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European Microwave Conference (EuMC)

Performance margins and application area of SQUID amplifiers

Michael A. Tarasov, A. Vy, Lyudmila V. Filippenko

Published Oct 1, 1995• 0 citations
Publisher

Abstract

A series of dc SQUID radiofrequency amplifiers in the frequency range 0.1-1.1 GHz with noise temperature 0.4-2 K has been designed, fabricated and experimentally studied. For resonant input tank circuit an analytical model of noise temperature has been developed. A new effect of the output noise increasing or decreasing with changing the sign of voltage-to-flux transfer coeff 1 cient has been observed experimentally and described analytically and numerically. Application of SQUID amplifiers as IF amplifiers in SIS, Josephson, hot-electron heterodyne detectors as well as in cellular base stations has been discussed.

DOI
10.1109/euma.1995.337137

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IEEE Transactions on Applied Superconductivity•Jun 1, 1997•11 citations
A series of dc SQUID radiofrequency amplifiers in the frequency range 0.1-1.1 GHz with noise temperature 0.4-2 K has been designed, fabricated and experimentally studied. For resonant input tank circuit an analytical model of noise temperature has been developed. A new effect of the output noise increasing or decreasing with changing the sign of voltage-to-flux transfer coeff 1 cient has been observed experimentally and described analytically and numerically. Application of SQUID amplifiers as IF amplifiers in SIS, Josephson, hot-electron heterodyne detectors as well as in cellular base stations has been discussed.
The optimal input impedance and noise of a DC SQUID RF amplifier at frequencies of the order of 1 GHz with a resonant input matching circuit have been studied analytically, numerically, and experimentally. A model for noise temperature and power gain has been developed for the practical resonant input tank circuit. A new effect of the output noise increasing or decreasing with changing the sign of voltage-to-flux transfer coefficient has been observed experimentally and explained analytically. The different values of noise temperature for the opposite dV/d/spl Phi/ values have been interpreted using a model with partially correlated current and voltage noise sources. The equivalent layout for optimal input matching of a SQUID amplifier comprising series and parallel resonant circuits has been presented. Using such a matching circuit and SIS junction as a signal source the SQUID amplifier noise temperature about 1 K has been measured at 1.1 GHz.
The goal of this studies is to use dc Squids as low noise radiofrequency amplifier (Tn ≈1K) in the frequency range 1-150 Mhz and to integrate them in NMR probe. DC Squids have been built using planar technology and with two types of superconducting materials : low Tc(Nb) and High Tc(YBa2Cu3O7). Contrary to the traditional set up used in magnetometry (flux locked loop) the dc Squid is here fluxed biased near Φz=(2n+1)Φo/4 and no flux locked loop is connected. Small variations of flux (Φs<<Φo) introduced from signal source via the input coil are amplified following the transfer characteristic VΦ=dV/dΦ. The low Tc devices are set up to now the best, concerning the reproducibility and the qualities of the Josephson Junctions obtained with a three layer process Nb/Al-Al2O3/Nb. Such junctions have been realized following the so called SNOP process, without anodization. The main characteristic obtained at 4.2K are RJ/RN=10, 2Δ≈2.8 meV and a Josephson current density J≈103 A/cm2. The high Tc devices have been built with bi-epitaxial YBa2Cu3O7 junctions and with a 30x30µm2 area loop. I(V) and V(Φ) characteristics curves obtained are promizing for applications as RF detection in the temperature range : 4-77K. Modelization studies are currently in progress for the optimization of those devices (low Tc and high Tc) as RF amplifiers (minimization of parasitic capacitance between the input coil and the Squid loop) in order to increase their upper frequency limit.\n* This work is partially supported by Ultimatech (CNRS), by the "région Rhône-Alpes" and E.E.C. "HTSC-GBJ" programs n°7100.
Integrated radio-frequency amplifiers comprising a 4-loop dc SQUID, seriesly connected input coil turns, a resonant capacitor parallel to the input coil, series capacitors at the input and output ports and bias resistors have been designed, fabricated and experimentally studied. A multiloop dc SQUID with parallel loops and seriesly connected single-turn input coils placed inside each loop and integration with the input resonant matching circuit elements and with elements of dc bias circuit allows one to increase signal frequency and reduce the influence of external noise. The amplifiers with three different capacitors have resonant frequencies 560, 656, 758 MHz and bandwidth about 50 MHz. The noise temperature of such amplifiers below 1.5 K has been measured using cold attenuator and room-temperature noise sources. The layout comprising three pairs of such amplifiers placed on the same 15/spl times/24 mm substrate was designed to increase the bandwidth over the bandwidth of the individual amplifiers.>
A 6 mm/spl times/6 mm chip comprising two identical DC SQUID based amplifiers (SQAs) has been designed, fabricated and tested as a two-stage RF amplifier in a frequency range 3.5-4.0 GHz. Each SQA consists of a double washer type DC SQUID with novel integrated input resonant circuit. The reflection coefficient of both input and output of the SQA has been measured in the two stage configuration. To avoid SQA saturation at the wide band noise tests a tunable 40 MHz bandpass YIG-filter has been used. The following parameters of the two-stage SQA have been measured at the 3.65 GHz: gain of (17.5/spl plusmn/1) dB, 3 dB bandwidth of about 250 MHz, and noise temperature (4.0/spl plusmn/0.5)K what corresponds to intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.6 /spl mu//spl Phi//sub 0/Hz/sup -1/2/ and energy sensitivity /spl epsiv//sub i//spl ap/75 /spl planck/ (7.8/spl middot/10/sup -33/ J/Hz). If the measured RF mismatch between the input/output of SQA and source signal/post-amplifier is taken into account a gain of (20.5/spl plusmn/1.5) dB and noise temperature as low as (2.5/spl plusmn/1.0) K (intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.4 /spl mu//spl Phi//sub 0/Hz/sup -1/2/, energy sensitivity /spl epsiv//sub i//spl ap/47 /spl planck/) can be estimated.
The dc SQUID based RF amplifier (SQA) looks very attractive as an IF amplifier for integration with a SIS mixer and a flux-flow oscillator (FFO) in a fully superconducting submillimeter wave receiver suitable for space applications. Important advantages of the SQA are its low noise, extremely low power consumption, and complete compatibility with the fabrication process currently used for SIS mixers. Single stage amplifiers with a novel signal coupling circuit have been developed and tested in the frequency range 3.6-4.1 GHz. The 1 /spl mu/m/sup 2/ area Nb-AlO/sub x/-Nb junctions shunted by Ti resistors are grouped in a double washer dc SQUID. Two samples with slightly different designs showed the following gain, noise temperature and 3 dB bandwidth: 10.0/spl plusmn/1 dB, 5.0/spl plusmn/1.5 K, 3.86-3.90 GHz, and 6.8/spl plusmn/1 dB, 22/spl plusmn/7 K, 3.89-4.05 GHz, respectively.
We describe a low-noise, two-stage dc Superconducting QUantum Interference Device (SQUID) amplifier that is designed for applications requiring high bandwidth and dynamic range. The output signal of a low-noise SQUID in the input stage coherently modulates a series array of identical SQUIDs in the output stage via a common modulation line. The input stage is designed so its output signal does not produce multiple modulation periods in the output stage. The output stage is designed to have sufficient gain so the output noise is dominated by the amplified noise of the input SQUID and exceeds the noise of a preamplifier in the room temperature readout electronics. The SQUID amplifier may therefore be operated without flux modulation or any impedance matching network, resulting in a large dynamic range and high bandwidth.