Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2002-07-12
2004-07-06
Nguyen, George (Department: 3729)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S011000, C451S010000, C451S041000
Reexamination Certificate
active
06758722
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to the fabrication of slider components for use in disk drives and the like. More particularly, the present invention pertains to a lapping guide to assist in the manufacturing of magneto-resistive head structures.
BACKGROUND OF THE INVENTION
Hard disk drives are common information storage devices essentially consisting of a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk data tracks. The high speed rotation of a magnetic disk generates a stream of air flow or wind along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing. The ABS of a slider is generally configured on the slider surface facing the rotating disk, and greatly influences its ability to fly over the disk under various conditions.
Many current disk drives include one or more magneto-resistive (MR) read-write heads. Such heads include MR sensor elements that are manufactured through the patterning of magneto-resistive layers. A description of the manufacture of such a MR read-write head can be found in U.S. Pat. No. 6,230,389, the disclosure of which is hereby incorporated by reference in its entirety. As these layers become smaller in dimension, it becomes more difficult to control the final operating characteristics of such heads.
An MR read head includes a giant magneto-resistive (GMR) head and includes at least one thin film sensor that has a “stripe-height” and resistance that must be precisely controlled. Traditionally, the precise sensor stripe-height is achieved through a lapping process. During the wafer process, a plurality of MR heads and a plurality of stripe-height sensors are interleaved and arranged in an orthogonal grid pattern. The size of the stripe-height sensor is usually much larger than the MR sensor, so that its dimensions can be made precisely.
A finished wafer is cut into rows. Each row contains a plurality of MR heads and a plurality of electronic lapping guides (ELGs). A surface of the row is then lapped to reduce the MR head stripe-height. By measuring the resistance of the stripe-height sensors, their stripe-height can be calculated precisely. Therefore, the stripe-height sensors are often called resistive lapping guides (RLGs) or ELGs. During lapping, the ELG stripe-heights are monitored frequently, so that inclination and bending of the row can be corrected by applying a suitable force or moment on the row. Provided that the difference (offset) between ELG stripe-height and MR read-head stripe-height is a constant, the read-head stripe-height can be controlled through the control of the ELG stripe-height. However, the offset between a narrow read-head and a wide LEG is neither precisely known, nor uniform Therefore, the resulting accuracy in read-head stripe-height is less than satisfactory.
Furthermore, a uniform stripe-height is not, alone, adequate. In a magnetic recording device, the electronic circuit is designed for specific read-head resistance. Due to variation in the read-head width and film resistivity across the wafer, a uniform stripe-height does not imply a uniform read-head resistance. Thus, it is strongly desirable to control the read-head resistance, instead of its stripe-height.
Accordingly, there is a need for an improved method and apparatus for providing a lapping guide in the production of MR heads.
SUMMARY OF THE INVENTION
According to an embodiment of the present invention, an integral lapping guide (ILG) is provided with at least one read-head and one rectangular ELG coupled in series. Two external leads are provided for measuring resistance across these components. In one embodiment, the read-head of the lapping guide is identical in structure to the actual read-heads (i.e., those to be included in the final product). The ELG width is selected to provide adequate range in stripe-height measurement. A large stripe-height offset between the read-head and the ELG is selected such that when the read-head resistance approaches the desired target value, the read-head resistance will be dominant over the ELG resistance.
The resistance of the ILG is approximately the sum of the read-head and ELG resistance. The resistance of the internal connections would be negligible. When the read-head stripe-height is large, the ILG resistance is predominantly that of the ELG. The stripe-height can be calculated simply and accurately by treating the read-heads as leads of the ELG. The ILG acts as an effective stripe-height sensor.
When the read-head stripe-height becomes small, the ILG resistance is dominated by the resistance of the read-head. Due to a large stripe-height offset between the ELG and the read-head, the ELG resistance is insensitive to stripe-height. The read-head resistance can be estimated by subtracting the ELG resistance from the ILG resistance. Since the ELG dimension is very large compared with the target stripe-height of the read head, the ELG resistance can be estimated accurately.
The ILG may be treated as a stripe-height sensor at a large stripe-height, and a resistance sensor at a low stripe-height. When the ILG is treated as a resistance sensor, the resistance should be converted into a pseudo stripe-height by approximation. A suitable method is provided according to an embodiment of the present invention that ensures smooth transition between the above two treatments. For example the ILG may be treated as both types of sensors at all times. Then a weighted average of ELG stripe-height and read-head pseudo stripe height can be obtained.
According to an embodiment of the present invention, a method is described to best utilize this structure. Instead of approximating the ILG has two distinct sensors at two extremes of the stripe-height, the ILG is approximated by a single model throughout the entire range of the stripe-height. A single formula may be derived to generate a pseudo stripe-height that approximates the ELG stripe-height when the latter is large, and approximately the read-head pseudo height when the latter is small. This method can be both simple and robust.
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Nguyen George
SAE Magentics (H.K.) Ltd.
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