Array of Superconducting Quantum Interference Devices with Multiturn Input Coil

Abstract

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/Hz 0:5 and a maximum input current of 11 mA 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.

Development of a low temperature SQUID gradiometer for magnetic microcalorimeters

“…small output voltage, the SQUID gradiometer was connected to a series SQUID amplifier 420-SSA made by SII [7] whose flux noise is F n o0:5 mF 0 = ffiffiffiffiffiffi ffi Hz p located at the 1 K stage. Since the R s derived from current-voltage characteristics of the SQUID is 80 mO, to fully utilize the dynamic range of the SQUID amplifier, we chose the load resistance to be R s =4 ¼ 20 mO.…”