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Spin valve films with the PtMn/Co/Ru/Co synthetic ferrimagnet pinned layer, in which the magnetization of the two Co layers is strongly coupled in an antiparallel orientation and the magnetization direction of one of the Co layers is pinned by unidirectional exchange coupling with PtMn, were investigated. PtMn synthetic ferrimagnet pinned layers were demonstrated to exhibit strong unidirectional exchange field Hex exceeding 2500 Oe at an optimum PtMn/Co/Ru/Co thickness combination for either PtMn on top or at the bottom. The Hex of PtMn/Co/Ru/Co rapidly increased at the PtMn layer thickness around 10–12 nm and was nearly constant from 12 to 30 nm. It was also found that the saturation field of the Co(3 nm)/Ru(0.8 nm)/Co(2 nm) sandwich, which represents the antiparallel interlayer coupling strength through Ru, remained 2200 Oe even at 300 °C. Thus the combination of the high blocking temperature of 380 °C for PtMn and the large antiparallel exchange interaction of Co/Ru/Co up to 300 °C makes the pinned layer highly stable against various magnetic fields during Joule heating of spin valve sensor stripes. Further, the PtMn synthetic-ferri-pinned-type dual spin valve films showed a large unidirectional exchange field of 2000 Oe and a giant magnetoresistance ratio of 11.0%.

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The concentric circle pattern of growth striations in Czochralski (CZ) silicon wafer has been found to cause the fixed pattern noise in the reproduced image by solid-state imagers with the p-well structure. The microgrowth striations of dopant impurities in 4-in. n-type CZ silicon wafers have been examined in terms of noise video signals of p-well Charge Priming Device imagers. Striation periods as narrow as 10 μm can be revealed, which may be overlooked by the conventional spreading resistance method.

The performance of CCD image sensors is strongly influenced by the crystal quality of the silicon wafer because it is an analog VLSI device which measures optical signals. In order to examine the relation between the imaging characteristics of the sensors and the crystal qualities of silicon wafers, the sensors were fabricated by the same process on three kinds of wafers (i.e., CZ, FZ and epitaxial wafers). It·is found that image striation is attributable to resistivity inhomogeneity in the wafer, the white blemish to crystal defects in the surface depletion layer, the smear to effective thickness of the photoelectric conversion layer and the black swirl to inhomogeneous distribution of recombination centers in the material. These difficulties are solved by the use of epitaxial wafers in which the photocarrier lifetime can be controlled. The fixed-pattern noise is suppressed to an S/N ratio greater than 60 dB and the smeared signal as low as 0.4%. The influence of the substrate on the crystal quality of the epitaxial layer is also discussed.