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Physical Review Applied

Dual-resonator kinetic inductance detector for distinction between signal and 1/f frequency noise

N. Foroozani, Bahman Sarabi, S. H. Moseley, Thomas R. Stevenson, Edward J. Wollack, Omid Noroozian, K. D. Osborn

Published Jan 8, 2024• 1 citation
Publisher

Abstract

Astronomical kinetic inductance detectors (KIDs), similar to quantum information devices, experience performance-limiting noise from materials. In particular, $1/f$ (frequency) noise arises from two-level system defects (TLSs) in the circuit dielectrics and material interfaces and can be a dominant noise mechanism. Here, we present a dual-resonator KID (DuRKID), which is designed for improved noise-equivalent power relative to standard $1/f$-noise-limited KIDs. In this study we present the DuRKID schematic, a fabricated example, our first measurement results, a theoretical model including $1/f$ noise, and a system-noise model containing additional noise sources. The circuit consists of two superconducting resonators sharing an electrical capacitance bridge of four capacitors, each of which hosts TLSs. The device is intended to operate using hybridization of the modes, which causes TLSs to either couple to one mode or the other, depending upon which capacitor they reside in. In contrast, the signal will affect a resonator inductance and, due to mode hybridization, this causes correlated frequency changes in both modes. Therefore, one can better distinguish the photon signal from the TLS frequency noise. To achieve hybridization, a $\mathrm{Ti}\mathrm{N}$ inductor is current biased to allow tuning of one bare-resonator mode into degeneracy with the other. Measurements show that the resonator modes hybridize as expected. The inter-resonator coupling and unintentional coupling of the two resonators to transmission lines are also characterized in measurements. A quantum information-science model allows device-parameter extraction from experimental data and a $1/f$ noise analysis with uncorrelated noise. A system-noise analysis of the DuRKID, with comparisons to standard KIDs, is performed with generation-recombination noise and amplifier noise. The study reveals that the DuRKID can exhibit a large performance advantage over TLS-limited KID detectors.

DOI
10.1103/physrevapplied.21.014009

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Astronomical Kinetic Inductance Detectors (KIDs), similar to quantum information devices, experience performance limiting noise from materials. In particular, 1/f (frequency) noise can be a dominant noise mechanism, which arises from Two-Level System defects (TLSs) in the circuit dielectrics and material interfaces. Here we present a Dual-Resonator KID (DuRKID), which is designed for improved signal to noise (or noise equivalent power) relative to 1/f-noise limited KIDs. We first show the DuRKID schematic, fabricated circuit, and we follow with a description of the intended operation, first measurements, theory, and discussion. The circuit consists of two superconducting resonators sharing an electrical capacitance bridge of 4 capacitors, each of which hosts TLSs. The device is intended to operate using hybridization of the modes, which causes TLSs to either couple to one mode or the other, depending upon which capacitor they reside in. In contrast, the intended KID signal is directed to an inductor, and due to hybridization this causes correlated frequency changes in both (hybridized) modes. Therefore, one can distinguish photon signal from TLS frequency noise. To achieve hybridization, a TiN inductor is current biased to allow tuning of one bare resonator mode into degeneracy with the other and measurements show that the intended resonator modes frequency tune and hybridize as expected. The interresonator coupling and unintentional coupling of the 2 resonators to transmission lines are also characterized in measurements. In the theory, based on a quantum-information-science modes, we calculate the 4-port S parameters and simulate the 1/f frequency noise of the device. The study reveals that the DuRKID can exhibit a large and fundamental performance advantage over 1/f-noise-limited KID detectors.

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Astronomical kinetic inductance detectors (KIDs), similar to quantum information devices, experience performance-limiting noise from materials. In particular, 1/f1/f1/f (frequency) noise arises from two-level system defects (TLSs) in the circuit dielectrics and material interfaces and can be a dominant noise mechanism. Here, we present a dual-resonator KID (DuRKID), which is designed for improved noise-equivalent power relative to standard 1/f1/f1/f-noise-limited KIDs. In this study we present the DuRKID schematic, a fabricated example, our first measurement results, a theoretical model including 1/f1/f1/f noise, and a system-noise model containing additional noise sources. The circuit consists of two superconducting resonators sharing an electrical capacitance bridge of four capacitors, each of which hosts TLSs. The device is intended to operate using hybridization of the modes, which causes TLSs to either couple to one mode or the other, depending upon which capacitor they reside in. In contrast, the signal will affect a resonator inductance and, due to mode hybridization, this causes correlated frequency changes in both modes. Therefore, one can better distinguish the photon signal from the TLS frequency noise. To achieve hybridization, a TiN\mathrm{Ti}\mathrm{N}TiN inductor is current biased to allow tuning of one bare-resonator mode into degeneracy with the other. Measurements show that the resonator modes hybridize as expected. The inter-resonator coupling and unintentional coupling of the two resonators to transmission lines are also characterized in measurements. A quantum information-science model allows device-parameter extraction from experimental data and a 1/f1/f1/f noise analysis with uncorrelated noise. A system-noise analysis of the DuRKID, with comparisons to standard KIDs, is performed with generation-recombination noise and amplifier noise. The study reveals that the DuRKID can exhibit a large performance advantage over TLS-limited KID detectors.
Astronomical Kinetic Inductance Detectors (KIDs), similar to quantum information devices, experience performance limiting noise from materials. In particular, 1/f (frequency) noise can be a dominant noise mechanism, which arises from Two-Level System defects (TLSs) in the circuit dielectrics and material interfaces. Here we present a Dual-Resonator KID (DuRKID), which is designed for improved signal to noise (or noise equivalent power) relative to 1/f-noise limited KIDs. We first show the DuRKID schematic, fabricated circuit, and we follow with a description of the intended operation, first measurements, theory, and discussion. The circuit consists of two superconducting resonators sharing an electrical capacitance bridge of 4 capacitors, each of which hosts TLSs. The device is intended to operate using hybridization of the modes, which causes TLSs to either couple to one mode or the other, depending upon which capacitor they reside in. In contrast, the intended KID signal is directed to an inductor, and due to hybridization this causes correlated frequency changes in both (hybridized) modes. Therefore, one can distinguish photon signal from TLS frequency noise. To achieve hybridization, a TiN inductor is current biased to allow tuning of one bare resonator mode into degeneracy with the other and measurements show that the intended resonator modes frequency tune and hybridize as expected. The interresonator coupling and unintentional coupling of the 2 resonators to transmission lines are also characterized in measurements. In the theory, based on a quantum-information-science modes, we calculate the 4-port S parameters and simulate the 1/f frequency noise of the device. The study reveals that the DuRKID can exhibit a large and fundamental performance advantage over 1/f-noise-limited KID detectors.
Context. Microwave kinetic inductance detectors (MKIDs) are superconducting detectors that have the potential to contribute to the construction of over 10 000 pixel cameras required for mm and submm astronomical observations over the next decade. One of the issues related to its application is two-level-system (TLS) noise that creates a 1/ f term in the power spectrum density (PSD) of the detectors. A hybrid-type MKID has been proposed for TLS noise suppression without affecting the MKID performance. In this paper, we present a systematic method to model a hybrid-type MKID for mitigating TLS noise while achieving high sensitivity. Aims. Previous studies have shown that TLS noise in MKIDs depends on the sampling frequency, internal power, device geometry, and temperature. The strength of the electrical field distribution along the resonator line also affects the TLS noise properties. Based on this knowledge, we constructed a noise model of a hybrid-type MKID. Methods. Using this model, we designed MKIDs for the cosmic microwave background radiation experiment, GroundBIRD. We evaluated the 1/ f noise properties and NET of the fabricated devices using the on-site measurements. Based on the NET measurements, we can confirm that the white noise of fabricated detectors is limited by atmospheric photon noise. From the 1/ f noise measurements, we also confirm that it is possible to reach an atmospheric photon noise limit down to a low sampling frequency (i.e., of a few Hz) at the typical observation conditions from Teide observatory. Results. We confirm the design methodology we propose for hybrid-type MKID works well in optimizing the TLS model to the hybrid-type MKID, as evidenced by performance verification measurements carried out in the laboratory and on site.
Noise performance is one of the most crucial aspects of any detector. Superconducting Microwave Kinetic Inductance Detectors (MKIDs) have an “excess” frequency noise that shows up as a small time dependent jitter of the resonance frequency characterized by the frequency noise power spectrum measured in units of Hz2/Hz. Recent studies have shown that this noise almost certainly originates from a surface layer of two‐level system (TLS) defects on the metallization or substrate. Fluctuation of these TLSs introduces noise in the resonator due to coupling of the TLS electric dipole moments to the resonator’s electric field. Motivated by a semi‐empirical quantitative theory of this noise mechanism, we have designed and tested new resonator geometries in which the high‐field “capacitive” portion of the CPW resonator is replaced by an interdigitated capacitor (IDC) structure with 10–20 μm electrode spacing, as compared to the 2 μm spacing used for our more conventional CPW resonators. Measurements show that this new IDC design has dramatically lower TLS noise, currently by about a factor of ∼29 in terms of the frequency noise power spectrum, corresponding to an improvement of about a factor of 29 in NEP. These new devices are replacing the CPW resonators in our next design iteration in progress for MKIDCam. Opportunities and prospects for future reduction of the TLS noise will be discussed.
Space-based astronomy is in need of a photon-noise limited detector with multiplexing opportunities. The kinetic inductance detector (KID) is capable of both properties. An incoming photon breaks Cooper pairs in the superconducting layer of the KID, which leads to a change in inductance, which can be detected with phase- and amplitude read-out. Photon noise, generation-recombination noise are inevitable noise sources, but two-level system noise can be minimized by adjusting the resonator and its geometry. To gain insight in the noise and loss sources this thesis investigates the difference between microstrip and co-planar waveguide resonators; and the difference between a silicon substrate and a silicon-on-insulator substrate. Numerical analysis shows that: noise in all types of resonators are dielectric bulk dominated; an Al superconducting layer shows has different losses in terms of Q-factor, compared to a NbTiN superconducting layer, but quantitatively the same internal Q-factor in the order of 105 is achieved; an Al superconducting layer in a microstrip has 5dBc/Hz and 2dBc/Hz higher noise in the metal-air and metal-edge interfaces, respectively, compared to a NbTiN superconducting layer; an Al on Si CPW and microstrip have the same Q-factor performance; an Al on Si CPW has a 2-8dBc/Hz more noise at all interfaces compared to an Al on Si microstrip; a buried oxide layer has no influence on the loss in terms of the Q-factor for 100nm Al on Si substrate CPWs; and that the noise of an Al on SOI CPW is bulk dominated, and the dielectric bulk contributes 10dBc/Hz more to the noise, compared to an Al on Si CPW. Experimental analysis shows that a gapwidth of wgap ? 10?m for Al on SOI CPWs shows no response, due to high two-level system noise. Low Q-factors in the order of 104 have been measured for Al on SOI CPWs, which is low compared to literature. A high set-up noise of -85dBc/Hz and divergent relationships with the internal power indicate that TLS-noise does not dominate the measurements, and set-up negatively influences the measurements. In conclusion, the resonator geometry is an important factor for the performance of a KID in terms of noise and Q-factors. A buried oxide layer has no consequence for the Q-factor, and negatively affects the noise of a CPW.
As a newly developed pair-breaking superconducting detector, microwave kinetic inductance detectors are simple to integrate in the frequency domain and have already been used in astronomical detection and array imaging at the (sub)millimeter and optical wavelengths. For these applications, the dark noise level of kinetic inductance detector is one of the key performance indicators. Herein a noise power spectrum analysis method is introduced in detail, which can accurately and effectively analyze the noise spectrum of kinetic inductance detector in a wide frequency range. This method can well balance the noise spectrum resolution and variance performance, by taking the noise data at the resonance frequency with two sampling rates and setting the appropriate frequency resolutions for different frequency bands. This method is used to characterize and compare the noise of aluminum (Al) kinetic inductance detectors made from two different micromachining processes. We deposite a 25-nm-thick aluminum film on high-resistivity silicon substrate for one device, while place one silicon nitride (SiNx) film on the top and one on the bottom of the aluminum film for another device. It is found that the frequency noise of the device with two silicon nitride films is about 25% to 50% of the bare aluminum device. Using this double silicon nitride film fabrication technique, we further fabricate a few groups of lumped-element aluminum kinetic inductance detectors with various inductor and interdigitated capacitor designs. We investigate the noise properties of these devices at different microwave driven power and bath temperatures, and the experimental results show typical two-level system noise behaviors. Our work provides a standard method to characterize the noise power spectrum of kinetic inductor detector, and also paves the way to developing low-noise aluminum kinetic inductance detectors for terahertz imaging, photon-counting and energy-resolving applications.
Parallel-plate capacitors (PPC) significantly reduce the size of superconducting microwave resonators, reducing the pixel pitch for arrays of single-photon energy-resolving kinetic inductance detectors (KIDs). The frequency noise of KIDs is typically limited by tunneling two-level systems (TLS), which originate from lattice defects in the dielectric materials required for PPCs. How the frequency noise level depends on the PPC's dimensions has not been experimentally addressed. We measure the frequency noise of 56 resonators with aaa-SiC\mathrm{Si}\mathrm{C}SiC:H\mathrm{H}H PPCs, which cover a factor of 44 in PPC area and a factor of 4 in dielectric thickness. To support the noise analysis, we measure the resonators' TLS-induced power-dependent intrinsic loss and temperature-dependent resonance frequency shift. From the TLS models, we expect a geometry-independent microwave loss and resonance frequency shift, which is set by the TLS properties of the dielectric. However, we observe a thickness-dependent microwave loss and resonance frequency shift; this is explained by surface layers that limit the performance of PPC-based resonators. For a uniform dielectric, the frequency noise level should scale directly inversely with the PPC area and thickness. We observe that an increase in PPC size reduces the frequency noise, but the exact scaling is, in some cases, weaker than expected. Finally, we derive engineering guidelines for the design of KIDs based on PPC-based resonators.