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Capacitive Measurements of Ferrite Head Air Bearing Surface

IP.com Disclosure Number: IPCOM000119613D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 95K

Publishing Venue

IBM

Related People

Cunningham, EA: AUTHOR [+2]

Abstract

Disclosed is a method of measuring the air bearing surface flatness of monolithic MnZn ferrite recording heads using capacitive measurements. The significant conductivity of MnZn is used to allow the slider to form one of the conductive planes for each of the capacitive measurements.

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Capacitive Measurements of Ferrite Head Air Bearing Surface

      Disclosed is a method of measuring the air bearing
surface flatness of monolithic MnZn ferrite recording heads using
capacitive measurements.  The significant conductivity of MnZn is
used to allow the slider to form one of the conductive planes for
each of the capacitive measurements.

      Multiple metal pads are made on an optical flat to form the
other plate of each capacitor used for measurement. Three pads are
also added for electrical and physical connection to the slider.
These three pads are made higher than the others, by adding a second
layer of metal over the original height pads.  A small force is
applied on the top of the slider within the triangle of the contact
points to hold the slider in contact with all three points.  This
holds the slider up from the other pads, such that the nominal
separation of the pads to the slider is equal to the second metal
layer thickness.  The capacitance of the other pads to the slider can
then be used to infer whether the slider is higher or lower than
nominal at each pad.

      With a standard design tri-rail monolithic MnZn head, the width
of the center rail is quite small compared to the outer flying rails.
Thus, the best configuration for the capacitance measurement system,
is to make two of the physical contact points on the center rail,
preferably at the center and near the back.  The other physical
contact is best located at the center of one of the side rails.  This
allows all the capacitive measurements to be done on the wider flying
rails.  Pads near the ends of the side rail with the physical contact
in the center allow a determination of the curvature of the surface
of the rail, using the measured capacitance of these pads to the
rail. The pad in the center of the opposite flying rail allows the
determination of the cross curvature of the head, since the center of
the center rail and of the first flying rail are referenced to the
flat surface.  Pads near the front and rear of the second flying
rail, along with that in the center, allow the curvature of that rail
to be determined independent of that of the first flying rail.  A
separate pad at the front of the center rail is not used, due to the
difficulty of accurate capacitance measurement on the very narrow
rail.  However, the curvature of the center rail can be approximated
as the average of the measured curvatures of the outer ra...