Noise properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/ step-edge junction dc SQUID magnetometers prepared on sapphire substrates

Step-edge YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) dc SQUID magnetometers on sapphire substrates have been fabricated. CeO/sub 2/ buffer layers and YBCO films were deposited in situ on the low angle (/spl sim/35/spl deg/) steps formed on the sapphire substrates with various thickness ratio of YBCO thin film to step height. Noise properties of the magnetometer exhibit quite different behavior according to the thickness ratio. The field noise of the dc SQUID magnetometer was measured to be 100/spl sim/300 fT//spl radic/Hz at 100 Hz and about 1.5 pT//spl radic/Hz at 1 Hz with a dc bias method, and 450 fT//spl radic/Hz at 1 Hz with an ac bias method.