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Tungsten silicide films for kinetic inductance detectors

T. Cecil, Antonino Miceli, Orlando Quaranta, Chian Liu, Daniel Rosenmann, Sean G. McHugh, Benjamin A. Mazin

Published Mar 22, 2012• 0 citations
OpenAlex

Abstract

Microwave Kinetic Inductance Detectors (MKIDs) provide highly multiplexed arrays of detectors that can be configured to operate from the sub-millimeter to the X-ray regime. We have examined two tungsten silicide alloys (W5Si3 and WSi2), which are dense alloys that provide a critical temperature tunable with composition, large kinetic inductance fraction, and high normal-state resistivity. We have fabricated quarter wavelength CPW superconducting resonators and provide measurement data on critical temperature, surface resistance, quality factor, noise, and quasiparticle lifetime. Tungsten silicide appears to be very promising for kinetic inductance detectors.

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Tungsten silicide films for microwave kinetic inductance detectors

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Microwave kinetic inductance detectors provide highly multiplexed arrays of detectors that can be configured to operate from the sub-millimeter to the x-ray regime. We have examined two tungsten silicide alloys (W5Si3 and WSi2), which are dense alloys that provide a critical temperature tunable with composition, large kinetic inductance fraction, and high normal-state resistivity. We have fabricated superconducting resonators and provide measurement data on critical temperature, surface resistance, quality factor, noise, and quasiparticles lifetime. Tungsten silicide appears to be promising for microwave kinetic inductance detectors.

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High quality factor platinum silicide microwave kinetic inductance detectors

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We report on the development of microwave kinetic inductance detectors (MKIDs) using platinum silicide as the sensor material. MKIDs are an emerging superconducting detector technology, capable of measuring the arrival times of single photons to better than two microseconds and their energies to around ten percent. Previously, MKIDs have been fabricated using either sub-stoichiometric titanium nitride or aluminum, but TiN suffers from the spatial inhomogeneities in the superconducting critical temperature and Al has a low kinetic inductance fraction, causing low detector sensitivity. To address these issues, we have instead fabricated the PtSi microresonators with the superconducting critical temperatures of 944 ± 12 mK and high internal quality factors (Qi≳106). These devices show typical quasiparticle lifetimes of τqp≈30–40 μs and spectral resolution, R=λ/Δλ, of 8 at 406.6 nm. We compare PtSi MKIDs to those fabricated with TiN and detail the substantial advantages that PtSi MKIDs have to offer.

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Submicron Kinetic Inductance Detectors for SAFARI: Improving MKID sensitivity through width reduction

R. M. J. Janssen

Spectroscopic observations of a large number of galaxies in the far-infrared are critical in the study of galaxy evolution. These observations are difficult at the moment, because of the lack of good far-infrared (FIR) detector technology. Microwave Kinetic Inductance Detectors (MKIDs) are showing promising results to fill this void. A common MKID design is the antenna-coupled coplanar waveguide (CPW) resonator patterned in a superconducting film. These resonators are extremely sensitive to changes in the Cooper pair density. FIR photons are energetic enough to break Cooper pairs. This means a superconducting resonator can be used as a pixel for a FIR camera. The inherent multiplexing advantage of MKIDs means they can easily be fabricated in arrays of up to 5000 pixels. By putting such an array in the SAFARI instrument on the cooled SPICA telescope a blind spectroscopic survey that can detect Milky Way sized galaxies out to redshift z = 2 will be possible. However, to achieve background limited performance on a cooled telescope like SPICA the sensivity of MKIDs needs to be improved by at least an order of magnitude. This project aims to investigate if this can be achieved by reducing the width of the CPW to much below what has typically been made using optical lithography (> 1 ?m). CPW resonators with a central line width as narrow as 300 nm were made in NbTiN using electron beam lithography and reactive ion etching. Using this fabrication method NbTiN resonators with a central line width varying between 0.3 ?m and 3 ?m were made. These resonators were used to do a systematic study of the width dependence of the kinetic inductance fraction, quality factor, responsivity, read-out power, noise and NEP. It is shown that the width dependence of all these properties does not change down to 300 nm. Encouraged by these results two prototype submicron pixel arrays were made in aluminum. These showed sensitivities comparable to resonators with a few micron wide CPW. The main reason for this lack of sensitivity improvement is the lower maximum read-out power of submicron wide aluminum resonators. Based on these results power handling seems a key issue that will determine if submicron resonators are a viable route to improve the MKIDs sensitivity. These results of this project indicate that aluminum has a different width dependence of its power handling compared to NbTiN. Therefore, a systematic study of submicron resonators in aluminum, which focuses on the power handling, is required.

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We describe measurements of the properties, at dc, gigahertz, and terahertz frequencies, of thin (10 nm) aluminum films with 10 Omega/square normal state sheet resistance. Such films can be applied to construct microwave kinetic inductance detector arrays for submillimeter and far-infrared astronomical applications in which incident power excites quasiparticles directly in a superconducting resonator that is configured to present a matched-impedance to the high frequency radiation being detected. For films 10 nm thick, we report normal state sheet resistance, resistance-temperature curves for the superconducting transition, quality factor and kinetic inductance fraction for microwave resonators made from patterned films, and terahertz measurements of sheet impedance measured with a Fourier Transform Spectrometer. We compare properties with similar resonators made from niobium 600 nm thick.

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Study of Superconducting Bilayer for Microwave Kinetic Inductance Detectors for Astrophysics

Agnès Dominjon, Masakazu Sekine, K. Karatsu +5 more

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.

IEEE Transactions on Applied Superconductivity•Feb 19, 2016•16 citations
Microwave Kinetic Inductance Detectors (MKIDs) provide highly multiplexed arrays of detectors that can be configured to operate from the sub-millimeter to the X-ray regime. We have examined two tungsten silicide alloys (W5Si3 and WSi2), which are dense alloys that provide a critical temperature tunable with composition, large kinetic inductance fraction, and high normal-state resistivity. We have fabricated quarter wavelength CPW superconducting resonators and provide measurement data on critical temperature, surface resistance, quality factor, noise, and quasiparticle lifetime. Tungsten silicide appears to be very promising for kinetic inductance detectors.
Microwave kinetic inductance detectors provide highly multiplexed arrays of detectors that can be configured to operate from the sub-millimeter to the x-ray regime. We have examined two tungsten silicide alloys (W5Si3 and WSi2), which are dense alloys that provide a critical temperature tunable with composition, large kinetic inductance fraction, and high normal-state resistivity. We have fabricated superconducting resonators and provide measurement data on critical temperature, surface resistance, quality factor, noise, and quasiparticles lifetime. Tungsten silicide appears to be promising for microwave kinetic inductance detectors.
We report on the development of microwave kinetic inductance detectors (MKIDs) using platinum silicide as the sensor material. MKIDs are an emerging superconducting detector technology, capable of measuring the arrival times of single photons to better than two microseconds and their energies to around ten percent. Previously, MKIDs have been fabricated using either sub-stoichiometric titanium nitride or aluminum, but TiN suffers from the spatial inhomogeneities in the superconducting critical temperature and Al has a low kinetic inductance fraction, causing low detector sensitivity. To address these issues, we have instead fabricated the PtSi microresonators with the superconducting critical temperatures of 944 ± 12 mK and high internal quality factors (Qi≳106). These devices show typical quasiparticle lifetimes of τqp≈30–40 μs and spectral resolution, R=λ/Δλ, of 8 at 406.6 nm. We compare PtSi MKIDs to those fabricated with TiN and detail the substantial advantages that PtSi MKIDs have to offer.
Spectroscopic observations of a large number of galaxies in the far-infrared are critical in the study of galaxy evolution. These observations are difficult at the moment, because of the lack of good far-infrared (FIR) detector technology. Microwave Kinetic Inductance Detectors (MKIDs) are showing promising results to fill this void. A common MKID design is the antenna-coupled coplanar waveguide (CPW) resonator patterned in a superconducting film. These resonators are extremely sensitive to changes in the Cooper pair density. FIR photons are energetic enough to break Cooper pairs. This means a superconducting resonator can be used as a pixel for a FIR camera. The inherent multiplexing advantage of MKIDs means they can easily be fabricated in arrays of up to 5000 pixels. By putting such an array in the SAFARI instrument on the cooled SPICA telescope a blind spectroscopic survey that can detect Milky Way sized galaxies out to redshift z = 2 will be possible. However, to achieve background limited performance on a cooled telescope like SPICA the sensivity of MKIDs needs to be improved by at least an order of magnitude. This project aims to investigate if this can be achieved by reducing the width of the CPW to much below what has typically been made using optical lithography (> 1 ?m). CPW resonators with a central line width as narrow as 300 nm were made in NbTiN using electron beam lithography and reactive ion etching. Using this fabrication method NbTiN resonators with a central line width varying between 0.3 ?m and 3 ?m were made. These resonators were used to do a systematic study of the width dependence of the kinetic inductance fraction, quality factor, responsivity, read-out power, noise and NEP. It is shown that the width dependence of all these properties does not change down to 300 nm. Encouraged by these results two prototype submicron pixel arrays were made in aluminum. These showed sensitivities comparable to resonators with a few micron wide CPW. The main reason for this lack of sensitivity improvement is the lower maximum read-out power of submicron wide aluminum resonators. Based on these results power handling seems a key issue that will determine if submicron resonators are a viable route to improve the MKIDs sensitivity. These results of this project indicate that aluminum has a different width dependence of its power handling compared to NbTiN. Therefore, a systematic study of submicron resonators in aluminum, which focuses on the power handling, is required.
We design and fabricate a 350GHz 8×8 Al Microwave Kinetic Inductance Detector (MKIDs) array for the demonstration of its characteristics, mainly focus on the quasiparticle lifetime of the resonators. The quasiparticle lifetime data is collected by measuring a resonator’s phase response to a LED pulse at resonant frequency in a dilution refrigerator cooled to mK stage. We also measure and discuss the influence of various parameters on the change of quasiparticle lifetime, including different LED voltage supply, bath temperature of the MKIDs, and superconducting film thickness.
We describe measurements of the properties, at dc, gigahertz, and terahertz frequencies, of thin (10 nm) aluminum films with 10 Omega/square normal state sheet resistance. Such films can be applied to construct microwave kinetic inductance detector arrays for submillimeter and far-infrared astronomical applications in which incident power excites quasiparticles directly in a superconducting resonator that is configured to present a matched-impedance to the high frequency radiation being detected. For films 10 nm thick, we report normal state sheet resistance, resistance-temperature curves for the superconducting transition, quality factor and kinetic inductance fraction for microwave resonators made from patterned films, and terahertz measurements of sheet impedance measured with a Fourier Transform Spectrometer. We compare properties with similar resonators made from niobium 600 nm thick.
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.