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

Журнал технической физики

Optimization of fabrication processes for Nb, NbN, NbTiN films and high-quality tunnel junctions for terahertz receiving circuits.

Artem M. Chekushkin, Lyudmila V. Filippenko, A. A. Lomov, Dong Liu, Shi Sheng-Cai, V. P. Koshelets

Published Jan 1, 2022• 2 citations
Publisher

Abstract

This paper describes the optimization of the existing technology for the fabrication of superconducting films and high-quality tunnel junctions on a magnetron sputtering facility. To expand the frequency range to 1.1 THz and to obtain the limiting parameters of superconducting elements, the regimes of production of Nb, NbN, NbTiN films were optimized. These films are used to fabricate superconductor-insulator-superconductor Nb/Al--AlN/NbN tunnel junctions. Al and NbTiN films are required to create receiving elements at frequencies above 700 GHz (the cutoff frequency for niobium); such structures are being developed for the radio astronomy array receiver located in the Atacama Pathfinder Experiment telescope. Keywords: superconductivity, tunnel junctions, magnetron sputtering, thin films.

DOI
10.21883/tp.2022.13.52234.135-21

Related papers

Design of Terahertz SIS Mixers Using Nb/AlN/Nb Junctions Integrated With All-NbTiN Tuning Circuits

Yoshinori Uzawa, M. Kroug, Takafumi Kojima +7 more

We have designed superconductor-insulator-superconductor (SIS) mixers using Nb/AlN/Nb tunnel junctions integrated with NbTiN/SiO2/NbTiN microstrip tuning circuits for the Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 (0.78-0.95 THz). In order to design the tuning circuits, we used terahertz time domain spectroscopy to experimentally derive the complex conductivity of relatively thick NbTiN films deposited on quartz substrate directly as a ground plane and on RF-sputtered SiO2as a microstrip. Results showed that the conductivities of both films can be described by a modified Mattis-Bardeen theory. We also investigated the junction heating effects originating from quasi-particle trapping in the Nb electrodes embedded in NbTiN circuits by varying the volume of the electrodes. It was confirmed that current-voltage curves of Nb/AlN/Nb tunnel junctions with thick (~200 nm) counter electrodes contacting NbTiN wirings showed higher gap voltages as well as reduced back-bending than those with thin (~50 nm) electrodes. Making use of these findings, our designed SIS mixers employing Nb/AlN/Nb junctions with a current density of 15 kA/cm2and all-NbTiN tuning circuits may cover the Band 10 with good sensitivity.

IEEE Transactions on Applied Superconductivity•Nov 28, 2016•12 citations

SuperGaN: Synthesis of NbTiN/GaN/NbTiN Tunnel Junctions

Michael E. Cyberey, Scott Hinton, Christopher W. Moore +2 more

Nb-based circuits have broad applications in quantum-limited photon detectors, low-noise parametric amplifiers, superconducting digital logic circuits, and low-loss circuits for quantum computing. The current state-of-the-art approach for superconductor-insulator-superconductor (SIS) junction material is the Gurvitch trilayer process based on magnetron sputtering of Nb electrodes with Al-Oxide or AlN tunnel barriers grown on an Al overlayer [1]. However, a current limitation of elemental Nb-based circuits is the low-loss operation of THz circuits operating above the 670 GHz gap frequency of Nb and operation at higher temperatures for projects with a strict power budget, such as space-based applications. NbTiN is an alternative higher energy gap material and we have previously reported on the first NbTiN/AlN/NbTiN superconducting-insulating-superconducting (SIS) junctions with an epitaxially grown AlN tunnel barrier [2]. One drawback of a directly grown tunnel barrier compared to thermal oxidation is control of the barrier thickness and the uniformity of thickness across a substrate, leading to variations in current density (Jc). Semiconductor barriers with smaller barrier heights enable thicker tunnel barriers for a given Jc[3]. GaN is an alternative semiconductor material with a closed-packed Wurtzite crystal structure similar to AlN and it can be epitaxially grown as a tunnel barrier using the Reactive Bias Target Ion Beam Deposition (RBTIBD) technique. This work presents the preliminary results of the first reported high-quality NbTiN/GaN/NbTiN heterojunctions with underdamped SIS I(V) characteristics

arXiv:2309.15100•IEEE Transactions on Applied Superconductivity•Nov 30, 2023•4 citations

NbN/AlN/NbN Josephson Junctions on Sapphire for SIS Receiver Applications

Michael Merker, Christian Bohn, Marvin Vollinger +2 more

The most developed integrated receivers for THz radiation nowadays are based on Josephson junction superconductor-insulator-superconductor devices. In this kind of devices, the highest receivable frequency is determined by the energy gap of the superconducting electrodes and limited to approximately 700 GHz in case of Nb/AlOx/Nb multilayers. We have developed a technology for NbN/AlN/NbN Josephson junctions on sapphire substrates which allow operation at frequencies above 1 THz. The trilayers are deposited in situ in a three-chamber dc-magnetron sputtering system at temperatures as high as 775 °C. Each layer is reactively sputtered in an argon and nitrogen atmosphere. By variation of the partial gas pressures and discharge current of the plasma, optimum deposition conditions for the tri-layers were found. So far, gap voltages as high as 5.1 mV at 4.2 K have been achieved which allows the operation frequency of the JJ devices to exceed 1 THz.

arXiv:1612.02713•IEEE Transactions on Applied Superconductivity•Dec 9, 2016•6 citations

Fabrication of High-Quality Josephson Junctions Based on Nb|Al-AlN|NbN

Artem M. Chekushkin, Lyudmila V. Filippenko, Fominskiy M. Yu. +1 more

A description of the fabrication technology of high-quality tunnel SIS junctions is presented, with following characteristics: energy gap in superconductors Vg=3.2-3.4 mV, tunnel current density up to J 35 kA/cm2, quality factor Rj/Rn (ratio of subgap resistance to normal-state resistance) up to 30, junction area up to 1 μm2. The SIS junctions are integrated into the NbTiN|SiO2|Al microstrip line. Keywords: superconducting devices, superconductor--insulator--superconductor tunnel junction, plasma etching.

Physics of the Solid State•Jan 1, 2022•1 citation

Fabrication and testing of NbN/MgO/NbN tunnel junctions for use as high-frequency heterodyne detectors

Jeffrey A. Stern

This thesis describes the development and testing of NbN/MgO/NbN tunnel junctions for use as superconductor-insulator-superconductor (SIS) mixers. SIS mixers are the most sensitive heterodyne detectors in the millimeter wavelength region. Most SIS mixers use Pb alloy tunnel junction. These tunnel junctions have several problems associated with the soft nature of Pb and its low superconducting transition temperature. NbN-based tunnel junctions are being developed to overcome these difficulties. These devices are intended to be used as mixers at millimeter and submillimeter wavelengths. This thesis describes the fabrication process involved in making NbN junctions, and the results of measurements on these devices. The purpose of these measurements is to determine the future possibilities of NbN tunnel junctions as high-frequency mixers. The first chapter is an introduction to SIS mixers and explains how tunnel junction properties affect mixer performance. The basic theory of tunneling and mixing in SIS mixers is first presented. A description of quantum mixer theory is included in this presentation. This theory makes several interesting predictions that cannot be explained using classical theories. This is followed by a description of how real SIS tunnel junctions differ from ideal junctions. The physical origin of these differences is discussed, along with how they affect SIS mixer performance. Finally, the advantages and disadvantages of the various superconducting materials available are discussed. The decision to develop NbN devices is based on these material properties. The second chapter describes the methods used to fabricate small-area NbN/MgO/NbN tunnel junctions. The chapter begins with a description of the various methods that have been used to deposit NbN films. Reactive magnetron sputtering is chosen as the best method for tunnel junction fabrication. Details on the vacuum systems and the methods used for depositing superconducting NbN are discussed. Next, the process used for depositing junction trilayers (NbN/MgO/NbN) is described. The probable growth mode of MgO on NbN is presented. The importance of this growth mode to the junction quality is explained in some detail. Next, standard junction processing steps are reported. The details and limitations of each step are put forth. The standard process allows for the fabrication of 1 [square micron] tunnel junctions. Finally, this chapter discusses several methods of fabaricating submicron junctions that are being pursued. The status of this work is given. The third chapter describes the characterization of NbN films and NbN/Mg0/NbN tunnel junctions. Film properties are described first. The correlation of these properties to deposition conditions is discussed in some detail. Next, values for the various features of the I-V characteristic are given; typical and exceptional values are noted. How these features limit mixer results is described in detail. Several important device attributes were measured using superconducting-quantum-interference-devices (SQUIDs). These attributes are the junction's specific capacitance and the film's magnetic penetration depth. The theory and results of measuring specific capacitance and penetration depth are presented. Following the SQUID results is a large section on RP testing. Mixer tests were made at 205 GHz. The receiver design used, integral inductive tuning circuit used and results are discussed. These results are well understood, with the exception of the temperature dependence of the mixer performance. Finally, measurements of the uniformity of many junctions on a single wafer are presented. The importance of junction uniformity is also described. The final chapter discusses the ultimate limits on NbN mixers, and tells what future work must be done to achieve these limits. The primary high-frequency limit on NbN junctions is the capacitance of NbN/MgO/NbN junctions. The limit imposed by the junction capacitance and circuits used to tune out this capacitance are discussed. Also, the low-frequency limits on NbN junctions are discussed. The status of submicron devices is presented. Junction area is the most immediate limitation on NbN mixer results. The possibility of using other barrier materials to increase the RC speed of NbN junctions is presented. Finally, the possibility of operating NbN junctions at temperatures above 4.2 K is discussed.

•Jan 1, 1991•0 citations

0.5-THz waveguide SIS mixers with NbN/AlN/NbN technology

Jing Li, Masanori Takeda, Zhen Wang +1 more

Heterodyne mixers based on superconducting SIS (superconductor-insulator-superconductor) tunnel junctions have been demonstrated to be the most sensitive coherent detectors at millimeter and submillimeter wavelengths. In fact, conventional superconducting SIS mixers with Nb/AlOx/Nb junction and Nb/SiO2/Nb tuning circuit have shown good performances with the noise temperature reaching as low as three times the quantum limit below 0.7THz, which is the gap frequency of Nb-based SIS junctions. However, due to the large loss in Nb thin-film superconducting microstrip lines, the noise performance of Nb SIS mixers deteriorates significantly above 0.7THz. With a gap frequency double that of Nb-based SIS junctions, NbN-based SIS junctions are of particular interest for the development of heterodyne mixers in the terahertz region. Considering the bandwidth and output power of local-oscillator (LO) signal sources are quite limited around 1THz, we firstly develop a waveguide NbN-based SIS mixer at 0.5THz. Three types of SIS junctions, i.e., long junction, parallel-connected tunnel junction (PCTJ) and distributed junction array (DJ) are investigated. They are all comprised of NbN-AlN-NbN tri-layer fabricated on an MgO substrate and have the same current density (Jc) of 10kA/cm2. In this paper, we describe their design, fabrication and preliminary experimental results.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Nov 29, 2007•3 citations
This paper describes the optimization of the existing technology for the fabrication of superconducting films and high-quality tunnel junctions on a magnetron sputtering facility. To expand the frequency range to 1.1 THz and to obtain the limiting parameters of superconducting elements, the regimes of production of Nb, NbN, NbTiN films were optimized. These films are used to fabricate superconductor-insulator-superconductor Nb/Al--AlN/NbN tunnel junctions. Al and NbTiN films are required to create receiving elements at frequencies above 700 GHz (the cutoff frequency for niobium); such structures are being developed for the radio astronomy array receiver located in the Atacama Pathfinder Experiment telescope. Keywords: superconductivity, tunnel junctions, magnetron sputtering, thin films.
We have designed superconductor-insulator-superconductor (SIS) mixers using Nb/AlN/Nb tunnel junctions integrated with NbTiN/SiO2/NbTiN microstrip tuning circuits for the Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 (0.78-0.95 THz). In order to design the tuning circuits, we used terahertz time domain spectroscopy to experimentally derive the complex conductivity of relatively thick NbTiN films deposited on quartz substrate directly as a ground plane and on RF-sputtered SiO2as a microstrip. Results showed that the conductivities of both films can be described by a modified Mattis-Bardeen theory. We also investigated the junction heating effects originating from quasi-particle trapping in the Nb electrodes embedded in NbTiN circuits by varying the volume of the electrodes. It was confirmed that current-voltage curves of Nb/AlN/Nb tunnel junctions with thick (~200 nm) counter electrodes contacting NbTiN wirings showed higher gap voltages as well as reduced back-bending than those with thin (~50 nm) electrodes. Making use of these findings, our designed SIS mixers employing Nb/AlN/Nb junctions with a current density of 15 kA/cm2and all-NbTiN tuning circuits may cover the Band 10 with good sensitivity.
Nb-based circuits have broad applications in quantum-limited photon detectors, low-noise parametric amplifiers, superconducting digital logic circuits, and low-loss circuits for quantum computing. The current state-of-the-art approach for superconductor-insulator-superconductor (SIS) junction material is the Gurvitch trilayer process based on magnetron sputtering of Nb electrodes with Al-Oxide or AlN tunnel barriers grown on an Al overlayer [1]. However, a current limitation of elemental Nb-based circuits is the low-loss operation of THz circuits operating above the 670 GHz gap frequency of Nb and operation at higher temperatures for projects with a strict power budget, such as space-based applications. NbTiN is an alternative higher energy gap material and we have previously reported on the first NbTiN/AlN/NbTiN superconducting-insulating-superconducting (SIS) junctions with an epitaxially grown AlN tunnel barrier [2]. One drawback of a directly grown tunnel barrier compared to thermal oxidation is control of the barrier thickness and the uniformity of thickness across a substrate, leading to variations in current density (Jc). Semiconductor barriers with smaller barrier heights enable thicker tunnel barriers for a given Jc[3]. GaN is an alternative semiconductor material with a closed-packed Wurtzite crystal structure similar to AlN and it can be epitaxially grown as a tunnel barrier using the Reactive Bias Target Ion Beam Deposition (RBTIBD) technique. This work presents the preliminary results of the first reported high-quality NbTiN/GaN/NbTiN heterojunctions with underdamped SIS I(V) characteristics
The most developed integrated receivers for THz radiation nowadays are based on Josephson junction superconductor-insulator-superconductor devices. In this kind of devices, the highest receivable frequency is determined by the energy gap of the superconducting electrodes and limited to approximately 700 GHz in case of Nb/AlOx/Nb multilayers. We have developed a technology for NbN/AlN/NbN Josephson junctions on sapphire substrates which allow operation at frequencies above 1 THz. The trilayers are deposited in situ in a three-chamber dc-magnetron sputtering system at temperatures as high as 775 °C. Each layer is reactively sputtered in an argon and nitrogen atmosphere. By variation of the partial gas pressures and discharge current of the plasma, optimum deposition conditions for the tri-layers were found. So far, gap voltages as high as 5.1 mV at 4.2 K have been achieved which allows the operation frequency of the JJ devices to exceed 1 THz.
A description of the fabrication technology of high-quality tunnel SIS junctions is presented, with following characteristics: energy gap in superconductors Vg=3.2-3.4 mV, tunnel current density up to J 35 kA/cm2, quality factor Rj/Rn (ratio of subgap resistance to normal-state resistance) up to 30, junction area up to 1 μm2. The SIS junctions are integrated into the NbTiN|SiO2|Al microstrip line. Keywords: superconducting devices, superconductor--insulator--superconductor tunnel junction, plasma etching.
This thesis describes the development and testing of NbN/MgO/NbN tunnel junctions for use as superconductor-insulator-superconductor (SIS) mixers. SIS mixers are the most sensitive heterodyne detectors in the millimeter wavelength region. Most SIS mixers use Pb alloy tunnel junction. These tunnel junctions have several problems associated with the soft nature of Pb and its low superconducting transition temperature. NbN-based tunnel junctions are being developed to overcome these difficulties. These devices are intended to be used as mixers at millimeter and submillimeter wavelengths. This thesis describes the fabrication process involved in making NbN junctions, and the results of measurements on these devices. The purpose of these measurements is to determine the future possibilities of NbN tunnel junctions as high-frequency mixers. The first chapter is an introduction to SIS mixers and explains how tunnel junction properties affect mixer performance. The basic theory of tunneling and mixing in SIS mixers is first presented. A description of quantum mixer theory is included in this presentation. This theory makes several interesting predictions that cannot be explained using classical theories. This is followed by a description of how real SIS tunnel junctions differ from ideal junctions. The physical origin of these differences is discussed, along with how they affect SIS mixer performance. Finally, the advantages and disadvantages of the various superconducting materials available are discussed. The decision to develop NbN devices is based on these material properties. The second chapter describes the methods used to fabricate small-area NbN/MgO/NbN tunnel junctions. The chapter begins with a description of the various methods that have been used to deposit NbN films. Reactive magnetron sputtering is chosen as the best method for tunnel junction fabrication. Details on the vacuum systems and the methods used for depositing superconducting NbN are discussed. Next, the process used for depositing junction trilayers (NbN/MgO/NbN) is described. The probable growth mode of MgO on NbN is presented. The importance of this growth mode to the junction quality is explained in some detail. Next, standard junction processing steps are reported. The details and limitations of each step are put forth. The standard process allows for the fabrication of 1 [square micron] tunnel junctions. Finally, this chapter discusses several methods of fabaricating submicron junctions that are being pursued. The status of this work is given. The third chapter describes the characterization of NbN films and NbN/Mg0/NbN tunnel junctions. Film properties are described first. The correlation of these properties to deposition conditions is discussed in some detail. Next, values for the various features of the I-V characteristic are given; typical and exceptional values are noted. How these features limit mixer results is described in detail. Several important device attributes were measured using superconducting-quantum-interference-devices (SQUIDs). These attributes are the junction's specific capacitance and the film's magnetic penetration depth. The theory and results of measuring specific capacitance and penetration depth are presented. Following the SQUID results is a large section on RP testing. Mixer tests were made at 205 GHz. The receiver design used, integral inductive tuning circuit used and results are discussed. These results are well understood, with the exception of the temperature dependence of the mixer performance. Finally, measurements of the uniformity of many junctions on a single wafer are presented. The importance of junction uniformity is also described. The final chapter discusses the ultimate limits on NbN mixers, and tells what future work must be done to achieve these limits. The primary high-frequency limit on NbN junctions is the capacitance of NbN/MgO/NbN junctions. The limit imposed by the junction capacitance and circuits used to tune out this capacitance are discussed. Also, the low-frequency limits on NbN junctions are discussed. The status of submicron devices is presented. Junction area is the most immediate limitation on NbN mixer results. The possibility of using other barrier materials to increase the RC speed of NbN junctions is presented. Finally, the possibility of operating NbN junctions at temperatures above 4.2 K is discussed.
Heterodyne mixers based on superconducting SIS (superconductor-insulator-superconductor) tunnel junctions have been demonstrated to be the most sensitive coherent detectors at millimeter and submillimeter wavelengths. In fact, conventional superconducting SIS mixers with Nb/AlOx/Nb junction and Nb/SiO2/Nb tuning circuit have shown good performances with the noise temperature reaching as low as three times the quantum limit below 0.7THz, which is the gap frequency of Nb-based SIS junctions. However, due to the large loss in Nb thin-film superconducting microstrip lines, the noise performance of Nb SIS mixers deteriorates significantly above 0.7THz. With a gap frequency double that of Nb-based SIS junctions, NbN-based SIS junctions are of particular interest for the development of heterodyne mixers in the terahertz region. Considering the bandwidth and output power of local-oscillator (LO) signal sources are quite limited around 1THz, we firstly develop a waveguide NbN-based SIS mixer at 0.5THz. Three types of SIS junctions, i.e., long junction, parallel-connected tunnel junction (PCTJ) and distributed junction array (DJ) are investigated. They are all comprised of NbN-AlN-NbN tri-layer fabricated on an MgO substrate and have the same current density (Jc) of 10kA/cm2. In this paper, we describe their design, fabrication and preliminary experimental results.