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IEEE Transactions on Magnetics

Current amplifier and flux-buffer designs using an exponential flux shuttle with a Josephson junction synthetic inductor

Meir Gershenson

Published Mar 1, 1989• 1 citation
Publisher

Abstract

A current amplifier design based on the principle of fluxon propagation in a multijunction exponential flux shuttle has been investigated. In this design, the critical current of the junctions is increased exponentially and the SQUID (superconducting quantum interference device) inductance is a Josephson-junction equivalent inductance. Current gain can be achieved by generating fluxons at the low end and dissipating them at the high end where the load is located. Advantages over other types of linear devices are discussed. Two parallel exponential flux shuttles can be used to duplicate flux from a high-inductance input coil to a low-inductance output. The device performance of the two circuits is evaluated by computer simulation, and noise performance is discussed.>

DOI
10.1109/20.92495

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A current amplifier design based on the principle of fluxon propagation in a multijunction exponential flux shuttle has been investigated. In this design, the critical current of the junctions is increased exponentially and the SQUID (superconducting quantum interference device) inductance is a Josephson-junction equivalent inductance. Current gain can be achieved by generating fluxons at the low end and dissipating them at the high end where the load is located. Advantages over other types of linear devices are discussed. Two parallel exponential flux shuttles can be used to duplicate flux from a high-inductance input coil to a low-inductance output. The device performance of the two circuits is evaluated by computer simulation, and noise performance is discussed.>
Arrays of dc-superconducting quantum interference devices (dc-SQUIDs) were investigated, in which each dc-SQUID element has a multiturn input coil. The dependence of flux noise on the number of turns of the input coil was studied for current amplifiers. SQUID arrays were fabricated by a Nb/AlO x /Nb Josephson tunnel junction fabrication process. Results show that the flux noise of the SQUID array amplifier does not depend on the turn number of the input coil. A SQUID array amplifier consisting of 128 dc-SQUID elements was fabricated, in which each element had a 7-turn input coil and a mutual inductance between the input coil and the SQUID loop of 460 pH. This amplifier showed an ultrahigh current resolution of 1 pA/Hz0.5 and a maximum input current of 11 µA for signals of 50 kHz, which is sufficient bandwidth for X-ray detection applications. These values correspond to a large dynamic range of 87 dB. The flux-voltage characteristics of this SQUID array, however, showed asymmetric behavior, which originated from electronic resonance in stray capacitance and the mutual inductance between the SQUID loop and the multiturn input coil.
A linear amplifier using a flux-flow phenomenon in a long Josephson junction has been designed and tested by connecting a load resistance. The present experiment has demonstrated that a current gain of 500/W s (1/µm) is obtained for the load resistance of 9 mΩ when an input signal is applied with a control line of width W s (µm). An equivalent circuit of the amplifier has also been presented, which shows that the device is most suitable for current amplification with large gain in low impedance circuits.
Superconducting quantum interference device (SQUID) amplifier is best known for its low input impedance, low noise and low power consumption. Nowadays it is widely used for detecting the weak signals. Compared with other methods, the Nb/Al-AlOx/Nb structure Josephson junction based SQUID has the advantages of high transition temperature, high voltage flux modulation index and good heat recycle ability, wide critical voltage range, so it is a very good option for making SQUID amplifier. In this work, we fabricate the overdamped Josephson junction and washer dc SQUID, and test the I-V characteristics at He3 3 K stage temperature and calculate the current resolution of SQUID. The result of SQUID modulation property is good. The magnification becomes larger after increasing the input line number of loops, and the system noise becomes smaller after the join of the LC filter. This work is very important for designing and manufacturing transition edge sensor readout circuits.
Flux transfer device theory is reviewed. In such devices, generalized magnetic flux, defined as the time integral of voltage, is used to describe the device characteristics. The Josephson junction and inductor are the main circuit elements in flux transfer devices, because they maintain a constant value for the time integral of voltage. Flux transfer devices are based on either an RF SQUID (superconducting quantum interference device) or a fluxon device. Four devices, including the parametric quantron and the quantum flux parametron, are reviewed as applications of the RF SQUID. The fluxon feedback oscillator and a soliton device are also reviewed as applications of fluxon devices. The quantum flux parametron is then described. The parametron principle and the fundamental properties of the quantum flux parametron such as gain, switching speed, and power dissipation are discussed. Logic circuits and a memory cell are also reviewed. A novel analog-to-digital converter is proposed as an application of the quantum flux parametron.>
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It is necessary to miniaturize inductors for large-scale integration of Josephson devices. Utilizing the equivalent inductance of Josephson junctions is one promising method to realize small inductors. In this paper we calculate the static characteristics of some superconducting quantum interference devices (SQUIDs) utilizing the equivalent inductance, and we compare the results with those of SQUIDs employing the normal inductors. We also discuss the current distribution before and after the transition of the gate junctions. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(6): 1–7, 1998