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 Applied Physics

Effect of large dielectric constant of SrTiO3 substrate on the characteristics of high T c dc superconducting quantum interference device

Keiji Enpuku, T. Maruo, Tadashi Minotani

Published Jul 15, 1996• 23 citations
Publisher

Abstract

Effects of large dielectric constant of SrTiO3 substrate on the characteristics of high Tc dc superconducting quantum interference device (SQUID) are studied theoretically. It is shown that parasitic capacitance, which is caused by the substrate and distributes along an inductance of the SQUID, cannot be neglected when we use SrTiO3 substrate. Due to the distributed parasitic capacitance, the inductance can no longer be described as lumped element, but behaves like a transmission line when the length of the inductance becomes long. Taking into account the resonant characteristics of the transmission line, we have modified the conventional equivalent circuit of the SQUID, and presented a circuit model for this case. Using numerical simulation, we have clarified quantitatively how the SQUID characteristics are affected by the resonance due to the parasitic capacitance. The obtained results indicate the importance of taking into account the resonance when we use the SrTiO3 substrate, especially for the case of large junction resistance. Numerical simulation of the model cases shows the possibility that the transfer function can be much increased without degrading the flux noise when the SQUID is properly designed. The present theoretical results explain well the experimental results reported recently.

DOI
10.1063/1.362858

Related papers

Inductance dependence of noise properties of a high-T c dc superconducting quantum interference device

Keiji Enpuku, G. Tokita, T. Maruo

Properties of white noise of a high-Tc dc superconducting quantum interference device (SQUID) have been studied using numerical simulation. It is shown that thermal noise at T=77 K significantly affects the noise properties of the SQUID. As a result, dependencies of noise properties on inductance become quite different from conventional results at T=4.2 K. In contrast to the case T=4.2 K, the voltage noise of the SQUID at T=77 K depends very weakly on the inductance, while the transfer function degrades rapidly with inductance. Consequently, rapid degradation of flux noise with inductance, as compared with the case T=4.2 K, is caused mainly by that of the transfer function. These simulation results explain reasonably experimental results reported recently. Therefore, it is necessary to improve the transfer function for the improvement of noise properties in the case of large inductances. Numerical simulation shows that a method for improving the transfer function using resistively shunted inductance or three Josephson junctions, which was proposed by the authors, is also useful for improving noise properties in the case of large inductances.

Journal of Applied Physics•Dec 15, 1994•23 citations

Effect of thermal noise on the characteristics of a high T c superconducting quantum interference device

Keiji Enpuku, Yuri Shimomura, Takanobu Kisu

Effects of thermal noise on the characteristics of the dc superconducting quantum interference device (SQUID) have been studied. Numerical simulation on the SQUID characteristics operating at T=77 K has been performed by taking into account the thermal noise. It is shown that the voltage versus flux relation of the dc SQUID is degraded considerably with the thermal noise. The degradation becomes significant when the inductance of the SQUID increases. Due to this degradation, there exists significant limitation for the range of the inductance available at T=77 K, unlike the case at T=4.2 K. The maximum inductance should be around 200 pH in order to avoid significant degradation of the transfer function. This limited value of the inductance must be taken into account when we realize the SQUID coupled to an input coil. The analytical expression for the degradation of the transfer function due to the thermal noise is also obtained. The theoretical result explains experimental results reported recently.

Journal of Applied Physics•Jun 1, 1993•125 citations

Effect of parasitic capacitance and inductance on the dynamics and noise of dc superconducting quantum interference devices

Tapani Ryhänen, Heikki Seppä, R. Cantor

Practical thin-film dc superconducting quantum interference devices (SQUIDs) are often built with an integrated input coil which leads to the formation of various parasitic elements. We have designed and fabricated several square washer-shaped dc SQUID test devices with various amounts of parasitic capacitance formed by covering the washer slits with superconducting coverplates of various widths. In the simplest approximation, the parasitic capacitance Cp appears entirely across the Josephson junctions; in a better approximation, Cp divides the total inductance into two parts, an effective SQUID loop inductance L and a small parasitic inductance Lp. For both models, noise-free and noise-rounded current-voltage and voltage-flux characteristics are calculated for various values of the ratios L/Lp and Cp/C, where C is the Josephson junction capacitance. The SQUID dynamics are significantly affected by Cp and Lp. The energy resolution ε at first deteriorates with increasing Cp for Cp/C ≲ 2, but as Cp/C becomes large, ε improves to less than twice the value for Cp/C ≊ 0. The optimal points of operation for large Cp, however, are found at voltages above the low-frequency resonance determined by L and Cp where the flux-to-voltage transfer function is low. Furthermore, for devices with Cp/C ≫ 1 and Lp≠0, the double-loop geometry leads to an additional resonance determined by Lp and C that appears at high frequencies. The energy resolution inside this high-frequency resonance is nearly independent of Cp and comparable to the energy resolution of a device having the same total inductance but with Cp/C ≪ 1. Extensive noise mappings on several different test devices have been carried out using a computer-controlled measurement system. The measured characteristics and noise performance are shown to be in good agreement with the simulations.

Journal of Applied Physics•Jun 15, 1992•32 citations

Effect of capacitive feedback on the characteristics of direct current superconducting quantum interference device coupled to a multiturn input coil

Tadashi Minotani, Keiji Enpuku, Y. Kuroki

Distortion of voltage versus flux (V–Φ) relation of a dc superconducting quantum interference device (SQUID) coupled to a multiturn input coil is studied. First, resonant behavior of the coupled SQUID due to the so-called input coil resonance is clarified. It is shown that large rf noise flux is produced by the input coil resonance. This rf flux is added to the SQUID, and results in large rf voltage across the SQUID. In the case where parasitic capacitance exists between the input coil and the ground of the SQUID, this rf voltage produces the rf flux again, i.e., a feedback loop for the rf flux is formed. Taking into account this capacitive feedback, we study the V–Φ relation of the coupled SQUID. Numerical simulation shows that the V–Φ relation is distorted considerably by the feedback mechanism. The simulation result explains well the experimental V–Φ relation of the coupled SQUID. The combination of the input coil resonance with the capacitive feedback is the most likely mechanism for the distorted V–Φ curve of the coupled SQUID. The condition for occurrence of the distorted V–Φ curve due to the capacitive feedback is also obtained, and methods to prevent degradation are discussed.

Journal of Applied Physics•Jul 1, 1997•15 citations

On transmission line resonances in highTCdc SQUIDs

U Sinha, A Sinha, E J Tarte

In this paper, we study transmission line resonances in high T C dc SQUIDs (superconducting quantum interference devices). These resonances are exhibited in the characteristics of SQUIDs which are fabricated on substrates with high dielectric constant, such as strontium titanate. The power balance equation is analytically derived both for symmetric and for asymmetric SQUIDs. Using this, we investigate SQUID current–voltage I ( V ), voltage–flux V (Φ) and voltage modulation Δ V characteristics.

arXiv:0806.3187•Superconductor Science and Technology•Jun 18, 2008•3 citations

Low noise operation of a DC SQUID in a large beta regime and its application to the design of a high T/sub c/ SQUID

Keiji Enpuku, Satoshi Kohjiro, Keiji Yoshida

The noise characteristics of a large- beta DC SQUID (superconducting quantum interference device) have been studied experimentally in the case where the SQUID inductance is resistively shunted. Energy resolutions of the SQUIDs, epsilon , have been measured for various beta values up to beta =19. It is shown experimentally that the energy resolution of these large- beta SQUIDs is as small as that of the conventional SQUID with beta =1. For example, an energy resolution of 25h was obtained for beta =12 (L= 340 pH and I/sub 0/=37 mu A), where h is Planck's constant. The experimental results agree quantitatively with theoretical ones. It is also shown that the present resistivity shunted inductance scheme is very useful in developing SQUIDs operating at T=77 K with high-T/sub c/ superconductors, where the value of beta will necessarily be large in order to avoid noise effects. Numerical simulations of the performance of the high-T/sub c/ SQUID are presented.>

IEEE Transactions on Magnetics•Mar 1, 1989•3 citations
Effects of large dielectric constant of SrTiO3 substrate on the characteristics of high Tc dc superconducting quantum interference device (SQUID) are studied theoretically. It is shown that parasitic capacitance, which is caused by the substrate and distributes along an inductance of the SQUID, cannot be neglected when we use SrTiO3 substrate. Due to the distributed parasitic capacitance, the inductance can no longer be described as lumped element, but behaves like a transmission line when the length of the inductance becomes long. Taking into account the resonant characteristics of the transmission line, we have modified the conventional equivalent circuit of the SQUID, and presented a circuit model for this case. Using numerical simulation, we have clarified quantitatively how the SQUID characteristics are affected by the resonance due to the parasitic capacitance. The obtained results indicate the importance of taking into account the resonance when we use the SrTiO3 substrate, especially for the case of large junction resistance. Numerical simulation of the model cases shows the possibility that the transfer function can be much increased without degrading the flux noise when the SQUID is properly designed. The present theoretical results explain well the experimental results reported recently.
Properties of white noise of a high-Tc dc superconducting quantum interference device (SQUID) have been studied using numerical simulation. It is shown that thermal noise at T=77 K significantly affects the noise properties of the SQUID. As a result, dependencies of noise properties on inductance become quite different from conventional results at T=4.2 K. In contrast to the case T=4.2 K, the voltage noise of the SQUID at T=77 K depends very weakly on the inductance, while the transfer function degrades rapidly with inductance. Consequently, rapid degradation of flux noise with inductance, as compared with the case T=4.2 K, is caused mainly by that of the transfer function. These simulation results explain reasonably experimental results reported recently. Therefore, it is necessary to improve the transfer function for the improvement of noise properties in the case of large inductances. Numerical simulation shows that a method for improving the transfer function using resistively shunted inductance or three Josephson junctions, which was proposed by the authors, is also useful for improving noise properties in the case of large inductances.
Effects of thermal noise on the characteristics of the dc superconducting quantum interference device (SQUID) have been studied. Numerical simulation on the SQUID characteristics operating at T=77 K has been performed by taking into account the thermal noise. It is shown that the voltage versus flux relation of the dc SQUID is degraded considerably with the thermal noise. The degradation becomes significant when the inductance of the SQUID increases. Due to this degradation, there exists significant limitation for the range of the inductance available at T=77 K, unlike the case at T=4.2 K. The maximum inductance should be around 200 pH in order to avoid significant degradation of the transfer function. This limited value of the inductance must be taken into account when we realize the SQUID coupled to an input coil. The analytical expression for the degradation of the transfer function due to the thermal noise is also obtained. The theoretical result explains experimental results reported recently.
Practical thin-film dc superconducting quantum interference devices (SQUIDs) are often built with an integrated input coil which leads to the formation of various parasitic elements. We have designed and fabricated several square washer-shaped dc SQUID test devices with various amounts of parasitic capacitance formed by covering the washer slits with superconducting coverplates of various widths. In the simplest approximation, the parasitic capacitance Cp appears entirely across the Josephson junctions; in a better approximation, Cp divides the total inductance into two parts, an effective SQUID loop inductance L and a small parasitic inductance Lp. For both models, noise-free and noise-rounded current-voltage and voltage-flux characteristics are calculated for various values of the ratios L/Lp and Cp/C, where C is the Josephson junction capacitance. The SQUID dynamics are significantly affected by Cp and Lp. The energy resolution ε at first deteriorates with increasing Cp for Cp/C ≲ 2, but as Cp/C becomes large, ε improves to less than twice the value for Cp/C ≊ 0. The optimal points of operation for large Cp, however, are found at voltages above the low-frequency resonance determined by L and Cp where the flux-to-voltage transfer function is low. Furthermore, for devices with Cp/C ≫ 1 and Lp≠0, the double-loop geometry leads to an additional resonance determined by Lp and C that appears at high frequencies. The energy resolution inside this high-frequency resonance is nearly independent of Cp and comparable to the energy resolution of a device having the same total inductance but with Cp/C ≪ 1. Extensive noise mappings on several different test devices have been carried out using a computer-controlled measurement system. The measured characteristics and noise performance are shown to be in good agreement with the simulations.
Distortion of voltage versus flux (V–Φ) relation of a dc superconducting quantum interference device (SQUID) coupled to a multiturn input coil is studied. First, resonant behavior of the coupled SQUID due to the so-called input coil resonance is clarified. It is shown that large rf noise flux is produced by the input coil resonance. This rf flux is added to the SQUID, and results in large rf voltage across the SQUID. In the case where parasitic capacitance exists between the input coil and the ground of the SQUID, this rf voltage produces the rf flux again, i.e., a feedback loop for the rf flux is formed. Taking into account this capacitive feedback, we study the V–Φ relation of the coupled SQUID. Numerical simulation shows that the V–Φ relation is distorted considerably by the feedback mechanism. The simulation result explains well the experimental V–Φ relation of the coupled SQUID. The combination of the input coil resonance with the capacitive feedback is the most likely mechanism for the distorted V–Φ curve of the coupled SQUID. The condition for occurrence of the distorted V–Φ curve due to the capacitive feedback is also obtained, and methods to prevent degradation are discussed.
In this paper, we study transmission line resonances in high T C dc SQUIDs (superconducting quantum interference devices). These resonances are exhibited in the characteristics of SQUIDs which are fabricated on substrates with high dielectric constant, such as strontium titanate. The power balance equation is analytically derived both for symmetric and for asymmetric SQUIDs. Using this, we investigate SQUID current–voltage I ( V ), voltage–flux V (Φ) and voltage modulation Δ V characteristics.
The noise characteristics of a large- beta DC SQUID (superconducting quantum interference device) have been studied experimentally in the case where the SQUID inductance is resistively shunted. Energy resolutions of the SQUIDs, epsilon , have been measured for various beta values up to beta =19. It is shown experimentally that the energy resolution of these large- beta SQUIDs is as small as that of the conventional SQUID with beta =1. For example, an energy resolution of 25h was obtained for beta =12 (L= 340 pH and I/sub 0/=37 mu A), where h is Planck's constant. The experimental results agree quantitatively with theoretical ones. It is also shown that the present resistivity shunted inductance scheme is very useful in developing SQUIDs operating at T=77 K with high-T/sub c/ superconductors, where the value of beta will necessarily be large in order to avoid noise effects. Numerical simulations of the performance of the high-T/sub c/ SQUID are presented.>