Magnetic head and magnetic recording/reproducing apparatus

A magnetoresistive magnetic head comprises a first magnetic shielding layer formed on an underlying layer, a first nonmagnetic insulating layer formed on the first magnetic shielding layer, a magnetoresistive device formed on the first nonmagnetic insulating layer, first and second leads formed on the first nonmagnetic insulating layer to be connected to both sides of the magnetoresistive device respectively, a second nonmagnetic insulating layer formed to cover the first and second leads and the magnetoresistive device, a second magnetic shielding layer formed on the second nonmagnetic insulating layer to be positioned over the magnetoresistive device, and a resistor element buried in at least one of the first and second nonmagnetic insulating layers to electrically connect the first lead to either the first magnetic shielding layer or the second magnetic shielding layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic head and a magnetic 
recording/reproducing apparatus and, more particularly, to a magnetic head 
employing a magnetoresistive effect and a magnetic recording/reproducing 
apparatus equipped with such magnetic head. 
2. Description of the Prior Art 
In a magnetic disk drive, magnetic information are written/read into/from a 
magnetic disk by virtue of the magnetic head. 
As shown in FIG. 13, for example, the magnetic head installed in the 
magnetic disk drive has such configuration a that both a magnetoresistive 
(MR) head 110 and an induction type head 120 are placed on a head 
substrate 101. In this configuration, the induction type head 120 is used 
to record the magnetic information into the magnetic disk, and the MR head 
110 is used to reproduce the magnetic information from the magnetic disk. 
A configuration as illustrated in FIGS. 14A and 14B and FIG. 15 has been 
employed as the MR head 110. FIG. 14A shows a planar placement of 
respective layers of the MR head 110 other than nonmagnetic insulating 
layers. FIG. 14B shows a layer structure of the MR head 110 except for the 
nonmagnetic insulating layers. FIG. 15 shows an end surface of the MR head 
110, wherein a portion encircled with a broken line corresponds to a 
portion encircled with a broken line in FIG. 14B. 
In FIGS. 14A, 14B and 15, a substrate protection insulating layer 102 is 
formed on a head substrate 101. Then, a lower magnetic shielding layer 
111, a lower nonmagnetic insulating layer 112, a magnetoresistive device 
113, an upper nonmagnetic insulating layer 114, and an upper magnetic 
shielding layer 115 are formed on the substrate protection insulating 
layer 102. 
The magnetoresistive device 113 is formed to have a three-layered structure 
consisting of, for example, a soft magnetic layer, a magnetic separating 
layer, a magnetoresistive layer made of NiFe. First and second hard 
magnetic layers are formed respectively on both sides of the three-layered 
structure. Both the first and second hard magnetic layers are magnetized 
along the direction from the first hard magnetic layer to the second hard 
magnetic layer. First and second leads 116, 117 are formed between the 
lower nonmagnetic insulating layer 112 and the upper nonmagnetic 
insulating layer 114 and are connected to both sides of the 
magnetoresistive device 113 respectively. 
In such a magnetoresistive head 110, when a sense current (constant 
current) is supplied to the magnetoresistive device 113 via the first and 
second leads 116, 117, a change in the electric resistance caused by a 
change in the magnetization direction by an external magnetic field is 
transmitted to a signal processing circuit (not shown) via the first and 
second leads 116, 117. Such change in the electric resistance appears as a 
change in voltage between the first and second leads 116, 117. 
Accordingly, the first and second leads 116, 117 formed on both sides of 
the magnetoresistive device 113 have a function of supplying the sense 
current to the magnetoresistive device 113 and a function of applying a 
detected voltage. 
The first and second leads 116, 117 are formed to have sufficiently large 
areas and thicknesses but small electric resistivity rather than the 
magnetoresistive device 113. For this reason, a total sum of the electric 
resistance of the first and second leads 116, 117 and the magnetoresistive 
device 113 can be substantially determined by the electric resistance 
value of the magnetoresistive device 113. Such electric resistance is set 
to about 20 to 40.OMEGA.. 
In FIG. 13, a reference numeral 105 denotes a magnetic disk. 
The magnetoresistive magnetic head having the above configuration, before 
being mounted on a magnetic disk drive, is easily destroyed by static 
electricity. Reasons for this phenomenon will be put forth in the 
following. 
First, when large static electricity is applied to the first lead 116, the 
static electricity moves from the first lead 116 toward the second lead 
117 due to their potential difference, as indicated by an arrow I in FIG. 
14A. In this event, the static electricity passes through the 
magnetoresistive device 113 as an electric route, and therefore the 
magnetoresistive device 113 becomes easily destroyed by the static 
electricity since it has larger electric resistance than the two leads 
116, 117. 
Then, as shown in FIG. 15, since the first and second leads 116, 117 and 
the lower and upper magnetic shielding layers 111, 115 may serve as 
electrodes while the lower and upper nonmagnetic insulating layer 112, 114 
may serve as dielectric substances between them, parasitic capacitances 
may be formed. If the static electricity that is larger than an allowable 
value of the parasitic capacitance is accumulated between these 
electrodes, sometimes dielectric breakdown of the lower and upper 
nonmagnetic insulating layer 112, 114 may be caused by discharge of such 
static electricity. Discharging directions of the static electricity are 
indicated by arrows in FIG. 15. 
In this manner, the reason why the static electricity enters into the first 
and second leads 116, 117 is that at first the static electricity enters 
into electrode pads (not shown) which are arranged on the magnetic head to 
be exposed to the outside, and then the static electricity moves to the 
first and second leads 116, 117 via wirings which are connected to the 
electrode pads. 
As has been shown in Figures of Patent Application Publication (KOKAI) 
6-243434, it may be thought out that a resistive film is coated on overall 
exposed ends of the magnetoresistive device in the magnetoresistive 
magnetic head, and then the leads are connected to the lower and upper 
magnetic shielding layers via the resistive film. However, according to 
such configuration, the static electricity accumulated in the leads is 
always discharged to the resistive film via the magnetoresistive device. 
Hence, such configuration is not preferable since it is likely that the 
magnetoresistive device is destroyed upon discharge of the static 
electricity. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a magnetic head which 
is capable of preventing electrostatic breakdown of both a 
magnetoresistive device and nonmagnetic insulating layers formed on and 
beneath the magnetoresistive device, and a magnetic recording/reproducing 
apparatus equipped with such magnetic head. 
According to an aspect of the present invention, resistors for preventing 
electrostatic discharge damage with high resistance are buried in 
nonmagnetic insulating layers which are put respectively between a lead 
connected to a magnetoresistive device and upper and lower magnetic 
shielding layers which are formed over and under the lead, so that the 
lead and the upper and lower magnetic shielding layers are electrically 
connected to each other via the resistor elements. 
Therefore, when static electricity accumulated in the lead becomes larger 
than an allowable capacitance of respective parasitic capacitors which are 
formed between the lead and the upper and lower magnetic shielding layers, 
such static electricity is discharged to the upper and lower magnetic 
shielding layers via the resistors for preventing electrostatic discharge 
damage. As a result, dielectric breakdown of the nonmagnetic insulating 
layers can be prevented and thus electrostatic breakdown of the magnetic 
head can also be prevented. 
According to another aspect of the present invention, in a magnetic head 
which comprises the first and second leads connected to a magnetoresistive 
device, upper and lower magnetic shielding layers formed to oppose a pair 
of leads in the film thickness direction, and nonmagnetic insulating 
layers formed between the first and second leads and the upper/lower 
magnetic shielding layers, a plurality of resistors for preventing 
electrostatic discharge damage are buried in the nonmagnetic insulating 
layers, so that the first lead and the second lead are connected 
electrically mutually via the resistors for preventing electrostatic 
discharge damage and the upper and lower magnetic shielding layers. 
If large static electricity is applied to a first electrode pad connected 
to the first lead, such static electricity is moved to a second lead and a 
second electrode pad connected to the second lead via one of the leads, 
the magnetic shielding layer, and the resistors for preventing 
electrostatic discharge damage. 
The magnetoresistive device is connected to top ends of the first and 
second leads, and the first electrode pad is connected to the first lead, 
and the second electrode pad is connected to the second lead. Two electric 
routes are formed from the first electrode pad to the second electrode pad 
through the magnetoresistive device or the resistor for preventing 
electrostatic discharge damage. Since a distance of an electric route 
which passes through the resistors for preventing electrostatic discharge 
damage and the upper and lower magnetic shielding layers is shorter than a 
distance of an electric route which passes through the magnetoresistive 
device, the static electricity does not pass through the magnetoresistive 
device. In this case, it is preferable that a resistance value of the 
electric route including the resistors for preventing electrostatic 
discharge damage is set, e.g., about 100 times higher than a resistance 
value of the electric route formed between the leads including the 
magnetoresistive device. 
In addition, the static electricity is easy to move via the route having 
the short distance rather than the route having the small resistance 
value. In other words, the static electricity which enters into the 
electrode pad exposed to the outside passes easily through the high 
resistance resistors being inserted in the electric circuit which is 
positioned close to the electrode pad rather than the location of the 
magnetoresistive device, whereby electrostatic breakdown of the 
magnetoresistive device can be prevented. 
Even if the resistance value of the resistor for preventing electrostatic 
discharge damage is set to such an extent, a rate of reduction of the 
sense current which are supplied to the magnetoresistive device via the 
leads is no more than about 1%. Therefore, there is caused no problem in 
practical use. 
In such configuration, the static electricity may be sometimes discharged 
from the leads to the magnetic shielding layers. However, since such 
static electricity can be discharged to the magnetic shielding layers via 
the resistors for preventing electrostatic discharge damage provided in 
the nonmagnetic insulating layers, electrostatic breakdown of the 
nonmagnetic insulating layers formed between the leads and the magnetic 
shielding layers can be prevented. 
According to still another aspect of the present invention, an 
electrostatic breakdown preventing resistor element is connected between 
the first and second electrode pads which are extended outwardly from the 
first and second leads connected to both sides of a magnetoresistive 
device. Since the static electricity applied to the first electrode pad 
moves to the second electrode pads via the electrostatic breakdown 
preventing resistor element which is provided in a short distance electric 
route between the electrode pads, such static electricity never passes 
through the magnetoresistive device. 
In this case, if a resistance value of the electrostatic breakdown 
preventing resistor element is set, e.g., 100 times higher than a 
resistance value of an electric route including the magnetoresistive 
device, an electric current passing through the electrostatic breakdown 
preventing resistor element can be limited to no more than about 1% of an 
electric current flowing through the magnetoresistive device upon 
supplying a sense current. Hence, there is caused no problem in practical 
use. 
Other and further objects and features of the present invention will become 
obvious upon an understanding of the illustrative embodiments about to be 
described in connection with the accompanying drawings or will be 
indicated in the appended claims, and various advantages not referred to 
herein will occur to one skilled in the art upon employing of the 
invention in practice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Various embodiments of the present invention will be described with 
reference to the accompanying drawings. It should be noted that the same 
or similar reference numerals are applied to the same or similar parts and 
elements throughout the drawings, and the description of the same or 
similar parts and elements will be omitted or simplified. 
First Embodiment 
FIG. 1 is a perspective view, partially in section, showing an example of a 
magnetic head according to a first embodiment of the present invention. 
FIG. 2 is a sectional view showing the magnetic head in FIG. 1. 
In FIGS. 1 and 2, a magnetoresistive (MR) head 10 for use in reproduction 
only and an induction type magnetic head 20 for use in recording only are 
formed in sequence on a head substrate 1 via a substrate protection layer 
2 made of Al.sub.2 O.sub.3. 
The MR head 10 comprises a lower magnetic shielding layer 11 made of NiFe, 
a lower nonmagnetic insulating layer 12 made of Al.sub.2 O.sub.3, a 
magnetoresistive device 13, an upper nonmagnetic insulating layer 14 made 
of Al.sub.2 O.sub.3, and an upper magnetic shielding layer 15 made of 
NiFe, which are all formed in sequence on the substrate protection layer 
2. The lower and upper nonmagnetic insulating layers 12, 14 are formed to 
have a thickness of 100 to 150 nm, respectively. 
As shown in FIG. 3, the upper magnetic shielding layer 15 is formed to 
spread over the magnetoresistive device 13 and its neighboring area and to 
oppose a part of the lower magnetic shielding layer 11. 
As shown in FIGS. 1 to 4, the first and second leads 16, 17 made of gold 
(Au) are connected to both sides of the magnetoresistive device 13 which 
is put between the lower nonmagnetic insulating layer 12 and the upper 
nonmagnetic insulating layer 14. The first and second leads 16, 17 formed 
on the lower magnetic shielding layer 11 are formed to protrude from the 
upper magnetic shielding layer 15. 
A first opening 12a having an area of about 100 .mu.m.sup.2 is formed in a 
certain region of the lower nonmagnetic insulating layer 12 located 
beneath the first lead 16. A first resistor element 18 with a resistance 
value of 100 k.OMEGA. to several M.OMEGA. is filled in the first opening 
12a. As a result, the lower magnetic shielding layer 11 and the first lead 
16 are electrically connected via the first resistor element 18. In FIG. 
3, the first opening 12a is formed on the outside of the upper magnetic 
shielding layer 15. 
A second opening 14a is formed in a certain region of the upper nonmagnetic 
insulating layer 14 that is separated from the magnetoresistive device 13. 
A second resistor element 19 with a resistance value of 100 k.OMEGA. to 
several M.OMEGA. is filled in the second opening 14a. As a result, the 
upper magnetic shielding layer 15 and the first lead 16 are electrically 
connected via the second resistor element 19. 
The first and second resistor elements 18, 19 are formed by filling 
conductive material in the first and second openings 12a, 14a 
respectively. Materials having large electric resistance such as nichrome, 
constantan, manganese, or the like may be employed as the conductive 
material. In addition, materials may be selected which have electric 
resistivity smaller than the lower and upper nonmagnetic insulating layers 
12, 14. 
Alternatively, a part of the upper magnetic shielding layer 15 may be 
employed as the second resistor element 19 by filling the second opening 
14a with the part of the upper magnetic shielding layer 15. In this case, 
a resistance value can be set by adjusting an opening area of the second 
opening 14a. 
In the magnetoresistive magnetic head 10 having such a configuration, a 
parasitic capacitance C1 is made up of the first lead 16, the first 
magnetic shielding layer 11, and the lower nonmagnetic insulating layer 
12. The static electricity accumulated in the first lead 16 can be 
discharged in the following manner. 
At first, the static electricity accumulated in the first lead 16, if 
increased higher than a storage capacitance of the parasitic capacitance 
C1, is discharged to the lower magnetic shielding layer 11 via the first 
resistor element 18 which can serve as a local resistor having a low 
resistance value. Therefore, the static electricity does not flow through 
the lower nonmagnetic insulating layer 12. 
Like the above, another parasitic capacitance C2 is formed between the 
upper magnetic shielding layer 15 and the first lead 16. If the static 
electricity in excess of a storage capacitance of the parasitic 
capacitance C2 is accumulated in the first lead 16, it can be discharged 
to the upper magnetic shielding layer 15 via the second resistor element 
19. 
In this manner, dielectric breakdown of the lower and upper nonmagnetic 
insulating layers 12, 14 can be prevented by discharging the static 
electricity via the first and second resistor elements 18, 19. 
In the meanwhile, since resistance values of the first lead 16 and the 
lower magnetic shielding layer 11 are more than 100 times higher than a 
resistance value of the magnetoresistive device 13 being formed between 
the first lead 16 and the second lead 17, neither a sense current passed 
through the magnetoresistive device 13 nor a rate of change in the 
electric resistance against an external signal magnetic field would be 
reduced. Furthermore, the same results can be achieved between the first 
lead 16 and the upper magnetic shielding layer 15. Accordingly, no current 
except for the static electricity would flow into the lower and upper 
magnetic shielding layer 11 and 15. 
Consequently, even if the foregoing configuration is adopted, no 
substantial trouble is caused in detecting the signal magnetic field by 
virtue of the magnetoresistive magnetic head. 
Next, a step of forming the first resistor element 18 in the first opening 
12a will be explained in brief hereinafter. 
First, steps of achieving a configuration shown in FIG. 5A will be 
explained hereunder. 
The lower nonmagnetic insulating layer 12 is formed on the lower magnetic 
shielding layer 11 having a substantially hexagonal planar shape. A 
photoresist 3 is then coated on the lower nonmagnetic insulating layer 12. 
A window 3a is formed in a part of the lead forming region by exposing and 
then developing the photoresist 3. In turn, as shown in FIG. 5B, the first 
opening 12a is formed in the lower nonmagnetic insulating layer 12 by 
etching the lower nonmagnetic insulating layer 12 through the window 3a. 
Subsequently, as shown in FIG. 5C, a film 18a made of electrically 
resistive material such as tungsten, tantalum, or the like is formed on 
the photoresist 3 and in the window 3a by virtue of sputtering, etc. Then, 
after the photoresist 3 is removed by solvent, the film 18a made of 
electrically resistive material remains only in the first opening 12a. 
Then, as shown in FIG. 5C, the film 18a made of electrically resistive 
material in the first opening 12a can be used as a first resistor element 
18. 
In the event that a second resistor element 19 is formed in the second 
opening 14a, it can be formed via the same steps as above. 
In any way, as the magnetoresistive device 13, there are an isotropic 
magnetoresistive device wherein a change in the electric resistance can be 
detected depending upon an angle between the magnetization direction and 
the direction of current flow, a spin valve magnetoresistive device 
wherein a change in the electric resistance can be detected depending upon 
a relative angle between respective magnetization directions of two 
magnetic layers, and the like. 
The isotropic magnetoresistive device is formed to have a configuration as 
shown in FIG. 6A, for example. In FIG. 6A, the isotropic magnetoresistive 
device has a three-layered configuration comprising a SAL (Soft Adjacent 
Layer) 13a made of nickel-iron-chromium (NiFeCr), a magnetic separating 
layer 13b made of tantalum (Ta), tungsten (W), or the like, and a 
magnetoresistive (MR) layer 13c made of nickel-iron (NiFe). Two hard 
magnetic layers 13d made of cobalt-iron (CoFe) are connected to both sides 
of the isotropic magnetoresistive device. Such two hard magnetic layers 
13d are magnetized along the direction from one end to the other end of 
the MR layer 13c. The first lead 16 and the second lead 17 are connected 
to these hard magnetic layers 13d respectively. 
The spin valve magnetoresistive device is formed to have a configuration, 
as shown in FIG. 6B, wherein two soft magnetic layers 13e, 13g made of 
NiFe are isolated by a magnetic separating layer 13f made of copper. A 
magnetic domain controlling layer 13h is connected to an upper soft 
magnetic layer 13g. The upper soft magnetic layer 13g is magnetized along 
the direction from one end to the other end of the magnetic domain 
controlling layer 13h by virtue of its exchange coupling with the magnetic 
domain controlling layer 13h. The magnetic domain controlling layer 13h is 
covered with a protection film 13i made of tantalum (Ta), or the like. The 
first and second leads 16, 17 are connected to neighboring areas of both 
ends of the spin valve magnetoresistive device. 
Such magnetoresistive device 13 is formed to be miniaturized such that its 
height is less than 2.0 .mu.m and its length between the two leads is less 
than 3 .mu.m. 
An induction type magnetic head 20 which is formed on the magnetoresistive 
head 10 constructed as above, as shown in FIGS. 1 and 2, employs the upper 
magnetic shielding layer 15 as a first magnetic pole layer. An insulating 
layer 21 is formed on the upper magnetic shielding layer 15. Spiral coils 
22 are arranged to penetrate the insulating layer 21. A second magnetic 
pole layer 23 is formed on the insulating layer 21. A part of the second 
magnetic pole layer 23 is passed through a substantially central clearance 
of the spiral coils 22 to be connected to the upper magnetic shielding 
layer 15. The second magnetic layer 23 and the upper magnetic shielding 
layer 15 are separated from each other at a certain distance over the 
magnetoresistive device 13 to put a nonmagnetic gap layer 24 therebetween. 
The head substrate 1 on which the MR magnetic head 10 and the induction 
type magnetic head 20 are formed is worked into a shape shown in FIG. 7 to 
thus form a head slider 1a. The head slider 1a has a plurality of air 
bearing surfaces 1b. The MR magnetic head 10 and the induction type 
magnetic head 20 are formed on a rear end surface of the air bearing 
surfaces 1b. In addition, first to fourth electrode pads 31 to 34 are 
formed on the rear end surface. The first and second leads 16, 17 of the 
MR head 10 are electrically connected to the first and second electrode 
pads 31, 32 via the wirings respectively. Both ends of the spiral coils 22 
of the induction type magnetic head 20 are electrically connected to the 
third and fourth electrode pads 33, 34 via the wirings respectively. 
Such head slider 1a is fitted onto a top end of an arm 35 shown in FIG. 8. 
The arm 35 is attached to an actuator 36 of a magnetic disk drive 30 shown 
in FIG. 9. The arm 35 is shifted over the magnetic disk 37 in terms of a 
lateral movement of the actuator 36. The first to fourth electrode pads 31 
to 34 which are provided on the head slider 1a secured to the top end of 
the arm 35 are connected electrically to a semiconductor integrated 
circuit device 38 via a wiring sheet 35s being placed on the arm 35. 
In FIG. 3, two resistor elements 18, 19 have been provided on and beneath 
the first lead 16. However, in the case that one of the two resistor 
elements 18, 19 is omitted, electrostatic breakdown of the nonmagnetic 
insulating layers 12, 14 can also be prevented. 
Second Embodiment 
The configuration according to the first embodiment is designed to prevent 
electrostatic breakdown of the nonmagnetic insulating layer in the case 
that the static electricity is accumulated gradually in the lead 16 via 
the first electrode pad 31. 
However, if the static electricity applied to the first electrode pad 31 or 
the second electrode pad 32 at a time is large, such a phenomenon occurs 
that the static electricity moves from the first lead 16 to the second 
lead 17 via the magnetoresistive device 13. It is likely that the 
magnetoresistive device 13 is destroyed upon a movement of the static 
electricity. 
In order to prevent destruction of the magnetoresistive device 13 by virtue 
of such static electricity, a configuration shown in FIGS. 10 and 11 will 
be employed, as will be explained hereunder. 
In FIGS. 10 and 11, an example is shown in which resistors for preventing 
electrostatic discharge damage are formed not only on and beneath the 
first lead 16, as in the first embodiment, but also on and beneath the 
second lead 17. 
In other words, a third opening 12b is formed in the lower nonmagnetic 
insulating layer 12 between the second lead 17 and the lower magnetic 
shielding layer 11. A third resistor element 41 is filled in the third 
opening 12b. Thus the second lead 17 and the lower magnetic shielding 
layer 11 can be electrically connected to each other via the third 
resistor element 41. 
Further, a fourth opening 14b is formed in the upper nonmagnetic insulating 
layer 14 between the second lead 17 and the upper magnetic shielding layer 
15. A fourth resistor element 42 is filled in the fourth opening 14b. 
Therefore the second lead 17 and the upper magnetic shielding layer 15 can 
be electrically connected to each other via the fourth resistor element 
42. 
The third resistor element 41 has the same configuration as the first 
resistor element 18, and the fourth resistor element 42 has the same 
configuration as the second resistor element 19. 
In this event, a resultant distance L1 of a first electric route S1 which 
passes through a first electrode pad 31, the first lead 16, the first 
resistor element 18, the lower magnetic shielding layer 11, the third 
resistor element 41, the second lead 17, and a second electrode pad 32 is 
set shorter than a resultant distance L2 of a second electric route S2 
which passes through the first electrode pad 31, the first lead 16, the 
magnetoresistive device 13, the second lead 17, and a second electrode pad 
32. Besides, a resultant resistance value R1 of the first electric route 
S1 is set about 100 times higher than a resultant resistance value R2 of 
the second electric route S2. 
Still further, a resultant distance L3 of a third electric route S3 which 
passes through the first electrode pad 31, the first lead 16, the second 
resistor element 19, the upper magnetic shielding layer 15, the fourth 
resistor element 42, the second lead 17, and the second electrode pad 32 
is set shorter than the resultant distance L2 of the second electric route 
S2 which passes through the first electrode pad 31, the first lead 16, the 
magnetoresistive device 13, the second lead 17, and the second electrode 
pad 32. In addition, a resultant resistance value R3 of the third electric 
route S3 is set about 100 times higher than the resultant resistance value 
R2 of the second electric route S2. 
In the MR magnetic head having the foregoing configuration, even if 
extremely large static electricity is applied to the first electrode pad 
31, for example, such static electricity can be discharged to the second 
electrode pad 32 via the first electric route S1 or the third electric 
route S3. 
This is because the static electricity is not discharged via the electric 
route having the smallest resultant resistance but via the electric route 
having the shortest resultant distance. However, if the resultant electric 
resistance of the shortest distance between the first electrode pad 31 and 
the second electrode pad 32 becomes infinite, the static electricity 
easily moves through the second electric route S2 including the 
magnetoresistive device 13. Accordingly, it is preferable that respective 
resultant electric resistances of the first and third electric routes S1, 
S3 are no more than several M.OMEGA. at their maximum. 
In such a situation that the MR magnetic head is used to reproduce the 
signal, an electric current which flows through the magnetoresistive 
device 13 of the MR head 10 via the first and second leads 16, 17 is about 
8 mA, for example. Therefore, if the resultant electric resistances of the 
first and third electric routes S1, S3 are made too small, a current 
flowing through the magnetoresistive device 13 becomes small, so that it 
is possible that a magnetic field signal detectivity of the 
magnetoresistive device 13 is lowered. However, if the resultant 
resistance value R3 of the first electric route S1 or the third electric 
route S3 is set about 100 times higher than the resistance value of the 
magnetoresistive device 13, the magnetic field signal detectivity of the 
magnetoresistive device 13 is hardly degraded since the current flowing 
through the magneto-resistive device 13 is reduced merely by no more than 
1%. For this reason, there is no trouble in practical use because loss in 
efficiency of the magnetoresistive device 13 is less than 1%. 
It is preferable that, since the resistance value of the magnetoresistive 
device 13 becomes 20 to 40.OMEGA., the resistance value of the first 
electric route S1 or the third electric route S3 is 2000 to 4000.OMEGA. or 
more. 
From the explanation of the first embodiment, it would be evident that such 
configuration of the second embodiment is also effective to prevent 
dielectric breakdown of the lower and upper nonmagnetic layers 12, 14. 
Although the resistors for preventing electrostatic discharge damage are 
buried in both the lower nonmagnetic layer 12 and the upper nonmagnetic 
layer 14 in the above configuration, either of the lower and upper 
resistors for preventing electrostatic discharge damage may be omitted. 
Third Embodiment 
As another configuration to prevent destruction of the magnetoresistive 
device because of large static electricity, a configuration shown in FIG. 
12 will be proposed by the inventors of the present invention. 
FIG. 12 is a view showing an end surface of a slider of a magnetoresistive 
head when it is viewed from the rear end side. The magnetoresistive device 
13 which is attached to the rear end of the head slider 1a is connected to 
the first electrode pad 31 and the second electrode pad 32 via the first 
and second leads 16, 17 provided on both sides thereof. Also, the first 
electrode pad 31 and the second electrode pad 32 are connected to each 
other via the electrostatic breakdown preventing resistor element 43. 
The electrostatic breakdown preventing resistor element 43 is formed to 
have a resistance value which is 100 times higher than the resistance 
value of the electric route which passes through the first lead 16, the 
magnetoresistive device 13, and the second lead 17. Also, the shortest 
distance L0 between the first electrode pad 31 and the second electrode 
pad 32 is set shorter than the resultant distance L2 of the route which 
passes through the first lead 16, the magnetoresistive device 13, and the 
second lead 17. 
For the purposes of example, the shortest distance L0 between the first 
electrode pad 31 and the second electrode pad 32 is less than 100 .mu.m, 
and the resultant distance L2 of the route including the magnetoresistive 
device 13 is approximately 1500 .mu.m. The resultant distance L1 is 
shorter than the resultant distance L2. In the region including the 
shortest distance L0 between the first electrode pad 31 and the second 
electrode pad 32, the electrostatic breakdown preventing resistor element 
43 made of NiFe is formed to have a width 1.5 .mu.m and a thickness 0.02 
.mu.m. Since a resistivity of NiFe is 20 .OMEGA..multidot.cm, a resistance 
value of the electrostatic breakdown preventing resistor element 43 
between the first electrode pad 31 and the second electrode pad 32 is 
about 2 k.OMEGA.. This resistance value may be applied in case the 
resistance value of the magnetoresistive device 13 is 2.OMEGA.. 
In the MR magnetic head 10 constructed as above, for example, even if the 
extremely large static electricity is applied to the first electrode pad 
31, such static electricity can be discharged to the second electrode pad 
32 via the electrostatic breakdown preventing resistor element 43 located 
in the electric route having the shortest distance between the first 
electrode pad 31 and the second electrode pad 32. This is because the 
static electricity is not discharged via the electric route having the 
smallest resultant resistance but via the electric route having the 
shortest resultant distance. However, if the electrostatic breakdown 
preventing resistor element 43 does not exist and also the electric 
resistance having the shortest distance between the first electrode pad 31 
and the second electrode pad 32 becomes infinite, the static electricity 
is easy to pass through the electric circuit including the 
magnetoresistive device 13. Accordingly, it is preferable that the 
resistance value of the electrostatic breakdown preventing resistor 
element 43 located in a region of the shortest distance L0 between the 
first electrode pad 31 and the second electrode pad 32 is set to no more 
than several M.OMEGA.. 
As material for the electrostatic breakdown preventing resistor element 43, 
such material having a large resistivity rather than NiFe, e.g., tungsten, 
tantalum, or the like may be employed. Besides, a film thickness and a 
width of the electrostatic breakdown preventing resistor element 43, and 
the shortest distance L0 between the first electrode pad 31 and the second 
electrode pad 32 are determined according to constituent material and the 
resistance value of the electrostatic breakdown preventing resistor 
element 43. 
In such a situation that the MR magnetic head 10 is used to reproduce the 
signal, an electric current which flows through the magnetoresistive 
device 13 of the MR head 10 via the first and second leads 16, 17 is about 
8 mA, for example. Therefore, if the electric resistance of the 
electrostatic breakdown preventing resistor element 43 is made too small, 
a current flowing through the magnetoresistive device 13 becomes small, 
whereby sometimes a magnetic field signal detectivity of the 
magnetoresistive device 13 is degraded. However, in the third embodiment, 
if the electric resistance of the electrostatic breakdown preventing 
resistor element 43 is set about 100 times higher than the resistance 
value of the magnetoresistive device 13, a detectivity of the magnetic 
field signal in the magnetoresistive device 13 is hardly degraded since 
the current flowing through the magnetoresistive device 13 is reduced by 
no more than 1% in contrast to the case where no electrostatic breakdown 
preventing resistor element is provided. For this reason, a sensitivity of 
the magnetoresistive device 13 is seldom reduced and therefore no trouble 
is caused in practical use because loss in efficiency of the 
magnetoresistive device 13 is less than 1%. 
Incidentally, although the case has been explained wherein the above MR 
magnetic head is attached to the magnetic disk drive, the MR magnetic head 
may be applied to an apparatus which is used to reproduce the magnetic 
signal recorded on the magnetic tape. 
Various modifications will become possible for those skilled in the art 
after receiving the teachings of the present disclosure without departing 
from the scope thereof.