Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Thin-film ma~netic head.
The invention relates to a thin-film magnetic
head which has an electric winding and comprises a number
of core parts of a magnetisable material of which at least
the gap-bounding core parts are thin layers and overlap
each other laterally while enclosing a gap-defining~layer
of a non-magnetisable material.
Such a magnetic head which is used for example
in sboring in~ormation in magnetic disc memories, is
10 ~ known from the published German Patent Application
2,104,445.
Presently there exists in the industry a
need of àn increase of memory storage capacity and hence
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o~ magnetic heads for very narrow tracks. The present
track width lies in the range of 150 to 200 microns.
; In connection with the above, however, there exists a need
of track widths of a few tens of microns. Since, however,
magnetic heads suitable for such narrow tracks can no
longer be realized in the conventional manner, in which
two core parts are placed in line with the interposition
o~ a non-magnetisable spacing member and in which the
thickness of the core parts determines the track width,
the thin-film magnetic head described in the above-mentioned
German Patent Application has been proposed. In this mag-
netic head, two core parts overlap each other laterally
at the area o~ the gap as a result of which the gap wi~th ~-
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is not determined by the thickness of the core parts but by the extent to
which the core parts overlap each other. Such a construction enables the
manufacture by means of thin-film methods and photolithographic methods of
heads which are suitable for track widths of a few tens of microns. A
drawback is~ however, that the area over which the core parts overlap each
other at the site of the gap, which area is large as compared with the thick-
ness of the core partsJ adversely influences the playback properties of ~he
head: the larger the extent of overlap, the smaller the playback efficiency.
It is the object of the lnvention to provide a head of the above-
mentioned kind in which the playback proper~ies are less dependent on the
extent of overlap of the core parts than in the known head and which more-
over has a number of extra advantages.
For that purpose, according to a broad aspect of the present in-
vention, there is provided a thin-film magnetic head comprising a first loop
shaped core part of magnetizable material having an upper surface with an
outer edge, a second core part of magnetizable material having a lower sur-
face and an outer edge and extending from one s.ide of the upper surfaces of
the first core part across the upper surface of the first core part to an
opposite side of the first core part and overlapping an area of the upper
surface of said opposite side of said first core part with a lower surface
of said second core part, said second core part being magnetically coupled
to said first core part at said one side of said first core part and provid-
ing an elongated surface parallel with the upper surface of the first core
part and having an elongated outer edge on said elongated surface parallel to
said outer edge of said first core part, and a layer of non-magne~izable
mater;al between the first and second core parts in the overlapping area
thereof, the outer edges of said first and said second core parts forming
therebetween a gap elongated in a direction perpendicular to the direction in
which the second core part exte~ds across the first core part.
~ith the same overlap area of the gap-bounding
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parts, the magnetic head according to the invention has considerably better
playback properties than the known head.
- If` desired, restriction of the overlap is possible by reducing the
width of the second core part at the area of and on either side of the first
core part.
The width of the second core part, at least at the area of the
first core part, preferably is at most half of the width of the first core
part.
Although the magnetic coupling of the above-mentioned ends of the
core parts may be carried out, for example, by means of a closing yoke on
which also an electric winding may be provided, a preferred embodiment of
the magnetic head according to the invention is characterized in that the
second core part is in the form of a closed loop and that the first core
part bridges the loop at least substantially in the centre. Such a con-
struction can be realized very suitably and in few steps by means of thin-
~ilm methods.
The symmetric structure of the magnetic head according to the
invention may advantageously be used to operate a number of said magnetic
~ heads in an x-y array.
A further preferred embodiment o~ the magnetic head according to
the invention is for that purpose characterized in that the parts of the
loop on either side of the bridging part are each provided with one or more
electric windings.~
A further preferred embodiment of the magnetic head according to
the invention is characterized in that in a symmetrically wound head as
described above, an auxiliary gap is provided in the loop-shaped second core
part exactly at the area o~ the centre of the gap, which auxiliary gap
intersects the core part entirely and extends at right angles to the gap.
The above-described constructlon of the head may advan*ageously
be used to position the head correctly with respect to an information track
to be followed. By providing the auxiliary gap, the actual gap is, as it
were, divided into two parts each covering one half of a track to be fol-
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lowed. When the head is not positioned correctly with respect to the track,
the wo windings provided on the outside of the loop will provide signals
which differ in amplitude during a playback operation. The difference sig-
nal may then be used to adJust the head in the correct place above the track
via a servo mechanism. Once the head has been ad~usted above the track, the
d~fference signal is equal to zero and the situation is maintained. The sum
signal then represents the complete playback signal.
Still a further preferred embodiment of the device according to
the invention is characterized in that at least one recording winding is
&rranged in the overlapping region of the gap. Herewith optimum recording
properties can be realized.
The invention ~ill be described in greater detail, by way of
example, wnth reference to the drawing.
Figure 1 shows a thin-film magnetic head of a known type.
Figure 2 shows a thin-film magnetic head according to the inven-
tion.
Figure 3 shows a special construction of the thin-film magnetic
head according to the invention.
Figure 4 shows a part of the magnetic head shown in Figure 3 on an
enlarged scale.
Figure 1 shows a known construction of a thin-film magnetic head 1
having gap-bounding parts 2 and 4 (made for example, of a nickel-iron alloy)
which overlap each other laterally and which are separated at the area of
the gap by a thin layer of a rlon-magnetic material 3, (for example glass).
The track width B is determdned by the extent to which the parts 2 and 4
overlap each other. The head 1 furthermore comprises electric windings 5.
Figure 2 shows a thin-film magnetic head 6 according to the inven-
tion. It consists of a loop-like magnetic layer 7 which is bridged in the
centre by an I-shaped magnetic layer 8. In the region of overlap of the
gap, the parts 7 and 8 are separated b~ a strip of non-mQgnetic material 9.
The trackwidth B is determined by the width o~ the part 8.
The provision of identical eiectric windings 10 and 11 makes it
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possible to operate a plurality of these heads on the same substrate in anx-y arrayO The overlap of the layers 7 and ô has been chosen to be so that
an optimum recording field can be realized. For that purpose, the layer 8
ends in the form of a trumpet and the two ends 12 and 13 of the layer 7
extend at an angle of approximately ~5 with respect to the la~er 8.
Such a construction of a head in itself is very suitable for the
magnetic recording on comparatively narrow tracks. With the positioning in
the usual manner by ~eans of a separate servo track, however, there is a
lower limit imposed upon the track width which can be used. When the track
becomes narrower than 100 /um it is necessary to derive a servo signal from
the signal-carrying track ~tself, since otherwise difficulties occur upon
playing back. A particular aspect of the invention resides in the fact that
a solution is given to adJust magnetic heads of the type shown above a track
recorded in a magnetic medium if the tracks become very narrow.
Identical recording windings 15 and 16 are provided around the two
outèr limbs ofthe magnetic circuit of a thin-film magnetic head 14 of the
three-limb type ~Figure 3) defined by a loop portion and on I-shaped portion.
AB ~shown on an enlarged scale in Figure ~, the front circuit 17 has two gaps.
The recording-playback gap 11 having a length equal to the track width B and
a small auxiliary gap 12, at right angles to 11, in the centre of the mag-
netic layer 12. The small auxiliary gap having a width equal to the thick-
ness of the magnetic layer thus separates the two outer limbs of the mag-
netic circuit from each other in the region of overlap. This has for its
result that, as it were, two gaps are formed in line with each other with a
length equal to half the track width. When the head is positioned roughly
above the track, the difference in the signals of the windings 15 and 16 may
be used to adiust the head above the track, while their sum constitutes the
play-back signal. When the head deviates from the track, there arises a
difference in sign~l amplitude of the windings 15 and 16. One half of the
gap l1 then sees more of the recorded track than the other. The difference
signal can readjust the head position via a servomechanism. The sign of
the difference signal is associated w1th a particular direction of the
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deviation.
The magnetic resistance between the two outer limbs in thé front
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circult 17 must be as large as possibleS because when there is a deviation
of the head, a maximum difference signal is necessary in view of the com-
paratively low flux level during playback. As a recording winding is used
a strip l30fanon-magnetisable electrically conductive materi~l present in
the region of overlap. The gap 12 must be small so as to minimize during
recording the disturbance in the centre of the recording field o~ the gap ll.
Said gap 12 otherwise requires no extra step in the manufacturing process of
the head.
As already noted above~ the integration of heads on batches creates
the possibility of operating the heads in the form of an array. One head of
said array may ensure the adjustment. Due ~o this ad~ustment, the mechanical
positioning becomes simpler also in the case of ver~v small tracks, tracks of
5 to 10 /um becoming realisable. In case the head which ensures the adjust-
ment is the Figure 3 head it may also fulfil its recording and playback
function nor~ally.
From a recording technical poi~t of view the inventive head is
further attractive due to the possibility which exists to provide a com-
- 20 paratively large number of windings and due to the favourable location of
the recording--layback gap.
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