High Resolution Current Imaging by Direct Magnetic Field Sensing

Two types of magnetic microscopes have been investigated for use in high resolution current mapping. The scanning fiber/SQUID microscope uses a SQUID sensor coupled to a nanoscale ferromagnetic probe, and the GMR microscope employs a nanoscale giant magnetoresistive sensor. Initial scans demonstrate that these microscopes can resolve current lines less than 10 µm apart with edge resolution of 1 µm. These types of microscopes are compared with the performance of a standard scanning SQUID microscope and with each other with respect to spatial resolution and magnetic sensitivity. Both microscopes show great promise for identifying current defects in die level devices.

SPIN-POLARIZED VACUUM TUNNELING: CORRELATION OF ELECTRONIC AND MAGNETIC PROPERTIES ON THE NANOMETER SCALE

The realization of spin-polarized vacuum tunneling is demonstrated for the Gd(0001) surface, which is ideally suited since it exhibits a surface state that is exchange-split into two parts with opposite spin polarization. Both appear as distinct features in the tunneling spectra. The use of ferromagnetic probe tips leads to magnetic-field-dependent asymmetries in the differential tunneling conductivity at bias voltages which correspond to the energies of the spin components. By mapping the asymmetry parameter we can image the magnetic domain structure of the sample. The spin polarization of the differential tunneling conductivity is found to be in excellent agreement with (inverse) photoemission data.