Magneto-resistive composite head and a magnetic disk device, having grounded magnetic shielding layers

To provide an MR composite head wherein damage of an MR element due to discharge of the static electricity is surely prevented with a simple configuration without degrading reproduction performance of the MR composite head, a first and a second magnetic shield layer (14 and 17), whereby the MR layer (20) is sandwiched, are designed to be grounded through a suspension (25). In an embodiment, a conductive member (24) is formed at an upper surface (11b) of the MR composite head (11) opposite to a facing surface (11a) facing to a magnetic disk (31), for electrically connecting the first and the second magnetic shield layer (14 and 17) to a slider (12) which is electrically connected to the suspension (25).

BACKGROUND OF THE INVENTION 
The present invention relates to a magneto-resistive composite head having 
a structure for evading damage of its magneto-resistive element caused by 
discharge current generated at read/write movement, and a magnetic disk 
device having the same. 
Along with recent development of large capacity and high density magnetic 
disk devices, reproduction output of magnetic recording media becomes 
finer and finer, and magneto-resistive composite heads, which have 
advantage for detecting the fine reproduction output, are to be used 
widely. 
In the magneto-resistive composite head, comparatively large reproduction 
output can be obtained making use of the magneto-resistive effect, 
independent of head speed relative to the recording medium. 
FIG. 5 is a perspective view illustrating a conventional example of a 
magnetic disk device provided with magneto-resistive composite heads. The 
magnetic disk device comprises a magnetic recording medium (a magnetic 
disk) 31 rotatably supported around an axis A, a magneto-resistive 
composite head (hereinafter simply called the composite head) 42. The 
composite head 42 is unitized in a slider 12 and supported by a suspension 
44 movable in a quasi-radial direction of the magnetic disk 31 for 
reading/writing information on a recording surface thereof. The suspension 
44 is driven by an actuator 47 by way of a fixation arm 45 and a carriage 
46. In the magnetic disk device of FIG. 5, a head amplifier 48 is provided 
at a side surface of the actuator 47 for amplifying the read/write signal. 
The slider 12, the suspension 44, the actuator 47 and the magnetic disk 31 
are connected electrically with each other and maintained at the same 
potential by way of a housing (not depicted in the drawings) whereby they 
are mounted and covered. 
With rotation movement of the magnetic disk 31, the slider 12 moves 
relative to the disk surface, flying Up or sliding on the disk surface in 
a circumference direction thereof, and moves in the radius direction 
according to rotation of the carriage 46, whereby the composite head 42 is 
positioned on a necessary point of the disk surface for reading/writing 
information on the recording surface of the magnetic disk 31. 
FIG. 6 is a magnified sectional view of the composite head 42 which is 
configured making use of a thin film forming process at a side surface of 
the slider 12 made of a conductive material. 
Referring to FIG. 6, the composite head 42 comprises a first insulation 
layer 13, a first magnetic shield layer 14, a second insulation layer 16, 
a second magnetic shield layer 17, a magnetic pole layer 18, and a third 
insulation layer 19, laminated in the order from the side surface of the 
slider 12. 
The second magnetic shield layer 17 functions as a second magnetic pole 
layer as well, and compose a magnetic core of the recording element of the 
composite head 42 together with the magnetic pole layer 18. Between the 
first magnetic shield layer 14 and the second magnetic shield layer 17, a 
magneto-resistive element (hereinafter called the MR layer) 20 is 
configured so as to align with a facing surface 11a of the composite head 
facing to the recording surface of the magnetic disk 31. 
The second magnetic shield layer 17 is configured as a straight plane and 
the magnetic pole layer 18 is configured as a concave plane, so as to 
create a space between them, wherein a fourth insulation layer 21 is 
configured. The second magnetic shield layer 17 and the magnetic pole 
layer 18 are magnetoelectrically connected with each other at their upper 
(of the drawing) ends, and their lower ends are aligned with the facing 
surface 11a being separated a little so as to make a magnetic gap 23. 
Traversing the third and the fourth insulation layer 19 and 21, a write 
coil 22 is configured and the write signal flows therein. To the MR layer 
20, lead patterns (not depicted in the drawings) are connected for 
supplying a sense current, which generates reproduction voltage to be 
amplified by the read/write amplifier 48 according to resistivity 
variation of the MR layer 20. 
By supplying the write signal current to the write coil 22 of the composite 
head 42 thus configured, magnetic information is recorded on the magnetic 
disk 31 with a magnetic field generated around the magnetic gap 23, and 
the recorded magnetic information is reproduced by supplying the sense 
current to the MR layer 20 through the lead patterns. 
There are magnetic recording devices employing a near-contact read/write 
system wherein the composite head 42 is intermittently contacting with the 
magnet disk 31, or a contact read/write system wherein the composite head 
42 is always contacting with the magnetic disk 31. By employing these 
read/write systems, a space between the facing surface 11a and the 
magnetic disk 31 is designed as narrow as possible for enlarging magnetic 
field intensity to be detected by the MR layer 20. 
Here, the surface of the magnetic disk 31 is usually covered with an 
insulation material such as a protection film or a lubricant film, and it 
is the same with the facing surface 11a of the composite head 42. 
Therefore, certain static electricity is charged between the facing 
surface 11a and the magnetic disk 31, due to their direct friction or 
their friction with air molecules flowing between them, especially in the 
magnetic disk devices employing the above contact or near-contact 
read/write systems. 
The composite head 42 is flying or sliding on the magnetic disk 31 
separated with a space smaller than 0.1 .mu.m. Therefore, the charged 
static electricity is discharged through the MR layer 20 when its 
potential becomes higher than a breakdown voltage of the air (about 3.5 
kV/.mu.m, at 20.degree. C., 1,013 hectopascal) or of the 
protection/lubrication film. 
The electric discharge generally occurs towards a narrowest point of the 
insulation space or towards a good conductor such as metallic material. 
Therefore, in the composite head 42 having such a structure as illustrated 
in FIG. 6, the static electricity is easy to be discharged through the MR 
layer 20 which is connected to the ground by way of a good conductor of 
the lead patterns. 
Furthermore, thickness of the second insulation layer 16 between the MR 
layer 20 and the first or the second magnetic shield layer 14 or 17 is 
very thin and within 0.3 .mu.m, for example. Therefore, electric 
discharges occurring towards the first or the second magnetic insulation 
layer 14 or 17, or towards the magnetic pole layer 18, which is 
electrically connected to the second magnetic shield 17, may also cause 
discharge current flowing through the MR layer 20 to the ground. 
Thickness of the MR layer 20 is usually within about 30 nm and width 
thereof is within about 2 .mu.m. Therefore, discharge current flowing in 
the very small cross section of the MR layer 20 may cause sufficient heat, 
even when its current value is small, for melting and breaking the MR 
layer 20, resulting in loss of the reproduction function of the composite 
head 42. 
For preventing this damage of the reproduction head, especially of the MR 
layer thereof, due to the discharge current, some devices have been 
proposed. 
In a Japanese patent application laid open as a Provisional Publication No. 
63019/'97 (hereinafter called the first prior art), there is disclosed a 
magnetic head provided with a grounding member, or a discharge arrestor, 
at a position nearest to the magnetic disk, for by-passing discharge 
current from the magnetic disk to the ground. In an composite head 
disclosed in another Japanese patent application laid open as a 
Provisional Publication No. 73419/'95 (hereinafter called the second prior 
art), each one of the first and the second magnetic insulation layer 14 
and 17 of FIG. 6 is so configured as to contact with each different one of 
the lead patterns of the MR layer 20 for preventing the discharge current 
flowing through the MR layer 20. 
In the first prior art, the first magnetic shield layer 14 and the second 
magnetic shield layer 17 connected with the magnetic pole layer 18 of FIG. 
6 are both electrically floating to the ground, and hence, the static 
electricity charged in the composite head 42 is easy to be discharged 
through the MR layer 20. Further, when the grounding member is not 
correctly positioned, discharge may occur to the MR layer 20 from the good 
conductors of the first magnetic shield layer 14 or the second magnetic 
shield layer 17 and the magnetic pole layer 18, or also direct discharge 
from the magnetic disk 31 to the MR layer 20 may occur depending on flying 
posture of the magnetic head at the CSS (Contact Start Stop) or the 
sliding. Still further, the grounding member is to be provided on the 
facing surface 11a at a position nearest to the magnetic disk 31, which 
means other elements including the MR layer 20 should be more separated 
than necessary from the magnetic disk 31, resulting in degradation of 
sensitivity and the resolution ability of the magnetic head. 
In the second prior art, complicated film growth processes are needed for 
configuring each of the first and the second magnetic shield layer 14 and 
17 to contact with each one of the lead patterns, resulting in a high 
production cost of the composite head. 
SUMMARY OF THE INVENTION 
Therefore, a primary object of the present invention is to provide a 
magneto-resistive composite head wherein damage of the MR element due to 
discharge of the static electricity is surely prevented with a simple 
configuration without degrading reproduction performance of the 
magneto-resistive composite head, and to provide a magnetic disk device 
having high reliability making use of the magneto-resistive composite 
head. 
In order to achieve the object, in a magneto-resistive composite head of 
the invention having a reproduction head comprising a magneto-resistive 
element provided between a first and a second magnetic shield layer formed 
on a side surface of a slider supported by a suspension; the first and the 
second magnetic shield layer are designed to be grounded through the 
suspension. 
In an embodiment of the invention, the magneto-resistive composite head 
comprises a conductive member formed at an upper surface of the 
magneto-resistive composite head opposite to a facing surface facing to a 
magnetic disk, for electrically connecting the first and the second 
magnetic shield layer to the slider which is electrically connected to the 
suspension. 
In another embodiment, the magneto-resistive composite head comprising 
conductive resin adhering to the upper surface of the magneto-resistive 
composite head, for electrically connecting the first and the second 
magnetic shield layer to the slider. 
The suspension may be designed to connect electrically to the first and the 
second magnetic shield layer at the upper surface of the magneto-resistive 
composite head. 
Therefore, the first and the second magnetic shield layer neighboring to 
the magneto-resistive element are grounded through good conductors, and 
hence, even when the static electricity charged in the magnetic disk is 
discharged towards the magneto-resistive composite head, the discharge 
current is grounded without affecting the magneto-resistive layer, and 
therefore, the magneto-resistive layer can be surely prevented from break 
or degradation due to melting because of the discharge current, enabling 
to heighten reliability of the magnetic disk device. 
Furthermore, the spacing between the magneto-resistive layer and the 
magnetic disk can be still reduced, evading as well the electric discharge 
towards the magneto-resistive layer, which enables further improvement of 
the resolution ability and consequently, recording density of the magnetic 
disk device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, embodiments of the present invention will be described in connection 
with the drawings. 
FIG. 1 is a magnified sectional view of a magneto-resistive composite head 
11 according to a first embodiment of the invention. 
The composite heard 11 of FIG. 1 comprises a first insulation layer 13, a 
first magnetic shield layer 14, a second insulation layer 16, a second 
magnetic shield layer 17, a magnetic pole layer 18, and a third insulation 
layer 19, which are laminated in the order on a side surface of a slider 
12. 
The second insulation layer 16 is made of an insulation material such as 
Al.sub.2 O.sub.3 having a volume resistivity of 10.sup.14 
.OMEGA..multidot.cm, and the first and the second magnetic insulation 
layer 14 and 17 and the magnetic pole layer 18 are made of metallic 
materials. 
In the second insulation layer 16 formed between the first and the second 
magnetic insulation layer 14 and 17, an MR (magneto-resistive) layer 20 is 
configured so as to align with a facing surface 11a of the composite head 
11 facing to the recording surface of the magnetic disk 31. To he MR layer 
20, lead patterns are connected for supplying a sense current and the 
first and the second magnetic shield layer 14 and 17 and the MR layer 20 
compose a reproduction head. 
The second magnetic shield layer 17 is configured as a straight plane and a 
center part of the magnetic pole layer 18 is configured to form a concave 
plane. In a space formed between the second magnetic layer 17 and the 
magnetic pole layer 18, a fourth insulation layer 21 is configured. The 
second magnetic shield layer 17 and the magnetic pole layer 18 are 
magnetoelectrically connected with each other at their upper (of the 
drawing) ends, and their lower ends are aligned with the facing surface 
11a being separated a little so as to make a magnetic gap 23. Thus 
configured, the second magnetic shield layer 17 and the magnetic pole 
layer 18 compose a recording head functioning as a pair of magnetic poles 
having the magnetic gap 23 between them. Traversing the third and the 
fourth insulation layer 19 and 21, a write coil 22 is configured and the 
write signal flows therein. 
In the composite head 11 according to the first embodiment, a conductive 
member 24 is provided at an tipper surface 11b (opposite to the facing 
surface 11a) covering upper ends of the first insulation layer 13, the 
first magnetic shield layer 14, the second insulation layer 16 and the 
second magnetic shield layer 17. Both ends of the conductive member 24 are 
electrically connected to the side surface of slider 12 and the upper part 
of the magnetic pole 18, respectively. In the embodiment of FIG. 1, an 
insulation material 15 is configured on the conductive member 24. However, 
the conductive member 24 may be exposed directly to the air without 
providing the insulation material 15. Tile conductive member 24 is made of 
paramagnetic conductive material and electrically connects the first and 
the second magnetic shield 14 and 17 to the slider 12 made of conductive 
material such as AlTiC having volume resistivity of about 2,000 to 3,000 
.mu..OMEGA..multidot.cm. 
To the upper surface (opposite to the facing surface 11a) of the slider 12, 
a suspension 25 is connected electrically and mechanically, 20 and the 
slider 12 is supported by a carriage (not depicted in FIG. 1) through the 
suspension 25. Therefore, the conductive member 24 is grounded by way of 
the slider 12, the suspension 25 and the carriage. 
As to the conductive member 24, it is also made of conductive paramagnetic 
material having volume resistivity of under 100 .mu..OMEGA..multidot.cn, 
such as gold (volume resistivity 2 .mu..OMEGA..multidot.cm) or copper, 
making use of a thin film forming process. 
Now, functions of the composite head 11 is described referring to FIGS. 2A 
and 2B. 
FIG. 2A is a circuit diagram schematically illustrating an equivalent 
circuit of the conventional composite head 42 of FIG. 6 and FIG. 2B is 
that of the composite head 11 according to the embodiment of FIG. 1. 
In the equivalent circuit of FIG. 2A, the write coil 22 of FIG. 6 is 
represented by a coil resistance Rc and a coil inductance Lc serially 
connected between terminals 22a and 22b, and the MR layer 20 is 
represented by a MR resistance Rmr connected between terminals 20a and 
20b. The second magnetic shield layer 17 and the magnetic pole layer 18, 
which are connected electrically, are represented by a conductive line 
17-18 in the same way with the first magnetic shield layer 14 and the 
slider 12 of FIG. 6 represented by conductive lines 14 and 12, 
respectively. 
In the conventional composite head 42 of FIG. 6, the slider 12, the first 
magnetic shield layer 14, the MR layer 20, a connection of the second 
magnetic shield 17 and the magnetic pole layer 18, and the write coil 22 
are electrically isolated from each other with the first, the second, the 
third and the fourth insulation layer 13, 16, 19 and 21, 20 which are 
represented by parasitic capacitance C1, C2, C2', C3, C3', C4 and C4'. 
On the other hand, the slider 12, the first and the second magnetic shield 
layer 14 and 17 and the magnetic pole layer 18 are electrically connected 
with each other by way of the conductive member 24 and grounded through 
the slider 12 and the suspension 25 in the composite head 11 of the 
embodiment of FIG. 1, which is represented by grounding of the conductive 
lines 12, 14 and 17-18 in the equivalent circuit of FIG. 2B. 
Therefore, the static electricity to be charged in the composite head 11, 
which is equivalent to electricity to be charged in the parasitic 
capacitance C1, C2, C2', C3, C3', C4 and C4', is evacuated to the ground 
by way of the conductive member 24 from the first and the second magnetic 
shield layer 14 and 17 and the magnetic pole layer 18 through the slider 
12 and the suspension 25, affecting nothing to the MR layer 20. 
Further, the electric discharge from the magnetic disk 31 towards the 
composite head 11, which may occur at the CSS or the sliding of the 
composite head 11 with the magnetic disk 31, is prevented to reach to the 
MR layer 20, flowing to the ground through either of the first and the 
second magnetic shield layer 14 and 17 without affecting the MR layer 20. 
This is because thickness of the first or the second magnetic shield layer 
14 or 17 is about 3 .mu.m and far larger than thickness of the MR layer 20 
which is about 30 .mu.m, and the first and the second magnetic layer 14 
and 17 are directly grounded through good conductors such as the slider 12 
and the conductive member 24. 
As heretofore described, the first and the second magnetic shield layer 14 
and 17, and the magnetic pole layer 18 are all electrically connected to 
the slider 12 by way of the conductive member 24 and grounded through good 
conductors. Hence, even when the static electricity charged in the 
magnetic disk 31 is discharged towards the composite head 11, the 
discharge current is grounded without affecting the MR layer 20, and 
therefore, the MR layer 20 can be surely prevented from break or 
degradation due to melting because of the discharge current, enabling to 
heighten reliability of the magnetic disk device. 
Furthermore, the spacing between the MR layer 20 and the magnetic disk 31 
can be still reduced, evading as well the electric discharge towards the 
MR layer 20 according to the first embodiment, which enables further 
improvement of the resolution ability and consequently, recording density 
of the magnetic disk device. 
Now, a composite head 11' according to a second embodiment of the invention 
will be described. 
FIG. 3 is a magnified sectional view of the composite head 11' having a 
configuration similar to the composite head 11 of FIG. 1. 
In the composite head 11' of FIG. 3, upper ends of the first and the second 
magnetic shield layer 14 and 17 and the first and the second insulation 
layer 13 and 16 are extended until the upper surface 11b of the composite 
head 11' so as to align with other layers, and the upper ends of the first 
and the second magnetic shield layer 14 and 17 and the magnetic pole layer 
18 are electrically connected making use of a conductive resin 26 to the 
suspension 25 which is connected to the upper surface of the slider 12. In 
FIG. 3, the conductive resin 26 is depicted to be extended over the upper 
end of the magnetic pole layer 18. However, the conductive resin 26 is 
sufficient to be electrically connected with the first and the second 
magnetic shield layer 14 and 17, extending onto the second magnetic shield 
layer 17. 
In the composite head 11' of FIG. 3, the first and the second magnetic 
shield layer 14 and 17 are grounded by way of the conductive resin 26, 
instead of the conductive member 24 of FIG. 1, giving the same equivalent 
circuit of FIG. 2B and the same effect with the composite head of FIG. 1. 
Further, according to the second embodiment of FIG. 3, no special thin film 
forming process should be added to the fabrication processes of the 
conventional composite head. Therefore, the second embodiment has a merit 
to reduce the fabrication cost, compared to the first embodiment of FIG. 
1. 
Still further, the conductive resin 26 can connect the first and the second 
magnetic shield layer 14 and 17 directly to the suspension 25. Therefore, 
the discharge current is effectively prevented from flowing through the MR 
head 20, by applying a material having higher conductivity than the slider 
12 to the suspension 25, such as stainless steel (volume resistivity of 
100 to 200 .mu..OMEGA..multidot.cm). 
In the following paragraphs, a composite head 11" according to a third 
embodiment is described. 
FIG. 4 is a magnified sectional view of the composite head 11" having a 
configuration similar to the composite head 11' of FIG. 3. 
In the composite head 11" of FIG. 4, upper ends of the first and the second 
magnetic shield layer 14 and 17 and the first and the second insulation 
layer 13 and 16 are extended until the upper surface 11b of the composite 
head 11" so as to align with other layers in the same way with the 
composite head 11' of FIG. 3, and the upper ends of the first and the 
second magnetic shield layer 14 and 17 and the magnetic pole layer 18 are 
electrically connected directly to the suspension 25 which is extended 
onto upper end of the third insulation layer 19. In FIG. 4, the suspension 
25 is depicted to be extended over the upper end of the third insulation 
layer 19. However, the suspension 25 is sufficient to be electrically 
connected with the first and the second magnetic shield layer 14 and 17, 
extending onto the second magnetic shield layer 17. 
Also in the composite head 11" of FIG. 4, the first and the second magnetic 
shield layer 14 and 17 are grounded through the suspension 25, giving the 
same equivalent circuit of FIG. 2B and the same effect with the composite 
head of FIG. 1 or FIG. 3. 
Furthermore, the discharge current can be evacuated directly to the 
suspension 25 having high conductivity, without passing through the 
conductive resin. Therefore, a discharge current route having still higher 
conductivity being provided, the break or the degradation of the MR layer 
20 due to the discharge current can be prevented more surely than the 
second embodiment of FIG. 3. 
Heretofore, the present invention is described in connection with some 
embodiments. However, it can be easily understood that a variety of 
modifications of the embodiments can be considered in the scope of the 
invention. 
In the magneto-resistive composite head according to the invention damages 
to the magneto-resistive element due to discharge currents of static 
electricity can be surely prevented with a simple configuration, as 
heretofore described, enabling to improve reliability of magnetic disk 
devices using the magneto-resistive composite head.