In order to improve the sensitivity of SQUID magnetometers made of high-T c films, we have studied the conditions of pulsed-laser deposition of YBCO films. Among the different deposition parameters examined, extensive degassing of the vacuum chamber before and precise control of the substrate temperature during the film deposition were found effective for obtaining high critical temperature T c and high critical current density J c . It was also found that the residual-resistance ratio has a clear correlation with J c , indicating that it can be a good, and easy to measure, index of the film quality. Films having T c ≈ 89-90 K and J c 5 × 10 6 A cm −2 at 77 K were used to fabricate SQUIDs without a pickup loop. Grain-boundary junctions formed on bicrystal substrates with a 30 • misorientation angle exhibited I c R n values of more than 100 µV at 77 K. The well-known scaling behaviour of the relation I c R n ∝ J GB c 1/2 was confirmed. Modulation voltages of 20-50 µV were obtained in the SQUIDs with 70 pH inductance.

Abstract-Effects of damping resistance on current versus voltage ( -) characteristics for highsuperconducting 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 3 substrates can induce resonance structures on -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 2 Cu 3 O 7 films.