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New Magneto Resistive Head Design to Improved Quality and Test Characteristics

IP.com Disclosure Number: IPCOM000118012D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 92K

Publishing Venue

IBM

Related People

Christoffer, B: AUTHOR [+3]

Abstract

The production of MagnetoResistive (MR) thinfilm read-write heads requires various metal layers. The used set of metals to determine the MR stripe itself needs to be magnetically shielded against the substrate and the inductive write head.

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New Magneto Resistive Head Design to Improved Quality and Test Characteristics

      The production of MagnetoResistive (MR) thinfilm read-write
heads requires various metal layers.  The used set of metals to
determine the MR stripe itself needs to be magnetically shielded
against the substrate and the inductive write head.

      It only can be effective if the inductive element, specifically
the plated Permalloy film, is electrically separated from the MR
stripe.

      During wafer processing, extensive test schemes are adopted to
screen every single element, which shows lower capacitance between
the shields and the MR layers.  Defect analysis has shown that Al sub
2 O sub 3 as the dielectric material can be damaged by wet chemical
reactions, like resist develop with base solutions or with
undercutting at via etching.  The amount and sensitivity of shield
shorts is related  to the overlapping area of plated NiFe and the
shield 1 metal, e.g., Sendust.

      Magnetical testing is done using probe cards which need
relatively large contact pads for a flawless test cycle.  Fig. 1
shows a typical MR head.  The testpads are pointed out.  An Alternate
Current (AC) is applied to determine the capacitance according to
Formula 1:
  C = epsilon sub 0 bullet epsilon sub r bullet  A over d
  where epsilon sub o is the field constant (8.85 bullet 10 sup -12 F
over m), epsilon sub r is the dielectrical constant of the used Al
sub 2 O sub 3 (5), A is the area of the shield-2 NiFe layer(2 bullet
10 sup -6 m sup 2) and d is the Al sub 2 O sub 3 gap thickness (2.5
bullet 10 sup -7 m).

      It is obvious that "A" drives the capacitance value.  The area
of interest, where imperfections cannot be allowed, has been pointed
out in Fig. 1.  The discrepancy between the tested and the important
area is huge.  Additionally, the larger area gives more room for
imperfections to take place assuming a statistically distributed
level of contamination.

      Fig. 2 shows a revised MR head design with the focus...