Low-noise YBa2Cu3O7−δ direct-current superconducting quantum interference device magnetometer with direct signal injection

Abstract

We have fabricated several low-noise direct-current superconducting quantum interference device (SQUID) magnetometers from single layers of YBa2Cu3O7−δ on 10 mm×10 mm bicrystal substrates. The magnetometer design consists of a single-turn pickup loop that is directly coupled to the SQUID inductance. At 77 K, these magnetometers exhibit large voltage modulation with applied flux of over 40 μV. The minimum flux noise, measured at 77 K using conventional flux-locked loop electronics with bias current reversal, is 3.5×10−6 Φ0/√Hz above 10 kHz and 6.5×10−6 Φ0/√Hz at 1 Hz. The field-to-flux conversion efficiency is measured to be 10 nT/Φ0, resulting in a white magnetic field noise of 35 fT/√Hz above 10 kHz, increasing to 65 fT/√Hz at 1 Hz.

Fabrication and characterization of high-T/sub c/ SQUID magnetometer with damping resistance

“…In the case of the SQUID without damping resistance, the curves exhibit multiple steps clearly due to the formation of higher modes standing electromagnetic waves. Observed voltages at the first ( ) steps for and agree well with the calculated values for of 172 and 86 V by (1). For the SQUID with damping resistance, contrary to results of the lump model simulation, a significant shift of the crossover point was not observed throughout this region of Au thickness.…”

“…N fabricating grain boundary junctions, SrTiO (STO) has been widely used as a substrate for YBa Cu O (YBCO) film deposition, though it has large dielectric constant, [1] at 77 K. This high permittivity was not thought to bring about serious problems in superconducting quantum interference devices (SQUIDs) where the frequency of Josephson oscillation is relatively low. However, for the practical SQUID with inductance formed by a pair of coplanar lines, the resonance phenomenon takes place as a result of the formation of standing electromagnetic waves within the STO between the strips.…”

“…The presence of this structure can degrade the modulation voltage, , of the SQUID. Especially for the transverse-type SQUID with a long hole parallel to the bicrystal line and junctions at each end of the hole, the resonance voltage, , is calculated [1] where, . One of the solutions to avoid resonance and to improve is the use of LaAlO Sr Al Ta O (LSAT) substrates with low permittivity [2].…”

Fabrication of Magnetometers With Multiple-SQUID Arrays

“…Magnetometers with field sensitivities below 50 at 77 K have been reported [3], [4]. However, in the case of biomagnetic applications such as magnetocardiograms (MCG) and magnetoencephalograms (MEG), the sensitivity of highSQUIDs is not enough for clinical diagnosis.…”

Thin Film Growth and Device Fabrication of Iron-Based Superconductors

“…40). The S È 1=2 -f spectrum exhibits 1=f noise in the low-f region (<20 Hz) and white noise with a constant È 0 /Hz 1=2 of a YBCO dc-SQUID with ÁV ¼ 10{20 V at 77 K. 190,191) The operation temperature of this Ba122:Co dc-SQUID must be near T c because I c , which must be smaller than 200 A owing to the requirement of dc-SQUID operation using the FLL circuit, rapidly increases with decreasing temperature. In addition, V È is low owing to the low R N , which is attributed to the metallic nature of normalstate Ba122:Co. Consequently, the high measurement temperature and low V È are responsible for the high noise level.…”