Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-11-02
2004-10-05
Ometz, David (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S320000
Reexamination Certificate
active
06801408
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 areal density, it is desirable to reduce the thickness of the insulative gap layers to optimize head sensitivity. Although reducing the thickness of the gap layers improves sensitivity by reducing the distance between the sensor and the shield, it also allows lead structures, deposited lateral 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 shield-to-shield spacing is not as critical away from the sensor element, it is not necessary to have a thin gap in the areas away from the sensor element. As such, to reduce shorting, extra gap layers typically are deposited over the gap layers, at areas apart from the location of the sensor element. This increases the gap thicknesses in the regions about the sensor element, and as such, reduces the occurrence of shorting between the lead structures and the shields.
An example of such a 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
and about a void
35
. Placed over the extra gap layers
30
and the shield
20
is a first gap layer
40
. Then, above the first gap
40
is a sensor layer
50
, which includes leads
54
. A cavity
60
is defined by the deformed shape of the sensor layer
50
, caused by the void
35
. Although the use of the extra gap layer
30
reduces shorting between the leads
54
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 15 Kilo tracks per inch and areal densities greater than about 7 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 within the cavity
60
.
Typically, photoresist thickness is controlled by spinning the workpiece to reduce the thickness of the photoresist. As the cavity
60
width and photoresist thickness is reduced, however, the surface tension of the photoresist causes a pool to form within the cavity
60
. The pooling makes the photoresist resistive to change in its thickness. As such, it is very difficult to control photoresist uniformity across the workpiece and to control the thickness of any small photoresist structure formed within the cavity
60
.
Because the track width of the sensor is directly related to the thickness of the photoresist used to define the sensor, the lack of photoresist uniformity causes a similar problem in controlling track widths. The resulting high variation in sensor track widths causes a significant number of devices to have track widths outside the manufacturing tolerances. Thus, the lack of photoresist uniformity caused by deposition over the cavity
60
results in a high rate of loss of devices during manufacture.
An another example of a sensor with increased gap thicknesses 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 areal density.
One approach to solve the problems associated with the use of extra gap material, involves etching the shield on either side of the sensor location to receive the deposition of the 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, with a minimum of width variation 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 a planar sensor element and an extra gap layer, and a method of fabrication thereof. The apparatus of the invention is a read sensor which includes a shield, a planar sensor element, a read gap positioned between the shield and the sensor element, and an extra gap positioned between the shield and the sensor element, and positioned adjacent the read gap. The sensor element is positioned in a sensor layer. With the sensor element and the shield separated by only the relatively thin gap layer, high sensitivity of the sensor element is obtained. Further, by placing the relatively thick extra gap between the shield and the sensor layer, and about the sensor element, the potential for shorting between the shield and the sensor layer is minimized. The shield can be planarized to provide a substantially planar read gap and sensor layer at, and about, the sensor element. This, in turn, results in improved control of sensor track widths by greatly reducing the potential for pooling of photoresist during fabrication of the read sensor.
By having the portion of the sensor layer containing the sensor element substantially planar, track width manufacturing variations are minimized. This is because the present invention eliminates the need to deform the sensor layer, as occurred in the prior art when the sensor layer had to be deposited over a cavity. That is, track width variations are reduced by positioning the sensor layer upon a substantially planar read gap layer. The read gap layer can be made substantially planar by laying it on a planarized upper surface of the shield.
The read gap is sufficiently wide to fully separate the sensor element from the shield. The read gap has edges on each of its sides. The extra gap is positioned generally adjacent to the read gap and the sensor element, and extends laterally therefrom. Preferably, the extra gap overlaps the edges of the read gap to assure electrical insulation between the sensor layer and the shield. In this manner, the sensitivity of the sensor element is maximized by pl
Barr Ronald A.
Chen Yingjian
Tong Hau-Ching
Haynes Beffel & Wolfeld LLP
Ometz David
Western Digital (Fremont) Inc.
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