DEVELOPMENT OF HIGH SENSITIVE THIN-FILM MAGNETIC SENSORS BY APPLYING THE IMPURITY REDULATED SPUTTERING PROCESS

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The giant magnetoresistance(GMR)effect in metallic multilayer has been actively investigated to be applied to magnetic sensors. Key technical factors to obtain sensitive MR response are 1)flat interfaces of multilayers to retain large MR ratio and 2)soft magnetic properties of ferromagnetic layers, such as Co iud Co-Fe. These two factors are realized with controlling impurities in fabrication process. Introducing oxygen into the sputtering atmosphere during the deposition is an effective way to improve the interfacial flatness, which has been demonstrated for Co/Cu multilayers by the present authors. Nitrogen and boron are well-know additives to make magnetic softering of Co-Fe films. In the present study, in order to clarify the role of oxygen on GMR more precisely, Co/Cu multilayers were fabricated under different sputtering atmospheres in which the impurity oxygen content was changed dramatically from 0.1 ppm to 0.1 % within processing Ar gas. The correlation between the MR ratio and microstructure of the multilayers, especially the interfacial roughess, was investigated as a function of the partial pressure of oxygen introduced into the sputtering chamber. The MR ratio drastically increased from less than 20 % to 54 % when the content of impurity oxygen was slightly increased from 20 ppm to 80 ppm, then nearly varished when the content become more than 200 ppm. In the former region where the MR ratio steeply increased, the root mean square rougtness of the multilayers decreased from 6.5 Å to 4.5 Å accompanied by a reduction of in grain size as the oxygen content was increased. The partial oxidation of the multilayers is the most probable mechanism by which the flattening of the interfaces in the multilayer can be explained.