&lt;title&gt;Use of hafnium-based superconducting tunnel junctions as high-resolution spectrometers for x-ray astronomy&lt;/title&gt;

Kraft, Stefan; Peacock, A.; Bavdaz, Marcos; Castelletto, B.; Collaudin, B.; Pérez, Daniel; Venn, R.; Harper, Tim E.

doi:10.1117/12.330280

Cited by 16 publications

(17 citation statements)

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“…This work adds to the existing literature in hafnium thin films developed for superconducting tunnel junction detectors [14,15] and transition edge sensors [16].…”

Section: Introductionmentioning

confidence: 99%

Characterization of sputtered hafnium thin films for high quality factor microwave kinetic inductance detectors

Coiffard

Daal

Zobrist

et al. 2020

Supercond. Sci. Technol.

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Hafnium is an elemental superconductor which crystallizes in a hexagonal close packed structure, has a transition temperature T C 400 mK, and has a high normal state resistivity around 90 µΩ cm. In Microwave Kinetic Inductance Detectors (MKIDs), these properties are advantageous since they allow for creating detectors sensitive to optical and near infra-red radiation. In this work, we study how sputter conditions and especially the power applied to the target during the deposition, affect the hafnium T C , resistivity, stress, texture and preferred crystal orientation. We find that the position of the target with respect to the substrate strongly affects the orientation of the crystallites in the films and the internal quality factor, Q i , of MKIDs fabricated from the films. In particular, we demonstrate that a DC magnetron sputter deposition at a normal angle of incidence, low pressure, and low plasma power promotes the growth of compressive (002)-oriented films and that such films can be used to make high quality factor MKIDs with Q i up to 600,000.

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“…This work adds to the existing literature in hafnium thin films developed for superconducting tunnel junction detectors [14,15] and transition edge sensors [16].…”

Section: Introductionmentioning

confidence: 99%

Characterization of sputtered hafnium thin films for high quality factor microwave kinetic inductance detectors

Coiffard

Daal

Zobrist

et al. 2020

Supercond. Sci. Technol.

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“…Here, we investigate hafnium as a potential candidate for this application. Its superconducting properties have been thoroughly investigated for use in superconducting tunnel junction detectors [14][15][16] and transition edge sensors. 17,18 Sputtered films have a hexagonal close-packed (hcp) crystal structure and are in the local superconducting limit with critical temperatures ranging from 140 to 450 mK depending on deposition conditions.…”

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confidence: 99%

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Zobrist

Coiffard

Bumble

et al. 2019

Applied Physics Letters

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We report on the design and performance of Microwave Kinetic Inductance Detectors (MKIDs) sensitive to single photons in the optical to near-infrared range using hafnium as the sensor material. Our test device had a superconducting transition temperature of 395 mK and a room temperature normal state resistivity of 97 µΩ cm with an RRR = 1.6. Resonators on the device displayed internal quality factors of around 200 000. Similar to the analysis of MKIDs made from other highly resistive superconductors, we find that modeling the temperature response of the detector requires an extra broadening parameter in the superconducting density of states. Finally, we show that this material and design is compatible with a full-array fabrication process which resulted in pixels with decay times of about 40 µs and resolving powers of ∼9 at 800 nm.Optical and near-IR (OIR) MKIDs are superconducting sensors capable of measuring the arrival time and energy of optical to near-infrared photons. 1 They are less sensitive to false counts and radiation damage 2 than semiconductor devices operating in the same wavelength range and can achieve higher readout speeds. Moreover, each MKID is a high quality factor resonator which allows for natural frequency domain multiplexing and distinguishes the technology from other superconducting detectors. These advantages make arrays of OIR MKIDs useful as astrophysics cameras focusing on timedomain astronomy 3-5 and high contrast imaging. 6-8 To date, commissioned instruments have used either nonstoichiometric titanium nitride or platinum silicide alloys as the photon-sensitive material in the resonators and have achieved resolving powers, R = E/∆E, of up to 8 at 800 nm. 9 This resolving power has been shown to be limited equally by stationary noise, generated by two-level systems (TLS) in the device and amplifiers in the readout chain, as well as an intrinsic variance in the photon signal pulse height, likely caused by phonon escape from the superconductor to the substrate during the initial photon energy down-conversion. 10

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“…The thin film transition temperature is a factor of 4 higher than its bulk value [23]. It also is a very disordered material resulting in an anomalously high normal state resistivity [44]. With this in mind, it is unsurprising that the material constants for hafnium provided in reference 14 do not provide sensible answers when calculating the phonon loss factor, J.…”

Section: Appendix G: Expected Phonon Trapping Improvementmentioning

confidence: 99%

Membrane-less phonon trapping and resolution enhancement in optical microwave kinetic inductance detectors

Zobrist,

Clay,

Coiffard

et al. 2022

Preprint

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Microwave Kinetic Inductance Detectors (MKIDs) sensitive to light in the ultraviolet to nearinfrared wavelengths are superconducting micro-resonators that are capable of measuring photon arrival times to microsecond precision and estimating each photon's energy. The resolving power of non-membrane MKIDs has remained stubbornly around 10 at 1 µm despite significant improvements in the system noise. Here we show that the resolving power can be roughly doubled with a simple bilayer design without needing to place the device on a membrane, avoiding a significant increase in fabrication complexity. Based on modeling of the phonon propagation, we find that the majority of the improvement comes from the inability of high energy phonons to enter the additional layer due to the lack of available phonon states.

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<title>Use of hafnium-based superconducting tunnel junctions as high-resolution spectrometers for x-ray astronomy</title>

Cited by 16 publications

References 0 publications

Characterization of sputtered hafnium thin films for high quality factor microwave kinetic inductance detectors

Characterization of sputtered hafnium thin films for high quality factor microwave kinetic inductance detectors

Design and performance of hafnium optical and near-IR kinetic inductance detectors

Membrane-less phonon trapping and resolution enhancement in optical microwave kinetic inductance detectors

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