U.S. patent application number 10/193514 was filed with the patent office on 2004-01-15 for method and apparatus for determining the magnetic track width of a magnetic head.
Invention is credited to Cheng-I Fang, Peter, Lin, Zhong-Heng, Tin-Lok Lam, Terence.
Application Number | 20040010391 10/193514 |
Document ID | / |
Family ID | 30000038 |
Filed Date | 2004-01-15 |
United States Patent
Application |
20040010391 |
Kind Code |
A1 |
Cheng-I Fang, Peter ; et
al. |
January 15, 2004 |
METHOD AND APPARATUS FOR DETERMINING THE MAGNETIC TRACK WIDTH OF A
MAGNETIC HEAD
Abstract
A method of determining a magnetic track width of a magnetic
head is disclosed. The method begins by obtaining a full track
profile of the magnetic head which includes a plurality of signal
amplitudes read across a track of a magnetic disk at a plurality of
magnetic head positions. An initial magnetic track width value is
then determined from the full track profile data. Preferably, this
initial value is the magnetic write width which is determined based
on the difference between left and right head positions which read
half of the maximum signal amplitude. To determine the final
magnetic write width, the initial value is adjusted with side
reading correction values. The side reading correction values are
determined based on left and right side reading "tails" of a
bell-shaped signal curve which is formed by the full track profile
data when graphed. It is not necessary to obtain the microtrack
profile to determine these side reading values. Off track read
capability (OTRC) and erase band width (EBW) values determined by
the triple track test can also be corrected.
Inventors: |
Cheng-I Fang, Peter; (San
Jose, CA) ; Tin-Lok Lam, Terence; (Cupertino, CA)
; Lin, Zhong-Heng; (Santa Clara, CA) |
Correspondence
Address: |
ATTN: John J. Oskorep
One Magnificent Mile Center
Suite 1400
980 N. Michigan Avenue
Chicago
IL
60611
US
|
Family ID: |
30000038 |
Appl. No.: |
10/193514 |
Filed: |
July 11, 2002 |
Current U.S.
Class: |
702/155 ;
G9B/20.01; G9B/5; G9B/5.024; G9B/5.145 |
Current CPC
Class: |
G11B 20/10009 20130101;
G11B 5/00 20130101; G11B 5/012 20130101; G11B 5/4886 20130101; G11B
2005/001 20130101; G11B 2005/0016 20130101; G11B 5/455
20130101 |
Class at
Publication: |
702/155 |
International
Class: |
G06F 015/00 |
Claims
What is claimed is:
1. A method of determining a magnetic write width of a magnetic
head, comprising: obtaining full track profile data for the
magnetic head; determining an initial write width value from the
track profile data; determining one or more side reading correction
values from the full track profile data; and adjusting the initial
write width value with the one or more side reading correction
values for determining the magnetic write width.
2. The method of claim 1, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a track of a magnetic disk at a plurality of magnetic head
positions.
3. The method of claim 1, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a track of a magnetic disk at a plurality of magnetic head
positions; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; and wherein the act of determining the one
or more side reading correction values comprises analyzing side
reading tail data from the bell-shaped signal curve.
4. The method of claim 1, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a track of a magnetic disk at a plurality of magnetic head
positions; wherein the act of determining the initial write width
value comprises the further acts of: identifying a maximum value in
the plurality of signal amplitudes; and finding a difference
between left and right magnetic head positions that correspond to
half of the identified maximum value.
5. The method of claim 1, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a track of a magnetic disk at a plurality of magnetic head
positions; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; wherein the act of determining the initial
write width value comprises determining a magnetic write track
width MWW.sub.FTP which includes the further acts of: identifying a
maximum value in the plurality of signal amplitudes; identifying
left and right side magnetic head positions X.sub.L1 and X.sub.R1
that correspond to half of the identified maximum value; finding a
difference .DELTA.X.sub.1 between X.sub.L1 and X.sub.R1;
determining a magnetic read width MRW.sub.FTP by: determining left
and right best-fit lines along on left and right sides of the
bell-shaped signal curve, respectively; identifying, along the left
and the right best-fit lines, left and right side magnetic head
positions X.sub.L2 and X.sub.R2 that correspond to a magnetic head
signal level of zero; finding a difference .DELTA.X.sub.2 between
X.sub.L2 and X.sub.R2; and finding a difference between
.DELTA.X.sub.2 and MWW.sub.FTP.
6. The method of claim 1, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a track of a magnetic disk at a plurality of magnetic head
positions; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; determining left and right best-fit lines
along left and right sides of the bell-shaped signal curve,
respectively; wherein the act of determining the initial write
width value comprises determining a magnetic write track width
MWW.sub.FTP; determining a magnetic read width MRW.sub.FTP from the
full track profile data; wherein the act of determining the one or
more side reading correction values, C.sub.SRL and C.sub.SRR,
comprises the further acts of: identifying left and right magnetic
head positions S.sub.L and S.sub.R, respectively, that correspond
to where left and right side reading tails of the bell-shaped curve
begin to deviate from the left and the right best-fit lines;
determining C.sub.SRL=.DELTA.Y.sub.L/a.sub.L and
C.sub.SRR=.DELTA.Y.sub.R- /a.sub.R, where:
.DELTA.Y.sub.L=A.sub.L(S.sub.L)-(.differential.A.sub.L+.d-
ifferential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.-
A.sub.L+.differential.A.sub.R)/2,
.differential.A.sub.L=A.sub.L(S.sub.L)-A- .sub.L(S.sub.L-X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub- .R+X),
A.sub.L and A.sub.R are signal amplitudes corresponding to
particular magnetic head positions, a.sub.L and a.sub.R are slopes
of the left and the right best-fit lines, respectively, and
X=(MWW.sub.FTP-MRW.sub.FTP)/2.
7. The method of claim 1, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a track of a magnetic disk at a plurality of magnetic head
positions; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; wherein the act of determining the initial
write width value comprises determining a magnetic write track
width MWW.sub.FTP which includes the further acts of: identifying a
maximum value in the plurality of signal amplitudes; identifying
left and right side magnetic head positions X.sub.L1 and X.sub.R1
that correspond to half of the identified maximum value; finding a
difference .DELTA.X.sub.1 between X.sub.L1 and X.sub.R1;
determining a magnetic read width MRW.sub.FTP by: determining left
and right best-fit lines along left and right sides of the
bell-shaped signal curve, respectively; identifying, along the left
and the right best-fit lines, left and right side magnetic head
positions X.sub.L2 and X.sub.R2 that correspond to a magnetic head
signal amplitude of zero; finding a difference .DELTA.X.sub.2
between X.sub.L2 and X.sub.R2; finding a difference between
.DELTA.X.sub.2 and MWW.sub.FTP; wherein the act of determining the
one or more side reading correction values, C.sub.SRL and
C.sub.SRR, comprises the further acts of: identifying left and
right magnetic head positions S.sub.L and S.sub.R, respectively,
that correspond to where left and right side reading tails of the
bell-shaped curve begin to deviate from the left and the right
best-fit lines; determining C.sub.SRL=.DELTA.Y.sub.L/a.sub.L and
C.sub.SRR=.DELTA.Y.sub.R- /a.sub.R, where:
.DELTA.Y.sub.L=A.sub.L(S.sub.L)-(.differential.A.sub.L+.d-
ifferential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.-
A.sub.L+.differential.A.sub.R)/2,
A.sub.L=A.sub.L(S.sub.L)-A.sub.L(S.sub.L- -X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub.R+X), A.sub.L
and A.sub.R are signal amplitudes corresponding to particular
magnetic head positions, a.sub.L and a.sub.R are slopes of the left
and the right best-fit lines, respectively,
X=(MWW.sub.FTP-MRW.sub.FTP)/2; and wherein the act of adjusting the
initial write width value comprises adjusting MWW.sub.FTP for
determining MWW based on MWW=MWW.sub.FTP-C.sub.SRL-C.sub.- SRR.
8. A computer program product, comprising: a computer storage
medium; computer instructions stored on the computer storage
medium; the computer instructions for: obtaining full track profile
data for a magnetic head; determining an initial write width value
from the full track profile data; determining one or more side
reading correction values from the full track profile data; and
adjusting the initial write width value with the one or more side
reading correction values for determining a magnetic write width of
the magnetic head.
9. The computer program product of claim 8, further comprising:
wherein the full track profile data comprises a plurality of signal
amplitudes read across a track of a magnetic disk at a plurality of
magnetic head positions.
10. The computer program product of claim 8, further comprising:
wherein the full track profile data comprises a plurality of signal
amplitudes read across a track of a magnetic disk at a plurality of
magnetic head positions; wherein the plurality of signal amplitudes
form a bell-shaped signal curve when graphed over the plurality of
magnetic head positions; and wherein the computer instructions
determine the one or more side reading correction values by
analyzing side reading tail data of the bell-shaped signal
curve.
11. The computer program product of claim 8, further comprising:
wherein the full track profile data comprises a plurality of signal
amplitudes read across a track of a magnetic disk at a plurality of
magnetic head positions, and wherein the computer instructions
determine the initial write width value by: identifying a maximum
value in the plurality of signal amplitudes; and finding a
difference between left and right magnetic head positions that
correspond to half of the identified maximum value.
12. The computer program product of claim 8, wherein the full track
profile data comprises a plurality of signal amplitudes read across
a track of a magnetic disk at a plurality of magnetic head
positions; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; wherein the computer instructions
determine the initial write width value by determining a magnetic
write track width MWW.sub.FTP which includes the acts of:
identifying a maximum value in the plurality of signal amplitudes;
identifying left and right side magnetic head positions X.sub.L1
and X.sub.R1 that correspond to half of the identified maximum
value; finding a difference .DELTA.X.sub.1 between X.sub.L1 and
X.sub.R1; wherein the computer instructions are also for
determining a magnetic read width MRW.sub.FTP by: determining left
and right best-fit lines along left and right sides of the
bell-shaped signal curve, respectively; identifying, along the left
and the right best-fit lines, left and right side magnetic head
positions X.sub.L2 and X.sub.R2 that correspond to a magnetic head
signal level of zero; finding a difference .DELTA.X.sub.2 between
X.sub.L2 and X.sub.R2; and finding a difference between
.DELTA.X.sub.2 and MWW.sub.FTP.
13. The computer program product of claim 8, wherein the full track
profile data comprises a plurality of signal amplitudes read across
a track of a magnetic disk at a plurality of magnetic head
positions; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; wherein the computer instructions are also
for determining left and right best-fit lines along left and right
sides of the bell-shaped signal curve, respectively; wherein the
computer instructions determine the initial write width value by
determining a magnetic write track width MWW.sub.FTP; wherein the
computer instructions are also for determining a magnetic read
width MRW.sub.FTP from the full track profile data; wherein the
computer instructions determine the one or more side reading
correction values, C.sub.SRL and C.sub.SRR, by: identifying left
and right magnetic head positions S.sub.L and S.sub.R,
respectively, that correspond to where left and right side reading
tails of the bell-shaped curve begin to deviate from the left and
the right best-fit lines; determining
C.sub.SRL=.DELTA.Y.sub.L/a.sub.L and C.sub.SRR=.DELTA.Y.sub.R-
/a.sub.R, where:
.DELTA.Y.sub.L=A.sub.L(S.sub.L)-(.differential.A.sub.L+.d-
ifferential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.-
A.sub.L+.differential.A.sub.R)/2,
.differential.A.sub.L=A.sub.L(S.sub.L)-A- .sub.L(S.sub.L-X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub- .R+X),
A.sub.L and A.sub.R are signal amplitudes corresponding to
particular magnetic head positions, a.sub.L and a.sub.R are slopes
of the left and the right best-fit lines, respectively, and
X=(MWW.sub.FTP-MRW.sub.FTP)/2.
14. The computer program product of claim 8, further comprising:
wherein the full track profile data comprises a plurality of signal
amplitudes read across a track of a magnetic disk at a plurality of
magnetic head positions; wherein the plurality of signal amplitudes
form a bell-shaped signal curve when graphed over the plurality of
magnetic head positions; wherein the computer instructions
determine the initial write width value by determining a magnetic
write width MWW.sub.FTP which includes the further acts of:
identifying a maximum value in the plurality of signal amplitudes;
identifying left and right side magnetic head positions X.sub.L1
and X.sub.R1 that correspond to half of the identified maximum
value; finding a difference .DELTA.X.sub.1 between X.sub.L1 and
X.sub.R1; wherein the computer instructions are also for
determining a magnetic read width MRW.sub.FTP by: determining left
and right best-fit lines along left and right sides of the
bell-shaped signal curve, respectively; identifying, along the left
and the right best-fit lines, left and right side magnetic head
positions X.sub.L2 and X.sub.R2 that correspond to a magnetic head
signal level of zero; finding a difference .DELTA.X.sub.2 between
X.sub.L2 and X.sub.R2; finding a difference between .DELTA.X.sub.2
and MWW.sub.FTP; wherein the computer instructions determine the
one or more side reading correction values, C.sub.SRL and
C.sub.SRR, comprises the further acts of: identifying left and
right magnetic head positions S.sub.L and S.sub.R, respectively,
that correspond to where left and right side reading tails of the
bell-shaped curve begin to deviate from the left and the right
best-fit lines; determining C.sub.SRL=.DELTA.Y.sub.L/a.sub.L and
C.sub.SRR=.DELTA.Y.sub.R- /a.sub.R, where:
.DELTA.Y.sub.L=A.sub.L(S.sub.L)-(.differential.A.sub.L+.d-
ifferential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.-
A.sub.L+.differential.A.sub.R)/2,
.differential.A.sub.L=A.sub.L(S.sub.L)-A- .sub.L(S.sub.L-X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub- .R+X),
A.sub.L and A.sub.R are signal amplitudes corresponding to
particular magnetic head positions, a.sub.L and a.sub.R are slopes
of the left and the right best-fit lines, respectively,
X=(MWW.sub.FTP-MRW.sub.F- TP)/2, and wherein the computer
instructions adjust the initial write width value by adjusting
MWW.sub.FTP for determining MWW based on
MWW=MWW.sub.FTP-C.sub.SRL-C.sub.SRR.
15. A system for determining a magnetic write width of a magnetic
head, the system comprising: a spinstand having: a magnetic disk; a
magnetic head for writing data to and reading data from the
magnetic disk; a read/write analyzer coupled to the spinstand; a
computer coupled to the read/write analyzer and the spinstand; the
computer being for: obtaining, from the read/write analyzer, full
track profile data for the magnetic head; determining an initial
write width value from the full track profile data; determining one
or more side reading correction values from the full track profile
data; and adjusting the initial write width value with the one or
more side reading correction values for determining the magnetic
write width.
16. The system of claim 15, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a plurality of magnetic head positions over a track of the
magnetic disk
17. The system of claim 15, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a plurality of magnetic head positions over a track of the
magnetic disk; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; and wherein the computer determines the
one or more side reading correction values by analyzing side
reading tail data of the bell-shaped signal curve.
18. The system of claim 15, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a plurality of magnetic head positions over a track of the
magnetic disk; wherein the computer determines the initial write
width value by: identifying a maximum value in the plurality of
signal amplitudes; and finding a difference between left and right
magnetic head positions that correspond to half of the identified
maximum value.
19. The system of claim 15, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a plurality of magnetic head positions over a track of the
magnetic disk; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; wherein the computer is also for
determining left and right best-fit lines along left and right
sides of the bell-shaped signal curve, respectively; wherein the
computer determines the initial write width value by determining a
magnetic write track width MWW.sub.FTP; wherein the computer is
also for determining a magnetic read width MRW.sub.FTP from the
full track profile data; wherein the computer determines the one or
more side reading correction values, C.sub.SRL and C.sub.SRR, by:
identifying left and right magnetic head positions S.sub.L and
S.sub.R, respectively, that correspond to where left and right side
reading tails of the bell-shaped curve begin to deviate from the
left and the right best-fit lines; determining
C.sub.SRL=.DELTA.Y.sub.L/a.sub.L and
C.sub.SRR=.DELTA.Y.sub.R/a.sub.R, where:
.DELTA.Y.sub.L=A.sub.L(S.sub.L)--
(.differential.A.sub.L+.differential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.A.sub.L+.differential.A.su-
b.R)/2, .differential.A.sub.L=A.sub.L(S.sub.L)-A.sub.L(S.sub.L-X)
and .differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub.R+X),
A.sub.L and A.sub.R are signal amplitudes corresponding to
particular magnetic head positions, a.sub.L and a.sub.R are slopes
of the left and the right best-fit lines, respectively, and
X=(MWW.sub.FTP-MRW.sub.FTP)/2.
20. The system of claim 15, further comprising: wherein the full
track profile data comprises a plurality of signal amplitudes read
across a plurality of magnetic head positions over a track of the
magnetic disk; wherein the plurality of signal amplitudes form a
bell-shaped signal curve when graphed over the plurality of
magnetic head positions; wherein the computer determines the
initial write width value by determining a magnetic write track
width MWW.sub.FTP which includes the further acts of: identifying a
maximum value in the plurality of signal amplitudes; identifying
left and right side magnetic head positions X.sub.L1 and X.sub.R1
that correspond to half of the identified maximum value; finding a
difference .DELTA.X.sub.1 between X.sub.L1 and X.sub.R1; wherein
the computer is also for determining a magnetic read width
MRW.sub.FTP by: determining left and right best-fit lines along
left and right sides of the bell-shaped signal curve, respectively;
identifying, along the left and the right best-fit lines, left and
right side magnetic head positions X.sub.L2 and X.sub.R2 that
correspond to a magnetic head signal level of zero; finding a
difference .DELTA.X.sub.2 between X.sub.L2 and X.sub.R2; finding a
difference between .DELTA.X.sub.2 and MWW.sub.FTP; wherein the
computer determines the one or more side reading correction values,
C.sub.SRL and C.sub.SRR, comprises the further acts of: identifying
left and right magnetic head positions S.sub.L and S.sub.R,
respectively, that correspond to where left and right side reading
tails of the bell-shaped curve begin to deviate from the left and
the right best-fit lines; determining
C.sub.SRL=.DELTA.Y.sub.L/a.sub.L and C.sub.SRR=.DELTA.Y.sub.R-
/a.sub.R, where:
.DELTA.Y.sub.L=A.sub.L(S.sub.L)-(.differential.A.sub.L+.d-
ifferential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.-
A.sub.L+.differential.A.sub.R)/2,
.differential.A.sub.L=A.sub.L(S.sub.L)-A- .sub.L(S.sub.L-X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub- .R+X),
A.sub.L and A.sub.R are signal amplitudes corresponding to
particular magnetic head positions, a.sub.L and a.sub.R are slopes
of the left and the right best-fit lines, respectively,
X=(MWW.sub.FTP-MRW.sub.F- TP)/2; and wherein the computer adjusts
the initial write width value by adjusting MWW.sub.FTP for
determining MWW based on MWW=MWW.sub.FTP-C.sub.SRL-C.sub.SRR.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to methods and apparatus for
determining the magnetic track width of a magnetic head.
[0003] 2. Description of the Related Art
[0004] A write head is typically combined with a magnetoresistive
(MR) or giant magnetoresistive (GMR) read head to form a merged
head, certain elements of which are exposed at an air bearing
surface (ABS). The write head is made of first and second pole
pieces having first and second pole tips, respectively, which
terminate at the ABS. The first and second pole pieces are
connected at the yoke by a back gap, whereas the first and second
pole tips are separated by a non-magnetic gap layer. An insulation
stack, which comprises a plurality of insulation layers, is
sandwiched between the first and second pole pieces, and a coil
layer is embedded in this insulation stack. A processing circuit is
connected to the coil layer for conducting write current through
the coil layer which, in turn, induces write fields in the first
and second pole pieces. Thus, write fields of the first and second
pole tips at the ABS fringe across the gap layer. In a magnetic
disk drive, a magnetic disk is rotated adjacent to, and a short
distance (fly height) from, the ABS so that the write fields
magnetize the disk along circular tracks. The written circular
tracks then contain information in the form of magnetized segments
with fields detectable by the read head.
[0005] An MR read head includes an MR sensor sandwiched between
first and second non-magnetic gap layers, and located at the ABS.
The MR sensor detects magnetic fields from the circular tracks of
the rotating disk by a change in resistance that corresponds to the
strength of the fields. A sense current is conducted through the MR
sensor, where changes in resistance cause voltage changes that are
received by the processing circuitry as readback signals. On the
other hand, a GMR read head includes a GMR sensor which manifests
the GMR effect In the GMR sensor, the resistance of the MR sensing
layer varies as a function of the spin-dependent transmission of
the conduction electrons between magnetic layers separated by a
non-magnetic layer (spacer) and the accompanying spin-dependent
scattering which takes place at the interface of the magnetic and
non-magnetic layers and within the magnetic layers. Recorded data
can be read from a magnetic medium because the external magnetic
field from the recorded magnetic medium (the signal field) causes a
change in direction of magnetization in the free layer, which in
turn causes a change in resistance of the GMR sensor and a
corresponding change in the sensed current or voltage.
[0006] One or more merged heads may be employed in a magnetic disk
drive for reading and writing information on circular tracks of a
rotating disk. A merged head is mounted on a slider that is carried
on a suspension. The suspension is mounted to an actuator which
rotates the magnetic head to locations corresponding to desired
tracks. As the disk rotates, an air layer (an "air bearing") is
generated between the rotating disk and an air bearing surface
(ABS) of the slider. A force of the air bearing against the air
bearing surface is opposed by an opposite loading force of the
suspension, causing the magnetic head to be suspended a slight
distance (flying height) from the surface of the disk.
[0007] One important parameter of a magnetic head is its magnetic
track width. If a magnetic head has a narrow track width, the
tracks along a magnetic disk can also be made narrow. If the tracks
on the disk can be made narrow, additional tracks can be formed on
the disk to thereby increase its storage capacity. Thus, much
emphasis has been placed on making the track widths of magnetic
heads as small as possible. In turn, therefore, quick and accurate
methods are needed to determine the magnetic widths of magnetic
heads with narrow track width sizes. At the present
state-of-the-art, magnetic track width sizes are less than 0.3
.mu.m.
[0008] Conventional methods for determining the magnetic track
width are either (1) quick but inaccurate or (2) accurate but slow,
particularly when dealing with magnetic heads having narrow track
widths. One conventional method determines the magnetic track width
from a full track profile of a magnetic track written on a disk.
The full track profile consists of a plurality of signal amplitudes
read by the magnetic head across a track of a magnetic disk at a
plurality of head positions. The full track profile generally forms
a bell-shaped curve when graphed (head position along x-axis,
signal level along y-axis). The full track profile magnetic write
width MWW.sub.FTP may be obtained based on the difference in left
and right head positions which read half of the maximum head signal
amplitude. Although this method can be performed relatively
quickly, it is only accurate when MWW>>MRW (the magnetic read
width) and when no side reading of the read sensor exists.
[0009] The off-track reading capability (OTRC), which is a measure
of how far the read head can go off track without picking up
interference from adjacent tracks, and erase band width (EBW) can
be found using the well-known "triple-track" method. In this
method, a particular track is selected on a disk and two adjacent
tracks which surround this track are written to. The middle track
is then subsequently written to at a different frequency than the
adjacent tracks for a partial erasure. Next, the full track
profiles from the adjacent tracks are obtained. Best-fit lines are
then fitted on the right side of the left adjacent track profile
and on the left side of the right adjacent track profile. The two
head positions where these best-fit lines intersect the x-axis are
identified, and the difference between these positions is the OTRC.
This method also suffers from inaccuracy due to side reading
error.
[0010] Another conventional method of determining the magnetic
track width is the convolution method. In this method, the track
width is determined by the convolution of the magnetic signal
profile of the written track (assumed to be rectangular) and the
micro-track width profile, based on
FTP(x)=.intg.R(x-y)MG(y)dy=MTP(x-y)MG(y)dy,
[0011] where R(x) is the reader response function, MG(x) is the
magnetization of the data track, and FTP(x) and MTP(x) are the full
and microtrack track profile, respectively. In this method,
accurate results may be obtained despite the side-reading error.
However, this method is too slow for use in production testing.
Also, the off-track reading capability (OTRC) and erase band width
(EBW) cannot be obtained using this method.
[0012] Accordingly, what is needed is a quick and accurate method
for determining the magnetic track width of a magnetic head,
especially for magnetic heads having very narrow track widths.
SUMMARY OF THE INVENTION
[0013] A quick and accurate method of determining the magnetic
track width of a magnetic head is described herein. A full track
profile of a magnetic track is obtained using the magnetic head.
The full track profile includes a plurality of signal amplitudes
read across a track of a magnetic disk at a plurality of magnetic
head positions. Next, an initial track width value is determined
from the full track profile data. Preferably, the initial value is
the magnetic write width (MWW.sub.FTP) which is determined based on
the difference in left and right head positions which read half of
the maximum head signal level. This initial track width value is
then adjusted with side reading correction values for determining
the magnetic track width. The side reading correction values are
based on an analysis of side reading "tails" of the bell-shaped
signal curve that is formed by the track profile data when
graphed.
[0014] In one particular embodiment, the correction value for the
left side reading tail (C.sub.SRL) is .DELTA.Y.sub.L/a.sub.L and
the correction value for the right side reading tail (C.sub.SRR) is
.DELTA.Y.sub.R/a.sub.R, respectively, such that the magnetic track
width MWW=MWW.sub.FTP-C.sub.SRL-C.sub.SRR. The values a.sub.L and
a.sub.R are slopes of best-fit lines fitted over left and right
sides of the bell-shaped curve
(Y.sub.L=a.sub.L*X.sub.offset+b.sub.L and
Y.sub.R=a.sub.R*X.sub.offset+b.sub.R), respectively. The values
.DELTA.Y.sub.L and .DELTA.Y.sub.R are obtained based on equations
.DELTA.Y.sub.L=A.sub.L(S.sub.L)-(.differential.A.sub.L+.differential.A.su-
b.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.A.sub.L+.differe-
ntial.A.sub.R)/2, respectively, where
.differential.A.sub.L=A.sub.L(S.sub.- L)-A.sub.L(S.sub.L-X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S-
.sub.R)-A.sub.R(S.sub.R+X); S.sub.L and S.sub.R are head offset
positions that reflect where the best-fit lines and the side
reading tails begin to deviate; A.sub.L and A.sub.R are signal
amplitudes at specified head positions; and
X=(MWW.sub.FTP-MRW)/2.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a fuller understanding of the nature and advantages of
the present invention, as well as the preferred mode of use,
reference should be made to the following detailed description read
in conjunction with the accompanying drawings:
[0016] FIG. 1 is a schematic block diagram of a system for
determining a magnetic track width of a magnetic head;
[0017] FIG. 2A is an illustration of an ideal track profile of a
magnetic head obtained from reading signal amplitudes measured at a
plurality of magnetic head positions over a track of a magnetic
disk;
[0018] FIG. 2B is a graph showing a full track profile of a
magnetic head, as well as equations for obtaining a magnetic track
width from the full track profile;
[0019] FIG. 3 is a graph showing the full track profile and a
microtrack profile of the magnetic head;
[0020] FIG. 4 is a graph of the microtrack profile of FIG. 3 at a
smaller scaling;
[0021] FIG. 5 is a flowchart which describes a method of
determining a magnetic track width of a magnetic head in accordance
with the present invention;
[0022] FIG. 6 is a graph which shows side reading tail data of a
full track profile;
[0023] FIG. 7 is a graph which compares magnetic track widths
obtained by the present invention and the measured physical track
widths;
[0024] FIG. 8 is a graph which compares magnetic track widths
obtained by the present invention and theoretically calculated
track widths;
[0025] FIG. 9 is another graph which is the same as FIG. 8 except
it uses micrometers (.mu.m) instead of microinches (.mu.in) for the
units;
[0026] FIG. 10 is a graph which shows full track profile data of
two tracks which lie adjacent to and surround a middle track, used
for determining an off-track read capability (OTRC) of a magnetic
head;
[0027] FIG. 11 is a graph which shows the full track profile data
of FIG. 10, scaled up to show fuller views of the track profiles of
the two tracks; and
[0028] FIG. 12 is a graph which compares OTRCs obtained by the
present invention and conventionally calculated OTRCs.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The following description is the best embodiment presently
contemplated for carrying out the present invention. This
description is made for the purpose of illustrating the general
principles of the present invention and is not meant to limit the
inventive concepts claimed herein.
[0030] A system 100 for determining a magnetic track width of a
magnetic head is shown in FIG. 1. The system 100 in FIG. 1 includes
a computer 102, a spinstand 104, and a read/write analyzer 106.
Computer 102 is coupled to spinstand 104 and read/write analyzer
106 through serial ports (not shown). Read/write analyzer 106 is
also coupled to spinstand 104 through serial ports (not shown).
Spinstand 104, which includes a replaceable magnetic head 112 and a
replaceable magnetic disk 114, is basically a conventional disk
drive device used for determining the magnetic track width of a
magnetic head. Such a spinstand 104 may be obtained from, for
example, Guzik Technical Enterprises of Mountain View, Calif.,
U.S.A. (e.g., Model # S-1701B). Read/write analyzer 106 is
basically a conventional signal analyzer device which serves to
measure, read, and write signals to and from spinstand 104. These
signals are converted from digital to analog (D/A) and analog to
digital (A/D) as necessary. Such a read/write analyzer 106 may be
obtained from, for example, Guzik Technical Enterprises of Mountain
View, Calif., U.S.A. (e.g., Model # RWA-2585S PMRL 1G).
[0031] Computer 102 may be a general purpose computer, such as a
personal computer (PC), which includes one or more processors 108
(or controllers) and memory 110. Memory 110 may be a disk, such as
a hard disk, computer diskette, or compact disc (CD), or
alternatively be memory of an integrated circuit (IC) device or
processor which is a permanent part of computer 102. Computer 102
includes software (i.e. computer instructions) which resides in
memory 110 and provides general control for system 100. For
example, the software instructs spinstand 104 to move magnetic head
112 to particular positions on magnetic disk 114, write data to
disk 114 at particular frequencies, and read data from disk 114.
Given the appropriate track profile data, the computer instructions
also perform calculations to determine the magnetic track width of
magnetic head 112 in accordance with the present invention. The
logic and calculations performed by the software are described
below in detail. The software may be implemented in any suitable
computer language, such as Visual Basic or Visual C++.
[0032] FIG. 2A is an illustrative example of an ideal track profile
205 of magnetic head 112 of FIG. 1, where the write track width is
made greater than the read track width. Ideal track profile 205 is
obtained as magnetic head 112 reads signal amplitudes across a
track 201 of a magnetic disk, which is illustrated by dashed-line
representations of magnetic head 112 that extend from left to right
in the figure. Track profile 205 is ideal in that it is not
affected by any side reading from the magnetization of the
positions that are not covered by the reader physically. Being
ideal, track profile 205 is shown to have a short flat top and
straight-lined sides with constant slopes.
[0033] As illustrated in FIG. 2A, the magnetic write width (w) is
equal to the magnetic width of track 201 whereas the magnetic read
width (r) is equal to the width of a step function which represents
an ideal reader response to magnetic fields. As indicated, the
magnetic write width can be obtained by calculating the difference
between the left and right head positions at half (1/2) of the
maximum signal amplitude. Put another way, the magnetic write width
from the full track profile (MWW.sub.FTP) can be found by
identifying a maximum value in the plurality of signal amplitudes;
identifying left and right side magnetic head positions X.sub.L1
and X.sub.R1 that correspond to half of the identified maximum
value; and finding a difference .DELTA.X.sub.1 between X.sub.L1 and
X.sub.R1. On the other hand, the magnetic read width can be
obtained by calculating the difference between the left and right
head positions at zero signal amplitude (which is r+w), and then
subtracting the magnetic write width from this value. Put another
way, the magnetic read width from the full track profile
(MRW.sub.FTP) can be found by identifying left and right side
magnetic head positions X.sub.L2 and X.sub.R2 that correspond to a
signal level of zero; finding a difference .DELTA.X.sub.2 between
X.sub.L2 and X.sub.R2 and finding a difference between
.DELTA.X.sub.2 and MWW.sub.FTP.
[0034] An ideal track profile, however, is difficult if not
impossible to obtain. The full track profile is typically affected
by side reading of the reader. This side reading error becomes
relatively large percentage-wise when the write width becomes
relatively small. FIG. 2B is a graph 200 showing a more realistic
full track profile 202. Full track profile 202 consists of a
plurality of signal amplitudes read across a track of a magnetic
disk at a plurality of head positions. The plurality of signal
amplitudes are represented along the y-axis in track average
amplitude (TAA), and the plurality of head positions are
represented along the x-axis in microinches (.mu.in) as offsets
from track center.
[0035] As shown in FIG. 2B, the data of full track profile forms a
bell-shaped curve. Best-fit straight lines 204 and 206 are fit
along left and right sides of this bell-shaped curve, which
represent the straight-lined sides of an ideal profile. As shown, a
left side reading tail 212 exists to the left of best-fit line 204,
and a right side reading tail 214 exists to the right of best-fit
line 205. Side reading tail data is hereby defined as that data
that exist outside of the best-fit lines fitted along the left and
right sides of the bell-shaped curve. These tails are caused by
side reading which also widens the full track profile. Due to the
side reading, the data and therefore the calculations for
determining the magnetic write width described above in relation to
FIG. 2A are not entirely accurate. The track width calculation
error due to side reading becomes larger percentage-wise when the
track width becomes smaller.
[0036] FIG. 5 is a flowchart which describes a method of
determining a magnetic write width of a magnetic head in accordance
with the present invention, which solves the problem of the prior
art methods. This method is implemented in the system of FIG. 1
with software, which is stored in memory and executed by one or
more processors. Referring back to the flowchart of FIG. 5, the
track profile data for the magnetic head are obtained (step 502).
The track profile data include a plurality of signal amplitudes
read across a track of a magnetic disk at a plurality of magnetic
head positions. In this embodiment, the track profile data is the
full track profile data of the magnetic head obtained from the
read/write analyzer and spinstand of FIG. 1. The plurality of
signal amplitudes of the full track profile form a bell-shaped
signal curve when graphed over the plurality of magnetic head
positions (e.g., see FIG. 2B).
[0037] Next, an initial track width value is determined from the
full track profile data using the conventional method (step 504).
In this embodiment, the initial track width value is the magnetic
write width, referred to as MWW.sub.FTP, which is determined by the
software from the full track profile. For example, MWW.sub.FTP may
be obtained by identifying a maximum value in the plurality of
signal amplitudes; identifying left and right side magnetic head
positions X.sub.L1 and X.sub.R1 that correspond to half of the
identified maximum value; and then finding a difference
.DELTA.X.sub.1 between X.sub.L1 and X.sub.R1. Thus, the relation
may be represented as MWW.sub.FTP=(X.sub.R1-X.sub.L1).
[0038] Correction values are then determined based on analyzing
side reading tail data in the full track profile (step 506). The
analysis of side reading tails and the determination of correction
values are described in a detailed analysis below. The initial
track width value is adjusted with these correction values (step
508), and the final magnetic track width is obtained (step
510).
[0039] To obtain the correction values, the magnetic read width
from the full track profile (MRW.sub.FTP) is determined. The
magnetic read width MRW.sub.FTP is found by first fitting left and
right best-fit lines along left and right sides of the bell-shaped
signal curve, respectively (see e.g., FIG. 2B). Once the best-fit
lines are obtained, left and right side magnetic head positions
X.sub.L2 and X.sub.R2 that correspond to a signal amplitude of zero
along the left and right best-fit lines are identified. The
difference .DELTA.X.sub.2 between X.sub.L2 and X.sub.R2 is then
found, and the MRW.sub.FTP is obtained by calculating the
difference between .DELTA.X.sub.2 and MWW.sub.FTP. The relation may
be summarily represented as
MRW.sub.FTP=(X.sub.R2-X.sub.L2)-MWW.sub.FTP=(X.sub.R2-X.su-
b.L2)-(X.sub.R1-X.sub.L1).
[0040] To obtain the actual magnetic write width MWW, two
correction values C.sub.SRL and C.sub.SRR are determined and used
to adjust the initial track width value (here, MWW.sub.FTP).
C.sub.SRL is the correction value for the left side reading tail
and C.sub.SRR is the correction value for the right side reading
tail. Once these correction values are obtained, the full track
profile magnetic write width MWW.sub.FTP is adjusted based on the
relation MWW=MWW.sub.FTP-C.sub.SRL-C- .sub.SRR.
[0041] FIG. 6 is a graph 600 which shows side reading tail data 602
of a full track profile. Although only one side reading tail is
shown for analysis (i.e., the left side reading tail), both left
and right side reading tails are analyzed to obtain each correction
value CSRL and C.sub.SRR. The correction values C.sub.SRL and
C.sub.SRR are more specifically determined based on the relations
C.sub.SRL=.DELTA.Y.sub.L/a- .sub.L and
C.sub.SRR=.DELTA.Y.sub.R/a.sub.R. Here, .DELTA.Y.sub.L=A.sub.L(-
S.sub.L)-(.differential.A.sub.L+.differential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.differential.A.sub.L+.differential.A.su-
b.R)/2, where
.differential.A.sub.L=A.sub.L(S.sub.L)-A.sub.L(S.sub.L-X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub.R+X). A.sub.L
and A.sub.R are signal amplitudes corresponding to particular
magnetic head positions for the left and right side reading tails,
respectively; a.sub.L and a.sub.R are slopes of the left and the
right best-fit lines, respectively; and
X=(MWW.sub.FTP-MRW.sub.FTP)/2.
[0042] In FIG. 6, best-fit line 604 is shown fitted over the side
reading tail data 602 and may represented by the equation
Y.sub.L=a.sub.L*X.sub.o- ffset+b.sub.L. S.sub.L and S.sub.R are
head positions that correspond to the point at which the left and
right side reading tails of the bell-shaped curve begin to deviate
from the left and the right best-fit lines, respectively. Since
FIG. 6 shows the left side reading tail, a representative value of
S.sub.L is shown. The signal amplitude value of A.sub.L(S.sub.L) is
identified by an extending line 606 which corresponds to head
position S.sub.L, and the signal level value of A.sub.L(S.sub.L-X)
is identified by an extending line 608 which corresponds to head
position (S.sub.L-X). Similar analysis of the right side reading
tail (not shown in FIG. 6) determines the signal amplitude values
of A.sub.R(S.sub.R) and A.sub.R(S.sub.R+X), using the best fit line
represented by Y.sub.R=a.sub.R*X.sub.offset+b.sub.R.
[0043] The above calculations used to find MWW can be quickly
executed and the results are highly accurate. FIG. 7 is a graph 700
which compares write widths obtained by the present invention and
those that were actually measured physically with a critical
dimension scanning electron microscope (CDSEM). A 45.degree. line
702 shown in FIG. 7 represents the actual physical write width,
which is typically smaller than the magnetic write width, such that
measured track width data will generally lie above 45.degree. line
702. Magnetic write width data is shown in graph 700 as diamonds,
two diamonds for each magnetic head. More particularly,
conventional write width data 704 from three wafers are denoted by
hollow diamonds and shown generally above inventive write width
data 710 which are from the same three wafers and denoted by solid
diamonds. A straight line 706 is fitted to conventional write width
data 704, and a straight line 712 is fitted to inventive write
width data 710. Note that straight line 712 (invention) lies closer
to and parallel with 45.degree. line 702, which is desirable,
whereas straight line 706 (conventional) lies further away from and
not parallel with 450 line 702. Straight lines 708 and 714 are
parallel with line 702 and away from line 702 a distance of 0.08
and 0.04 nm, respectively. These two lines are used to identify how
close the above two types of data are to the actual physical head
write width.
[0044] To further illustrate the accuracy obtained, FIGS. 8 and 9
are graphs 800 and 900 which compare theoretically calculated write
widths (using convolution integral and average magnetic read width)
and magnetic write widths obtained by the present invention. Graphs
800 and 900 are different only in the units utilized; graph 800
uses microinches (.mu.in) whereas graph 900 uses micrometers
(.mu.m). Theoretical magnetic write widths are graphed in FIG. 8
(clear diamonds) and a curve 802 was fitted to this data. Write
width data 804 obtained by the present invention was also graphed
in FIG. 8 (solid squares). Note how closely experimental write
width data 804 fits along theoretical write width curve 802. The
same data exists in graph 900 of FIG. 9, which shows a theoretical
write width curve 902 and experimental write width data 904
obtained by the present invention.
[0045] The off-track read capability (OTRC) for the magnetic head
may also be obtained in a relatively accurate manner. FIGS. 10 and
11 show a graph 1000 (smaller scale) and a graph 1100 (larger
scale), respectively, which reveal the full track profile data of
two tracks which lie adjacent to and surround a middle track. In
accordance with a conventional method, a middle track is selected
on the disk and two adjacent tracks which lie adjacent to this
track are written to. The middle track is then subsequently written
to at a different frequency than the adjacent tracks for a partial
erasure. The full track profiles from the adjacent tracks are then
obtained, shown as track profile data 1002 and 1004 in FIGS. 10 and
11. Best-fit lines 1006 and 1008 are then fitted on the right side
of the left adjacent track profile 1002 and on the left side of the
right adjacent track profile 1004, respectively. The two head
positions where best-fit lines 1006 and 1008 intersect with the
x-axis are identified, and the difference between these head
positions is two times (2.times.) the OTRC 1010 as indicated in
FIG. 10. Side reading tail data 1012 are also shown in the
figures.
[0046] As apparent from the figures, the side reading shifts lines
1006 and 1008 and interferes with the conventional analysis to
thereby produced inaccurate OTRC data. The greater the side reading
the closer lines 1006 and 1008 become, which reduces the value of
the OTRC. In accordance with the present invention, an OTRC value
with side-reading correction ("OTRC.sub.S") can be determined based
on the initial OTRC value described above plus half of the sum of
two side-reading correction values C.sub.SRL and C.sub.SRR. An EBW
value with side-reading correction can also be obtained using the
relation OTRC.sub.S=EBW+DWR. DWR is the "differential write and
read width" found by DWR=(MWW.sub.S-MRW.sub.FTP)/- 2, where MWWs is
the MWW obtained in accordance with the present invention.
[0047] As with the magnetic write widths, the OTRC obtained in
accordance with the present invention is accurate. FIG. 12 is a
graph which compares OTRCs obtained by the present invention and
those obtained using the conventional method. The x-axis is the DWR
in microinches (.mu.in), and the y-axis is the OTRC in microinches
(.mu.in). Conventional OTRC data 1206, shown as solid diamonds for
each magnetic head, generally lies below a 45.degree. line 1202
which results in abnormal negative EBW. Note also that some of
these conventional OTRC data 1206 have negative values, which is
not physically possible. On the other hand, inventive OTRC data
1204, shown as hollow squares for each magnetic head, generally
lies above 45.degree. line 1202 as they should be.
[0048] Thus, a quick and accurate method of determining a magnetic
track width of a magnetic head has been described. First, a full
track profile for the magnetic head is obtained. This full track
profile data includes a plurality of signal amplitudes read across
a track of a magnetic disk at a plurality of magnetic head
positions. Next, an initial write width value (having no side
reading correction) is determined from the full track profile data.
Preferably, the initial magnetic write width from the full track
profile (MWW.sub.FTP) is determined based on the difference in left
and right head positions which read half of the maximum head signal
amplitude. The initial write width value is then adjusted with side
reading correction values for determining the magnetic write width.
The side reading correction values are based on an analysis of side
reading "tails" of the bell-shaped signal curve that is formed by
the full track profile data when graphed.
[0049] In one particular embodiment, the correction value for the
left side reading tail is .DELTA.Y.sub.L/a.sub.L and the correction
value for the right side reading tail is .DELTA.Y.sub.R/a.sub.R,
respectively, such that the magnetic write width
MWW=MWW.sub.FTP-.DELTA.Y.sub.L/a.sub.L-.DEL- TA.Y.sub.R/a.sub.R.
The values a.sub.L and a.sub.R are slopes of best-fit lines fitted
over left and right sides of the bell-shaped curve
(Y.sub.L=a.sub.L*X.sub.offset+b.sub.L and
Y.sub.R=a.sub.R*X.sub.offset+b.- sub.R), respectively. The values
.DELTA.Y.sub.L and .DELTA.Y.sub.R are obtained based on equations
.DELTA.Y.sub.L=A.sub.L(S.sub.L)-(.differentia-
l.A.sub.L+.differential.A.sub.R)/2 and
.DELTA.Y.sub.R=A.sub.R(S.sub.R)-(.d-
ifferential.A.sub.L+.differential.A.sub.R)/2, respectively, where
.differential.A.sub.L=A.sub.L(S.sub.L)-A.sub.L(S.sub.L-X) and
.differential.A.sub.R=A.sub.R(S.sub.R)-A.sub.R(S.sub.R+X); S.sub.L
and S.sub.R are head offset positions that reflect where the
best-fit lines and the side reading tails begin to deviate; A.sub.L
and A.sub.R are signal amplitudes at specified head positions; and
X=(MWW.sub.FTP-MRW.sub.FTP)/2.
[0050] It is to be understood that the above is merely a
description of preferred embodiments of the invention and that
various changes, alterations, and variations may be made without
departing from the true spirit and scope of the invention as set
for in the appended claims. None of the terms or phrases in the
specification and claims has been given any special particular
meaning different from the plain language meaning to those skilled
in the art, and therefore the specification is not to be used to
define terms in an unduly narrow sense.
* * * * *