Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2002-11-19
2004-09-07
Hail, III, Joseph J. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S005000, C451S009000
Reexamination Certificate
active
06786803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetoresistive and giant magnetoresistive sensors for reading magnetically-recorded information from data storage media, and particularly to methods for lapping such heads during manufacturing.
2. Description of the Prior Art
By way of background, magnetic media-based DASD systems, such as disk drives, use magnetoresistive and giant magnetoresistive sensors (hereinafter collectively referred to as “MR” sensors) to read data recorded on the storage media. An MR sensor is a magneto-electrical device that produces a variable voltage output in response to magnetic field fluctuations emanating from the recorded magnetic domains that represent stored information. The MR sensors used in disk drives are commonly integrated with inductive write heads to form merged read/write heads. Such heads are conventionally formed by building thin film layer structures on a wafer substrate. The wafer substrate is then divided into multiple slider bars that each carry a row of multiple (e.g., 60) read/write heads. Processing of the slider bars into finished read/write heads requires lapping along one longitudinal edge of the slider bar to precisely define an air bearing surface (ABS) of each read/write head, followed by division of the slider bar into individual heads.
Slider bar lapping is typically performed as a wet grinding process in which material is removed to define a read head parameter known as “stripe height” for each of the read/write heads on the slider bar. Stripe height is the distance from the ABS to the back of each MR sensor. It is a parameter that greatly influences sensor responsiveness to recorded magnetic domains, and thus must be carefully controlled. The conventional technique used to monitor slider bar lapping is by way of one or more electronic lapping guides (ELGs) formed in kerf areas of the slider bar. Each ELG includes an electrically conductive sensor structure whose ends are connected to electrical leads that carry current from a control circuit. Lapping is controlled by sensing resistance increases in the ELG as sensor material is removed by the grinding process. The ELG resistance increases are used to determine changes in MR sensor stripe height so that the lapping process can be terminated at the required stripe height.
It is to improvements in the ELG art that the present invention is directed. In particular, the invention addresses the need for increased lapping accuracy and reduced variability in final stripe height from one slider to another during manufacturing.
SUMMARY OF THE INVENTION
The foregoing problems are solved and an advance in the art is obtained by an onboard electronic lapping guide for lapping a magneto-resistive head having a magneto-resistive sensor element connected between a pair of sensor electrical leads. The lapping guide includes an electronic lapping guide resistive element that is also connected between the sensor electrical leads so as to form part of the in-process head structure. The lapping guide resistive element has a predetermined height in a lapping direction and is adapted to produce an electrical resistance in the presence of a lapping current that increases as the resistive element height is reduced during lapping. The lapping process ultimately consumes the ELG and produces a finished MR sensor.
In preferred embodiments of the invention, the resistive element is disposed between the sensor element and a portion of the head that will receive a lapping tool, and comprises two resistive elements providing a coarse lapping guide and a fine lapping guide. The coarse lapping guide has a greater width and height than the fine lapping guide. The coarse lapping guide is separated from the fine lapping guide by a gap that is of sufficient height to support a lapping clean-up phase. The fine lapping guide may have a height corresponding to a height of the sensor element, and has a width corresponding to a track width of the sensor element. The sensor electrical leads can be shaped to define the width of the fine lapping guide and the track width of the sensor element, and to further define a width of the coarse lapping guide that is larger than the fine lapping guide width and the sensor element track width. The resistive element and the sensor element may comprise identical thin film layers.
The invention further contemplates a lapping method and a method of forming the onboard electronic lapping guide.
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Crawforth Linden J.
Minvielle Timothy J.
Wang Benjamin L.
Werner Douglas J.
Duft Walter W.
Hail III Joseph J.
Thomas David B.
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