Study of Superconducting Bilayer for Microwave Kinetic Inductance Detectors for Astrophysics
| Autor: | Agnes Dominjon, Masakazu Sekine, Yutaro Sekimoto, Tom Nitta, Kenichi Karatsu, Takashi Noguchi, Shibo Shu, Shigeyuchi Sekiguchi |
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| Rok vydání: | 2016 |
| Předmět: |
Physics
Superconductivity Condensed matter physics Band gap Astrophysics::Instrumentation and Methods for Astrophysics Niobium Center (category theory) chemistry.chemical_element 02 engineering and technology Astrophysics 021001 nanoscience & nanotechnology Condensed Matter Physics 01 natural sciences Kinetic inductance Electronic Optical and Magnetic Materials chemistry 0103 physical sciences Proximity effect (superconductivity) Electrical and Electronic Engineering 010306 general physics 0210 nano-technology Noise-equivalent power Microwave |
| Zdroj: | IEEE Transactions on Applied Superconductivity. 26:1-6 |
| ISSN: | 1558-2515 1051-8223 |
| Popis: | Due to their multiplexing capability and their good sensitivity to radiation from submillimeter to X-ray wavelengths, microwave kinetic inductance detectors (MKIDs) are increasingly used in the field of astrophysics. The Advanced Technology Center of the National Astronomical Observatory of Japan is developing MKIDs for astronomical observations such as CMB B-mode search with LiteBIRD. MKIDs are made of superconductors whose energy gap determines the detector frequency range. The energy gap depends on Tc, the critical temperature of the superconductor. It is thus important to be able to adjust Tc in order to choose the suitable frequency range. When using a single-layer MKID, the Tc is fixed by the superconducting gap energy of the unique component and cannot be changed. One possibility is to make a bilayer MKID using the proximity effect to adjust its critical temperature. This paper presents our new study on MKIDs made of superconductor/metal bilayers. We investigated niobium and copper bilayers (Nb/Cu) and fabricated different bilayers in our clean room. The critical temperature of each of them has been measured. We show that the Tc depends on the ratio between Nb and Cu thicknesses and that we are able to control it. Then, we characterized one of these Nb/Cu bilayers ( $\text{Nb} = 8\ \text{nm}$ and $\text{Cu} = 22\ \text{nm}$ ) once integrated in a MKID. We measured the temperature dependence of the resonant frequency, and we achieved quality factors as high as $2 \times 10^{4}$ . The measurement of the noise spectrum provided a lower limit equal to −85 dBc/Hz, and the calculation of the noise equivalent power has shown that the sensitivity of the Nb/Cu bilayer MKID is not very far from that of an Al monolayer MKID. |
| Databáze: | OpenAIRE |
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