Effect of deposition conditions on the properties of thin permalloy film

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Abstract
The saturationmagnetostriction λ s of thin Permalloyfilms, used in magnetoresistive reproduce heads, has to be strictly controlled to be negative and less than 3×10−7. The value of λ s for NiFe is a strong function of film composition. [E. Klokholm and J. A. Aboaf, J. Appl. Phys. 5 2, 2474, (1981).] [R. M. Borzorth and J. G. Walker, Phys. Rev. 8 9, 624 (1951).] Since the composition of the target material could be controlled to only ±0.2% of Ni, the potential changes in λ s could have been as large as 6×10−7, which exceeded the material specification. Therefore, the effect of substrate bias (0 to −60 V), sputtering pressure (2 to 20 mTorr), and target voltage (200 to 1000 V) on magnetostriction has been investigated to identify the best process control parameter. Sputtering has been performed in an argon atmosphere using a triode source. The target was vacuum cast NiFe. Thermal oxide‐coated Si wafers were used as a substrate. It was found that the substrate bias has a strong effect on λ s ; however, the thickness uniformity becomes unacceptable. The target voltage has been found to have no effect on magnetostriction. The value of λ s however, can easily be modified by varying the sputtering pressure. Varying the pressure from 4 to 10 mTorr can change λ s as much as 4×10−7 without degradation of the other film magnetic properties, such as anisotropy, coercivity, and magnetoresistance. Therefore, this method has been successfully used in control of λ s in our thin‐film magnetoresistive heads.

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