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International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

Superconducting Lumped Element Kinetic Inductance resonators for millimeter, sub-millimeter and far infrared detection

Simon M. Doyle, Philip D. Mauskopf, A. Monfarnadini, Loren J. Swenson, S. Withington, D. J. Goldie

Published Sep 1, 2010• 0 citations
Publisher

Abstract

The Lumped Element Kinetic Inductance Detector (LEKID) is an ultra sensitive superconducting detector suitable for use from the mm to FIR wavebands. Due to its simple design, the LEKID can easily be fabricated into large multiplexed arrays. This presentation will provide an overview of the LEKID and its applications.
DOI
10.1109/icimw.2010.5612457

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The development of large multi-pixel detector applications with lumped element kinetic inductance detectors (LEKID) requires a detailed knowledge about the mode of operation in respect of the microwave regime. In this paper the basic properties of LEKID structures for applications at liquid helium temperatures were investigated. In consideration of the operation temperature, the different microwave behavior of LEKID structures coupled to microstrip and coplanar strip readout transmission lines, e.g. loaded and unloaded quality factors, have been examined. For this purpose several test structures, which are suitable for large arrays, in multi-pixel applications, were designed and characterized with frequency around 6 GHz. Loaded quality factorsQLQ_{L}QL​up to 10,000 at 4.2 K were achieved. The devices were fabricated in niobium thin film technology on silicon substrates. LEKID arrays with 3 resonators were designed, fabricated and measured with our self-developed FDM readout system. The results of the measurements will be presented and discussed.
Aluminum lumped-element kinetic inductance detectors (LEKIDs) sensitive to millimeter-wave photons have been shown to exhibit high quality factors, making them highly sensitive and multiplexable. The superconducting gap of aluminum limits aluminum LEKIDs to photon frequencies above 100 GHz. Manganese-doped aluminum (Al-Mn) has a tunable critical temperature and could therefore be an attractive material for LEKIDs sensitive to frequencies below 100 GHz if the internal quality factor remains sufficiently high when manganese is added to the film. To investigate, we measured some of the key properties of Al-Mn LEKIDs. A prototype eight-element LEKID array was fabricated using a 40 nm thick film of Al-Mn deposited on a 500 μm thick high-resistivity, float-zone silicon substrate. The manganese content was 900 ppm, the measured Tc = 694 ± 1mK, and the resonance frequencies were near 150 MHz. Using measurements of the forward scattering parameter S21 at various bath temperatures between 65 and 250 mK, we determined that the Al-Mn LEKIDs we fabricated have internal quality factors greater than 2 × 105, which is high enough for millimeter-wave astrophysical observations. In the dark conditions under which these devices were measured, the fractional frequency noise spectrum shows a shallow slope that depends on bath temperature and probe tone amplitude, which could be two-level system noise. The anticipated white photon noise should dominate this level of low-frequency noise when the detectors are illuminated with millimeter-waves in future measurements. The LEKIDs responded to light pulses from a 1550 nm light-emitting diode, and we used these light pulses to determine that the quasiparticle lifetime is 60 μs.
We have developed and characterized an on-chip polarimeter based on Lumped Element Kinetic Inductance Detectors (LEKIDs) optimized for the whole W -band frequency range (75−110GHz\mathbf{7 5 - 1 1 0} \mathbf{G H z}75−110GHz). The chip consists of two3×3\mathbf{3} \times \mathbf{3}3×3LEKID arrays fabricated on opposing faces of a silicon substrate. Both arrays have been fabricated from a titanium/aluminum superconducting bilayer and they present orthogonal inductor orientations to resolve horizontal and vertical polarization modes. A second silicon substrate is coated at its rear part with an aluminum thin film and works as a back-reflector to enhance the forward absorption efficiency via constructive interference. In this work, we report the absorption response and performances in theWWWband of this on-chip polarimeter configuration in both polarizations at cryogenic temperatures. The noise spectrum and the noise equivalent power (NEP) is also characterized using a blackbody source at two different temperatures to demonstrate its functionality.