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Register a new userDesign and performance of dual-polarization lumped-element kinetic inductance detectors for millimeter-wave polarimetry
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Lumped-element kinetic inductance detectors (LEKIDs) are an attractive technology for millimeter-wave observations that require large arrays of extremely low-noise detectors. We designed, fabricated and characterized 64-element (128 LEKID) arrays of horn-coupled, dual-polarization LEKIDs optimized for ground-based CMB polarimetry. Our devices are sensitive to two orthogonal polarizations in a single spectral band centered on 150 GHz with $Delta u/ u=0.2$. The $65times 65$ mm square arrays are designed to be tiled into the focal plane of an optical system. We demonstrate the viability of these dual-polarization LEKIDs with laboratory measurements. The LEKID modules are tested with an FPGA-based readout system in a sub-kelvin cryostat that uses a two-stage adiabatic demagnetization refrigerator. The devices are characterized using a blackbody and a millimeter-wave source. The polarization properties are measured with a cryogenic stepped half-wave plate. We measure the resonator parameters and the detector sensitivity, noise spectrum, dynamic range, and polarization response. The resonators have internal quality factors approaching $1times 10^{6}$. The detectors have uniform response between orthogonal polarizations and a large dynamic range. The detectors are photon-noise limited above 1 pW of absorbed power. The noise-equivalent temperatures under a 3.4 K blackbody load are $<100~mumathrm{Ksqrt{s}}$. The polarization fractions of detectors sensitive to orthogonal polarizations are >80%. The entire array is multiplexed on a single readout line, demonstrating a multiplexing factor of 128. The array and readout meet the requirements for 4 arrays to be read out simultaneously for a multiplexing factor of 512. This laboratory study demonstrates the first dual-polarization LEKID array optimized for CMB polarimetry and shows the readiness of the detectors for on-sky observations.
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Lumped-element kinetic inductance detectors(LEKIDs) have recently shown considerable promise as direct absorption mm-wavelength detectors for astronomical applications. One major research thrust within the Neel Iram Kids Array (NIKA) collaboration has been to investigate the suitability of these detectors for deployment at the 30-meter IRAM telescope located on Pico Veleta in Spain. Compared to microwave kinetic inductance detectors (MKID), using quarter wavelength resonators, the resonant circuit of a LEKID consists of a discrete inductance and capacitance coupled to a feedline. A high and constant current density distribution in the inductive part of these resonators makes them very sensitive. Due to only one metal layer on a silicon substrate, the fabrication is relatively easy. In order to optimize the LEKIDs for this application, we have recently probed a wide variety of individual resonator and array parameters through simulation and physical testing. This included determining the optimal feed-line coupling, pixel geometry, resonator distribution within an array (in order to minimize pixel cross-talk), and resonator frequency spacing. Based on these results, a 144-pixel Aluminum array was fabricated and tested in a dilution fridge with optical access, yielding an average optical NEP of ~2E-16 W/Hz^1/2 (best pixels showed NEP = 6E-17 W/Hz^1/2 under 4-8 pW loading per pixel). In October 2010 the second prototype of LEKIDs has been tested at the IRAM 30 m telescope. A new LEKID geometry for 2 polarizations will be presented. Also first optical measurements of a titanium nitride array will be discussed.
Mapping the polarization of the Cosmic Microwave Background is yielding exciting data on the origin of the universe, the reionization of the universe, and the growth of cosmic structure. Kilopixel arrays represent the current state of the art, but advances in detector technology are needed to enable the larger detector arrays needed for future measurements. Here we present a design for single-band dual-polarization Kinetic Inductance Detectors (KIDs) at 20% bandwidths centered at 145, 220, and 280 GHz. The detection and readout system is nearly identical to the successful photon-noise-limited aluminum Lumped-Element KIDs that have been recently built and tested by some of the authors. Fabricating large focal plane arrays of the feed horns and quarter-wave backshorts requires only conventional precision machining. Since the detectors and readout lines consist only of a single patterned aluminum layer on a SOI wafer, arrays of the detectors can be built commercially or at a standard university cleanroom.
We report photon-noise limited performance of horn-coupled, aluminum lumped-element kinetic inductance detectors at millimeter wavelengths. The detectors are illuminated by a millimeter-wave source that uses an active multiplier chain to produce radiation between 140 and 160 GHz. We feed the multiplier with either amplified broadband noise or a continuous-wave tone from a microwave signal generator. We demonstrate that the detector response over a 40 dB range of source power is well-described by a simple model that considers the number of quasiparticles. The detector noise-equivalent power (NEP) is dominated by photon noise when the absorbed power is greater than approximately 1 pW, which corresponds to $mathrm{NEP} approx 2 times 10^{-17} , mathrm{W} , mathrm{Hz}^{-1/2}$, referenced to absorbed power. At higher source power levels we observe the relationships between noise and power expected from the photon statistics of the source signal: $mathrm{NEP} propto P$ for broadband (chaotic) illumination and $mathrm{NEP} propto P^{1/2}$ for continuous-wave (coherent) illumination.
We present a technique for increasing the internal quality factor of kinetic inductance detectors (KIDs) by nulling ambient magnetic fields with a properly applied magnetic field. The KIDs used in this study are made from thin-film aluminum, they are mounted inside a light-tight package made from bulk aluminum, and they are operated near $150 , mathrm{mK}$. Since the thin-film aluminum has a slightly elevated critical temperature ($T_mathrm{c} = 1.4 , mathrm{K}$), it therefore transitions before the package ($T_mathrm{c} = 1.2 , mathrm{K}$), which also serves as a magnetic shield. On cooldown, ambient magnetic fields as small as approximately $30 , mathrm{mu T}$ can produce vortices in the thin-film aluminum as it transitions because the bulk aluminum package has not yet transitioned and therefore is not yet shielding. These vortices become trapped inside the aluminum package below $1.2 , mathrm{K}$ and ultimately produce low internal quality factors in the thin-film superconducting resonators. We show that by controlling the strength of the magnetic field present when the thin film transitions, we can control the internal quality factor of the resonators. We also compare the noise performance with and without vortices present, and find no evidence for excess noise beyond the increase in amplifier noise, which is expected with increasing loss.
We show measurements of thermal kinetic inductance detectors (TKID) intended for millimeter wave cosmology in the 200-300 GHz atmospheric window. The TKID is a type of bolometer which uses the kinetic inductance of a superconducting resonator to measure the temperature of the thermally isolated bolometer island. We measure bolometer thermal conductance, time constant and noise equivalent power. We also measure the quality factor of our resonators as the bath temperature varies to show they are limited by effects consistent with coupling to two level systems.
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