Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Japanese Journal of Applied Physics

Enlargement of Kinetic Inductance of NbN Superconducting Thin Films for Device Applications

Mohammad Sajjad Hossain, Keiji Yoshida, Keisuke Kudo, Keiji Enpuku, Kaoru Yamafuji

Published Apr 1, 1992• 8 citations
Publisher

Abstract

Experimental studies to enlarge kinetic inductance of NbN thin films using the effects of quality and thickness of the film are made by measuring Fiske current steps in the current-voltage (I-V) characteristics of NbN/Pb-In Josephson junctions. Experiments demonstrate that the specific kinetic inductance L K can be enlarged over a wide range by changing stoichiometry of the film, as well as by making the film thickness thin, and that this enlargement becomes larger by both effects when the film thickness is in an ultra thin regime. This inductance is shown to be well fitted to L K=µ0λ2/d, w h e r e µ_0 i s t h e v a c u u m p e r m e a b i l i t y, d i s t h e t h i c k n e s s, a n d λ i s t h e m a g n e t i c p e n e t r a t i o n d e p t h i n t h e d i r t y l i m i t. I n t h e p r e s e n t e x p e r i m e n t w e a t t a i n e d t h e i n d u c t a n c e a s h i g h a s L_K=130 p H b y t h e c o m b i n e d e f f e c t s o f i m p u r i t y a n d t h i c k n e s s f o r a f i l m w i t h

DOI
10.1143/jjap.31.1033

Related papers

Inductance and penetration depth measurements of polycrystalline NbN films for all-NbN single flux quantum circuits

Yulong Zhong, Lu Zhang, Junjie Xie +9 more

Abstract In this paper, we report on a systematic study of the inductance and magnetic field penetration depth (λ) of polycrystalline NbN superconducting thin films. By employing a four-metal-layer fabrication process specifically designed for all-NbN single-flux-quantum circuits, we constructed a superconducting quantum interference device loop composed of two parallel NbN SNS junctions, NbN microstrips, and NbN ground planes for precise inductance measurement. At 4.2 K, as the linewidth increases from 1 μm to 30 μm, the inductance per unit length (L u) of NbN microstrips significantly decreases, for example, the L u of 250 nm thick NbN microstrips drops from 0.907 pH/μm to 0.047 pH/μm. Compared to Nb, the L u of polycrystalline NbN microstrips is approximately two to three times that of Nb, offering an advantage for manufacturing smaller superconducting inductors. Furthermore, we conducted simulation analysis using InductEx software to extract the λ of NbN films of varying thicknesses. The results indicate that as the film thickness increased from 45 nm to 600 nm, λ initially decreased sharply and then stabilized, with values ranging from 430 nm to 323 nm. Notably, once the film thickness exceeded 200 nm, λ remained essentially constant, even at a temperature of 10 K, where it showed good stability, albeit with a slight increase (about 50 nm) compared to 4.2 K. This dependence of λ on thickness is reasonably explained by considering the effects of NbN film thickness on the superconducting critical temperature and residual resistivity. These research findings not only deepen our understanding of the characteristics of superconducting films but also lay a solid foundation for the future design and manufacture of more compact superconducting circuits at the higher temperature of 10 K.

Superconductor Science and Technology•Nov 18, 2024•3 citations

Anomalous current-dependence of kinetic inductance in ultrathin NbN meander lines

Mark W. Johnson, Alan M. Kadin

We have measured the rf impedance of 10-nm thick superconducting granular NbN meander lines between 5 /spl mu/m and 20 /spl mu/m wide. The complex reflection coefficient was obtained directly using a vector network analyzer. The impedance (at 10 MHz for a 5 /spl mu/m wide line) is dominated by the large kinetic Inductance of the film, with a sheet inductance of order 1 nH, giving a total inductance of 400 nH for a 5 /spl mu/m/spl times/2 mm line. The kinetic inductance diverges as T/spl rarr/T/sub c/=6.5 K, as expected from Ginzburg-Landau theory (GL). Of particular interest is a substantial decrease of measured inductance with increasing dc current, contrary to the dependence expected from GL. This anomalous current dependence is not well understood, but may be related to vortex dynamics and Josephson effects in these granular films, as supported by preliminary Josephson array simulations. These results have important implications for potential devices such as tunable rf phase shifters and kinetic inductance photodetectors.

IEEE Transactions on Applied Superconductivity•Jun 1, 1997•6 citations

Tunable superconducting nanoinductors

Anthony J. Annunziata, Daniel F. Santavicca, Luigi Frunzio +4 more

We characterize inductors fabricated from ultra-thin, approximately 100 nm wide strips of niobium (Nb) and niobium nitride (NbN). These nanowires have a large kinetic inductance in the superconducting state. The kinetic inductance scales linearly with the nanowire length, with a typical value of 1 nH µm(-1) for NbN and 44 pH µm(-1) for Nb at a temperature of 2.5 K. We measure the temperature and current dependence of the kinetic inductance and compare our results to theoretical predictions. We also simulate the self-resonant frequencies of these nanowires in a compact meander geometry. These nanowire inductive elements have applications in a variety of microwave frequency superconducting circuits.

arXiv:1007.4187•Nanotechnology•Oct 5, 2010•262 citations

NbN films with high kinetic inductance for high-quality compact superconducting resonators

Simone Frasca, Ivo Arabadzhiev, Sebastien Yves Bros de Puechredon +7 more

Niobium nitride ($\mathrm{Nb}\mathrm{N}$) is a particularly promising material for quantum technology applications, as it shows the degree of reproducibility necessary for large-scale superconducting circuits. We demonstrate that resonators based on $\mathrm{Nb}\mathrm{N}$ thin films present a one-photon internal quality factor above ${10}^{5}$ maintaining a high impedance (larger than $2\mathrm{k}\mathrm{\ensuremath{\Omega}}$), with a footprint of approximately $50\ifmmode\times\else\texttimes\fi{}100\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{m}}^{2}$ and a Kerr nonlinearity of few tenths of a hertz. These quality factors, mostly limited by losses induced by the coupling to two-level systems, have been maintained for kinetic inductances ranging from tenths to hundreds of picoHenry per square. We also demonstrate minimal variations in the performance of the resonators during multiple cooldowns over more than nine months. Our work proves the versatility of niobium nitride high-kinetic-inductance resonators, opening perspectives towards the fabrication of compact, high-impedance, and high-quality multimode circuits, with sizable interactions.

arXiv:2302.13930•Physical Review Applied•Oct 9, 2023•37 citations

Self- and Mutual Inductance of NbN and Bilayer NbN/Nb Inductors in a Planarized Fabrication Process With Nb Ground Planes

Sergey K. Tolpygo, Evan B. Golden, Terence J. Weir +2 more

We present measurements of the self- and mutual inductance of NbN and NbN/Nb bilayer inductors (microstrips, striplines, serpentines, etc.) with Nb ground plane(s) fabricated in an advanced process for superconductor electronics developed at MIT Lincoln Laboratory. In this process, the signal traces of logic cell inductors are made either of a 200-nm NbN layer with${{\bm{T}}}_{\bm{c}} \approx $15.5 K or an in-situ deposited NbN/Nb bilayer, replacing a 200-nm Nb layer M6 in the standard SFQ5ee process with nine superconducting layers on 200-mm wafers. Nb ground planes are preserved to maintain a high level of interlayer shielding and low intralayer mutual coupling. A two-step patterning of the top Nb and the bottom NbN layers of the NbN/Nb bilayer allows the creation of inductors with a very wide range of inductances, from low values ∼0.4 pH/μm typical for Nb geometrical inductors to ∼35 pH/μm typical for thin-film kinetic inductors. The mutual inductance of various combinations of NbN, Nb, and NbN/Nb inductors does not depend on superconducting properties of the signal traces in the studied range of linewidths,${\bm{w}}$; it equals the mutual inductance of the Nb inductors with the equivalent geometry and placement between the ground planes. The measured magnetic field penetration depth in NbN films deposited by reactive sputtering at 200 °C isλNbN= 491 ± 5 nm. The measured kinetic inductance of the films with thicknesses${\bm{t}}\ = {\bm{\ }}$200 nm and 150 nm, respectively 1.51 pH/sq and 2.06 pH/sq, is larger than that expected for conventional superconductors with short mean free path, corresponding to about 25% lower superfluid density. We also measured kinetic inductance of the right-angle bends of NbN striplines and found it to be negligible at${\bm{w}} < {\bm{\lambda }}_{{\bm{NbN}}}^2/{\bm{t}}$, indicating an insignificant effect of current crowding in the presence of superconducting ground plane(s). Implementing NbN and NbN/Nb kinetic inductors enables a significant increase in the integration scale of superconductor digital electronics.

arXiv:2210.10705•IEEE Transactions on Applied Superconductivity•Feb 14, 2023•12 citations

Superconducting NbN-Al hybrid technology for quantum devices

E. Mutsenik, S. Linzen, Evgeni V. Il’ichev +7 more

The high kinetic inductance of niobium nitride (NbN) thin films can be used for an implementation of compact on-chip inductances in cryoelectronic circuits. Here, for the first time, we demonstrate the implementation of a hybrid superconducting technology that includes the fabrication of standard aluminum submicron Josephson junctions and the NbN atomic layer deposition process. As an example, we fabricated and characterized a single and array of Al Josephson junctions together with NbN interconnections. The main Al Josephson junction parameters as well as NbN superconducting properties are in a good agreement with the values obtained by our standard fabrication process. The combination of technological processes for the NbN layers with Al Josephson junction allows implementing a new generation of innovative superconducting devices for different applications.

Low Temperature Physics•Jan 1, 2023•4 citations
Experimental studies to enlarge kinetic inductance of NbN thin films using the effects of quality and thickness of the film are made by measuring Fiske current steps in the current-voltage (I-V) characteristics of NbN/Pb-In Josephson junctions. Experiments demonstrate that the specific kinetic inductance L K can be enlarged over a wide range by changing stoichiometry of the film, as well as by making the film thickness thin, and that this enlargement becomes larger by both effects when the film thickness is in an ultra thin regime. This inductance is shown to be well fitted to L K=µ0λ2/d, w h e r e µ_0 i s t h e v a c u u m p e r m e a b i l i t y, d i s t h e t h i c k n e s s, a n d λ i s t h e m a g n e t i c p e n e t r a t i o n d e p t h i n t h e d i r t y l i m i t. I n t h e p r e s e n t e x p e r i m e n t w e a t t a i n e d t h e i n d u c t a n c e a s h i g h a s L_K=130 p H b y t h e c o m b i n e d e f f e c t s o f i m p u r i t y a n d t h i c k n e s s f o r a f i l m w i t h
Abstract In this paper, we report on a systematic study of the inductance and magnetic field penetration depth (λ) of polycrystalline NbN superconducting thin films. By employing a four-metal-layer fabrication process specifically designed for all-NbN single-flux-quantum circuits, we constructed a superconducting quantum interference device loop composed of two parallel NbN SNS junctions, NbN microstrips, and NbN ground planes for precise inductance measurement. At 4.2 K, as the linewidth increases from 1 μm to 30 μm, the inductance per unit length (L u) of NbN microstrips significantly decreases, for example, the L u of 250 nm thick NbN microstrips drops from 0.907 pH/μm to 0.047 pH/μm. Compared to Nb, the L u of polycrystalline NbN microstrips is approximately two to three times that of Nb, offering an advantage for manufacturing smaller superconducting inductors. Furthermore, we conducted simulation analysis using InductEx software to extract the λ of NbN films of varying thicknesses. The results indicate that as the film thickness increased from 45 nm to 600 nm, λ initially decreased sharply and then stabilized, with values ranging from 430 nm to 323 nm. Notably, once the film thickness exceeded 200 nm, λ remained essentially constant, even at a temperature of 10 K, where it showed good stability, albeit with a slight increase (about 50 nm) compared to 4.2 K. This dependence of λ on thickness is reasonably explained by considering the effects of NbN film thickness on the superconducting critical temperature and residual resistivity. These research findings not only deepen our understanding of the characteristics of superconducting films but also lay a solid foundation for the future design and manufacture of more compact superconducting circuits at the higher temperature of 10 K.
We have measured the rf impedance of 10-nm thick superconducting granular NbN meander lines between 5 /spl mu/m and 20 /spl mu/m wide. The complex reflection coefficient was obtained directly using a vector network analyzer. The impedance (at 10 MHz for a 5 /spl mu/m wide line) is dominated by the large kinetic Inductance of the film, with a sheet inductance of order 1 nH, giving a total inductance of 400 nH for a 5 /spl mu/m/spl times/2 mm line. The kinetic inductance diverges as T/spl rarr/T/sub c/=6.5 K, as expected from Ginzburg-Landau theory (GL). Of particular interest is a substantial decrease of measured inductance with increasing dc current, contrary to the dependence expected from GL. This anomalous current dependence is not well understood, but may be related to vortex dynamics and Josephson effects in these granular films, as supported by preliminary Josephson array simulations. These results have important implications for potential devices such as tunable rf phase shifters and kinetic inductance photodetectors.
We characterize inductors fabricated from ultra-thin, approximately 100 nm wide strips of niobium (Nb) and niobium nitride (NbN). These nanowires have a large kinetic inductance in the superconducting state. The kinetic inductance scales linearly with the nanowire length, with a typical value of 1 nH µm(-1) for NbN and 44 pH µm(-1) for Nb at a temperature of 2.5 K. We measure the temperature and current dependence of the kinetic inductance and compare our results to theoretical predictions. We also simulate the self-resonant frequencies of these nanowires in a compact meander geometry. These nanowire inductive elements have applications in a variety of microwave frequency superconducting circuits.
Niobium nitride (NbN\mathrm{Nb}\mathrm{N}NbN) is a particularly promising material for quantum technology applications, as it shows the degree of reproducibility necessary for large-scale superconducting circuits. We demonstrate that resonators based on NbN\mathrm{Nb}\mathrm{N}NbN thin films present a one-photon internal quality factor above 105{10}^{5}105 maintaining a high impedance (larger than $2\mathrm{k}\mathrm{\ensuremath{\Omega}}$), with a footprint of approximately $50\ifmmode\times\else\texttimes\fi{}100\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{m}}^{2}$ and a Kerr nonlinearity of few tenths of a hertz. These quality factors, mostly limited by losses induced by the coupling to two-level systems, have been maintained for kinetic inductances ranging from tenths to hundreds of picoHenry per square. We also demonstrate minimal variations in the performance of the resonators during multiple cooldowns over more than nine months. Our work proves the versatility of niobium nitride high-kinetic-inductance resonators, opening perspectives towards the fabrication of compact, high-impedance, and high-quality multimode circuits, with sizable interactions.
We present measurements of the self- and mutual inductance of NbN and NbN/Nb bilayer inductors (microstrips, striplines, serpentines, etc.) with Nb ground plane(s) fabricated in an advanced process for superconductor electronics developed at MIT Lincoln Laboratory. In this process, the signal traces of logic cell inductors are made either of a 200-nm NbN layer with${{\bm{T}}}_{\bm{c}} \approx 15.5Koranin−situdepositedNbN/Nbbilayer,replacinga200−nmNblayerM6inthestandardSFQ5eeprocesswithninesuperconductinglayerson200−mmwafers.Nbgroundplanesarepreservedtomaintainahighlevelofinterlayershieldingandlowintralayermutualcoupling.Atwo−steppatterningofthetopNbandthebottomNbNlayersoftheNbN/Nbbilayerallowsthecreationofinductorswithaverywiderangeofinductances,fromlowvalues∼0.4pH/μmtypicalforNbgeometricalinductorsto∼35pH/μmtypicalforthin−filmkineticinductors.ThemutualinductanceofvariouscombinationsofNbN,Nb,andNbN/Nbinductorsdoesnotdependonsuperconductingpropertiesofthesignaltracesinthestudiedrangeoflinewidths,15.5 K or an in-situ deposited NbN/Nb bilayer, replacing a 200-nm Nb layer M6 in the standard SFQ5ee process with nine superconducting layers on 200-mm wafers. Nb ground planes are preserved to maintain a high level of interlayer shielding and low intralayer mutual coupling. A two-step patterning of the top Nb and the bottom NbN layers of the NbN/Nb bilayer allows the creation of inductors with a very wide range of inductances, from low values ∼0.4 pH/μm typical for Nb geometrical inductors to ∼35 pH/μm typical for thin-film kinetic inductors. The mutual inductance of various combinations of NbN, Nb, and NbN/Nb inductors does not depend on superconducting properties of the signal traces in the studied range of linewidths,15.5Koranin−situdepositedNbN/Nbbilayer,replacinga200−nmNblayerM6inthestandardSFQ5eeprocesswithninesuperconductinglayerson200−mmwafers.Nbgroundplanesarepreservedtomaintainahighlevelofinterlayershieldingandlowintralayermutualcoupling.Atwo−steppatterningofthetopNbandthebottomNbNlayersoftheNbN/Nbbilayerallowsthecreationofinductorswithaverywiderangeofinductances,fromlowvalues∼0.4pH/μmtypicalforNbgeometricalinductorsto∼35pH/μmtypicalforthin−filmkineticinductors.ThemutualinductanceofvariouscombinationsofNbN,Nb,andNbN/Nbinductorsdoesnotdependonsuperconductingpropertiesofthesignaltracesinthestudiedrangeoflinewidths,{\bm{w}};itequalsthemutualinductanceoftheNbinductorswiththeequivalentgeometryandplacementbetweenthegroundplanes.ThemeasuredmagneticfieldpenetrationdepthinNbNfilmsdepositedbyreactivesputteringat200°CisλNbN=491±5nm.Themeasuredkineticinductanceofthefilmswiththicknesses; it equals the mutual inductance of the Nb inductors with the equivalent geometry and placement between the ground planes. The measured magnetic field penetration depth in NbN films deposited by reactive sputtering at 200 °C isλNbN= 491 ± 5 nm. The measured kinetic inductance of the films with thicknesses;itequalsthemutualinductanceoftheNbinductorswiththeequivalentgeometryandplacementbetweenthegroundplanes.ThemeasuredmagneticfieldpenetrationdepthinNbNfilmsdepositedbyreactivesputteringat200°CisλNbN=491±5nm.Themeasuredkineticinductanceofthefilmswiththicknesses{\bm{t}}\ = {\bm{\ }}200nmand150nm,respectively1.51pH/sqand2.06pH/sq,islargerthanthatexpectedforconventionalsuperconductorswithshortmeanfreepath,correspondingtoabout25200 nm and 150 nm, respectively 1.51 pH/sq and 2.06 pH/sq, is larger than that expected for conventional superconductors with short mean free path, corresponding to about 25% lower superfluid density. We also measured kinetic inductance of the right-angle bends of NbN striplines and found it to be negligible at200nmand150nm,respectively1.51pH/sqand2.06pH/sq,islargerthanthatexpectedforconventionalsuperconductorswithshortmeanfreepath,correspondingtoabout25{\bm{w}} < {\bm{\lambda }}_{{\bm{NbN}}}^2/{\bm{t}}$, indicating an insignificant effect of current crowding in the presence of superconducting ground plane(s). Implementing NbN and NbN/Nb kinetic inductors enables a significant increase in the integration scale of superconductor digital electronics.
The high kinetic inductance of niobium nitride (NbN) thin films can be used for an implementation of compact on-chip inductances in cryoelectronic circuits. Here, for the first time, we demonstrate the implementation of a hybrid superconducting technology that includes the fabrication of standard aluminum submicron Josephson junctions and the NbN atomic layer deposition process. As an example, we fabricated and characterized a single and array of Al Josephson junctions together with NbN interconnections. The main Al Josephson junction parameters as well as NbN superconducting properties are in a good agreement with the values obtained by our standard fabrication process. The combination of technological processes for the NbN layers with Al Josephson junction allows implementing a new generation of innovative superconducting devices for different applications.