Fabrication of magnetometers with multiple-SQUID arrays

We have designed and fabricated magnetometers with multiple-SQUID arrays to achieve higher signal to noise ratio compared to that for a single SQUID. In our directly coupled scheme, ten SQUIDs are connected in parallel with the same pickup coil composed of four parallel rectangular loops. Each SQUID having inductance of 70 pH and junctions of 1.5 /spl mu/m width was fabricated from an Au/YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film on a SrTiO/sub 3/ bicrystal substrate with 30/spl deg/ misorientation angle. To avoid forming superconducting loops between junctions of adjoining SQUIDs, a Au wiring layer interrupts a current bias line. The obtained critical current of 20I/sub c/ and normal resistance of R/sub n//20 including contact resistance for the Au wiring layer are 350 /spl mu/A and 0.4 /spl Omega/, respectively. The modulation voltage of 25 /spl mu/V for multiple-SQUIDs is the same level as for a single SQUID. On the other hand, the modulation current of 40 /spl mu/A is several times larger than that for a single SQUID, but rather smaller than the expected value when all SQUIDs have equal parameters. A flux noise level of 15 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ at 100 Hz, including preamplifier noise, was observed by using flux-locked loop electronics in a magnetically shielded room

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

Effects of damping resistance on current versus voltage (I-V) characteristics for high-T/sub c/ superconducting quantum interference devices (SQUIDs) were studied. In the transverse-type SQUID with coplanar strip lines, parasitic capacitance originating from the large dielectric constant of SrTiO/sub 3/ substrates can induce resonance structures on I-V curves and degrade the modulation voltage. In our simulations, it is shown that the modulation voltage is much improved by using damping resistance. However, the obtained experimental results for our SQUIDs with Au damping do not agree well with those in the simulations. The discrepancy is likely due to existence of the large contact resistance between Au and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films

High-Tc SQUID magnetometers for use in moderatemagnetically-shielded room

We have fabricated and characterized high-Tc planar SQUID magnetometers and first derivative gradiometers with directly-coupled pickup loops. The devices were made from single layer of YBa2Cu3O7-δ thin film on LSAT bicrystal substrate with 30° or 24° misorientation angle. Magnetic properties were investigated by applying a magnetic field B0 for the SQUID magnetometer patterned with holes to reduce the maximum structural width. We found an increasing low frequency noise with cooling fields B0 larger than 1.5 μT. This value consists with the threshold field estimated from the maximum structural width. A magnetic field noise level of 500 fT/Hz1/2 at 10 Hz was observed by using FLL electronics with a bias current reversal in a moderate magnetically-shielded room consisting of only two 1 mm thick layers of permalloy. Measurements of magnetocardiograms demonstrate the suitability of this magnetometer for biomagnetic applications. On the other hand, the gradiometer with two symmetric pickup loops was operated without any shielding. The performance obtained was a field gradient resolution of about 1 pT/cmHz1/2 at 1 kHz and 10 pT/cmHz1/2 at 1 Hz, with a baseline of 4 mm. The imbalance of this gradiometer was around 0.7%, limited by the sensitivity to homogeneous field of the SQUID itself

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

application/pdfEffects of damping resistance on current versus voltage (I-V) characteristics for high-T/sub c/ superconducting quantum interference devices (SQUIDs) were studied. In the transverse-type SQUID with coplanar strip lines, parasitic capacitance originating from the large dielectric constant of SrTiO/sub 3/ substrates can induce resonance structures on I-V curves and degrade the modulation voltage. In our simulations, it is shown that the modulation voltage is much improved by using damping resistance. However, the obtained experimental results for our SQUIDs with Au damping do not agree well with those in the simulations. The discrepancy is likely due to existence of the large contact resistance between Au and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films