Mutual inductance and noise of high-Tc SQUIDs with flip-chip and integrated input coils

We investigated the mutual inductance and the noise of high-Tc superconducting quantum interference devices (SQUIDS) with flip-chip and integrated input coils. The dc SQUIDs are prepared on bicrystal substrates with misorientation angle of 30°. The number of turns of the input coils is varied between 5 and 25 turns. For 19-turn input coils, the mutual inductance is about 0.75 nH and 1 nH for the flip-chip and integrated SQUIDs, respectively. The spread in noise at 1 Hz is less than a factor of 2 for the flip-chip devices and about a factor of 5 for the integrated devices