Dynamic magnetic information storage or retrieval – Head – Gap spacer
Reexamination Certificate
2001-07-27
2004-04-13
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Head
Gap spacer
C360S125020, C360S125330
Reexamination Certificate
active
06721129
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to magnetic heads in disk drives, and more particularly to magnetic write heads configured to write data at high data rates.
2. Description of the Related Art
Prior art magnetic write heads have serious impediments for writing data at today's ever-increasing high data rates. Such write heads either cannot produce enough magnetic flux within the short cycle times available during high frequency operation to write sufficiently to a storage medium or, if structurally compensated to produce enough flux to write sufficiently during high frequency operation, they tend to produce excessive flux during low frequency operation such as to cause undesirable side-writing or adjacent track interference (ATI).
To illustrate,
FIG. 1
is a planar view of a conventional magnetic write head
100
for writing to a storage medium, such as a disk
102
, wherein the driving coil is omitted from the diagram for clarity. Write head
100
is made from pole pieces which form a write gap
104
at an air bearing surface (ABS), where magnetic flux is produced for writing data to disk
102
. Write head
100
has a flare point
106
and a flare angle
108
with dimensions that may not be sufficient for writing at high data rates. That is, the magnetic flux that can be produced at write gap
104
within the short cycle times available during high data rate operation is not sufficient to write data to disk
102
, especially at today's high level of disk coercivity (e.g., 4000 Oersteds or greater).
In
FIG. 2
, a magnetic write head
200
which is configured to sufficiently write data to disk
102
at high data rates is shown. The high data rate may be, for example, one that is greater than or equal to 500 MHz. Similar to write head
100
of
FIG. 1
, write head
200
has a flare point
206
and a flare angle
208
. However, so that write head
200
can sufficiently write at a high data rate, flare point
206
of write head
200
is shorter in length than flare point
106
of write head
100
(i.e., the flare point is closer to the ABS), and/or flare angle
208
of write head
200
is greater than flare angle
108
of write head
100
. For example, flare point
106
of write head
100
is 1.0-1.5 &mgr;m whereas flare point
206
of write head
200
is 0.5-1.0 &mgr;m, and flare angle
108
of write head
100
is 30° whereas flare angle
208
of write head
200
is 60°.
Although write head
200
is capable of producing adequate flux to write at high data rates, it may produce excessive flux when writing at low data rates which tends to cause undesirable side-writing and interference on disk
102
. This is because the magnetic materials making up the pole pieces (i.e., the wide magnetic core or “yoke” in the back, and the relatively narrow pole tips in the front) have a magnetic permeability that is frequency-dependent and decreases as the operating frequency increases. Put another way, the efficiency of a conventional write head is much better at low frequencies than it is at high frequencies. This phenomenon will be referred to herein as “efficiency roll-off” of the write head.
To further illustrate this low frequency situation,
FIG. 3
shows a pole tip view of write head
200
of
FIG. 2
which reveals a pole piece
302
(e.g., P
2
) and a pole piece
304
(e.g., P
1
) forming write gap
204
. In this example, write head
200
is writing data at a low data rate where magnetic fluxes
306
are undesirably produced excessively in areas away from write gap
204
. This is likely to cause interference to other data written on adjacent tracks on disk
102
. Unfortunately, write head
200
may therefore not be usable since it will overwrite and erase where it should not be doing so, resulting in a large erase-band and high level of ATI. This problem is only exacerbated by today's required high recording density and, in particular, a large number of tracks-per-inch. For example, today's high recording density is greater than 50 kilotracks per inch (KTPI).
Referring to
FIGS. 4A-4C
, timing diagrams related to the production of magnetic flux at write gap
204
of write head
200
of
FIG. 2
are shown. These diagrams help to illustrate the interference issues that must be considered when using the geometry of high-frequency write head
200
. More particularly,
FIG. 4A
is a timing diagram for high frequency operation;
FIG. 4B
is a timing diagram for low frequency operation; and
FIG. 4C
is a timing diagram for DC operation (lowest frequency=0 MHz which is typical for data erasure). The binary write current sequencing scheme used throughout
FIG. 4
is represented in the well-known Non-Return-to-Zero (NRZ) format, where “1” represents one current or magnetization direction and “0” represents the opposite direction.
In
FIG. 4A
, a data signal
402
represents high speed data in binary form (‘1’ for binary one and ‘0’ for binary zero) to be written to disk
102
, and a flux signal
404
represents magnetic flux which appears at write gap
204
of write head
200
to write the high speed data to disk
102
. As illustrated, data signal
402
reflects the binary write current sequence “10101010” to be written to disk
102
. Data signal
402
has a frequency for writing data to disk
102
at a high data rate, which may be any suitable data rate that is higher than the nominal rate or average rate of writing using write head
200
. This high data rate may be the maximum operating frequency of write head
200
, which exists when bit transitions (“1” to “0” or “0” to “1”) occur for each one of a plurality consecutive cycles. The high data rate may be, for example, 500 MHz or greater, or even 1 GHz or greater. As a result of writing at the high data rate, flux signal
404
peaks at a high data rate flux level, which is desirably lower than a maximum flux level beyond which excessive side-writing and interference with other data tracks on disk
102
would tend to occur.
In
FIG. 4B
, a data signal
406
represents low speed data in binary form to be written to disk
102
, and a flux signal
408
represents the magnetic flux which appears at write gap
204
of write head
200
to write this low speed data to disk
102
. As illustrated, data signal
406
reflects the binary write current sequence “11001100” to be written to disk
102
. In contrast to data signal
402
of
FIG. 4A
, data signal
406
of
FIG. 4B
has a frequency for writing to disk
102
at a low data rate, which may be any suitable data rate that is less than or equal to the nominal rate or average rate of writing using write head
200
. This particular example reflects a data rate that is half of the high data rate described in relation to FIG.
4
A. Referring to the previous example of
FIG. 4A
, the low data rate may be 250 MHz or less. As a result of writing at this low data rate, flux signal
408
may peak at or exceed the maximum flux level, beyond which excessive side-writing and interference with other data on disk
102
tends to occur. In
FIG. 4C
, a data signal
410
illustrates DC operation (binary data sequence of “11111111”) which also causes flux signal
412
to peak or exceed the maximum flux level at which interference tends to occur.
For a write head that has been structurally compensated for high data rates, excessive flux generation during low data rate operation is very likely to happen. This is due to the efficiency roll-off phenomenon previously referred to: a write head configured to have good efficiency at a high data rate will have an even higher—perhaps even excessively higher—efficiency at a low data rate.
Thus, as shown and described in relation to
FIGS. 2-4
, a write head that is geometrically configured so that sufficient flux is produced during high data rate operation tends to cause excessive side-writing or ATI during low data rate or DC operation. Accordingly, what is needed is a magnetic head that has the ability to write data at high data rates but also produces minimal interference when writing data a
Figueroa Natalia
Hudspeth David
Oskorep John J.
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