Noise in DC-SQUIDs with quasiplanar all-oxide Josephson junctions

We describe the noise performance of dc-SQUIDs fabricated with quasiplanar ramp-type Josephson junctions on the basis of c-axis-oriented YBa2Cu3O7/PrBa2Cu3O7 thin film heterostructures. The noise spectrum of the dc-SQUIDs was measured with dc- and ac-bias schemes at different temperatures and showed values below 10(-5) Phi(0)/Hz(1/2) down to frequencies of about 1 Hz at 70 K. Up to now for the magnetic flux noise and the energy resolution obtained at 1 kHz and 77 K the best values were 2.5 . 10(-6) Phi(0)/Hz(1/2) and 3 . 10(-31) J/Hz respectively. For a 8 x 6 mm(2) current injection pickup loop a magnetic field sensitivity of about 27 fT/root Hz at 1 kHz and 77 K was achieved. Noise at 1 Hz measured with an ac-bias scheme was about 165 fT/root Hz. The influence of magnetic flux, bias current, high static magnetic fields and aging on the SQUID noise were investigated. The junctions and devices do not degrade due to aging in air or thermal cycling.