1. Field of the Invention
The present invention relates to read/write heads for reading and writing digital data to storage media such as magnetic disks. More particularly, the invention concerns a read/write head with a unique embedded planar dual coil structure, and a process for manufacturing such a head.
2. Description of the Related Art
In this modern information age, there is a tremendous volume of electronic data for people and computers to manage. The management requirements not only involve transmission, receipt, and processing of this information, but storage of the data as well. And, with more data to store, computer users are demanding extremely high capacity digital data storage devices. One of the most popular data storage devices is the magnetic disk drive system, also known as a "hard drive."
In magnetic disk drives, one of the most critical components is the read/write head. Read/write head characteristics ultimately determine how densely, quickly, and accurately data can be written to magnetic disk media. As a result, engineers are continually developing better and better read/write heads. Two of the chief areas of focus in read/write head development are data storage density ("areal density"), and read/write speed. In this respect, one improvement in the signal storage ability of read/write heads has been the use of two write coils. This has been shown to significantly improve the strength and efficiency of the data storage.
FIG. 1 shows a partial cross-sectional view of an exemplary dual write coil read/write sensor 100, with the slider's deposit end ("trailing") being shown at 103, and the air bearing surface shown 101. The leading edge (not shown) resides in the direction 105. The sensor 100 is built upon a slider 102, beginning with an undercoat 104. Upon the undercoat 104 lies a first shield 106, known as "S1," followed by first and second gap layers 108, 110. Between the gap layers 108, 110 lies a magneto resistive ("MR") stripe 107. Upon the gap layer 110 lies a combination shield/pole 112 known as "S2/P1." The shield 106, MR stripe 107, and shield/pole 112 cooperatively form a magneto resistive read head 113 of the read/write sensor.
A write gap layer 113 is built upon the shield/pole 112, followed by an organic insulating layer 114. Upon the insulating layer 114 is based a first write coil 116, which includes a conductive coil embedded in an organic insulating material that is applied to fill the spacing between coil turns and separate the first coil layer from a second coil layer to follow. The second write coil 118 is layered on top of the first write coil 116, and similarly includes insulating material applied to fill the spacing between coil turns. A second pole 120, known as "P2," lies atop the second write coil 118. After fabricating the second write coil layer 118 and its insulation, a plating seed layer (not shown) is deposited, followed by a photo lithography process that defines the shape of the second pole 120. The "track width" constitutes the width of the second pole 120 (in a direction perpendicular to the page depicting FIG. 1) at the air bearing surface 101. Track width determines the track density on the disk where bits are written to and read from. The second pole 120 is protected by an overcoat layer 122. The shield/pole 112, write coils 116/118, write gap 113, insulation layer 114, and second pole 120 provide the write head 123 aspect of the read/write sensor 100.
One drawback of the sensor 100 is the severe topography created by the substantial height of the coil layers 116, 118 and insulation layer 114. This topography is severe because it presents a significant curvature beneath the pole 120, instead of a normally flat surface. In a two coil layer structure with organic insulation, the height of this structure can be as great as ten microns. This great height makes it extremely difficult to define the second pole 120, especially when a narrow track width is required, for the following reasons. The track width corresponds to the dimension of the second pole 120 in a direction perpendicular to the view of FIG. 1 (i.e., into the page). When track width is extremely narrow, there is a high "aspect ratio," defined as the ratio of the second pole's width (track width) to its length (from right to left in FIG. 1). Normally, when track width is larger than the second pole's length, no difficulty is presented for creating the pole 120 with known photo lithography processes. However, with the dual coil structure of FIG. 1, the second pole 120 exhibits a high aspect ratio, rendering photo lithography difficult or impossible. Moreover, this difficulty increases dramatically with more severe topographies, especially with today's track widths, which are frequently in the submicron range. In some cases, this difficulty may be so great that fabrication of the desired write head may be impossible.
Another drawback of the arrangement 100 is the amount of organic insulation present in the head. As mentioned above, organic insulation is present around the write coils 116, 118 as well as the insulating layer 114. The organic insulating material is typically a polymeric material. During operation, the write head is heated from current passing the coils. Organic insulation has a lower thermal conductivity than dielectric materials in the head, such as silicon-oxygen and aluminum-oxygen based materials. This low thermal conductivity impedes heat dissipation, causing the temperature of the write head to increase. Increased operating temperatures have various undesirable effects, such as decreasing head life. Furthermore, due to the organic insulation's relatively high thermal expansion coefficient, the organic insulation responds to the heat by expanding more than the nearby layers of the head. This expansion may cause portions of the head to protrude from the normally flat air bearing surface 101. With the head now enlarged by the protrusions, the head's effective flying height is smaller, and there is a greater danger of the head contacting the storage surface. Such contact may cause further heating of the head, or a disastrous head crash in extreme cases. To avoid head/disk contact, a higher flying height is necessary between the head and disk surface. However, with a higher flying height, signals stored by the write head are weaker, and require more surface area to safely store adjacent signals that are distinguishable from each other. Thus, the protrusion due to the presence of the organic insulation ultimately lowers the areal density of stored signals, diminishing the disk drive's storage capability.
In view of the foregoing, then, the structure and fabrication of known dual coil write heads present a number of unsolved problems.