Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-03-11
2004-06-29
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C360S123090
Reexamination Certificate
active
06757134
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to magnetic head assemblies applicable to magnetic disk drive systems. More particularly this invention relates to high data rate, high efficiency, inductive, thin film heads.
BACKGROUND OF THE INVENTION
Magnetic transducers (read-write heads) are used for reading and writing magnetically coded data stored on a magnetic storage medium such as a magnetic tape or magnetic disk. In a disk drive system
8
, as seen in
FIG. 1
, a magnetic read-write head
10
is attached to an actuator
12
that flies above a rotating magnetic disk
14
. A voice coil motor (VCM)
16
pivots the actuator to position the head
10
over selected circular tracks on the disk
14
. The actuator rides on an air-bearing surface over the rotating disk. The disk
14
is attached to a spindle
18
that is rotated by a spindle motor. The disk
14
comprises a substrate having a plurality of thin films deposited thereon. The thin films include ferromagnetic material that is used to record the magnetic transitions, written by the magnetic transducer
10
, in which information is encoded. A tape based storage system uses a magnetic transducer in essentially the same way as a disk drive with the moving tape being used in place of a rotating disk.
The magnetic transducer is composed of elements that perform the tasks of writing magnetic transitions and reading the magnetic transitions. In that way, the magnetic transducer is composed of a write-head and a read-head. The electrical signals to and from the read and write heads travel along conductive paths, which are attached to or embedded in the actuator.
A thin film recording head (write head) includes first and second pole pieces that are magnetically coupled together at the “pole tip region” and the “back gap”. In the pole tip region, the first and second pole pieces provide first and second pole tips. The pole pieces are typically fabricated using plating techniques. A thin insulative, nonmagnetic gap layer separates the pole tips. The pole tip region is defined by a head surface in what is referred to as the “zero throat height” between the air bearing surface (ABS) and the back gap. A yoke, or body portion of the head lies between zero throat height and the back gap. The term back gap is used in the art to mean the back of the yoke. Historically, there was a gap in the back of the yoke and the term back gap continues to be used even though the back of the yoke is now continuous. The back gap is also, more accurately, referred to as the “back flux closure.” The body portion of the head contains one or more layers of pancake coils and plurality of insulation layers. The pancake coils couple flux into the pole pieces and/or receive flux there from. Each layer of the head is applied using photolithographic techniques such as photo-resist exposure systems.
There is a continuing strong felt need to increase the data storage density in magnetic storage media. Most efforts to increase magnetic storage density involve techniques for increasing the aerial bit density of the magnetic medium.
In rotating magnetic disk drive systems, the aerial density is the product of the number of flux reversals per millimeter along a data track and the number of tracks available per millimeter of disk radius. Thus, a high aerial data storage density requires recording heads with high linear resolution and a narrow track well.
The thickness of the gap layer at the head's air-bearing surface determines the linear density of the head, namely how many bits per linear unit length along a data track of a magnetic medium the head can write. The width of the second pole tip determines head track width. The head track width establishes how many data tracks across the width of a magnetic medium per unit length the head can write. The product of these two factors is aerial density.
One way to increase the data rate of a head is to decrease the pitch of the coil layer. The pitch is the distance across one turn of the coil plus one space between the turn and the next turn. It would be desirable for the coil to have a pitch of 1 micrometer (um) or less. Unfortunately, when the data rate is increased with a low pitch coil, the head suffers from an increase in heat and an increase in eddy currents between the first and second pole pieces. Eddy currents reduce the write current, which in turn reduces the write signal across the write gap. One way to reduce eddy currents in the write head is to employ two coil layers which are stacked one above the other, which allows for a shorter write head. However, when designing a head with two layers of coils certain extra steps need to be taken in order to minimize increased sensitivities inherent in such a structure. For example, there is an increased need to planarize and protect the coil layers.
Inductive heads, especially the ones having very high recording densities, have to use full planarization techniques when manufacturing the thin film layers in order to obtain maximum efficiency from the imaging systems used to produce the heads. Independent of the photo-resist exposure system used in the fabrication of the critical photo-resist layers, each layer needs to have a reproducible photo-resist coating thickness as well as a very tight focal plane (which means a small total indicated run-out). Such basic requirements are in order to produce a tight control and resolution. Two of the most critical structures for effectiveness of the inductive head are the magnetic pole (which defines the track width available for the magnetic recording media) and the inductive coil system. While the poles control the aerial recording densities, the size and shape of the coils, together with the basic head design, control the efficiency and speed of the recording head.
There is a need for a head design and a method to produce such a head, which produces a high-density, high data rate head with high magnetic recording efficiency. Such a design can be used with heads designed having a pedestal to improve efficiency as disclosed in commonly owned U.S. Pat. No. 6,259,583, hereby incorporated by reference.
Inductive head designs need to use planarization techniques in order to produce high-resolution coils and poles. The pole fabrication process does not face planarization issues since the pole piece is an isolated structure. However, there are basic problems that arise in planarizing the coils since the coils comprise a plurality of metalized lines.
FIG. 2
illustrates an example of the problems that arise in providing planarization of the already formed coil structure during the manufacturing of a readwrite head. The read portion of the head
20
comprises a first shield (S
1
)
21
, insulation layers
23
that surround a sensor element
22
, and a second shield (S
2
)
24
. In the merged head that is shown, the second shield also serves as a first pole piece (P
1
)
24
(referred to as S
2
/P
1
). A coil
26
is deposited on a layer of Al
2
O
3
, referred to as alumina (or sapphire)
28
, which is used to insulate the coil from P
1
. The coil comprises a plurality of loops or turns
29
of conductive material (such as copper) with voids
30
in between the loops. Referring to
FIG. 2
b
, the next step in the manufacturing process is the fabrication of the pedestal
31
(when used) and back flux closure (back gap)
32
using NiFe (or other ferromagnetic material) atop the S
2
/P
1
24
after etching the alumina layer
28
.
As shown in
FIG. 2
c
, prior art head designs use alumina (Al
2
O
3
)
34
as the filler for the coils
26
. Alumina is preferred because it provides good thermal conductivity as well as structural rigidity. Alumina also provides minimum protrusion and has a small expansion coefficient. However, the preferred high data rate head designs call for a very small separation for the high-resolution coil metal loops. For 1-micrometer pitch coils, the separation between loops can be as small as 0.2 micrometers. For such coils where the filler had been just alumina, the alumina sputtering system is incapable of compl
Evans Jefferson
Feece Ron
Hitachi Global Storage Technologies - Netherlands B.V.
Klein Esther E.
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