Gabriel Daalmans

Low 1/f noise single‐layer YBa2Cu3Ox dc SQUID at 77 K

Autonomous single‐layer dc superconducting quantum interference devices (SQUIDs) have been prepared from epitaxial, laser‐deposited YBa2Cu3Ox films on step edge SrTiO3 and LaAlO3 substrates. For device patterning, a SiOx inhibit technique as well as conventional ethylenediaminetetraacetic wet etch was used. The Josephson junctions are of grain boundary type. Their widths are 5 μm. The SQUID hole is a square of about 5 μm; the SQUID inductance is estimated to be about 20 pH. We obtained a very regular, nonhysteretic flux to voltage modulation over more than 100 flux quanta (Φ0). The maximum voltage signal is of the order of 15 μV peak to peak and the maximum transfer function dV/dΦ at the appropriate flux bias is 50 μV/Φ0 at 77 K. The best value of the equivalent flux noise as measured in the flux locked loop mode is 1.4×10−5 Φ0/Hz1/2 at 1 Hz and 1×10−5 Φ0/Hz1/2 in the white noise region for f≳5 Hz. This results in an energy resolution en,w(f≳5 Hz)=1×10−29 J/Hz in the white noise region and 2×10−29 J/Hz at...

Low 1/ f noise single-layer YBa sub 2 Cu sub 3 O sub x dc SQUID at 77 K

Autonomous single‐layer dc superconducting quantum interference devices (SQUIDs) have been prepared from epitaxial, laser‐deposited YBa2Cu3Ox films on step edge SrTiO3 and LaAlO3 substrates. For device patterning, a SiOx inhibit technique as well as conventional ethylenediaminetetraacetic wet etch was used. The Josephson junctions are of grain boundary type. Their widths are 5 μm. The SQUID hole is a square of about 5 μm; the SQUID inductance is estimated to be about 20 pH. We obtained a very regular, nonhysteretic flux to voltage modulation over more than 100 flux quanta (Φ0). The maximum voltage signal is of the order of 15 μV peak to peak and the maximum transfer function dV/dΦ at the appropriate flux bias is 50 μV/Φ0 at 77 K. The best value of the equivalent flux noise as measured in the flux locked loop mode is 1.4×10−5 Φ0/Hz1/2 at 1 Hz and 1×10−5 Φ0/Hz1/2 in the white noise region for f≳5 Hz. This results in an energy resolution en,w(f≳5 Hz)=1×10−29 J/Hz in the white noise region and 2×10−29 J/Hz at...

Multichannel DC SQUID sensor array for biomagnetic applications

A biomagnetic multichannel system for medical diagnosis of the brain and heart has been developed. 37 axial first order gradiometers (manufactured as flexible superconducting printed circuits) are arranged in a circular flat array of 19 cm in diameter. Additionally, three orthogonal magnetometers are provided. The DC SQUIDs are fabricated in all-Nb technology, ten on a chip. The sensor system is operated in a shielded room with two layers of soft magnetic material and one layer of Al. The everyday noise level is 10 fT/Hz/sup 1/2/ at frequencies above 10 Hz. Within two years of operation in a normal urban surrounding, useful clinical applications have been demonstrated (e.g., for epilepsy and heart arrhythmias). For the first time current sources of sporadic events causing epilepsy or ventricular extrasystoles have been localized from coherent recordings of complete biomagnetic field distributions with spatial resolution of millimeters and temporal resolution of 1 ms.

Single layer YBaCuO-gradiometer

A single layer YBaCuO-gradiometer galvanically coupled to DC-SQUIDs were prepared on bicrystal substrates. The devices were operated at 77 K without any shielding. The best performance obtained was a field gradient resolution of 0.5 pT/cm/spl radic/(Hz) for a device with a baseline of 7 mm and a pickup-area of 2 cm/sup 2/.<<ETX>>

HTS DC SQUIDs for practical applications

Abstract This paper deals with HTS DC SQUID sensors for practical purposes that can be operated without magnetic shielding. In the first part of the paper the parameter for HTS DC SQUIDs with an optimized field(gradient) resolution are derived. In a following chapter external noise reduction techniques are discussed, because they are unavoidable in operating SQUID devices without shielding. Finally experimental results, obtained on single layer HTS gradiometer devices, are presented and discussed.

Noise properties of YBaCuO step edge DC-SQUIDs with different inductance

Autonomous step edge DC-SQUIDs (superconducting quantum interference devices) with inductances between 20 pH and 140 pH have been prepared on one chip. The noise properties of these devices have been determined by operating them in the flux locked loop. The best energy sensitivity of 6*10/sup -31/ J/Hz was obtained for a 20 pH SQUID and frequencies above 100 Hz. The frequency-dependent noise for the best devices was about 2*10/sup -29/ J/Hz at 1 Hz and could be reduced by applying an AC bias.<<ETX>>

Ultra low noise all niobium DC-SQUIDs

The noise and signal properties of SQUIDs with amorphous silicon barriers and Al/sub 2/O/sub 3/ barriers are studied. The barrier material is found to be of great importance for the value of the 1/f noise component. The best results were obtained for SQUIDs with Al/sub 2/O/sub 3/ barriers and a 1/f noise level at 1 Hz of about 1*10/sup -6/ Phi / square root Hz was found. After integration of coupling coils onto the SQUIDs, a signal limitation and a dramatic increase of the noise were found. Implementation of a damping circuitry over the coupling coil results in optimized signals ( Delta V( Phi /sub 0//2) approximately=I/sub c/R) and a white noise level comparable to the white noise level without a coupling coil. The 1/f noise component for SQUIDs with a damped coupling coil is higher than for 1/f noise component of SQUIDs without a coupling coil. For SQUIDs with Al/sub 2/O/sub 3/ barriers, the 1/f noise level keeps below 3*10/sup -6/ Phi /sub 0// square root Hz at 1 Hz. For SQUIDs with an amorphous silicon barrier the 1/f noise component changes per cooling cycle in an irregular way. The stability for thermal cycling and room-temperature storage is very good for all the devices.

Development and Performance of a Multichannel System for Studies of Biomagnetic Signals of Brain and Heart

Biomagnetic systems operating with 4 to 7 channels have been described before [Ilmoniemi 1984, Williamson 1984, Romani 1985, Kajola 19871]. With noise levels of less than 20 fT/√Hz their performance was sufficient for various biomagnetic applications. So far the number of channels was insufficient for obtaining a complete set of magnetic signals. We have developed a biomagnetic system (KRENIKON) that is capable to collect complete coherent data sets under routine conditions.

Single-layer and integrated YBCO gradiometer coupled SQUIDs

For many SQUID applications such as biomagnetism or non-destructive evaluation it is convenient or even necessary to work without the restrictions of a magnetically shielded room. This contribution deals with two sensors appropriate for this purpose. In the first concept we present a flip chip arrangement of a single-layer flux transformer and a single-layer SQUID, taking advantage of a simple technology. The SQUID was prepared on a bicrystal and located in the common line of two-parallel-loop arrangements. The flipped antenna was designed as a two-parallel-loop gradiometer with 26 mm baseline on a single-crystal substrate. A field gradient sensitivity of was obtained. We could demonstrate a field gradient resolution of at 1 kHz in an unshielded environment. In the second concept we integrated both the flux antenna and the SQUID on a bicrystal. The tighter coupling scheme results in smaller devices for similar field gradient sensitivities. The integrated SQUID is designed as a device on a bicrystal substrate. The remaining space is used for test structures and SQUIDs without antennae, in order to control the technology as well as the SQUID design. Parallel processed dummy substrates were used to monitor the quality of film growth by x-ray analysis. The quality of our SQUID design will be discussed on the basis of the measured field gradient sensitivity and noise. The reliability of the devices is demonstrated by an NDE type measurement.

Noise properties of single-layer YBaCuO step-edge DC SQUID's on MgO substrates

Abstract DC-SQUIDs prepared on MgO substrates with deep steps have been investigated. The I-V characteristics at 77 K of devices with 6 μm wide junctions can be described by the resistively shunted junction model for steep step edges and by the flux-flow model for low-angle step edges. Steep substrate steps result in a higher yield of working devices. Peak-to-peak flux modulated voltages up to 60 μV could be measured, corresponding to transfer functions between 20 and 200μV/Φ0 at 77 K. Energy sensitivities between 1 × 10−30 and 8 × 10−30J/Hz in the white-noise region and between 2.5 × 10−29 and 8 × 10−28J/Hz at 1 Hz for SQUID inductances up to 100 pH could be obtained. There was no obvious dependence of the energy sensitivity on the step angle of the Josephson junctions for devices with 20 pH inductance. These results are comparable to our best results obtained with step-edge DC SQUIDs on SrTiO3 substrates.