Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-07-14
2003-04-01
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S603130, C029S603140, C029S603150, C029S603160, C029S603180, C360S119050, C360S122000, C360S125330
Reexamination Certificate
active
06539610
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to thin film inductive read-write heads for use in magnetic storage systems. More particularly, the present invention is directed to high throughput methods for the rapid production of thin film inductive read-write heads having very narrow write track widths, to inductive read write heads so produced, and to the associated apparatus and methods for their use.
2. Description of Related Art
In magnetic disk drives, data is written and read by magnetic transducers called “heads.” The magnetic disks are rotated at high speeds, producing a thin layer of air called an air bearing surface (ABS). The read and write heads are supported over the rotating disk by the ABS, where they either induce or detect flux on the magnetic disk, thereby either writing or reading data. Layered thin film structures are typically used in the manufacture of read and write heads. In write heads, thin film structures provide high areal density, which is the amount of data stored per unit of disk surface area, and in read heads they provide high resolution.
A thin film write head comprises two pole pieces, a top pole piece P
1
and a bottom pole piece P
2
. A write head generally has two regions, denoted a pole tip region and a back region. The pole pieces are formed from thin magnetic material films and converge in the pole tip region at a magnetic recording gap, known as the zero throat level, and in the back region at a back gap. The zero throat level delineates the pole tip region and back region. A write head also has two pole tips, P
1
T and P
2
T, associated with and extensions of P
1
and P
2
respectively. The pole tips, which are relatively defined in their shape and size in contrast to the pole pieces, are separated by a thin layer of insulation material such as alumina, referred to as a gap. As a magnetic disk is spinning beneath a write head, the P
2
pole tip trails the P
1
pole tip and is therefore the last to induce flux on the disk. Thus, the P
2
T dimension predominantly defines the write track width of the write head, and is generally considered an important feature.
The write track width, P
2
B, is especially important because it limits the areal density of a magnetic disk. A narrower track width translates to greater tracks per inch (TP
1
) written on the disk, which in turn translates to greater areal density. However, with present manufacturing methods for read-write heads, the ability to produce very narrow track widths is limited. These limitations will be further explained with reference to a specific type of inductive head. Inductive heads commonly employed at present are magnetoresistive (MR) sensors, which are highly sensitive to changes in magnetic flux on a disk written by inductive write heads. An MR sensor comprises a thin film layer sandwiched between bottom and top insulation layers, or gaps, which are in turn sandwiched between bottom and top shield layers, S
1
and S
2
. An MR head can read information on a magnetic disk with much narrower track widths an much higher fidelity than other known types of read heads. The apparent ability of MR sensors to read very narrow track widths may enable the use of narrow track width write heads and therefore lead to high areal densities. While this advantage has been sought through the use of photoresist frame plating and ion beam milling of write heads, manufacturing heads with very narrow P
2
B track widths remains a significant challenge.
A particular type of MR head is a merged MR head. A merged MR head uses the top shield S
2
of the MR head as the bottom pole P
1
of the write head. Thus, this layer is shared by each of the read and write heads. While merged MR heads have a high capacity for both reading and writing, they are limited in the narrowness of the track width they may utilize because they have been found to possess large side-fringing fields during recording. These fields are caused by differences in P
1
T and P
2
T widths. The fringing field, caused by flux leakage from P
2
to P
1
beyond the width of P
2
, is the portion of the magnetic field which extends toward the tracks adjacent to the tracks being written. The fringing fields require lower TP
1
in order not to impinge adjacent tracks, thereby limiting the achievable areal density.
Prior art practitioners have sought to reduce fringing fields in merged MR heads. Typically, this involves manufacturing heads with vertically aligned P
1
T and P
2
T side walls. A method exemplary of one which addresses this issue is found in U.S. Pat. No. 5,438,747, entitled “Method of Making a Thin Film Merged MR Head With Aligned Pole Tips,” incorporated herein by reference. Manufacturing techniques directed to achieving P
1
and P
2
pole tips of substantially similar widths do effectively reduce the fringing field. However, they may be unfortunately limiting in their ability to produce substantially narrow P
2
B track widths. Therefore, while the capacity for high areal density is preserved through manufacturing methods which are aimed at reduction of fringing fields, it may actually be hampered by those same manufacturing methods which place an undesirable lower limit on the size of P
2
B write head track width. Furthermore, they produce an additional manufacturing burden in the form of cleanup of redeposited material, which translates to greater time and higher production costs.
Other MR head manufacturing methods have addressed the issue of reducing the write track width. An example is U.S. Pat. No. 5,726,841 entitled, “Thin Film Magnetic Head With Trimmed Pole Tips Etched by Focused Ion Beam for Undershoot Reduction,” incorporated herein by reference. While the use of a focused ion beam tool (FIB) may effectively produce a narrow P
2
B track width, the technique would be performed a separate time for each head. In typical manufacturing processes which develop more than 20,000 heads per wafer, use of FIB is not feasible.
As previously mentioned, other methods for manufacturing heads with vertically aligned pole tip side walls include forming the P
2
pole tip either by photoresist frame plating or ion beam milling. In these cases, the P
2
T is plated with additional thickness as it is used as a mask during the processing which trims the pole tip width, removing pole tip thickness in the process. Sufficient pole tip thickness must be retained throughout the milling process for a pole tip to have a suitable aspect ration. Aspect ratio is the thickness/width of a pole tip, and should generally be greater than about 2. The width of the pole tip P
2
B that may be fabricated by present methods is limited, then, by the amount of pole tip thickness that may be lost during pole tip width milling. This, and other limitations inherent to current manufacturing technology, reates significant challenges in the production of very narrow pole tip read/write heads.
SUMMARY OF THE INVENTION
It is a purpose of the present invention to improve the current limitations known in read-write head track widths incurred by practical limitations of current manufacturing methods. Specifically, an object of the present invention is to improve write head track width by nearly an order of magnitude.
The invention utilizes a preliminary milling step before standard P
1
notching in order to create a P
2
B track width that is substantially sub-micrometer and narrower than that which could previously be realized. Larger amounts of P
1
material may then be removed during P
1
milling procedures, the write track dimension having already been reduced.
It is a further object of the invention to produce the narrow write track heads by a method that enables high throughput manufacturing. A preliminary milling step may be utilized on a wafer in a high throughput manufacturing system, wherein the write track width P
2
B may be milled to a very narrow dimension before it is divided into multiple heads. The invention thereby enables a novel application of a preliminary precision milling step to substantially reduce the w
Kim John I.
Lo Jyh-Shuey (Jerry)
Moran Timothy J.
Arbes Carl J.
Feece Ron
Kim Paul
Oppenheimer Wolff & Donnelly LLP
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