EDDY-CURRENT MICROSCOPY USING A 77-K SUPERCONDUCTING SENSOR

We have used a scanning magnetic flux microscope based on a high trans ition temperature YBa2Cu3O7 superconducting quantum interference devic e (SQUID) to produce magnetic images of eddy currents in patterned Cu thin films and 11-30-mum-thick Cu on printed circuit boards. The field s produced by the eddy currents are imaged with a spatial resolution o f about 80 mum over a 100-mm2 sample area. With the sample and SQUID a t 77 K, the microscope uses typical probing fields of 80 nT and can ob tain simultaneously eddy current and static magnetic field images. At probing frequencies of 26-100 kHz, the system achieves a field sensiti vity of about 7 pT Hz-1/2.