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Superconductor Science and Technology

A superconducting diplexer for cosmic microwave background experiments

Mohammad Madi, Michael Mattes, Juan Ramon Mosig, D. Rauly, Pascal Febvre

Published Dec 5, 2013• 0 citations
Publisher

Abstract

Cosmic microwave background (CMB) studies require observations in several frequency bands simultaneously. For example, the detection of clusters of remote galaxies can be performed by comparing CMB photon fluxes at different frequencies, using the spectral deformation of the Planck law, due to the Sunyaev–Zeldovich effect. We propose a single pixel design to receive and detect simultaneously two frequency bands of the (CMB), centered at 150 and 220 GHz. It is composed of a bow-tie antenna, sensitive to the polarization of the incident radiation, feeding a diplexer structure to separate the signal towards two kinetic inductance resonators associated respectively with the 130–170 and 200–270 GHz frequency bands. The diplexer makes use of 150 nm thick niobium-based superconducting transmission lines of the coplanar strip-lines (CPS) type, for filtering and separation purposes, deposited on a 30 μm thick quartz substrate. A new coplanar matching structure, taking into account the kinetic inductance of the superconducting films, is proposed and achieves a nearly perfect match over more than 25% of each frequency band, along with a signal separation ratio above 30 dB at both center frequencies. The size of a single pixel is 0.9 mm × 1.2 mm.

DOI
10.1088/0953-2048/27/1/015011

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Cosmic microwave background (CMB) studies require observations in several frequency bands simultaneously. For example, the detection of clusters of remote galaxies can be performed by comparing CMB photon fluxes at different frequencies, using the spectral deformation of the Planck law, due to the Sunyaev–Zeldovich effect. We propose a single pixel design to receive and detect simultaneously two frequency bands of the (CMB), centered at 150 and 220 GHz. It is composed of a bow-tie antenna, sensitive to the polarization of the incident radiation, feeding a diplexer structure to separate the signal towards two kinetic inductance resonators associated respectively with the 130–170 and 200–270 GHz frequency bands. The diplexer makes use of 150 nm thick niobium-based superconducting transmission lines of the coplanar strip-lines (CPS) type, for filtering and separation purposes, deposited on a 30 μm thick quartz substrate. A new coplanar matching structure, taking into account the kinetic inductance of the superconducting films, is proposed and achieves a nearly perfect match over more than 25% of each frequency band, along with a signal separation ratio above 30 dB at both center frequencies. The size of a single pixel is 0.9 mm × 1.2 mm.
We propose a pixel design, aimed to be included in an array, receiving and de- tecting simultaneously two bands of the Cosmic Microwave Background (CMB). It is composed of a bowtie antenna, feeding a diplexer structure to separate the signal towards two bolomet- ric detectors at 150 and 220GHz. The diplexer makes use of difierential transmission lines of Coplanar Striplines (CPS) and Broadside Coupled Lines (BCL) types, for flltering and separation purposes. The antenna and diplexer are planned to be fabricated in a superconductive niobium thin fllm deposited on a Silicon substrate, while NbSi bolometers will lie on a SiN membrane. The device has been simulated by means of ADS (Agilent), CST Microwave Studio and HFSS (Ansoft) softwares. Final dimensions that take into account the kinetic inductance of the super- conducting lines are proposed. Promising computation results are found, with signal separation up to 20dB.
The design of a diplexer, coupled to a planar bowtie antenna for two-band Cosmic Microwave Background detection is proposed, using both HFSS™ and ADS™ softwares. The two photometric bands are centered on 150 GHz and 220 GHz respectively. The diplexer is composed of two three-elements distributed filtering circuits, taking into account the complex impedance of the antenna and the impedance of the two resistive loading bolometers. The distributed elements are transmission lines Coplanar Strip Lines (CPS) and Broadside Coupled Lines (BCL). Their balanced geometry matches to the differential signal delivered by the bow-tie antenna, avoiding the addition of a balun circuit. The envisaged technology for strips and antenna is superconducting niobium at a few 100mK on Si substrate. The overall size of the antenna/diplexer structure is around 2 mm2, allowing to consider it as a pixel suitable for integration in a bolometer array.
Future ground-based cosmic microwave background (CMB) experiments will require more than 10510^5105 polarization sensitive pixels covering multiple atmospheric bands. The scientific potential for such an experiment is impressive; however, the technical challenges are daunting: such an instrument will require square meters of focal plane covered in background limited cryogenic detectors and a dramatic increase in readout capability. We are developing novel kinetic inductance detectors (KIDs) optimized for this purpose. These devices use a twin-slot microwave antenna, superconducting Nb transmission line, and a novel coupling scheme that deposits mm-wavelength power onto a high-resistivity meander deposited as the first layer on a bare Si wafer. This architecture allows us to independently adjust the detector and antenna properties and to pursue multi-band designs. We have fabricated superconducting resonators made from atomic layer deposited (ALD) titanium nitride (TiN), with thicknesses ranging from 3 to 40 nm. We find a strong dependence of transition temperature on thickness, from 0.6 to 4.2 K for our thinnest and thickest films, respectively. In dark measurements, we find internal quality factors that range from 10410^4104 to 7×1057\times 10^57×105 depending on film thickness, and kinetic inductance as high as 8 nH/square. The very small volumes and high kinetic inductance make it possible to engineer extremely sensitive detectors with inductor volumes approaching a few cubic microns that operate at readout frequencies of tens to hundreds of MHz. By taking advantage of the large fractional bandwidth available at low frequencies, we expect to achieve multiplexing densities that exceed that of state of the art TES arrays even without further improvements in film quality factor. We will present the characterization of film properties and dark devices, as well as well as initial optical results for antenna coupled single-band and single-pol devices. We will also discuss designs and sensitivity projections for future dual-pol and multi-band arrays ready for deployment in near-future CMB instruments.
This article presents a multichroic Kinetic Inductance Bolometer (KIB) polarimeter that utilizes coplanar waveguide (CPW) diplexers. The CPW diplexers function as filters, providing two passbands centered at 220 GHz and 280 GHz. The high-quality-factor resonant units deliver excellent transmission and isolation characteristics. Additionally, the quasi-lumped-element resonator design enables a significant reduction in size compared to conventional microstrip diplexers. The entire polarimeter—comprising orthomode transducer (OMT) probes, diplexers, KIBs, and CPW feed lines—is integrated on a single plane, allowing for one-layer superconducting thin-film fabrication with a simplified process. The compact size, superior frequency response, and streamlined fabrication process make the proposed pixel scheme suitable for integrated array development.
We present our recent development of superconducting detectors for measurements of cosmic microwave background. We have fabricated antenna-coupled superconducting tunnel junctions (STJs). Two different types of STJs have been fabricated: the parallel-connected twin junction and the microstrip. Both types of STJs made of Nb and Al have successfully detected 80 GHz millimeter wave radiation with photon-assisted tunneling. We have also developed microwave kinetic inductance detectors (MKIDs). The MKIDs offer us high multiplexing factors with a single readout line using the frequency-domain readout. We have developed abosrption-type and transmission-type MKIDs whose resonators are formed with either coplanar waveguides (CPW) or microstrips. The quality factor of the CPW MKID made of Nb is measured to be about 105. The microstrip MKID is being developed for the multichroic measurements.
Kinetic inductance detectors (KIDs) are superconducting thin-film microresonators that are sensitive photon detectors. These detectors are a candidate for the next generation of experiments designed to measure the polarization of the cosmic microwave background (CMB). I discuss the basic theory needed to understand the response of a KID to light, focusing on the dynamics of the quasiparticle system. I derive an equation that describes the dynamics of the quasiparticle number, solve it in a simplified form not previously published, and show that it can describe the dynamic response of a detector. Magnetic flux vortices in a superconducting thin film can be a significant source of dissipation, and I demonstrate some techniques to prevent their formation. Based on the presented theory, I derive a corrected version of a widely-used equation for the quasiparticle recombination noise in a KID. I show that a KID consisting of a lumped-element resonator can be sensitive enough to be limited by photon noise, which is the fundamental limit for photometry, at a level of optical loading below levels in ground-based CMB experiments. Finally, I describe an ongoing project to develop multichroic KID pixels that are each sensitive to two linear polarization states in two spectral bands, intended for the next generation of CMB experiments. I show that a prototype 23-pixel array can detect millimeter-wave light, and present characterization measurements of the detectors.