U.S. patent application number 14/033671 was filed with the patent office on 2014-03-27 for method of making a multi-channel time based servo tape media.
This patent application is currently assigned to Advanced Research Corporation. The applicant listed for this patent is Advanced Research Corporation. Invention is credited to Matthew P. Dugas.
Application Number | 20140085751 14/033671 |
Document ID | / |
Family ID | 23887495 |
Filed Date | 2014-03-27 |
United States Patent
Application |
20140085751 |
Kind Code |
A1 |
Dugas; Matthew P. |
March 27, 2014 |
METHOD OF MAKING A MULTI-CHANNEL TIME BASED SERVO TAPE MEDIA
Abstract
A thin film magnetic recording head is fabricated by forming a
substrate from opposing ferrite blocks which have a ceramic member
bonded between them. This structure is then diced to form a
plurality of columns, wherein each column has a ferrite/ceramic
combination. Each column represents a single channel in the
completed head. A block of ceramic is then cut to match the
columned structure and the two are bonded together. The bonded
structure is then cut or ground until a head is formed, having
ceramic disposed between each channel. A ferrite back-gap is then
added to each channel, minimizing the reluctance of the flux path.
The thin film is patterned on the head to optimize various channel
configurations.
Inventors: |
Dugas; Matthew P.; (North
Oaks, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advanced Research Corporation |
White Bear Lake |
MN |
US |
|
|
Assignee: |
Advanced Research
Corporation
White Bear Lake
MN
|
Family ID: |
23887495 |
Appl. No.: |
14/033671 |
Filed: |
September 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13595602 |
Aug 27, 2012 |
8542457 |
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14033671 |
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13113598 |
May 23, 2011 |
8254052 |
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13595602 |
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12430653 |
Apr 27, 2009 |
7948705 |
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13113598 |
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11842692 |
Aug 21, 2007 |
7525761 |
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12430653 |
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11126956 |
May 11, 2005 |
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11842692 |
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10160397 |
May 31, 2002 |
6894869 |
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11126956 |
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09475420 |
Dec 30, 1999 |
6496328 |
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10160397 |
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Current U.S.
Class: |
360/121 ;
29/603.2; 29/603.21 |
Current CPC
Class: |
G11B 5/193 20130101;
G11B 20/1211 20130101; G11B 5/4893 20130101; G11B 5/23 20130101;
G11B 5/235 20130101; G11B 5/295 20130101; G11B 5/584 20130101; G11B
5/3116 20130101; Y10T 29/49055 20150115; G11B 5/1276 20130101; G11B
5/232 20130101; G11B 20/1217 20130101; G11B 5/127 20130101; G11B
5/29 20130101; Y10T 29/49057 20150115 |
Class at
Publication: |
360/121 ;
29/603.2; 29/603.21 |
International
Class: |
G11B 5/23 20060101
G11B005/23; G11B 5/235 20060101 G11B005/235 |
Claims
1. A multi-channel surface film magnetic recording head comprising:
a plurality of magnetically permeable columns, each column being
divided into two parts by a substantially magnetically impermeable
gap member, the gap member forming a sub-gap on a writing side of
the head; at least one magnetically impermeable barrier, located
between and magnetically isolating the plurality of magnetically
permeable columns from one another; and a magnetically permeable
thin film layer spanning at least a portion of the sub-gap and
magnetically coupling the two parts of each column.
2. The magnetic recording head of claim 1, further comprising: a
plurality of magnetically permeable back-bars, wherein each
magnetically permeable column has a back-bar coupled to it and the
back-bar bypasses the magnetically impermeable gap member at one
end of the magnetically permeable column.
3. The magnetic recording head of claim 2, wherein each back-bar is
a substantially U shaped ferrite block.
4. The magnetic recording head of claim 2, further comprising: a
single coil wrapped about each of the back-bars.
5. The magnetic recording head of claim 2, further comprising: a
plurality of coils wherein each back-bar has a single coil wrapped
about it
6. The magnetic recording head of claim 1 wherein the magnetically
impermeable barrier is ceramic.
7. The magnetic recording head of claim 1 wherein the thin film
layer is located over an entire upper surface of the recording
head.
8. The magnetic recording head of claim 1 wherein the thin film
layer is located only over a portion of the recording head, the
portion being the area between air bleed slots cut into the
head.
9. The magnetic recording head of claim 1 wherein the thin film
layer has been removed in portions so as to magnetically isolate
each of the magnetically permeable columns.
10. A method of making a multi-channel surface film magnetic
recording head, comprising: forming a sub-gap substrate by bonding
a ceramic member between two magnetically permeable blocks; cutting
the substrate to form a plurality of columns, wherein each column
is divided by a portion of the ceramic member; providing a ceramic
block having a plurality of notches corresponding to the plurality
of columns; bonding the columns within the notches to form a head
member; processing the head member so that the head member has
alternating sections of the ceramic and the columns with the
columns extending therethrough; coupling at least one winding to a
first side of the columns; and forming writing gaps in a second
side of the columns.
11. The method of claim 10 wherein bonding the columns within the
notches includes: providing glass within the notches; heating the
glass so as to melt the glass; allowing the melted glass to wick
between the notches and the columns; and allowing the glass to cool
thereby forming a bond.
12. The method of claim 10 wherein processing the head member
includes cutting a top and bottom portion of the head member to
expose portions of the columns in both the top and bottom
portion.
13. The method of claim 10 wherein coupling a winding further
includes; coupling a back-bar to each of the columns; and winding
the coil about the back-bar.
14. The method of claim 13 wherein the back-bar is formed from a
continuous piece of magnetically permeable material.
15. The method of claim 10 wherein forming writing gaps further
includes: forming a magnetically permeable surface thin film; and
creating gaps in the thin film.
16. The method of claim 15 wherein the thin film is foamed over an
entire upper surface of the head.
17. The method of claim 15 wherein the thin film is only located
between air bleed slots cut into the head.
18. The method of claim 15 wherein the thin film is absent in
strips between each column thereby magnetically isolating each
column.
19. A surface film magnetic recording head comprising: a
magnetically permeable core; a substantially magnetically
impermeable member dividing the core into two poles and forming a
sub-gap; a magnetically permeable thin film coupling the two poles
across the sub-gap, wherein the thin film includes at least one
writing gap; and a back-bar, formed from magnetically permeable
material, the back bar bypassing the impermeable member to complete
a magnetic circuit between the two poles.
20. The surface film magnetic recording head of claim 19, wherein
the core and back-bar are formed from ferrite.
21.-51. (canceled)
Description
[0001] This application is a continuation of application Ser. No.
09/475,420, filed on Dec. 30, 1999, which is hereby incorporated in
its entirety by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to magnetic recording heads
and more particularly to a structure for a ferrite driven, surface
thin-film magnetic recording head wherein a substantial portion of
the ferrite core has been replaced with a magnetically impermeable
material and an optimal back-bar arrangement which reduces the
inductance and increases the efficiency of the head.
BACKGROUND OF THE INVENTION
[0003] While a variety of data storage mediums are available,
magnetic tape remains a preferred forum for economically storing
large amounts of data. In order to facilitate the efficient use of
this media, magnetic tape will have a plurality of data tracks
extending in a transducing direction of the tape. Once data is
recorded onto the tape, one or more data read heads will read the
data from those tracks as the tape advances, in the transducing
direction, over the read head. It is generally not feasible to
provide a separate read head for each data track, therefore, the
read head(s) must move across the width of the tape (in a
translating direction), and center themselves over individual data
tracks. This translational movement must occur rapidly and
accurately.
[0004] In order to facilitate the controlled movement of a read
head across the width of the media, a servo control system is
generally implemented. The servo control system consists of a
dedicated servo track embedded in the magnetic media and a
corresponding servo read head (which is usually one of the standard
read heads, temporarily tasked to servo functions) which correlates
the movement of the data read heads.
[0005] The servo track contains data, which when read by the servo
read head is indicative of the relative position of the servo read
head with respect to the magnetic media in a translating direction.
In one type of traditional amplitude based servo arrangement, the
servo track was divided in half. Data was recorded in each half
track, at different frequencies. The servo read head was
approximately as wide as the width of a single half track.
Therefore, the servo read head could determine its relative
position by moving in a translating direction across the two half
tracks. The relative strength of a particular frequency of servo
signal would indicate how much of the servo read head was located
within that particular half track. The trend toward thinner and
thinner magnetic tape layers causes amplitude modulation problems
with this and other amplitude based heads. That is, as the
thickness of the magnetic layer decreases, normal variations on the
surface represent a much larger percentage variation in the
magnetic layer, which will dramatically affect the output
signal.
[0006] Recently, a new type of servo control system was created
which allows for a more reliable positional determination by
reducing the amplitude based servo signal error traditionally
generated by debris accumulation, media thickness non-uniformity
and head wear. U.S. Pat. No. 5,689,384, issued to Albrecht et al.
on Nov. 19, 1997, introduces the concept of a timing based servo
pattern on a magnetic recording head.
[0007] In a timing based servo pattern, magnetic marks
(transitions) are recorded in pairs within the servo track. Each
mark of the pair will be angularly offset from the other. For
example, a diamond pattern has been suggested and employed with
great success. The diamond will extend across the servo track in
the translating direction. As the tape advances, the servo read
head will detect a signal or pulse generated by the first edge of
the first mark. Then, as the head passes over the second edge of
the first mark, a signal of opposite polarity will be generated.
Now, as the tape progresses no signal is generated until the first
edge of the second mark is reached. Once again, as the head passes
the second edge of the second mark, a pulse of opposite polarity
will be generated. This pattern is repeated indefinitely along the
length of the servo track. Therefore, after the head has passed the
second edge of the second mark, it will eventually arrive at
another pair of marks. At this point, the time it took to move from
the first mark to the second mark is recorded. Additionally, the
time it took to move from the first mark (of the first pair) to the
first mark of the second pair is similarly recorded.
[0008] By comparing these two time components, a ratio is
determined. This ratio will be indicative of the position of the
read head within the servo track, in the translating direction. As
the read head moves in the translating direction, this ratio will
vary continuously because of the angular offset of the marks. It
should be noted that the servo read head is relatively small
compared to the width of the servo track. Ideally, the servo head
will also be smaller than one half the width of a written data
track. Because position is determined by analyzing a ratio of two
time/distance measurements, taken relatively close together, the
system is able to provide accurate positional data, independent of
the speed (or variance in speed) of the media.
[0009] Of course, once the position of the servo read head is
accurately determined, the position of the various data read heads
can be controlled and adjusted with a similar degree of accuracy on
the same substrate. Namely, the various read heads are fabricated
on the same substrate with a known spacing between them. Hence
knowing the location of one allows for a determination of the
location of the remainder of the read heads.
[0010] When producing magnetic tape (or any other magnetic media)
the servo track is generally written by the manufacturer. This
results in a more consistent and continuous servo track, over time.
To write the timing based servo track described above, a magnetic
recording head bearing the particular angular pattern as its gap
structure, must be utilized. As it is advantageous to minimize the
amount of tape that is dedicated to servo tracks, to allow for
increased data storage, and it is necessary to write a very
accurate pattern, a very small and very precise servo recording
head element must be fabricated.
[0011] Two types of servo recording heads having a timing based
pattern are known. The first is a pure thin film head, such as that
disclosed by Aboaf et al. in U.S. Pat. No. 5,572,392, issued on
Nov. 5, 1996. With a pure thin film head, all of the components of
the head are created from layering different materials, as thin
films, on an inert substrate. For example, the magnetic core, the
windings and any barrier materials are formed by producing thin
films. Such a head has very low inductance, however, it is
extremely difficult to manufacture. To date, pure thin film heads
are generally not utilized for time based servo heads and are not
seen as a practical way to produce such a magnetic head.
[0012] A very different type of recording head is taught by
Albrecht et al. in the '384 patent. This second type of head is
referred to herein as a surface film or surface thin film head and
is illustrated as 100, in FIG. 18. The surface film head 100
includes two C-shaped ferrite blocks 110, 112 that are bonded to a
ceramic member 114 that extends the entire width of the head 100. A
surface is then polished flat or contoured and prepared for this
film deposition. A magnetically permeable thin film 116 is
deposited over an upper surface of the ferrite blocks 110, 112 and
the exposed upper portion of the ceramic member 114. The thin film
116 is shown much larger than it would actually be, respective to
the other elements. Gaps 118 are formed in the thin film 116, in an
appropriate timing based pattern. Windings 120 are wrapped and are
electrically driven to drive flux around the ferrite core and
through the thin film 116 (in the direction of arrow A). The flux
leaks from the gaps 118 and writes media passing over it.
[0013] Such a surface film head has a high inductance due to the
large volume of ferrite forming the core and a high reluctance
"back-gap", due to the separation of the ferrite block 110, 112 by
the ceramic member 114, on the underside of the head (i.e.,
opposite the thin film 116). The size and dimensions of the head
are determined by the end use characteristics. For example, the
width of the head 100 is defined by the width of the media; i.e., a
head that is 19 mm wide is appropriate to support a tape that is
12.5 mm wide. The ceramic member 114 must be thick enough to allow
the proper patterns 118 to be located above it and is approximately
0.012'' in the known versions of the Albrecht et al. head, produced
by IBM. The length of the head must be sufficient to support the
media as it travels over the tape bearing surface and the depth
(especially of the ferrite cores) must be sufficient to allow
appropriate windings to be attached and to allow the head to be
securely fixed in a head mount.
[0014] With the surface film head, flux is forced to travel through
a magnetically permeable thin film that bridges a generally
magnetically impermeable bather between sections of the core. The
writing gap is located within this thin film and the magnetic flux
is expected to leak from this gap and write the media. The width of
the ferrite is much larger than the sum of the channel widths.
Hence, there is a large amount of unnecessary ferrite inductance,
In other words, as a result of the relatively large amount of
extraneous ferrite, an unnecessarily high amount of inductance is
created. Therefore, to produce a relatively small amount of flux
leakage through a small gap in the thin film, very high levels of
current are required to generate sufficient magnetic flux
throughout the relatively large core. This requires greater write
current from the drive circuitry, lowers the frequency response of
the head, and increases the rise time of the writing pulses from
the head.
[0015] The thin film layer bridges a "gap" between the ferrite
sections of the substrate, at one end of the head. This is, of
course, the writing end of the head. This gap, referred to as the
"sub-gap" by the present inventor to distinguish it from the
writing gaps in the thin film, is formed from and defined by the
ceramic insert. As discussed above, the ceramic insert extends
through the entire height of the write head. This forms a very
large "back-gap" in a portion of the head opposite the thin film
layer. This back-gap, in some prior recording heads, is a portion
of the head where the magnetic flux must travel through the ceramic
member in order to complete the magnetic circuit. Ultimately, this
forms a barrier which hampers the magnetic flux; in other words the
reluctance through the back-gap is relatively high and again, the
head must be driven harder to compensate. This is only really
problematic in heads having a larger back-gap with respect to the
writing gap, such as in Albrecht et al. Various other magnetic
heads, video for example, will have a back-gap length equal to the
writing gap length. In addition, the video core back-gap is made
very tall, thus increasing its area and reducing the
back-reluctance. Techniques used to reduce the reluctance of video
recording heads are not applicable to sub-gap driven heads.
[0016] Such problems are intensified with heads having multiple
writing gaps, or channels. As shown in FIG. 18, a single core is
driven and simultaneously writes multiple channels (each of the
writing gaps 118 forms a separate channel). In order to do so, a
multi-channel head will necessarily have to be wider than a single
channel head. This in turn necessitates that the core become
larger. All of this leads to a head having a larger amount of
magnetically permeable material through which a predetermined
amount of magnetic flux must flow while attempting to consistently
and simultaneously write multiple channels. In other words, excess
and unused ferrite material is provided in between the channels
which unnecessarily increases the overall inductance of the
head.
[0017] Therefore, there exists a need to provide an efficient
multi-channel timing based head having a lower overall inductance,
a lower reluctance through the back-gap, a higher frequency
response, and greater efficiency. Furthermore, there exists a need
to provide such a multi-channel head with the ability to
individually and separately drive and control each channel.
SUMMARY OF THE INVENTION
[0018] The present invention relates to a low inductance, high
efficiency sub-gap, surface thin film magnetic recording head and a
method of fabricating the same.
[0019] A substrate consisting of a ceramic member, glass bonded
between a pair of ferrite blocks is prepared. After the substrate
is created, it is diced to form a base from which a plurality of
columns extend. The number of columns will correspond to the
eventual number of channels in a completed recording head. A
ceramic block is prepared which corresponds to the dimensions of
the substrate. Channels or notches are cut into the ceramic block
so that the substrate columns engage them in a male/female
relationship. The channels allow for the entirety of the column to
be accepted within the channel so that the base of the substrate
flushly abuts the corresponding base of the ceramic block. The
ceramic block is then adhered to the substrate. In particular, the
columns of the substrate are glass bonded to the interior of the
channels in the ceramic block, thus forming a head member.
[0020] The top and bottom of the head member are then cut or ground
to produce a uniform block of alternating ceramic portions and
substrate columns wherein each substrate column includes a sub-gap.
A sufficient amount of the head member is cut or ground so that the
substrate columns extend through the entire height of the remaining
portion of the head member. During this process, the upper portion
of the head member can be appropriately radiused, as it is this
section which will become the tape bearing surface of the writing
head.
[0021] If desired, air bleed slots can be cut into the head member,
perpendicular to the direction of tape travel. On top of the head
member, a magnetically permeable thin film is deposited, preferably
by a sputtering process. It is within this thin film that the
writing gaps will be produced. As such, any known process of
forming these gaps in the thin film is acceptable. To the extent
that various plating techniques will be utilized, those gaps would
be formed accordingly.
[0022] At this point, a back-bar is attached to the head member.
The back-bar is formed from an appropriate magnetically permeable
material, such as ferrite. The back-bar is provided with a
structure so that it may be wrapped with an appropriate winding to
produce a coil. The back-bar can be formed in a wide variety of
configurations. In the simplest form, a single winding is provided
around all of the back-bars, and when driven, will engage each of
the channels simultaneously. Alternatively, a separate winding is
provided for each channel, thus allowing each channel to be
separately driven and controlled. Furthermore, any intermediary
combination is allowable. That is, any particular combination of
channels can be tied together. When the channels are timed and
driven independently, sections of the magnetically permeable thin
film must be removed between the channels. This prevents magnetic
flux from passing from one channel to another through the thin film
layer. It is the prevention of this cross talk which allows the
multi-channel head to have its channels driven independently in
time or phase. To produce such isolation, sections of the thin film
can be removed by ion milling, wet chemical etching, or by any
other known process. Other techniques such as selective plating or
selective spattering could also be used.
[0023] In one embodiment, the present recording head provides a
magnetically impermeable barrier between each channel so that
actuation of one channel will in no way interfere with any other
channel in the head. Hence, a significant portion of the magnetic
volume of the head laying between each channel has been replaced
with a ceramic material. Furthermore, in the back-gap area a
back-bar has been incorporated. Utilization of the back-bar serves
to reduce the reluctance of the back-gap and increase the
efficiency of the head. Due to the reduction in overall volume of
the ferrite core in the interchannel area, the head has a lower
total inductance and is therefore more easily driven. Due to the
lower inductance per channel, the frequency response of the head
can be greatly increased. This increased response time translates
into faster current rise times for the output flux signal
generated. This ultimately leads to sharper written transitions
when the head is used to apply servo patterns to magnetic media.
It-also allows for specific patterns to be accurately and quickly
written by individually controlling and driving the various
channels of the head.
[0024] In another aspect of the present invention, the magnetically
permeable thin film layer is optimally configured to complete a
magnetic circuit for each channel, while limiting mechanical
interference of the film with the air bleed slots. Consideration
must be given to the minimal requirements for completing the
circuit and the engagement of the media against a head having a
non-planar surface while minimizing the complexity of providing the
air bleed slots. In addition, when working with components of this
scale, consideration must be given to the etching or milling
technique utilized to impart and define the thin film layer so that
mechanical shear or peeling of the film is not induced by the
tape's motion.
[0025] It is an object of the present invention to provide a
multi-channel magnetic surface film servo write head having a
reduced volume of magnetically permeable material.
[0026] It is a further object of the present invention to reduce
the reluctance of the back-gap portion of the magnetic recording
head.
[0027] It is another object of the present invention to provide a
magnetic recording head having multiple channels wherein each
channel is separately and individually controllable.
[0028] It is still another object of the present invention to
provide a method of making a multi-channel head wherein each
channel is isolated from the next.
[0029] It is yet another object of the invention to provide a
highly efficient multi-channel recording head having a relatively
high frequency response suitable for use as a servo write head.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a side planar view of a substrate composed of
ferrite blocks glass bonded to a ceramic member.
[0031] FIG. 2 is a top planar view of the substrate shown in FIG.
1.
[0032] FIG. 3 is a side view of the substrate of FIG. 1, diced into
a plurality of columns.
[0033] FIG. 4 is a side view of a ceramic block having a plurality
of notches.
[0034] FIG. 5 is a side view of the ceramic block and the substrate
bonded together.
[0035] FIG. 6 is a top view of the bonded substrate after the top
and bottom have been cut or ground.
[0036] FIG. 7 is a side view of the bonded substrate after the top
and bottom have been cut or ground.
[0037] FIG. 8 is a top view of a head assembly.
[0038] FIG. 9 is a side view of a head assembly.
[0039] FIG. 10 is an end sectional view taken about line 10-10.
[0040] FIG. 11 is an end sectional view taken about line 10-10 and
having a back-gap attached.
[0041] FIG. 12 is a side view of a head assembly having a plurality
of back-bars affixed thereto, with coils individually wrapped about
each back-bars.
[0042] FIG. 13 is a side view of a head assembly having a plurality
of back-bars affixed thereto, with a single coil wrapped about all
of the back-gaps.
[0043] FIG. 14 is a head assembly showing a pattern of thin
film.
[0044] FIG. 15 is a head assembly showing various patterns of thin
film.
[0045] FIG. 16 is a head assembly showing various patterns of thin
film.
[0046] FIG. 17 is a head assembly showing various patterns of thin
film.
[0047] FIG. 18 is a perspective view in a prior art surface thin
film magnetic recording head.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0048] The present invention is a multi-channel head and method of
making the same. Referring to FIG. 1, a substrate 10 is created by
glass bonding two C-shaped ferrite blocks 12 to a medially disposed
ceramic member 14. The sizes, shapes and relative proportions of
the ferrite blocks 12 and ceramic member 14 may vary as dictated by
the desired parameters of the completed recording head.
Furthermore, the choice of materials may also vary so long as
blocks 12 remain magnetically permeable while member 14 remains
substantially magnetically impermeable. FIG. 2 is a top view of the
substrate 10.
[0049] Referring to FIG. 3, substrate 10 is diced so as to form a
plurality of columns 16A-16E which remain adhered to base 18.
Columns 16A-16E are also shown by the dashed lines in FIG. 2, which
illustrates how each column will have a ceramic portion (sub-gap)
bonded between two ferrite poles. The dashed lines are merely
illustrative of future columns, as the substrate 10 in FIG. 2 has
yet to be diced. As shown is FIG. 4, a ceramic block 20, or slider,
is cut to form a plurality of channels or notches 22A-22E. The
ceramic block 20 can be formed from barium titanate, or any other
suitable magnetically impermeable material. The notches 22A-22E are
cut to correspond with columns 16A-16E. As such, the relative size
and shape of the columns 16A-16E and the notches 22A-22E should
correspond; beyond that the selection of size and shape will simply
depend on the desired final parameters of the completed magnetic
head.
[0050] As illustrated in FIG. 5, substrate 10 is mated with ceramic
block 20. More specifically, columns 16A-16E are inserted into
notches 22A-22E until the upper surface 26 of the base 18 of
substrate 10 flushly meets the lower surface 28 of ceramic block
20. Subsequently, substrate 10 is adhered to ceramic block 20. This
can be accomplished in any known way. In its most preferred form,
substrate 10 is glass bonded to ceramic block 20. To accomplish
this, the substrate 10 is clamped or otherwise secured to ceramic
block 20, as shown in FIG. 5. Glass rods are placed into the
various notches 22A-22E, in a space left by the columns 16A-16E.
The assembly is then heated to a temperature sufficient to melt the
glass rods. This causes the melted glass to wick along the abutting
sides of the columns 16A-16E and the notches 22A-22E. Once allowed
to cool, the glass hardens and bonds the members together.
[0051] The top and the bottom of this assembly are then cut or
ground away to arrive at the head substrate 30 shown in FIGS. 6 and
7. From a top view and moving left to right (as illustrated), head
substrate 30 has a ceramic portion 32A, which is a remainder of
ceramic block 20. A bead of glass 33 bonds ceramic portion 32A to
ferrite column 16A. Medially dissecting ferrite column 16A is a
portion of ceramic member 14, which is likewise glass bonded to
ceramic portion 32A. It is to be understood that the portion of the
non-magnetic ceramic member 14 extends through the entire length of
the remaining ferrite column 16A, thus dividing it into two
magnetic poles. Glass bonds 33 likewise join ceramic portion 32B
between ferrite columns 16A and 16B. This pattern is repeated
across the head, with the number of ferrite columns 16A-16E,
representing the eventual number of channels in the completed write
head. FIG. 7 is a side view of head substrate 30 and illustrates
that the ferrite columns 16A-16E (with included sections of ceramic
member 14, not visible in this view) forming a sandwich pattern
with the ceramic portions 32A-32F. As illustrated (in FIG. 4), the
notches 22A-22E extend through the entire width of the ceramic
block 20. Thus, the ferrite columns 16A-16E are visible from a side
view (FIG. 7).
[0052] Head substrate 30 is now ready to be formed into a completed
magnetic recording head. To summarize the remainder of the
fabrication, a slight radius or curvature is caused on the upper
surface of the head substrate 30. This step could occur when
removing the top section from the bonded substrate 10 and ceramic
block 20, or it could be done at this stage as a separate
operation. The curvature is imparted to the head substrate 30
because its upper-surface will become the tape bearing surface of
the completed head. This curvature facilitates smooth contact with
the media under tension. A magnetically permeable thin film layer
34 is deposited across the upper surface of the head substrate 30.
Writing gaps 36 (FIG. 8) are caused to be farmed in this thin film
34, aligned with the visible portion of ceramic member 14, or in
other words, above the sub-gap. Alternatively, the head contour
could be finished into a generally flat surface having integrated
negative pressure channels. The use of these various contours is
known in the art.
[0053] Either prior to depositing the thin film or after, air bleed
slots 38 may be cut into head substrate 30 along the tape bearing
surface as is known in the art. Once head substrate 30 has been
fabricated into a recording head, magnetic tape will move across
its upper surface in a transducing direction. Therefore, the air
bleed slots 38 are cut perpendicular to the transducing direction.
As the tape moves over the recording head at relatively high speed,
air entrainment occurs. That is, air is trapped between the lower
surface of the tape and the upper surface of the recording head. As
the tape moves over the recording head, the first air bleed slot
encountered serves to skive off the trapped air. The second and
subsequent slots continue this effect, thus serving to allow the
tape to closely contact the recording head. As the tape passes over
the recording gaps 36, it is also held in place by the other air
bleed slots 38 encountered on the opposite side of the gaps 30.
[0054] FIG. 10 is an end, partially sectional view of head
substrate 30 taken about line 10-10. This figure illustrates the
relationship between the ferrite column 16A and the remaining
portion of ceramic member 14. Thin film layer 34 is located on its
upper surface and write gaps 36 are located immediately above the
portion of ceramic member 14. Air bleed slots 38 are located on
opposite side of ceramic member 14 and traverse the whole assembly.
FIG. 11 illustrates the back-bar 40 of the present invention as it
is attached to ferrite column 16A (again an end, partially
sectional view taken about line 10-10). Back-bar 40 is a
substantially U-shaped ferrite block which is caused to abut each
side of the ferrite column 16A. The shape is chosen to efficiently
complete a magnetic circuit and allows a coil 44 to be wound. The
back-bar 40 flushly abuts column 16A at is held in place by a
bonding agent that is applied at glue points 42. The use of
back-bars 40 is advantageous in and of itself. In other words,
using the back-bar 40 of the present invention will allow a better
surface film head to be produced irrespective of the number of
channels formed, or whether the combed structure is utilized to
achieve channel separation or to lower stray inductance by reducing
the volume of magnetically permeable material in the core.
[0055] Reluctance is proportional to the length and inversely
proportional to the area of the barrier. In the prior art surface
film recording head (Albrecht et al.), the barrier in the back-gap
is defined by the ceramic member 14. The area in question will be
defined by the area of contact between the ferrite blocks 110, 112
(FIG. 18) and the ceramic member 114. Length corresponds to the
thickness of the ceramic member 114. The thickness of the ceramic
member 114, is necessitated by the spatial requirements of the
writing gaps 36, and in other words cannot be reduced. In the
present invention (FIG. 11) back-bar 40 has been added. The ceramic
member 14 has been removed (effectively bypassed) as a flux
barrier, but replaced with two much smaller air gap barriers where
the back-bar 40 abuts the ferrite column 16A. Again, the barrier in
question will be defined by the amount of contact, which is in turn
defined by the parameters chosen for the ferrite block 12 (as the
back-bar 40 is chosen to correspond). However, the length involved
is minuscule as it is defined by the "air gap" created by the
abutment of two substantially planar surfaces. As such, the total
amount of reluctance in the present back-bar 40 is a very small
fraction of the total reluctance in prior art surface film
recording heads. This leads to the fabrication of a highly
efficient magnetic recording head, as the reluctance of the core
has been significantly reduced.
[0056] By using the columned or combed structure, the volume of
unnecessary or non-useful magnetically permeable materials is
greatly reduced, thus decreasing the overall inductance of the
head. As such, the frequency response is dramatically increased,
thus allowing faster and more accurate writing of data on the
media. This is possible because the inducement of sufficient
magnetic flux requires substantially less energy input. As such,
the rise time of the written pulse is substantially shortened. Thus
allowing for a sharper written transition in the media.
[0057] The above description relates to the general fabrication of
a highly efficient surface thin film magnetic recording head
according to the teachings of the present invention. That is, by
using the columned (or combed) structure for the body of the head
which reduces the overall inductance of the head, and by applying
back-bars 40 which reduces the reluctance, an improved head is
necessarily formed. In addition there are various other parameters
which can be modified to apply the head of the present invention to
a wide variety of writing functions: It should be noted that simply
using a combed or columned structure in and of itself produces a
better, more efficient head. Likewise, the use of back-bars 40 is
also independently advantageous and can be utilized on heads having
a combed or non-combed core, as efficiency will be increased in
both cases.
[0058] Referring to FIGS. 12 and 13, two substantially completed
heads 46 are shown. In FIG. 12, head 46 is a multi-channel head
having five independent channels. That is, each channel can be
individually triggered and caused to write, independent of the
other four channels. To accomplish this, each back-bar 40 has its
own coil 44 wrapped about it. In a variety of known ways, these
coils 44 can be coupled to a controller and appropriately driven.
In FIG. 13, the back-gaps 40 are configured in the same way,
however a single coil 44 is coupled to all of the back-gaps 40. In
this way, when the coil is energized, the various channels will
each write simultaneously. Any intermediate combination is likewise
achievable. That is, the individually wrapped coils 44 (FIG. 12)
can be tied together, achieving the same result as utilizing a
single coil 44. Alternatively, any number or combination of
channels can be coupled mechanically or electrically together.
[0059] In the preferred-embodiment each back-bar 40 is sized to
correspond to an individual channel. As discussed, these back-bars
40 can then be separately wound or wound as a single unit. In
addition, a single elongate back-bar 40 could be provided that
extends along the entire length of the recording head 46. For
example, as shown in FIG. 11, back-bar 40 would extend into the
page along the entire length of the head.
[0060] An additional advantage of separately driving each channel
individually, is the ability to fine tune each channel. As is known
in the art and is generally represented by an "I-Sat" curve, each
head and more particularly each channel will saturate at different
levels of current input (respective to the number of turns in the
coil). Therefore, it is desirable to select a particular level of
current input to maximize the efficiency and output of each
channel. This optimal value often varies from channel to channel.
As such, by performing this evaluation for each channel, the
optimal current input for each channel can be determined. This
information is moot in those heads where all the channels are
driven by a single coil. However, with independently driven
channels, each channel is driven at its optimal level of current
input (ampere-turns).
[0061] The head 46 of the present invention has been shown to have
five channels. Any number of servo channels could be so fabricated.
Five channel or two channel heads seem to be an industry standard
for the moment. As the number of servo channels increases, the
width of each channel must become narrower in order to prevent
excessive depletion of the space available for data.
[0062] The choice to produce a multi-channel head having
independent channels or one having its channels tied together also
affects the application of the thin film 34 to the tape bearing
surface of the head 46. More specifically, a multi-channel head
having independently driven channels may need to have those
channels magnetically isolated from one another to avoid cross
talk, depending upon the timing of the information being
written.
[0063] When cross-talk is not an issue, the surface thin film layer
34 can extend across the entire surface of the head, producing a
unitary sheet film. However, the areas of sheet film between the
channels may not be well saturated, due to the limited width of the
channels and hence the driven core(s), in relation to the overall
area of the sheet film: Thus, the areas of sheet film between
adjacent channels may provide an undesirable high permeable flux
leakage path which limits the amount of signal flux actually
passing across the writing gaps 36. Hence, even when cross-talk is
not an issue, the preferred embodiment of the low inductance,
multi-channel timing based servo head of the present invention will
include a separate thin film layer 34 that is dedicated to a single
channel and is magnetically isolated from the adjacent channels.
The process of providing channel separated thin film 34 areas is
discussed below.
[0064] In addition, the application of the thin film 34 affects the
creation of the air bleed slots 38. Namely, if the slots 38 are cut
into the head 46 after the thin film 34 has been deposited, rough
corners may be produced which negatively affects the interaction
between the head 46 and the media. If the thin film 34 is deposited
after the slots are cut, thin film step coverage over the slots
becomes yet another issue.
[0065] The present invention contemplates a variety of techniques
to deal with the above mentioned considerations. The particular
technique selected will also depend on the method used to form the
writing gaps 36 into the thin-film layer 34.
[0066] FIG. 14 represents the simplest head fabrication format.
Here, head 46 is a multi-channel head wherein the various channels
are all coupled together. Though not shown, the gaps 36 will be
patterned into each channel above the ceramic member 14 (i.e., that
of FIG. 13). Assuming a staggered pattern is desired, the various
gaps 36 would be so arranged. Thin film layer 34 (designated by the
hash lines) has been deposited over the entire surface of head 46.
As discussed above, this makes the cutting of air bleed slots 38
problematic. However, this problem can be reduced by slitting the
heads prior to applying the film. As such, a relatively high
quality head 46 can be produced. The advantage of such an
arrangement is that the thin film layer 34 provides a uniform tape
bearing surface over the entirety of the upper surface of head 46.
Conversely, the photolithography becomes more difficult due to the
slots.
[0067] FIG. 15 represents a modified embodiment of a multi-channel
head wherein the channels are all coupled together. Once again,
cross talk between channels is not an issue. Here, thin film layer
34 is contained between upper and lower bounds defined by air bleed
slots 38. This arrangement avoids the above discussed issue of
cutting through the thin film layer 34 or depositing the thin film
layer 34 over existing air bleed slots 38. The production of this
thin film 34 pattern can be accomplished in various ways. For
example, prior to creating air bleed slots 38, a thin film 34 could
be deposited over the entire upper surface of head 46. Then, areas
of that thin film could be removed; leaving only the area
designated in FIG. 15. This deposition could be selectively defined
by a selective plating or a selective sputtering process used with
the appropriate masks, or the film could be selectively removed
after deposition, using any known technique.
[0068] Turning to FIG. 16, thin film layer 34 can also be
configured for use with independently driven channels in a
multi-channel head. In order to be operable, each channel must be
magnetically isolated from its adjoining channels. Primarily, this
accomplished by ceramic sections 32A-32E. However, if thin film
layer 34 were continuous from one channel to the next, cross talk
would occur, thus eliminating the ability to independently control
the channels. As such, with any independently driven, multi-channel
head 46, the magnetically permeable thin film layer 34 must be
absent between the various channels. The pattern 48 of thin film 34
(covering channels 1 and 2) in FIG. 16, illustrates the simplest
way of accomplishing this. A strip 50 is devoid of the thin film
34, over the entire length of the head. In this arrangement, the
remaining thin film layer 34 extends across the air bleed slots 38.
Strip 50 can be formed by preventing the deposition of the thin
film 34 in this area during formation, i.e., platting or
lithography, or by removing it after its application. The minimum
width of strip 50 is determined by the minimum barrier required to
prevent problematic cross talk and depends on the specific
parameters of the completed head 46. This embodiment has the
advantage of maintaining a large film surface which may be
advantageous in minimizing the-wear of the surface film and thus
increase the lifetime of the head.
[0069] Alternatively, elimination of areas of thin film 34 between
adjacent channels is advantageous in that it eliminates a high
permeability flux leakage path that limits the flux across the
writing gaps. Hence, elimination of the surface film between the
channels will provide for the maximization of magnetic flux flowing
uniformly across the writing gaps 36.
[0070] Channel 3 is shown devoid of a thin film layer 34 for ease
of illustration. Writing gaps 36 simply illustrate their position,
if thin film layer 34 were present. Channels 4 and 5 have thin film
layer 34 applied over them by pattern 52. Here, pattern 52 is
contained within the air bleed slots 38, while also providing
adequate channel separation. Pattern 52 illustrates that smaller
areas of thin film layer 34 are sufficient to accomplish the
completion of the head 46. FIG. 17 illustrates a furtherance of
this concept. Specifically, channel 1 shows an approximation of
what would be the minimal acceptable amount of coverage for thin
film layer 34. Here, thin film layer 34 is just sufficient to
contact each pole of ferrite column 16A. The amount of contact need
only be sufficient to allow the generated magnetic flux to enter
and pass through thin film layer 34. The width of thin film layer
34 is shown to be contained within glass beading 33. This width
could be reduced further, however the minimum width must be
sufficient to allow for writing gaps 36. Though such further
minimization is possible, it is optimal to have thin film layer 34
at least equal the width of the ferrite poles 16A to assure proper
flux transfer and to prevent the exposure of the corners of ferrite
column 16A. For purposes of patterning the channel width of thin
film 34, the relevant edges can be defined to fall within the width
of the glass bond 33. Such exposed corners will be localized
maximums in the magnetic field and will likely improperly write the
media. Channel 2 is devoid of thin film layer 34 (for ease of
illustration), while channels 3-5 show other patterns which are
possible. Virtually any size or shaped pattern could be obtained,
so long as sufficient channel separation occurs.
[0071] Though various patterns are achievable, certain factors will
determine which patterns are preferable for any given head 46. To
illustrate these factors it should be understood that the thin film
34 layer serves a dual purpose. First, it completes a magnetic
circuit by coupling together the poles in the ferrite columns (with
or without the additional consideration of channel separation).
Second, the thin film layer 34 acts as a tape bearing surface as
the media is pulled across the recording head 46. As such, the
minimum amount of coverage provided is limited by what is
acceptable to create the magnetic circuit. Ultimately, the maximum
amount could encompass the entire upper surface of the recording
head 46. In some cases, such maximized coverage is acceptable. As
discussed, it is often desirable to avoid any interaction between
the thin film layer 34 and the'air bleed slots 38. Then, the
maximum amount of coverage is defined by the distance D (FIG. 17)
between the innermost air bleed slots 38.
[0072] An additional consideration arises when an edge (E1-E4) of
the thin film layer 34 is located within the area defined by
distance D and the width of the head 46. Namely, the media will
strike or engage that surface E1-E4 as it moves across the head 46.
This is normally not a consideration when the thin film 34 covers
the entire head 46 because the edge of the thin film 34 corresponds
with the edge of the head 46 and this occurs at the most extreme
point of curvature (due to the radiused head 46). When an edge
E1-E4 is located closer to the gaps 36 located over ceramic member
14, and the media engages this edge at speed, it may be caused to
skip or jump away from the head 46. This issue is problematic if it
is random and unpredictable and/or if the media does not reengage
the head prior to the writing gaps 36. Obviously, if it skips the
writing gaps 36 the media cannot be properly written. Therefore, if
an edge E1-E4 is to occur, it is preferable that it occur further
from the writing gaps 36 occurring over ceramic member 14, as
illustrated in channel 5, by edge E4. In this location, if skipping
or jumping occurs, the media has a longer distance to correct
itself. This self correction may also be aided by the curvature of
the head 46. Furthermore, the pattern shown by channels 4 and 5 is
also advantageous in that a majority of the material transition
regions are covered by the thin film 34, thus preventing them from
damaging or inappropriately writing the media. The transition
regions include the transition from ceramic to glass, from glass to
ferrite, and from ferrite to ceramic.
[0073] To create the various patterns of thin film layer 34, any
known method of generating and defining a thin film can by
utilized. For example, larger areas can have a thin film deposited
on them and then wet etching or ion milling can be used to remove
sections. Alternatively, the thin film may simply be deposited in
the specific pattern desired. Such techniques are well known and
relatively easy to perform.
[0074] In operation, magnetic recording head 46 is secured to an
appropriate head mount. Magnetic tape is caused to move over and in
contact with the tape bearing surface of the head 46. At the
appropriate periodic interval, electrical current is caused to flow
through the coils 44. As a result, magnetic flux is caused to flow
through the back-bar 40, through the ferrite columns 16A-16E, and
through the magnetic thin film 34 (as the ceramic member 14
minimizes a direct flow from one pole of the ferrite column 16A-16E
to the other, causing the magnetic flux to shunt through the
permeable magnetic film). As the magnetic flux travels through the
magnetic thin film 34, it leaks out through the writing gaps 36,
thus causing magnetic transitions to occur on the surface of the
magnetic tape, in the same pattern and configuration as the gaps 36
itself.
[0075] The above head fabrication process has been described with
respect to a magnetic recording head employing a timing based servo
pattern. However, the process could be applied equally well to any
type of surface film recording head.
[0076] The present disclosure presents a plurality of elements and
concepts which work in a synergistic arrangement to arrive at a
highly efficient surface film magnetic recording head. It is to be
understood that these various elements and concepts can be
effectively utilized alone or in other combinations than disclosed
while still remaining within the spirit and scope of the present
invention. Namely, using a columned or combed head member in and of
itself produces a higher quality and more efficient head.
Similarly, removing the high reluctance back-gap and replacing it
with one or more magnetically permeable back-bars leads to a better
and more efficient surface film recording head. Utilizing both the
combed structure and back-bars produces an optimal head, achieving
synergistic results. Finally, utilizing a specific pattern of
magnetically permeable thin film to isolate the channels and to act
as the tape bearing surface, can be used alone or in combination
with the above aspects of the present invention to arrive at a
superior recording head.
[0077] Comparing two heads, each wound with two turns of wire and
driven by the same single channel drive circuit, the head pursuant
to this invention (FIG. 13) exhibits a current rise time in the 20
nanosecond range while the high inductance head made pursuant to
the Albrecht et al. patent (FIG. 18) exhibits current rise time in
the 50 nanosecond range. The corresponding inductances were
measured to be about 250 nH and 700 nH, respectively, for the two
heads. The shorter rise time corresponds roughly to the LIR time
constant of the head as a circuit element. Hence the low inductance
magnetic recording heads of the present invention are capable of
recording timing based signals on media resulting in sharper
magnetic transitions than media written with previously known
heads. As a result, both the heads produced and the media written
by those heads will perform significantly better than the prior art
heads and the media produced by them. With due consideration to the
details of the write circuitry, one can expect to at least double
the bandwidth by the use of the low inductance head of the present
invention. Even more dramatic results can be expected with the
independently driven, multi-channel low inductance head, as
illustrated in FIG. 12, while taking into account the limitations
of the multi-channel drive circuitry.
[0078] Those skilled in the art will further appreciate that the
present invention may be embodied in other specific forms without
departing from the spirit or central attributes thereof. In that
the foregoing description of the present invention discloses only
exemplary embodiments thereof, it is to be understood that other
variations are contemplated as being within the scope of the
present invention. Accordingly, the present invention is not
limited in the particular embodiments which have been described in
detail therein. Rather, reference should be made to the appended
claims as indicative of the scope and content of the present
invention.
* * * * *