Magnetic head for perpendicular magnetic recording system

A magnetic head for perpendicular magnetic recording system which assures low write current and high recording reproduction efficiency by using a flat coil and increasing the number of turns of the coil. The flat coil is formed on a substrate and a main pole piece is arranged in the center of the coil and vertically to the surface on which the coil is formed. This magnetic head is suitable particularly for manufacture as a thin film magnetic head.

FIELD OF THE INVENTION 
This invention relates to a magnetic head for perpendicular magnetic 
recording systems which is suitable for manufacture as a thin film 
magnetic head and which increases the recording/reproduction efficiency by 
providing a flat coil on a substrate and a main pole piece at the center 
of said coil in order to allow the magnetic flux of the magnetic field 
generated by said coil to flow vertically to the surface on which said 
coil is formed. 
BACKGROUND OF THE INVENTION 
As is well known, magnetic recording methods are classified generally into 
two kinds of modes. The first one is a recording mode utilizing the 
longitudinal residual magnetization to the surface of the recording 
medium, while the other is a mode utilizing the perpendicular residual 
magnetization. The former longitudinal magnetic recording method has long 
been employed, but investigation and development of the latter 
perpendicular magnetic recording mode have been widely continued because 
this latter method provides higher recording density as compared with the 
longitudinal recording method. 
As to this perpendicular recording mode, the systems as indicated in FIG. 1 
and FIG. 2 are currently known. 
Namely, known is the perpendicular magnetic recording system comprising a 
magnetic head obtained by providing a main pole piece 2, as indicated in 
FIG. 1, perpendicular to the magnetic recording medium, where the Co-Cr 
alloy film having the magnetic anisotropy in the perpendicular direction 
is provided on a plastic or aluminium base material 3, and by forming a 
coil 1' around said main pole piece 2. 
This recording system is generally called the main pole excitation system. 
Also known is the perpendicular magnetic recording system having a 
magnetic head, as indicated in FIG. 2, where the main pole piece 2 and the 
auxiliary pole piece 4 are provided perpendicular to the magnetic 
recording medium as indicated in FIG. 1 mutually facing the medium and a 
coil 1' is formed around the auxiliary pole piece 4. This system is 
generally called the auxiliary pole excitation system. In such 
perpendicular magnetic recording systems, the perpendicular magnetic 
recording is carried out as indicated in FIGS. 1 and 2 on the recording 
medium by exciting the coil 1' of the magnetic head. 
Such perpendicular recording systems, however, have the disadvantages as 
explained below. 
Namely, in the perpendicular recording system employing the main pole 
excitation method indicated in FIG. 1, this main pole piece 2 itself 
determines the recording density of the medium and is designed in a very 
small size. Therefore, it is difficult to form a coil having a large 
number of turns to said main pole piece 2, and resultingly it cannot 
generate an intensified magnetic field. 
In addition, since the coil is formed around this main pole piece 2, it 
cannot be formed in a large size because it would be difficult to generate 
a sharp magnetic field for the recording medium. 
Moreover, a thin film magnetic head has been employed recently in order to 
miniaturize the magnetic head, but if formation of such a magnetic head 
using a thin film head is attempted, formation of the coil will become 
difficult and the manufacturing processes will also be complicated. 
On the other hand, in the case of the auxiliary pole excitation system 
indicated in FIG. 2, recording is carried out on the recording medium by 
concentrating the magnetic flux generated by the auxiliary pole 4 to the 
main pole 2. The recording efficiency is rather bad, however, because the 
magnetic film of the recording medium 1 and the magnetic field generation 
position are apart. Moreover, the coil 1' has a large inductance and it is 
difficult to drive such a magnetic head at a high speed. 
Since the main pole 2 and the auxiliary pole 4 are provided face to face on 
both sides of the recording medium, this system also cannot be used for 
magnetic recording systems using a thick substrate recording medium, such 
as a magnetic disk unit. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of this invention is to offer a magnetic head to be used for the 
perpendicular recording system of the main pole excitation type, where the 
number of turns of the coil in the main pole excitation system can be 
increased and such head can be manufactured easily as a thin film magnetic 
head by forming a flat coil on a substrate and forming the main pole 
vertically to the surface where said coil is formed and at the center of 
said flat coil. According to this invention, a magnetic head comprises a 
flat coil formed on a substrate and a main pole piece formed at the center 
of said coil vertical to the surface where said coil is formed, and 
wherein said substrate, coil and main pole piece are integrated into one 
unit. 
Further features and advantages of the present invention will be apparent 
from the ensuring description with reference to the accompanying drawings 
to which, however, the scope of the invention is in no way limited.

DETAILED EXPLANATION OF THE INVENTION 
The magnetic head for the perpendicular magnetic recording system of the 
present invention will be explained by referring to a first embodiment, as 
depicted in FIGS. 3 and 4. As best seen from FIG. 4, a main pole 5 is 
obtained by evaporating or sputtering or plating a ferromagnetic thin 
film, such as permalloy, on an edge of the insulated glass substrate 10-1. 
A main pole or upper block 7 can be obtained by bonding the insulated 
glass substrate 10-1 on which edge the main pole 5 is formed and an 
insulated glass substrate 10-2 with a bonding layer 11. The cross section 
of the main pole 5 is about 4 .mu.m .times.70 .mu.m, while the thickness 
of bonding layer 11 is about 20 .mu.m. 
A ferromagnetic substrate 16 is obtained by using, for example, NiZn 
ferrite. A coil 6 is formed on the ferromagnetic substrate 16 by thin film 
technology, for example, evaporation or sputtering, and a magnetic core 
14, such as permalloy, is formed on the substrate 16 in the same way at 
the center of the thin film coil 6. The thin film coil 6 is, for example, 
a laminated coil with 5.times.2 turns, and an insulation layer 15, such as 
SiO.sub.2, exists between the first and second layers. A conductor 13 of 
the thin film coil 6 is formed, for example, having a cross section of 4 
.mu.m.times.30 .mu.m. In addition, the size of the magnetic core 14 is, 
for example, about 12 .mu.m.times.100 .mu.m.times.100 .mu.m. The coil or 
lower block 8 can be obtained by forming the thin film coil 6 and the 
magnetic core 14 on the ferromagnetic substrate 16. The main pole block 7 
and the coil block 8 are bonded by means of a bonding layer 12. Depth d, 
as shown in FIG. 4, from the surface of the main pole block 7 to the thin 
film coil 6 is, for example, about 50 .mu.m. 9-1 and 9-2, as shown in FIG. 
3, are terminals for the thin film coil 6. 
FIG. 5 indicates the magnetic field generation characteristic of the coil. 
The characteristic indicated in FIG. 5 is measured by using a model 
obtained by magnifying 100 times the coil indicated in FIG. 4. The coil 
has a winding of 180 turns and the magnetic field intensity is measured 
just above the center of the coil. In FIG. 5, the curve obtained by 
plotting the triangle marks indicates the characteristic when no 
ferromagnetic substrate 16 is used at the rear side of the coil, the curve 
obtained by plotting circles indicates the characteristic when the 
ferromagnetic substrate 16 is used at the rear side of the coil, and the 
curve obtained by plotting large dots indicates the characteristic when 
the ferromagnetic core 14 exists at the coil center and the ferromagnetic 
substrate 16 exists at the rear side. As can be seen from FIG. 5, when the 
ferromagnetic material exists at the rear side of the coil, an intensified 
magnetic field is generated, and when a magnetic core exists at the coil 
center, magnetic field intensity is improved by about 30%. 
FIG. 6 shows the vertical distribution characteristic of the magnetic field 
obtained by using the model of FIG. 5. The curves obtained by plotting 
circles and large dots have the same meaning as those of FIG. 5. As can be 
seen from FIG. 6, both the magnetic field decrease in vertical Y 
distribution but the magnetic field when a magnetic core exists is larger 
than that when a magnetic core does not exist. 
The magnetic field of the coil required for saturated writing to the Co-Cr 
layer of the recording medium is considered about 1500e when measured at 
the end of the main pole of the magnetic head. From FIG. 5, the AT (ampere 
turn) required for obtaining 1500e is 220 AT at the area being apart by 5 
mm from the coil surface. In the case of an actual magnetic head, the AT 
becomes 2.2 AT at the area being apart by 50 .mu.m from the coil surface 
and when a coil of 10 turns is obtained, the saturated writing can be 
realized with 200 mA. The thin film coil with 10 flat turns of winding can 
be obtained easily and in this case the inductance is about 0.1 .mu.H. In 
the conventional auxiliary pole excitation system, the a coil inductance 
is about 100 .mu.H. From this fact, this invention has fantastically 
improved the operation speed as compared with the conventional auxiliary 
pole excitation system. The head of the present invention and the 
conventional head are compared in the following table. However, a current 
value indicated is necessary for generation of coil magnetic field of 150 
Oe. 
______________________________________ 
Excitation No. of 
system Shape turns Current 
Inductance 
______________________________________ 
Auxiliary 
0.7 .times. 3 .times. 1.5 mm 
100 turns 
0.2 A 100 .mu.H 
pole 
Main pole 
0.01 .times. 0.5 .times. 0.03 
3 turns 1 A 0.001 .mu.H 
Present 1 .times. 1 .times. 0.1 
10 turns 
0.22 A 0.1 .mu.H 
invention 
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As will be apparent from the above table, the present invention realizes a 
magnetic head for the perpendicular magnetic recording system providing 
only the merits of both the auxiliary pole excitation system and the main 
pole excitation system. 
FIG. 3 and FIG. 4 show the embodiment where the coil 6 is obtained by thin 
film fabrication technology, but a similar characteristic can also be 
obtained by arranging ordinary small size winding coil. 
FIG. 7 to FIG. 16 respectively show other embodiments of this invention. In 
these figures, 16' is a nonmagnetic substrate and 17 is a ferromagnetic 
thin film, layer. The same portions or elements of the magnetic head shown 
in FIG. 3 and FIG. 4 are given the same symbols for the embodiments shown 
in FIGS. 7-16. 
In the embodiment of FIG. 7, a composite substrate having the ferromagnetic 
thin film 17 formed on the non magnetic substrate 16' is provided in place 
of the ferromagnetic substrate 16 used in the embodiment indicated in 
FIGS. 3 and 4. 
In the embodiment of FIG. 8, the upper block, after bonding the glass 
substrate 10-1 with the main pole 5 and the glass substrate 10-2 and 
forming a thin film coil 6 on the glass substrates 10-1 and 10-2, and the 
lower block , after forming the magnetic core 14 on the ferromagnetic 
substrate 16, are coupled together. 
In the embodiment of FIG. 9, a composite substrate having the ferromagnetic 
thin film 17 formed on the nonmagnetic substrate 16' is provided in place 
of the ferromagnetic substrate used in the embodiment of FIG. 8. 
In the embodiment of FIG. 10, the upper block, after bonding the glass 
substrate 10-1 with the main pole 5 and the glass substrate 10-2 and 
forming a magnetic core 14 on the glass substrates, and the lower block, 
after forming a magnetic core 14 and the thin film coil 6 on the lower 
block head substrate, are coupled together. As the lower block head 
substrate, either the ferromagnetic substrate or the composite substrate 
as previously described may be used. 
In the embodiment of FIG. 11, the upper block, obtained after bonding the 
glass substrate 10-1 with the main pole 5 and the glass substrate 10-2 and 
forming the thin film coil 6 and a magnetic core 14 on the substrate, and 
the lower block obtained by forming a magnetic core 14 on the lower block 
head substrates are coupled together. 
In the embodiment of FIG. 12, the lower block, where the coil 6 is formed 
on a composite substrate obained by first forming the ferromagnetic core 
14 on the nonmagnetic substrate 16' and then forming the ferromagnetic, 
thin film 17 on the nonmagnetic substrate 16' and over the core 14 and the 
upper block, obtained by bonding the glass substrate 10-1 with the main 
pole 5 and the glass substrate 10-1 are coupled together. Ferromagnetic 
core 14 also may be provided on both the upper and lower blocks. 
In the embodiment of FIG. 13, in place of the ferromagnetic core 14 and 
ferromagnetic thin film 17 being formed on the lower block as in the 
embodiment of FIG. 9, the ferromagnetic thin film 17 is formed on the 
upper block after formation of coil 6 on substrates 10-1 and 10-2 in order 
to obtain the effects of both the ferromagnetic core and ferromagnetic 
thin film. The nonmagnetic substrate 16' may be replaced by the magnetic 
substrate. 
In the embodiment of FIG. 14, the magnetic core 14 used in the embodiments 
of FIG. 7, FIG. 8 and FIG. 9 is not used and the main pole piece 5 reaches 
the lower block. The lower block substrate may be a magnetic substrate or 
nonmagnetic substrate or composite substrate of the nonmagnetic substrate 
and magnetic substrate. 
In the embodiment of FIG. 15, the main pole piece 5 used in the embodiments 
of FIG. 1 to FIG. 14 has a magnetic flux focusing structure 6' in order to 
improve the characteristic. The magnetic flux focusing structure is 
classified into the structure for focusing the magnetic flux to the end 
from the point of view of the shape. 
In the embodiment of FIG. 16, a coil 6' is arranged at the end of the main 
pole 5. The coil 6' is connected to the coil 6 in order to improve 
reproduction efficiency. 
In the above embodiments, the recording/reproduction head is obtained by 
coupling the main pole block and the coil block, i.e., the upper block and 
the lower block, but the recording/reproduction head of this invention can 
be obtained by other methods. For example, in case of obtaining the 
recording/reproduction head indicated in FIG. 3 and FIG. 4, the magnetic 
core 14 and the thin film coil 6 are formed on the ferromagnetic substrate 
16 by the ordinary evaporation method, etc., and thereon the main pole 5 
may be formed by such a method as mask evaporation, etc. 
As is apparent from the above explanation, the present invention offers a 
magnetic head for the perpendicular magnetic recording system having only 
the merits of recording/reproduction heads of both the conventional main 
pole excitation system and the auxiliary pole excitation system.