MICROSTRUCTURAL ORIGIN OF 1 F NOISE IN HIGH T-C BICRYSTAL SQUID MAGNETOMETERS/

The origin of noise in YBa2Cu3O7-x (YBCO) bicrystal SQUID magnetometer s on SrTiO3 substrates is investigated by comparing the microstructure of actual low-noise and high-noise devices. The most obvious differen ce in the microstructure is the presence of a-axis oriented particles in the high-noise devices, whereas the low-noise devices consist exclu sively of c-axis oriented YBCO films. The growth of the a-axis particl es in the YBCO films induces many defects, including amorphous regions , distortion in c-axis lattice planes and extra a-c interfaces. The qu ality of the junction boundary is also degraded by the a-axis particle s. The existence of these defects are expected to affect the supercond ucting current and the motion of the magnetic flux in the films and he nce generate extra noise in the devices. (C) 1997 American Institute o f Physics. [S0003-6951(97)00151-4].