Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-05-25
2004-07-06
Chen, Tianjie (Department: 2752)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06760197
ABSTRACT:
FIELD OF THE INVENTION
This application relates to hard disc drives and more particularly to an apparatus and method for controlling a lapping process, so as to create a read/write head that contains a primary magnetoresistive read element with a desired stripe height.
BACKGROUND OF THE INVENTION
The storage medium for a disc drive is a flat, circular disc capable of retaining localized magnetic fields. The data that are stored upon the disc find physical representation through these localized magnetic fields. The data are arranged on the disc in concentric, circular paths known as tracks.
The localized magnetic fields can be detected by a magnetically sensitive head when they are brought in close proximity to the head. During operation, the disc continually rotates, meaning that for each rotation, a head fixed a given radius from the center of the disc would encounter every localized magnetic field along a given track.
A read/write head
100
capable of reading and writing localized magnetic fields upon the surface of a disc is depicted in FIG.
1
. The read/write head
100
depicted in
FIG. 1
is constructed from a body
102
composed of AlTiC (Aluminum, Titanium and Carbide) wafer material. Conjoined to the body
102
is a magnetoresistive read element and a write element, shown jointly as
104
. The resistance of the magnetoresistive read element
104
changes when introduced to a magnetic field. Generally, the greater the magnetic field in which the magnetoresistive read element
104
is immersed, the higher its resistance. Accordingly, the magnetoresistive read element
104
is used to detect a localized magnetic field stored on the surface of the disc by orienting the localized magnetic field under the read element
104
and observing a change in the element's
104
resistance.
To detect a change in the resistance of the read element
104
, a constant current is passed through the magnetoresistive read element
104
and the voltage across the element
104
is observed. As the resistance of the element
104
increases due to the influence of a proximate magnetic field, the voltage across the element
104
increases proportionately. Thus, the change in resistance is observed as a corresponding rise in voltage across the read element
104
. The constant current used to detect the localized magnetic fields is propagated through conductors
106
,
108
, which electrically contact opposite ends of the magnetoresistive element
104
. The conductors
106
,
108
run to a pair of wire bonds
110
,
112
, which join the conductors
106
,
108
to a pair of elongated conductors
114
,
116
that extend the length of the head
100
, and join to detection circuitry (not pictured). The read/write head
100
also contains conductors
118
,
120
through which a current is passed to record a magnetic field upon the surface of the disc. Conductors
118
,
120
also run to a pair of wire bonds
122
,
124
, which join the conductors
118
,
120
to a pair of elongated conductors
126
,
128
that extend the length of the head
100
, and join to writing circuitry (not pictured).
FIG. 2
shows a magnified view of a magnetoresistive read element
104
. As can be seen from
FIG. 2
, the bottom edge
200
of the magnetoresistive read element
104
extends to the air bearing surface of the slider. The air bearing surface functions to create a “cushion” of air upon which the read/write head
100
floats as it is positioned over a rotating disc.
The top edge of the magnetoresistive read element
104
is identified by reference numeral
204
. The distance between the bottom edge
200
and the top edge
204
of the magnetoresistive read element
104
is referred to as the “stripe height.” The stripe height of a magnetoresistive read element is an important variable, as it determines the sensitivity of the magnetoresistive element to a magnetic field. Generally, the shorter the stripe height, the more sensitive the magnetoresistive element, and vice versa.
As shown by
FIG. 3
, prior to processing, a magnetoresistive read element
104
has a stripe height on the order of 100,000 Å. The conductors
106
,
108
have approximately the same height. During manufacture, the magnetoresistive head is “lapped,” thereby reducing the magnetoresistive read element's
104
stripe height to that which is shown in
FIG. 2
, on the order of 500 Å (with a typical tolerance of ±10%), depending upon product requirements. “Lapping” is a term used to describe a grinding process in which the magnetoresistive read element
104
and its associated conductors
106
,
108
are literally ground down by an abrasive slurry, until the desired stripe height is achieved. The purpose of the lapping process is to reduce the stripe height of the magnetoresistive read element until the proper magnetic sensitivity has been created.
Ideally, it would be possible to directly test the sensitivity of the magnetoresistive read element during lapping, so that when the proper sensitivity had been achieved, lapping could be ceased. Unfortunately, by passing an electrical signal through the magnetoresistive read element, as is necessary in order to directly test the read element's resistance, the likelihood of an electrostatic discharge between the magnetoresistive read element and the abrasive slurry is enhanced. Such an electrostatic discharge is harmful to the read element, and it is therefore desirable to minimize the likelihood of such a discharge.
It is known in the art that, during lapping, the resistance of a secondary resistive element can be monitored and used as a proxy for directly measuring the stripe height of a primary magnetoresistive element. When the resistance of the secondary magnetoresistive element reaches a predetermined level, it can be assumed that the stripe height of the primary magnetoresistive element is in its appropriate range, and lapping can be ceased. In order to use such a measurement-by-proxy scheme, the primary and secondary elements should be arranged so that there exists a known relationship between the sensitivity of the primary and secondary elements.
FIG. 4
shows an undiced, untapped wafer
400
containing two read/write heads
402
,
404
and a lapping guide
406
. Read/write head
402
contains a primary magnetoresistive element
408
, and lapping guide
406
contains a secondary resistive element
410
, the resistance of which is in known relation to magnetoresistive element
408
. During lapping, the resistance of the secondary resistive element
410
is monitored. When the resistance of the secondary resistive element
410
reaches a certain level, it is assumed that the stripe height of the primary magnetoresistive element
408
is in its appropriate range, and lapping is ceased. To ensure that the resistance of the secondary resistive element
410
is in known relation to the stripe hieght of the primary magnetoresistive element
408
, the top edges of the primary and secondary elements are aligned. Therefore, during lapping, the stripe height of the primary and secondary elements should be equivalent, and the resistance of the secondary element should serve as a suitable proxy for the stripe height of the primary element. This solution, which is known in the art, has problems, however. The distance between the primary and secondary elements
408
,
410
is relatively great (perhaps 500 microns). Because of this great distance, the alignment of the top edges of the primary
408
and secondary elements
410
necessarily has a wide tolerance. Such a wide tolerance is undesirable, because it detracts from the accuracy with which the secondary resistive element
410
indicates the stripe height of the primary element
408
. Thus, the secondary resistive element
410
is an unreliable proxy for the primary magnetoresistive element
408
. Accordingly there exists a need for a means for accurately measuring and controlling the stripe height of a primary magnetoresistive element without subjecting the element to the risk of damage from electrostatic discharge.
SUMMAR
Boutaghou Zine-Eddine
Murdock Edward Stephens
Chen Tianjie
Seagate Technology LLC
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