Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-05-26
2002-12-17
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06496334
ABSTRACT:
BACKGROUND
Typical thin film read heads are located between shields. The shields improve head performance by shielding stray magnetic flux from the sensor element. Gap layers electrically insulate the shields from the sensor element and from abutting lead structures.
As read head structures become smaller to improve aerial density, it is desirable to reduce the thickness of the insulative gap layers to optimize head linear density. Although reducing the thickness of the gap layers improves linear density by reducing the distance between the sensor and the shield, it also allows lead structures which are deposited laterally to the sensor element, to more easily short to the shields. Such shorting can be due to flaws in, or degradation of, the gap material, or by defects created during the fabrication process. For example, a pinhole in the gap material can allow current to flow from a lead element to the shield.
Because the sensor-to-shield spacing is not as critical in areas away from the sensor element, it is not necessary to have a thin gap in such areas. As such, to reduce shorting, typically extra gap layers are deposited over the gap layers in areas away from the sensor element. This greatly increases the overall gap thickness in these areas. As a result, a reduction in the occurrence of shorting between the lead structures and the shields is achieved.
An example of such an extra gap structure is shown in FIG.
1
. In this device the read head
10
has a shield
20
with extra gap layers
30
placed over the shield
20
about a void
35
. Over the extra gap layers
30
and the shield
20
is the first gap layer
40
. Then, above the first gap
40
is a sensor layer
50
. A cavity
60
is defined by the deformed shape (caused by the void
35
) of the sensor layer
50
. Although the use of the extra gap layer
30
reduces shorting between the leads
54
of the sensor layer
50
and the shield
20
, the present inventors have found such structures difficult to reliably manufacture with submicron track widths. Sub-micron track widths are necessary for high track density applications greater than about 42 Kilo tracks per inch and aerial densities greater than about 20 Giga bits per square inch.
Because of the uneven surface created by laying the first gap layer
40
and sensor layer
50
over the void
35
and the relatively small width W of the cavity
60
, variations in the track widths of the sensor element
52
of the sensor layer
50
tend to occur. These track width variations are due to the inherent variations in the width W and depth H of the cavity
60
and the effect the dip of the cavity
60
has on controlling the flow of the photoresist (which tends to pool in the cavity) used to etch the sensor layer
50
and define the track width of the sensor element. In addition, as the thickness of the photoresist is reduced to provide small structures, it is very difficult to adjust the thickness of the photoresist within the cavity
60
.
Typically, photoresist thickness is controlled by spinning the workpiece to reduce the depth of the fluid photoresist. As the width of the trench and thickness of the photoresist are reduced, the surface tension of the photoresist tends cause pooling within the trench. This makes the photoresist resistive to any changes in its thickness. Which in turn makes it difficult to control photoresist uniformity across the workpiece and to control the thickness of any small photoresist structure formed within the cavity
60
. This lack of thickness uniformity, and the resulting high variation in track width, cause a high rate of loss of devices during manufacture.
An another example of a sensor with increased gap thicknesses at areas away from the sensor, is the sensor disclosed in U.S. Pat. No. 5,568,335, by Fontana, et al., issued Oct. 22, 1996, entitled MULTI-LAYER GAP STRUCTURE FOR HIGH RESOLUTION MAGNETORESISTIVE READ HEAD, herein incorporated by reference in its entirety. In this device, the extra gap layer is deposited over the gap layer lateral to and away from the sensor element. It has been found that this type of structure is also difficult to reliably manufacture with submicron track widths. Therefore, such structures, while improving reliability of the read heads, prove to be an impediment to obtaining high aerial densities.
One approach to solve the problems associated with the use of an extra gap material, involves etching the shield on either side of the sensor location so to receive a later deposited extra gap layer. This approach is advantageous as it avoids a deformed sensor layer by providing a relatively flat and smooth surface for the application of the sensor layer. An example of this approach is disclosed in U.S. patent application Ser No. 09/325,104 by Knapp, et al., Filed: Jun. 3, 1999, entitled DATA STORAGE AND RETRIEVAL APPARATUS WITH THIN FILM READ HEAD INSET EXTRA GAP INSULATION LAYER AND METHOD OF FABRICATION, herein incorporated by reference in its entirety. Although this approach significantly reduces the variations in track widths associated with the prior methods, some measure of sensor to shield shorting still may still occur. This shorting is typically due to the fencing of material at the edges of the extra gap layer. This fencing can cause shorts by providing connections between the shield and the sensor leads.
Therefore, a need exists for a narrow gap read sensor, and method of fabrication thereof, which provides sufficiently small read track widths (e.g. 0.25&mgr;-0.50&mgr;), having a minimum of variation in the width over a series of such sensors, and which sensor to shield shorting is significantly reduced or effectively eliminated.
SUMMARY
The present invention provides a thin film read head having planarized extra gap and shield layers and a method of fabrication thereof. The apparatus of the invention is a read sensor which includes a shield, a sensor element, an extra shield positioned between the shield and the sensor element, an extra gap set between the shield and the sensor and adjacent the extra shield, and a gap layer which is located between the sensor element and the extra shield. The sensor element is positioned in a sensor layer.
The extra shield is typically positioned adjacent (e.g. below) the sensor element, with the extra gap positioned about the extra shield and lateral to the sensor element. By making the extra shield somewhat wider than the sensor element, the potential for shorting is minimized by placing both the gap and the extra gap, between the majority of the sensor leads, and the shield. At the same time, the linear density of the sensor element is maximized by placing only the thinner gap layer between the sensor element and the extra shield.
In at least one embodiment, variations of the width of sensor element during manufacture are minimized by having the sensor layer substantially planar. This is achieved by positioning the sensor layer upon a substantially planar gap layer. The gap layer in turn is planar as the upper surfaces of the extra gap and extra shield lie substantially in a common plane (the upper surfaces are substantially flat and aligned with one another). Preferably, the extra gap and extra shield are commonly planarized.
Preferably the shield and the extra shield are a plated nickel iron (NiFe) and the extra gap and the gap layer are alumina (Al
2
O
3
). Also, the extra shield and extra gap are each about 1000 Å thick and the gap layer is between about 300 Å thick and about 700 Å thick. Further, the upper surface of the shield is sufficiently rough to substantially prevent delamination of the extra gap from the shield.
In at least one embodiment, the invention includes a data storage and retrieval apparatus which includes a magnetic recording media, a head assembly located adjacent to the magnetic recording media, and a motor coupled to the media so as to move the media with respect to the head assembly. The head assembly in turn includes a write head and a read head. The read head includes a shield, a sensor element, an extra shield set betw
Dong Zi-Wen
Hsiang Joyce
Lin Kevin
Pang Song
Tong Lijun
Letscher George J.
Read-Rite Corportion
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