Increase the Tensile Stress of Plated Permalloy with a Mechanical Solution
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Brottier, F: AUTHOR [+3]
Disclosed is a method to increase the tensile stress of plated permalloy using a mechanical process.
Increase the Tensile Stress of Plated Permalloy with a
a method to increase the tensile stress of plated
permalloy using a mechanical process.
magnetic heads often suffer from an instability
problem, which is the unwanted variation of the head output measured
in micro Volts during read cycle in a hard disk drive application.
As a figure
of stability, one can simply use the fraction of
amplitude standard deviation divided by the average amplitude value
after several reading cycles. The industry refers to this number as
'wiggle noise' or avarage-AlJohn number.
One of the
major factors to control the head stability is the
Nickel/Iron concentration of the plated magnetic layer. Besides the
general issues of head design and used production equipments itself
the control and sign of stress in terms of applied or intrinsic film
stress is crucial.
Given a more
or less stable product one cannot simply increase
the Ni content to increase head stability, although it will work,
because the magnetic head will also reduce its needed output voltage
(amplitude) by as much as 100 micro V per wt% Nickel. The only
source to gain head stability but keep the desired amplitude is the
increase of intrinsic film stresses built in the layers which
encapsulate the head.
experiments done on totally different head design show
that the NiFe composition and the stress level always needs to be
individually adjusted and are not predictable with mathematical
models so far.
magnetic heads are fabricated similar to integrated
chips. Since important disk drive parameters like read and write
trackwidth on the magnetic disk are specified tightly, the wafer
flatness during production and especially during photo lithographie
to form the wanted resist patterns has to be very high.
For a bent
wafer the photo resist exposure tool like Perkin
Elmer Aligner tools may create out of focus areas which won't give
the specified track width after resist development. Relatively thick
substrates like Greenleaf Al&sub2.O&sub3./TiO ceramics the described
problem rarely appears. Thin Silicon substrates, on the other hand,
are much more sensitive to highly stressed layers. There are many
applications where Si substrates are used: inductive and
magnetoresistive thin film heads, video heads and other sensors.
Those wafers can show significant bow during the production which
might be too high for production.
To keep the
needed flatness of such Si substrates all media
stress during the wafer production needs to be controlled such, they
are relatively flat during photo lithographie. To increase the
desired effect of intrinsic stress the wafers can be artificially
bent during NiFe plating. This will induce an additional stress
effect if the substrate is bent in the right direction.
In most cases, the NiFe composition i...