorimeters for applications in cryogenic neutrinoless double beta decay searches, we have been investigating methods to reduce the T c of an Ir film down to 20 mK. Here, utilizing the proximity effect between a superconductor and a normal metal, we found two room temperature fabrication recipes for making Ir-based low- T c films. In the first approach, an Ir film sandwiched between two Au films, a Au/Ir/Au trilayer, has a tunable T c in the range of 20–100 mK depending on the relative thicknesses. In the second approach, a paramagnetic Pt thin film is used to create the Ir/Pt bilayer with a tunable T c in the same range. We present a detailed study of fabrication and characterization of Ir-based low- T c films and compare the experimental results to the theoretical models. We show that Ir-based films with a predictable and reproducible critical temperature can be consistently fabricated for use in large scale detector applications.