Study of superconducting bi-layer for Microwave Kinetic Inductance Detectors (MKID) for Astrophysics
Study of superconducting bi-layer for Microwave Kinetic Inductance Detectors (MKID) for Astrophysics
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天体物理学微波动感电感探测器（MKID）超导双层的研究
DOI：
10.1109/tasc.2016.2530998
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Tom Nitta
中科院分区：
文献类型：
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作者：
Agnes Dominjon;Masakazu Sekine;Kenichi Karatsu;Takashi Noguchi;Yutaro Sekimoto;Shibo Shu;Shigeyuchi Sekiguchi;Tom Nitta
由于其多路复用能力和对亚毫米到X射线波长的辐射的良好灵敏度，微波动力学电感探测器（MKID）越来越多地用于天体物理学领域。日本国家天文台先进技术中心正在开发用于天文观测的MKID，例如使用LiteBIRD进行CMB B模式搜索。MKID由超导体制成，其能隙决定了检测器的频率范围。能隙取决于超导体的临界温度Tc。因此，重要的是能够调节Tc以便选择合适的频率范围。当使用单层MKID时，Tc由独特组件的超导能隙固定并且不能改变。一种可能性是使用邻近效应来调节其临界温度来制造双层MKID。本文介绍了我们对超导/金属双层膜MKID的最新研究。我们研究了铌和铜双层膜（Nb/Cu），并在我们的洁净室中制造了不同的双层膜。测定了它们的临界温度。我们发现，Tc依赖于Nb和Cu的厚度之间的比例，我们能够控制it. Then，我们的特点是这些Nb/Cu双层（Nb = 8 nm和Cu = 22 nm）一旦集成在MKID。我们测量了谐振频率的温度依赖性，并获得了高达2 × 104的品质因数。噪声谱的测量提供了等于-85dBc/Hz的下限，并且噪声等效功率的计算表明Nb/Cu双层MKID的灵敏度与Al单层MKID的灵敏度相差不远。
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 (Nb = 8 nm and Cu = 22 nm) once integrated in a MKID. We measured the temperature dependence of the resonant frequency, and we achieved quality factors as high as 2 × 104. 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.