DC SQUID series array amplifiers with 120 MHz bandwidth

We report on the performance of dc SQUID (Superconducting Quantum Interference Device) series array amplifiers from dc to 500 MHz. The arrays consist of up to 100 dc SQUIDs, with varying degrees of intracoil damping; the flux focusing washer of each SQUID is electrically isolated from the SQUID loop (L/sub sq/=18 pH). Using an rf network analyzer, we have observed high-frequency resonances in the response at bias points corresponding to distortions in the dc transfer functions. Increasing distance between SQUIDs in the array reduces the distortions. Distortions are also more pronounced, and bandwidth reduced, in devices incorporating the flux-focusing washer into the SQUID body. With intracoil damping of 0.25 /spl Omega/ per turn on the input coil, the voltage-flux transfer characteristics of the isolated-washer design and 300 /spl mu/m center-to-center SQUID spacing are free of significant distortions, and the bandwidth is not degraded compared to undamped devices. The 100-SQUID array has 150 nH input inductance, 500 V/A transimpedance, 2.5 pA/ Hz equivalent input current noise at 4 K, and 120 MHz bandwidth.

[1]  M. Huber,et al.  Resonance damping in tightly coupled d.c. SQUIDs via intra-coil resistors , 2001 .

[2]  H. Koch,et al.  Modeling the direct current superconducting quantum interference device coupled to the multiturn input coil. II , 1992 .

[3]  Matti Kajola,et al.  Design, optimization, and construction of a dc SQUID with complete flux transformer circuits , 1988 .

[4]  K. Enpuku,et al.  Noise characteristics of a dc SQUID with a resistively shunted inductance. II. Optimum damping , 1986 .

[5]  H. Seppa,et al.  Influence of the signal coil on DC-SQUID dynamics , 1987 .

[6]  John Clarke,et al.  Measurements of the dynamic input impedance of a dc SQUID , 1985 .

[7]  J. Knuutila,et al.  Effects on DC SQUID characteristics of damping of input coil resonances , 1987 .

[8]  Mark B. Ketchen,et al.  Planar coupling scheme for ultra low noise DC SQUIDs , 1981 .

[9]  M. Huber,et al.  Tightly coupled dc SQUIDs with resonance damping , 1997, IEEE Transactions on Applied Superconductivity.

[10]  J. Luine,et al.  Application of a DC SQUID array amplifier to an electrically small active antenna , 1999, IEEE transactions on applied superconductivity.

[11]  G. Hilton,et al.  DC SQUID series arrays with intracoil damping to reduce resonance distortions 1 1 Contribution of th , 1997 .

[12]  C. Burroughs,et al.  Superconducting integrated circuit fabrication with low temperature ECR-based PECVD SiO/sub 2/ dielectric films , 1995, IEEE Transactions on Applied Superconductivity.

[13]  Sae Woo Nam,et al.  Cryogenic detectors based on superconducting transition-edge sensors for time-energy-resolved single-photon counters and for dark matter searches , 2000 .

[14]  W. Johnson,et al.  Well coupled, low noise, dc SQUIDs , 1985 .

[15]  Adrian T. Lee,et al.  A superconducting bolometer with strong electrothermal feedback , 1996 .

[16]  G. Hilton,et al.  X‐ray detection using a superconducting transition‐edge sensor microcalorimeter with electrothermal feedback , 1996 .

[17]  J. Martinis,et al.  A series array of DC SQUIDs , 1991 .

[18]  Risto J. Ilmoniemi,et al.  SQUID magnetometers for low-frequency applications , 1989 .

[19]  R. Reed,et al.  Broadband nuclear magnetic resonance using DC SQUID amplifiers , 1999 .