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

Journal of Micromechanics and Microengineering

Micromachining of SrTiO3steps for high-Tcstep edge junction dc SQUIDs

Jing Wang, Bing Han, Genghua Chen, Fengzhi Xu, Qiansheng Yang, Tianhong Cui

Published Aug 19, 2003• 32 citations
Publisher

Abstract

In this paper, we establish a model of the micromachined SrTiO 3 substrate steps for high- T c direct-current (dc) superconducting quantum interference devices (SQUIDs). The step angle is determined by the local ion milling rate and re-deposition rate, which is caused by back sputtering of ion milling. At dynamic balance, the maximum possible step angle is predicted to be 75° with an ion beam incidence angle of 45°, which agrees well with the measured value of 71°. In order to obtain a better step sidewall profile, we consider the influences of Nb metal mask micromachining. To avoid a rounded angle at the step upper corner, the minimum thickness of the Nb mask should be 440 nm when the desired step height is 300 nm. At optimized process conditions, steps with sharp, steep angles, and flawless profiles have been fabricated. Nine of the twelve dc SQUIDs thus obtained exhibited resistively shunted junction current–voltage behavior and magnetic field modulation at 77 K.

DOI
10.1088/0960-1317/14/1/301

Related papers

Fabrication of step-edge Josephson junctions for low-noise dc-SQUIDs

C. Francke, M. Offner, A Krämer +2 more

We report the development of a fabrication process of high-resistance step-edge Josephson junctions on sharp argon ion beam etched substrate steps. For a reproducible fabrication, the redeposition of material at the step during the etch process has to be avoided. This is achieved by an alternating angle of ion incidence parallel to the edge of the photoresist mask. The reproducible straight step profile exhibits an angle around and is reflected in reproducible electrical properties of the junctions. Critical current and asymptotic normal state resistance both scale with the junction width w . The current-voltage ( I - V ) characteristics depend on the ratio of film thickness t to step height h . For > 0.85 they are flux-flow-like; for < 0.8 they correspond to the resistively shunted junction (RSJ) model. Lower ratios of correspond to higher specific resistances resulting at 77 K typically in asymptotic normal state resistances between 5 and per junction, depending on w . At 77 K we achieve products of more than . The junctions are applied to dc superconducting quantum interference devices (dc-SQUIDs) with inductances between 25 and 35 pH. At 77 K transfer functions of more than are achieved. noise of the step-edge dc-SQUIDs is observed, but using bias current modulation it is entirely suppressed resulting in a spectral density of flux noise of measured at 1 Hz and 77 K for a SQUID with an inductance of 30 pH.

Superconductor Science and Technology•Nov 1, 1998•0 citations

YBa2Cu3O7 step-edge dc SQUID with coplanar control lines

H. Hasegawa, Y. Tarutani, Tokuumi Fukazawa +2 more

A dc superconducting quantum interference device (SQUID) with coplanar control lines has been fabricated from a single layer of YBa2Cu3O7 thin film. Step-edge junctions were formed using resist/Si double-mask layers. Current–voltage characteristics of this SQUID at 77 K show Shapiro steps under microwave irradiation and are qualitatively consistent with the resistively shunted junction (RSJ) model. The spacing between the closed loop and the coplanar control lines in the tested SQUIDs ranged from 0.2 to 1.5 μm. The measured output voltage-control current characteristics showed that the experimentally derived mutual inductances were a function of the spacing, in agreement with the calculated results. The typical mutual inductance for a spacing of 1.0 μm was ∼0.5 pH, which is adequate for detecting signals of flux-transfer logic gates in which the typical logic amplitude is ∼0.1 mA. A coplanar structure is thus useful for logic gate applications.

Applied Physics Letters•Nov 20, 1995•14 citations

Origin of 1/f noise in Y1Ba2Cu3O7−x step-edge dc SQUIDs

Dirk Grundler, Rainer Eckart, Bernd R. David +1 more

We have fabricated Y1Ba2Cu3O7−x step-edge junction dc superconducting quantum interference devices (SQUIDs) and characterized their noise performance. The current-voltage characteristics of our SQUIDs are of resistively shunted junction type with critical current densities jc of about 104 A/cm2 and maximum flux to voltage transfer functions δV/δΦ of 20 μV/Φ0 at 77 K. We compare model predictions for 1/f noise in dc SQUIDs with experimental data and show that the frequency dependent noise in our devices results from critical current fluctuations of the Josephson junctions. A bias current reversing technique is effective in suppressing this noise contribution. A flux noise Φn of 80 μΦ0/Hz1/2 at 1 Hz and 77 K was measured on a dc SQUID with an inductance Ls of 60 pH.

Applied Physics Letters•Apr 26, 1993•24 citations

Fabrication of Nb/Al(AlOx)/Nb DC SQUID by focused ion beam sculpturing

Yuvaraj, D., Gil Bachar, Oren Suchoi +2 more

Highly reproducible Nb/Al(AlOx)/Nb Josephson junction based direct current superconducting quantum interference devices (DC SQUID) were fabricated by three dimensional etching using focused ion beam. Hysteretic and non-hysteretic DC SQUID with critical current ranging from 25 to 1100 microampere were fabricated by varying the Al barrier and oxygen exposure time. The fabricated DC SQUIDs have shown periodic flux dependence with high modulation factor reaching a value of 92% at 4.2 K.

arXiv:1107.0635•Jul 4, 2011•2 citations

YBa 2 Cu 3 O 7 nano superconducting quantum interference devices on MgO bicrystal substrates

Jianxin Lin, Benedikt Müller, Julian Linek +5 more

We report on nanopatterned YBa2Cu3O7-δ (YBCO) direct current superconducting quantum interference devices (SQUIDs) based on grain boundary Josephson junctions. The nanoSQUIDs are fabricated by epitaxial growth of 120 nm-thick films of the high-transition temperature cuprate superconductor YBCO via pulsed laser deposition on MgO bicrystal substrates with 24° misorientation angle, followed by sputtering of dAu = 65 nm thick Au. Nanopatterning is performed by Ga focused ion beam (FIB) milling. The SQUID performance is comparable to devices on SrTiO3 (STO), as demonstrated by electric transport and noise measurements at 4.2 K. MgO has orders of magnitude smaller dielectric permittivity than STO; i.e., one may avoid Au as a resistively shunting layer to reduce the intrinsic thermal flux noise of the nanoSQUIDs. However, we find that the Au layer is important for avoiding degradation during FIB milling. Hence, we compare devices with different dAu produced by thinning the Au layer via Ar ion milling after FIB patterning. We find that the reduction of dAu yields an increase in junction resistance, however at the expense of a reduction of the critical current and increase in SQUID inductance. This results in an estimated thermal flux noise that is almost independent of dAu. However, for two devices on MgO with 65 nm-thick Au, we find an order of magnitude lower low-frequency excess noise as compared to nanoSQUIDs on STO or those on MgO with reduced dAu. For one of those devices we obtain with bias-reversal readout ultra-low flux noise of ∼175 nΦ0 Hz-1/2 down to ∼10 Hz.

Nanoscale•Jan 1, 2020•16 citations

Large RF-controlled voltage steps in DC SQUIDs applicable to voltage standards and sources

G.S. Lee, H.L. Ho, Rich Ruby +1 more

The current height of RF-induced voltage steps in nonhysteretic single Josephson junctions is usually a small fraction of the critical current. It is demonstrated that when a resistively shunted DC superconducting quantum interference device (SQUID) is subjected to an RF magnetic flux, a voltage step with a large current height is obtained. In contrast to weak selection rules for single Josephson junctions, strong selection of the step harmonic number occurs in a shunted DC SQUID for appropriate choice of RF amplitude and DC flux offset, with odd harmonic numbers selected by half-integer flux quantum offsets and even harmonic numbers by integer flux quantum offsets. This pronounced effect has immediate implications for voltage standards and fast, high-precision digital-to-analog converters.>

IEEE Transactions on Applied Superconductivity•Mar 1, 1993•16 citations
In this paper, we establish a model of the micromachined SrTiO 3 substrate steps for high- T c direct-current (dc) superconducting quantum interference devices (SQUIDs). The step angle is determined by the local ion milling rate and re-deposition rate, which is caused by back sputtering of ion milling. At dynamic balance, the maximum possible step angle is predicted to be 75° with an ion beam incidence angle of 45°, which agrees well with the measured value of 71°. In order to obtain a better step sidewall profile, we consider the influences of Nb metal mask micromachining. To avoid a rounded angle at the step upper corner, the minimum thickness of the Nb mask should be 440 nm when the desired step height is 300 nm. At optimized process conditions, steps with sharp, steep angles, and flawless profiles have been fabricated. Nine of the twelve dc SQUIDs thus obtained exhibited resistively shunted junction current–voltage behavior and magnetic field modulation at 77 K.
We report the development of a fabrication process of high-resistance step-edge Josephson junctions on sharp argon ion beam etched substrate steps. For a reproducible fabrication, the redeposition of material at the step during the etch process has to be avoided. This is achieved by an alternating angle of ion incidence parallel to the edge of the photoresist mask. The reproducible straight step profile exhibits an angle around and is reflected in reproducible electrical properties of the junctions. Critical current and asymptotic normal state resistance both scale with the junction width w . The current-voltage ( I - V ) characteristics depend on the ratio of film thickness t to step height h . For > 0.85 they are flux-flow-like; for < 0.8 they correspond to the resistively shunted junction (RSJ) model. Lower ratios of correspond to higher specific resistances resulting at 77 K typically in asymptotic normal state resistances between 5 and per junction, depending on w . At 77 K we achieve products of more than . The junctions are applied to dc superconducting quantum interference devices (dc-SQUIDs) with inductances between 25 and 35 pH. At 77 K transfer functions of more than are achieved. noise of the step-edge dc-SQUIDs is observed, but using bias current modulation it is entirely suppressed resulting in a spectral density of flux noise of measured at 1 Hz and 77 K for a SQUID with an inductance of 30 pH.
A dc superconducting quantum interference device (SQUID) with coplanar control lines has been fabricated from a single layer of YBa2Cu3O7 thin film. Step-edge junctions were formed using resist/Si double-mask layers. Current–voltage characteristics of this SQUID at 77 K show Shapiro steps under microwave irradiation and are qualitatively consistent with the resistively shunted junction (RSJ) model. The spacing between the closed loop and the coplanar control lines in the tested SQUIDs ranged from 0.2 to 1.5 μm. The measured output voltage-control current characteristics showed that the experimentally derived mutual inductances were a function of the spacing, in agreement with the calculated results. The typical mutual inductance for a spacing of 1.0 μm was ∼0.5 pH, which is adequate for detecting signals of flux-transfer logic gates in which the typical logic amplitude is ∼0.1 mA. A coplanar structure is thus useful for logic gate applications.
We have fabricated Y1Ba2Cu3O7−x step-edge junction dc superconducting quantum interference devices (SQUIDs) and characterized their noise performance. The current-voltage characteristics of our SQUIDs are of resistively shunted junction type with critical current densities jc of about 104 A/cm2 and maximum flux to voltage transfer functions δV/δΦ of 20 μV/Φ0 at 77 K. We compare model predictions for 1/f noise in dc SQUIDs with experimental data and show that the frequency dependent noise in our devices results from critical current fluctuations of the Josephson junctions. A bias current reversing technique is effective in suppressing this noise contribution. A flux noise Φn of 80 μΦ0/Hz1/2 at 1 Hz and 77 K was measured on a dc SQUID with an inductance Ls of 60 pH.
We report on nanopatterned YBa2Cu3O7-δ (YBCO) direct current superconducting quantum interference devices (SQUIDs) based on grain boundary Josephson junctions. The nanoSQUIDs are fabricated by epitaxial growth of 120 nm-thick films of the high-transition temperature cuprate superconductor YBCO via pulsed laser deposition on MgO bicrystal substrates with 24° misorientation angle, followed by sputtering of dAu = 65 nm thick Au. Nanopatterning is performed by Ga focused ion beam (FIB) milling. The SQUID performance is comparable to devices on SrTiO3 (STO), as demonstrated by electric transport and noise measurements at 4.2 K. MgO has orders of magnitude smaller dielectric permittivity than STO; i.e., one may avoid Au as a resistively shunting layer to reduce the intrinsic thermal flux noise of the nanoSQUIDs. However, we find that the Au layer is important for avoiding degradation during FIB milling. Hence, we compare devices with different dAu produced by thinning the Au layer via Ar ion milling after FIB patterning. We find that the reduction of dAu yields an increase in junction resistance, however at the expense of a reduction of the critical current and increase in SQUID inductance. This results in an estimated thermal flux noise that is almost independent of dAu. However, for two devices on MgO with 65 nm-thick Au, we find an order of magnitude lower low-frequency excess noise as compared to nanoSQUIDs on STO or those on MgO with reduced dAu. For one of those devices we obtain with bias-reversal readout ultra-low flux noise of ∼175 nΦ0 Hz-1/2 down to ∼10 Hz.
The current height of RF-induced voltage steps in nonhysteretic single Josephson junctions is usually a small fraction of the critical current. It is demonstrated that when a resistively shunted DC superconducting quantum interference device (SQUID) is subjected to an RF magnetic flux, a voltage step with a large current height is obtained. In contrast to weak selection rules for single Josephson junctions, strong selection of the step harmonic number occurs in a shunted DC SQUID for appropriate choice of RF amplitude and DC flux offset, with odd harmonic numbers selected by half-integer flux quantum offsets and even harmonic numbers by integer flux quantum offsets. This pronounced effect has immediate implications for voltage standards and fast, high-precision digital-to-analog converters.>