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Inductive Thin Film Head Performance Calculation

IP.com Disclosure Number: IPCOM000114308D
Original Publication Date: 1994-Dec-01
Included in the Prior Art Database: 2005-Mar-28
Document File: 4 page(s) / 97K

Publishing Venue

IBM

Related People

Eickelmann, H: AUTHOR [+4]

Abstract

The magnetoelastic energy is the main factor for inductive thin film instability. A model is demonstrated, in which the magnetostrictive contstant lambda is measured on monitor wafers and the stress anisotropy &Delta.&sigma. in the Permalloy layer is determined from the overcoat stress &sigma.(OC) and the ratio of thickness t and width w of the pole tips. The product lambda times &Delta.&sigma. is used to optimize thin film head performance.

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Inductive Thin Film Head Performance Calculation

      The magnetoelastic energy is the main factor for inductive thin
film instability.  A model is demonstrated, in which the
magnetostrictive contstant lambda is measured on monitor wafers and
the stress anisotropy &Delta.&sigma.  in the Permalloy layer is
determined from the overcoat stress &sigma.(OC) and the ratio of
thickness t and width w of the pole tips.  The product lambda times
&Delta.&sigma.  is used to optimize thin film head performance.

      Head stability is one of the key parameters in the performance
of thin film inductive heads.  The most critical region for head
performance stability is slope of the P2 pole tip.  From magnetic
domain observations it is known that a high magnetic anisotropy
yields in a favored domain configuration.  The magnetic anisotropy
has three sources: the induced uniaxial anisotropy, the shape
anisotropy and the magnetoelastic anisotropy.

      The induced uniaxial anisotropy is well controlled by the
plating process, the magnetostatic shape anisotropy is defined by the
pole tip geometry.  But the magnetoelastic anisotropy depends on
various film and process parameters.  One factor is the
magnetostriction constant lambda, which correlates to the plating
bath composition.  The stress anisotropy, however, depends on the
elastic properties of the magnetic layers, the isolation photo resist
layers and the AL(2)0(3) overcoat and on the processes, especially
thermal treatments are changing the stress state.

      Stress anisotropy - From various experiments and stress
calculations (1), it is known that the overcoat is a major factor for
the principal stress in the critical slope region of the P2 pole tip.
Therefore, in a first approximation the stress in the Permalloy can
be derived from the overcoat stress, measured at flat large monitor
wafers by the deflection method.  The compressive stress in the
overcoat is compensated by a tensile stress in the Permalloy.  The
stress anisotropy is created by the geometry of the pole tips.  In a
large area the stress is isotropic.  Only at edges the stress can
relaxe, e.g., in long narrow stripes the stress relaxes in the
direction perpendicular to the stripes, in the parallel direction the
stress remains (2).  Assuming the stress relaxation takes place in a
short distance in the order of the film thickness, the stress
anisotropy in the P2 slope is therefore parallel to the edges along
the strip...