Magnetic head having a core provided on a substrate by means of thin-film technology

A thin-film magnetic head in which the electrically conductive magnetic material of the core is wound directly a number of times around an electrical conductor which ensures the energization of the head presents the advantage that the manufacture can take place by means of exclusively electroplating methods, since in this configuration no insulating layers are necessary between the material of the core and the conductor.

The invention relates to a magnetic transducer head having a magnetic flux 
conductive core of metallic ferro-magnetic material deposited on a 
non-magnetic substrate by means of a thin-film technology process, and 
means for generating a magnetic flux in the core. 
A magnetic head of this kind is described in British Patent Specification 
No. 1,117,067. The patent discloses a head manufactured by means of 
thin-film technology which is formed by successively providing on a 
substrate a first electrically conductive pattern of strips, a first 
insulating layer, a layer of metallic ferromagnetic material, a second 
insulating layer, and a second pattern of conductive strips. The second 
pattern of strips is connected to said first pattern in such manner as to 
form an electrical winding with which a magnetic flux can be generated in 
the magnetic layer when a current is passed through the winding. A 
disadvantage of this construction of head is that two insulating layers 
(usually glass) are necessary between the core material (usually a 
nickel-iron alloy) and the winding so as to prevent the turns of the 
winding from being electrically short-circuited. The need to provide said 
two insulating layers requires the use of additional process steps during 
the manufacturing operation. 
It is an object of the invention to provide a magnetic head of the 
aforementioned kind which can be manufactured in a simple manner without 
requiring the deposition of insulating layers. For that purpose the 
magnetic head according to the invention is characterized in that the flux 
generating means comprises a flat pattern of electrical conductors and in 
that a plurality of flat turns formed from the core material are wound 
directly around a part of the conductor pattern. 
An advantage of the configuration in which the magnetic material is laid 
directly on the electrical conductor is that the current which is passed 
through the conductor does not flow to any significant extent through the 
metallic magnetic material of the core wound around it because the path 
length through the core material is longer than that through the 
conductor. This construction can allow the insulating layers to be 
omitted. If in the head of the aforementioned patent with the electrical 
conductor wound around the magnetic material, there had been an omission 
of the insulation layers, the winding turns would become shortcircuited 
since the current flow would then take a short path through the core 
material instead of the path through the turns. 
Within the scope of the invention, several alternative configurations are 
possible. In one example, the manufacturing operation can start from a 
metallized substrate and the metallic ferromagnetic layers for the core 
and the conductive material can be formed thereon via electrode-position 
methods. In the manufacture of the head configuration of the forementioned 
patent on the contrary, sputtering steps to provide the glass deposit for 
the insulation layer are needed in addition to the steps of the 
electrode-position process. 
In one embodiment, the magnetic head is characterized by a first core 
pattern of metallic ferromagnetic material which is provided on the 
substrate, a pattern of electrical conductors which is provided on the 
first core pattern and on the substrate and partly covers the first core 
pattern, and by a second core pattern of metallic ferromagnetic material 
which is provided on the pattern of conductors, the first core pattern and 
the substrate and partly covers the first core pattern while forming at 
least two flat turns, a part of the first core pattern on which a part of 
the pattern of conductors is provided and a part of the second core 
pattern provided thereon forming two poleshoes separated by a non-magnetic 
gap. 
A configuration as described above is very simple to manufacture. Since, 
however, both the turns and the poleshoes have to be formed from the core 
material, the poleshoe configuration is not readily adapted to specific 
applications, which may be experienced as a disadvantage in certain 
circumstances. 
To overcome this problem a second embodiment of the magnetic head according 
to the invention is characterized in that a closed path for conducting 
magnetic flux is formed from the material of the core, and a flat turn 
which is laid around the core couples same to a second core which 
comprises a first and a second magnetic layer, of which layers the ends 
are connected together magnetically in a first place and form poleshoes 
which are separated from each other by a part of the flat turn in a second 
place. 
An advantage of this configuration is that it is built up from two magnetic 
cores. A first one of said cores is laid around a conductor in a number of 
turns and the second core forms a separate magnetic flux path with 
separate poleshoes the selected configuration of which is capable of a 
wide variation. 
The invention will be described in greater detail, by way of example, with 
reference to the accompanying drawings but is not restricted to this 
embodiment.

FIG. 1 shows a multiturn magnetic head comprising a non-magnetic substrate, 
in this embodiment the substrate is a silicon slice 1, on which a pattern 
of conductors and patterns of magnetic material are provided by means of 
thinfilm technology. The head 9 also comprises a core of metallic 
ferromagnetic material which is composed of the parts 3 and 8 which form 
three flat turns which are wound around a flat electrical conductor 4. The 
ends of the parts 3 and 8 form poleshoes 5 and 6, while the region between 
these poleshoes acts as a transducing gap 7. During the manufacturing 
operation the slice 1 is oxidized and provided, by means of sputtering, 
with a so-called plating base 2 which has a thickness of 1000 A and 
consists of an electrically conductive material on which a desired 
electrode pattern can be grown by means of electrodeposition methods. 
During the manufacturing process, a layer of photolacquer (not shown) is 
provided on said plating base 2. At the area where the pattern a (see FIG. 
2) is to be provided, the photolacquer is removed by means of exposure to 
light through a suitable mask and development. In the lacquer pattern thus 
obtained, a layer 3 of nickeliron (Ni.sub.80 Fe.sub.20), approximately 4 
microns thick, is grown in a electroplating bath according to pattern a 
which forms the first layer of a magnetic core. The pattern of 
photolacquer is then removed and a fresh layer of photolacquer is provided 
of which the lacquer is removed in places where the pattern b (see FIG. 2) 
is to be provided by means of exposure to light and development. In the 
lacquer pattern thus obtained a layer 4 of copper, approximately 4 microns 
thick, is grown in an electroplating bath according to the pattern b. Said 
thickness is necessary for a good operation of the magnetic head described 
here. The thickness of the copper layer 4 at the area where the ends of 
the magnet core form poleshoes 5 and 6 also determines the length of the 
effective gap 7 of the magnetic head. When a gaplength L is desired which 
is less than the thickness of the copper layer 4, this may be grown, for 
example, in two steps, the first step determining the gaplength and the 
second determining the thickness of the part of the layer of conductors 
which is not present between the poleshoes 5 and 6. The pattern of 
photolacquer used is then removed and a fresh layer of photolacquer is 
provided of which at the area where the pattern c (see FIG. 2) is to be 
provided the lacquer is removed by means of exposure to light and 
development. In the lacquer pattern thus formed, a layer 8 of nickel-iron 
(Ni.sub.80 Fe.sub.20), thickness 4 microns, is grown according to pattern 
c in an electroplating bath. The layers 3 and 8 then form a magnetic core 
which is wound three times around the conductor 4 and has two ends which 
constitute poleshoes 5 and 6 which are separated from each other by the 
non-magnetic material of the layer 4. Finally, the last-used pattern of 
photolacquer, as well as the excessive unused portion of the plating base 
2 are to be removed, which may be done, for example, by means of 
sputter-etching. FIG. 1 shows the magnetic head according to the invention 
before this step has been carried out. The sputter-etching step slightly 
attacks the grown copper and nickel-iron layers but due to the small 
thickness of the plating base 2 only a short period of time is necessary 
for the sputter-etching step so that in practice the effect of the said 
attack is negligible. If desired, the formed three-turn-magnetic head 9 
may be covered with a protective layer of quartz (not shown). 
As a result of the above described construction, the poleshoe configuration 
is already fixed beforehand to a considerable extent. If one wants to be 
less restricted in choice of the poleshoe configuration, the alternative 
construction shown diagrammatically in FIG. 3 may be preferable. FIG. 3 is 
a plan view of a double track magnetic head 10 which consists of two 
mirror-symmetrical single heads 11 and 12. Since the construction of the 
heads 11 and 12 is similar, only the construction of head 11 will be 
described in detail. The head 11 consists of a first magnetic core 13 
which is wound once around an electrical conductor 14 as shown in the side 
elevation view-depicted in FIG. 4. The ends of the core 13 constitute 
poleshoes 15 and 16 which are separated from each other by the 
non-magnetic material of the conductor 14. Via the conductor 14 the magnet 
core 13 is coupled to a second magnetic core 17 which is wound four times 
around a conductor 18 in the manner as described above. In fact, the left 
hand half of FIG. 3 shows a single turnhead having a transformer. The 
poleshoe configuration in this construction is capable of variation 
through a wide range. A further advantage is that, since the turns of the 
magnetic core 17 are situated mainly behind the poleshoes, and not beside 
them, the construction of the head 11 is suitable to be combined with a 
second similar head (in this case the head 12) to form a double track 
head. 
The properties of the three-turn-head shown in FIG. 3 have been measured in 
a disk memory apparatus in which the surface speed of the disk was 40 
m/sec and the height on which the head was floating above the surface was 
0.5 micron. With a track width W of 50 microns, a gap length L of 2 
microns and a relative permeability of the material of the magnetic core 
of 2500, the output voltage obtained was 0.1 mV. This corresponds to 65% 
of the output voltage which a conventional thin-film head having three 
turns (conductor wound around the core; insulation between core and 
winding) can theoretically supply under the same conditions. 
With respect to the dimensions of the head shown in FIG. 1 it may be noted 
that the widths W.sub.1 and W.sub.2 of the provided pattern were each 50 
microns and that the distance d between the turns was 10 microns.