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

IEEE Transactions on Applied Superconductivity

Fabrication of NbTiN Josephson Junctions With Thermally Oxidized Hf Tunnel Barriers

Hiroyuki Akaike, Kentaro Munemoto, Yoshito Sakakibara, Akira Fujimaki

Published Mar 19, 2019• 2 citations
Publisher

Abstract

We fabricated NbTiN Josephson junctions (JJs) with HfOxbarriers on thermally oxidized Si substrates. Hf overlayers with different resistivities were used for the HfOxbarrier formation. The Hf overlayer with low resistivity produced junctions with high quality parameters. The critical current density (Jc) was obtained in the range of 0.01-0.4 kA/cm2by changing the thermal oxidation conditions of the Hf layer. The critical current uniformity was estimated at a maximum-to-minimum spread of ±10.1% for 85 of the 100 JJs. We evaluated the specific capacitance, which was approximately 110 fF/μm2for the Jcranging from 0.1 to 0.4 kA/cm2. The quasiparticle tunnel characteristics were improved by using the NbN electrodes instead of the NbTiN electrodes.

DOI
10.1109/tasc.2019.2906278

Related papers

Fabrication of NbTiN/Al–AlNX/NbTiN Josephson Junctions for Superconducting Circuits Operating Around 10 K

Hiroyuki Akaike, Shunya Sakamoto, Kentaro Munemoto +1 more

We have fabricated NbTiN/Al-AlNX/NbTiN Josephson tunnel junctions on thermally oxidized Si substrates for their applications to single-flux-quantum circuits operating around 10 K. NbTiN films with a critical temperature Tcof 14.2 K and a root-mean-square value of their surface roughness of 0.45 nm were used as junction electrodes. For a junction barrier, radical-nitrided AlNXwas used to realize high uniformity in the critical current Icof the junctions. We obtained NbTiN junctions with a gap voltage Vg of 4.3 mV and an IcRn. product of 2.6 mV at 4.2 K, where R. is the junction resistance. The critical current density Jc, at 4.2 K was obtained in the range between 0.2 and 6.2 kA/cm2by changing a nitridation time for the AlNXbarrier formation. A series array of 200 junctions with an area of 10 μm × 10 μm exhibited a small I', spread, and the standard deviation 1-σ in Icuniformity was less than 1.6% in the temperature range between 4 K and 10 K.

IEEE Transactions on Applied Superconductivity•May 10, 2016•8 citations

Niobium nitride Josephson tunnel junctions with oxidized amorphous silicon barriers

Fujitoshi Shinoki, Alexandre Shoji, S. Kosaka +2 more

High-quality NbN/NbN Josephson tunnel junctions have been fabricated by rf sputtering. Tunneling barriers are formed by oxidizing amorphous silicon films produced with rf glow discharge deposition. For patterning the base and counter electrode, sputtered ZnO films are employed as a resist mask. The juncitons are found to have large gaps (2ΔNbN) =4.4 mV), to have low leakage current, and to be quite stable for storage and thermal cyclings.

Applied Physics Letters•Feb 15, 1981•44 citations

NbN Josephson Junctions for Single-Flux-Quantum Circuits

Hiroyuki Akaike, Naoto Naito, Yuki NAGAI +1 more

We describe the fabrication processes and electrical characteristics of two types of NbN junctions. One is a self-shunted NbN/NbNx/AlN/NbN Josephson junction, which is expected to improve the density of integrated circuits; the other is an underdamped NbN/AlNx/NbN tunnel junction with radical-nitride AlNx barriers, which has highly controllable junction characteristics. In the former, the junction characteristics were changed from underdamped to overdamped by varying the thickness of the NbNx layer. Overdamped junctions with a 6-nm-thick NbNx film exhibited a characteristic voltage of Vc =0.8mV and a critical current density of Jc =22A/cm2 at 4.2K. In the junctions with radical-nitride AlNx barriers, Jc could be controlled in the range 0.01-3kA/cm2 by varying the process conditions, and good uniformity of the junction characteristics was obtained.

IEICE Transactions on Electronics•Jan 1, 2011•0 citations

Nb/a-Si/Nb Josephson junctions for high-density superconducting circuits

David I. Olaya, John Biesecker, Manuel A. Castellanos-Beltran +4 more

We present electrical characterization data of sputtered Nb/a-Si/Nb Josephson junctions (JJs) for high-speed and high-density superconducting circuits. Junctions were studied with critical current densities (Jc) ranging from 0.01 to 3 mA/μm2 at 4 K. For junctions deposited at room temperature and processed to a maximum temperature of 150 °C, the dependence of Jc on barrier thickness d is exponential, Jc∝exp (−d/d0), with d0 constant over the entire range of Jc values studied. Junctions were annealed at temperatures up to 300 °C to study changes in their electrical properties and possible compatibility with high temperature fabrication processes. Current–voltage characteristics, critical current uniformity, critical current modulation with in-plane magnetic field, and sub-gap resistance behavior of these junctions were measured at 4 K and demonstrate that the junction properties do not degrade with annealing. These data indicate that Nb/a-Si/Nb JJs are a potential candidate for higher speed and higher density superconducting circuits.

Applied Physics Letters•May 1, 2023•16 citations

Overdamped NbN Josephson Junctions Based on Nb/AlOx/Nb Trilayer Technology

Takao Iwai, Takashi Aoyama, Ryutaro Oke +3 more

We have fabricated overdamped NbN Josephson junctions based on Nb/AlO x /Nb trilayer technology. The junctions have the structure of NbN/Nb/AlO x /Nb/NbN, where Nb/AlO x /Nb acts as a junction barrier. The overdamped junctions showed a critical current density J c and characteristic voltage as high as 0.44 kA/cm2 and 160 µV at 10 K, respectively. The junction characteristics at 4.2 K were investigated from the viewpoint of their dependence on the film thickness of the Nb layers. The junction uniformity was also evaluated. The standard deviation, 1-σ, was 2.1% for a series of 64 5×5 µm2 junctions at 4.2 K.

Japanese Journal of Applied Physics•Aug 1, 1999•5 citations

Self-Shunted NbN Junctions With ${\rm NbN}_{x}/{\rm AlN}$ Bilayered Barriers for 4 K Operation

R. Kanada, Y. Nagai, Hiroyuki Akaike +1 more

We report the fabrication and electrical characteristics of self-shunted Josephson junctions consisting of NbN electrodes, an AlN barrier, and an NbNx normal layer for an SFQ circuit application. To fabricate such junctions with a high characteristic voltage V c, we have studied their preparation conditions including the surface treatments of MgO substrates. Junction characteristics at 4 K were dependent on the electrical properties and film thickness of the NbNx layer; the underdamped junctions changed into overdamped ones with an increase in the film thickness. The overdamped junctions showed a characteristic voltage Vc of 0.8 mV and a critical current density Jc of 22 A/cm2 at 4.2 K.

IEEE Transactions on Applied Superconductivity•May 27, 2009•5 citations
We fabricated NbTiN Josephson junctions (JJs) with HfOxbarriers on thermally oxidized Si substrates. Hf overlayers with different resistivities were used for the HfOxbarrier formation. The Hf overlayer with low resistivity produced junctions with high quality parameters. The critical current density (Jc) was obtained in the range of 0.01-0.4 kA/cm2by changing the thermal oxidation conditions of the Hf layer. The critical current uniformity was estimated at a maximum-to-minimum spread of ±10.1% for 85 of the 100 JJs. We evaluated the specific capacitance, which was approximately 110 fF/μm2for the Jcranging from 0.1 to 0.4 kA/cm2. The quasiparticle tunnel characteristics were improved by using the NbN electrodes instead of the NbTiN electrodes.
We have fabricated NbTiN/Al-AlNX/NbTiN Josephson tunnel junctions on thermally oxidized Si substrates for their applications to single-flux-quantum circuits operating around 10 K. NbTiN films with a critical temperature Tcof 14.2 K and a root-mean-square value of their surface roughness of 0.45 nm were used as junction electrodes. For a junction barrier, radical-nitrided AlNXwas used to realize high uniformity in the critical current Icof the junctions. We obtained NbTiN junctions with a gap voltage Vg of 4.3 mV and an IcRn. product of 2.6 mV at 4.2 K, where R. is the junction resistance. The critical current density Jc, at 4.2 K was obtained in the range between 0.2 and 6.2 kA/cm2by changing a nitridation time for the AlNXbarrier formation. A series array of 200 junctions with an area of 10 μm × 10 μm exhibited a small I', spread, and the standard deviation 1-σ in Icuniformity was less than 1.6% in the temperature range between 4 K and 10 K.
We describe the fabrication processes and electrical characteristics of two types of NbN junctions. One is a self-shunted NbN/NbNx/AlN/NbN Josephson junction, which is expected to improve the density of integrated circuits; the other is an underdamped NbN/AlNx/NbN tunnel junction with radical-nitride AlNx barriers, which has highly controllable junction characteristics. In the former, the junction characteristics were changed from underdamped to overdamped by varying the thickness of the NbNx layer. Overdamped junctions with a 6-nm-thick NbNx film exhibited a characteristic voltage of Vc =0.8mV and a critical current density of Jc =22A/cm2 at 4.2K. In the junctions with radical-nitride AlNx barriers, Jc could be controlled in the range 0.01-3kA/cm2 by varying the process conditions, and good uniformity of the junction characteristics was obtained.
We present electrical characterization data of sputtered Nb/a-Si/Nb Josephson junctions (JJs) for high-speed and high-density superconducting circuits. Junctions were studied with critical current densities (Jc) ranging from 0.01 to 3 mA/μm2 at 4 K. For junctions deposited at room temperature and processed to a maximum temperature of 150 °C, the dependence of Jc on barrier thickness d is exponential, Jc∝exp (−d/d0), with d0 constant over the entire range of Jc values studied. Junctions were annealed at temperatures up to 300 °C to study changes in their electrical properties and possible compatibility with high temperature fabrication processes. Current–voltage characteristics, critical current uniformity, critical current modulation with in-plane magnetic field, and sub-gap resistance behavior of these junctions were measured at 4 K and demonstrate that the junction properties do not degrade with annealing. These data indicate that Nb/a-Si/Nb JJs are a potential candidate for higher speed and higher density superconducting circuits.
We have fabricated overdamped NbN Josephson junctions based on Nb/AlO x /Nb trilayer technology. The junctions have the structure of NbN/Nb/AlO x /Nb/NbN, where Nb/AlO x /Nb acts as a junction barrier. The overdamped junctions showed a critical current density J c and characteristic voltage as high as 0.44 kA/cm2 and 160 µV at 10 K, respectively. The junction characteristics at 4.2 K were investigated from the viewpoint of their dependence on the film thickness of the Nb layers. The junction uniformity was also evaluated. The standard deviation, 1-σ, was 2.1% for a series of 64 5×5 µm2 junctions at 4.2 K.
Self-Shunted NbN Junctions With NbNx/AlN{\rm NbN}_{x}/{\rm AlN}NbNx​/AlN Bilayered Barriers for 4 K Operation
We report the fabrication and electrical characteristics of self-shunted Josephson junctions consisting of NbN electrodes, an AlN barrier, and an NbNx normal layer for an SFQ circuit application. To fabricate such junctions with a high characteristic voltage V c, we have studied their preparation conditions including the surface treatments of MgO substrates. Junction characteristics at 4 K were dependent on the electrical properties and film thickness of the NbNx layer; the underdamped junctions changed into overdamped ones with an increase in the film thickness. The overdamped junctions showed a characteristic voltage Vc of 0.8 mV and a critical current density Jc of 22 A/cm2 at 4.2 K.