Thin film magnetic head

In a magnetoresistive (MR) effect head, electrodes for supplying a current to an MR element and a bias current conductor are not exposed at a contact surface of the MR head which is brought into sliding contact with a magnetic recording medium, thus preventing surface roughening of the contact surface.

BACKGROUND OF THE INVENTION 
The present invention relates to a thin film magnetic head (to be referred 
to as an MR head) having a magnetoresistive effect element (to be referred 
to as an MR element hereinafter). 
In a conventional MR head using an MR element, the distal end of an 
electrode for supplying a current to the MR element and a bias current 
conductor are exposed at a surface of the MR head which contacts a 
magnetic recording medium. Surface roughening occurs at a portion of the 
electrode which is located at the contact surface. This surface roughening 
is also effected in the vicinity of a magnetic substrate, a nonmagnetic 
insulating layer, the MR element, and a magnetic shield film. As a result, 
the conventional MR head cannot be effectively used in practice. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an MR head which has a 
long service life and good wear resistance. 
It is another object of the present invention to provide an MR head which 
has a proper resistivity as a magnetic head. 
According to the MR head of the present invention, an electrode for 
supplying a current to an MR element and a bias current conductor are not 
exposed at a surface of the MR head which contacts a magnetic recording 
medium, thereby preventing the tip of the electrode from contacting the 
magnetic recording medium and hence from being subjected to surface 
roughening. 
Other objects, features and advantages of the present invention will be 
apparent from the following detailed description taken in conjunction with 
the accompanying drawings.

CONCRETE DESCRIPTION OF PRIOR ART 
FIGS. 1 and 2 show conventional MR heads, respectively. In the MR head 
(FIG. 1) having a single magnetic domain configuration, a magnetization M 
is rotated by a signal magnetic field generated from a magnetic recording 
medium 1 and has an angle .theta. with respect to a current i flowing 
through MR elements 2 and 3. It is conventionally considered that change 
in resistivity .DELTA..rho. is proportional to cos.sup.2 .theta.. In order 
to obtain good linearity, a bias magnetic field is generated by a current 
supplied to a bias current conductor 4. Electrodes 5 and 6 supply a 
current to the MR elements 2 and 3 and the bias current conductor 4 so as 
to flow a current through a command electrode 7. 
In this MR head, the MR elements 2 and 3 extend to the electrodes 5, 6 and 
7. The magnetic domains of the MR element portions in practical operation 
do not exhibit a single magnetic domain configuration, and the utilization 
efficiency of the MR characteristics is degraded below that required for 
industrial applications. Moreover, in the electrode configuration in FIG. 
1, a combined resistivity of the MR elements and the bias current 
conductor 4 for generating the bias magnetic field is increased since the 
bias current conductor 4 is made of Ti having a resistivity of 100 
.mu..OMEGA. cm although the MR elements are made of an Ni-Fe alloy (83:17) 
having a resistivity of 30 .mu..OMEGA. cm. Therefore, when a plurality of 
elements are used to constitute a magnetic head, heat dissipated upon 
application of a current cannot be neglected. Thus, the magnetic head of 
this type cannot be used in practice. 
FIG. 2 shows another example of a conventional MR element. Two electrodes 8 
and 9 are disposed at the two ends of a single MR element 10. A current 
flows from one of the electrodes, and a change in resistivity of the MR 
element 10 is detected as a change in voltage. A bias magnetic field 
H.sub.B is applied to the MR element 10 such that the secondary harmonic 
distortion of a reproduction output from the MR element 10 is minimized. 
The electrodes comprise a two-layer (Au and Cr) structure or a thin 
lower-resistivity metal film such as an Al film. This conventional MR head 
dissipates little heat and can be easily used. 
When the magnetic head having the construction shown in FIG. 2 is used in 
practice, the front surface of the head having a structure as shown in 
FIG. 3A is brought into sliding contact with the magnetic recording 
medium. Referring to FIG. 3A, an insulating layer 12 is formed on a 
magnetic substrate 11. An Fe-Ni alloy for providing an MR element 10 is 
deposited on the insulating layer 12. Electrodes 8 and 9 are disposed at 
the two ends of the MR element. An insulating layer 13 is deposited on the 
MR element and the electrodes and a magnetic shield layer 14 is formed on 
the insulating layer 13. A protective substrate 16 made of glass or the 
like is formed on the magnetic shield layer 14 through an adhesive layer 
15 to protect the MR head. The front surface of the resultant structure is 
polished to form a tape contact surface, thereby providing a tape head. 
On the front surface of the magnetic head having the construction described 
above, when the magnetic recording medium is brought into sliding contact 
with the tape contact surface of the magnetic head, roughened portions 17 
are formed starting in the vicinity of the electrodes 8 and 9 and 
extending to the magnetic substrate 11, the nonmagnetic insulating layers 
12 and 13, the MR element 10 and the magnetic shield layer 14, as shown in 
FIG. 3B. As a result, this magnetic head is not suitable for practical 
industrial applications. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 4A and 4B show an MR head according to a first embodiment of the 
present invention, and FIG. 5 shows a head front surface thereof. The same 
reference numerals as used in FIGS. 3A and 3B denote the same parts in 
FIGS. 4A, 4B and 5, and a detailed description thereof will be omitted. 
The MR element 10 is formed in a strip shape. Electrodes 18 electrically 
and physically contact with parts of the MR element 10 respectively, and 
extend to couple to an external circuit. 
FIG. 5 shows a contact surface of the MR head which is brought into sliding 
contact with the magnetic recording medium. An insulating layer as a 
magnetic gap 13 is formed on the multilayer structure shown in FIG. 5, and 
a magnetic shield film 14 is deposited on the magnetic gap 13. A 
protective glass body 16 is formed on the magnetic shield film 14 through 
an adhesive layer 15. Electrode materials Au/Cr, Al, Cu, Ag and so on are 
not exposed at the front surface of the head. The MR element comprises an 
Fe-Ni alloy or a Co-Ni alloy and has a Mohs hardness of 5 As a result, the 
head wear and chipping shown in FIG. 3B do not occur. In addition to this 
advantage, the MR element directly contacts the electrodes, so that a 
combined resistance is very low, thus providing a practical advantage. 
However, since the contact portion between the MR element and the 
electrodes is small, alignment of a resist pattern to the MR element is 
difficult to achieve, and the resist film at the time of contact exposure 
tends to be damaged by the sliding contact with the photomask. 
For improving reliability of electrical contact between the MR element and 
the electrodes, FIGS. 6A and 6B show an MR head according to a second 
embodiment of the present invention. Metal conductor layers 19 are formed 
on one of the major surfaces of an MR element 10 and serve as a base. As 
shown in FIG. 6A, the MR element 10 is formed in a strip shape. The metal 
conductor layers 19 extend from behind the MR element such that these 
metal layers overlap electrodes 18, respectively. Each electrode 18 is 
formed to cover a portion of the MR element 10 and the corresponding 
conductor layer 19. Each electrode 18 extends toward the rear side of the 
magnetic substrate 11 as compared with the corresponding metal conductor 
layer 19. 
FIG. 7 shows a recording medium contact surface of the MR head shown in 
FIG. 6. The contact surface shown in FIG. 7 is substantially the same as 
that shown in FIG. 3A except that the metal conductor layers 19 are formed 
below the MR element and the electrodes 18 are not exposed at the front 
surface of the head. The metal conductor layers 19 cause the MR element to 
sufficiently electrically contact the electrodes 18. In this sense, a 
resistivity of the metal conductor layer itself does not substantially 
cause heat dissipation of the head as a contact area. 
In general, metals used as electrodes are good conductors, i.e., copper, 
silver and gold of Group Ib, and aluminium of Group IIIb. The 
resistivities of these metals are not more than 3 .mu..OMEGA. cm. Tables 1 
and 2 show the relationships between the elements and their Mohs hardness 
values and between the elements and their resistivities, respectively. The 
elements excluding the elements of Groups Ib and IIb and boron of Group 
IIIb have a low hardness value of 3 or less. When the metal conductor 
layers 19 are exposed as shown in FIG. 3A, a gap deterioration occurs, as 
shown in FIG. 3B. 
The Mohs hardness values of elements of Groups IIIa, IVa, Va, VIa, VIIa and 
VIII fall within the range between 4 and 9, and are higher than that of 
any other good conductor, providing good wear resistance, and these wear 
resistance conductors are used for a biasing conductors in this 
embodiment. 
TABLE 1 
__________________________________________________________________________ 
Mohs Hardness 
Ia IIa 
IIIa 
IVa 
Va 
VIa 
VIIa 
VIII Ib 
IIb 
IIIb 
IVb 
Vb 
VIb 
VIIb 
__________________________________________________________________________ 
2 Li 
Be B C N O F 
0 6 9 10 
3 Na 
Mg Al 
Si P S Cl 
0 2 2 7 0 
4 K Ca So Ti V Cr Mn Fe 
Co 
Ni 
Cu 
Zn Ga 
Ge As 
Se Br 
0 1 -- 4 -- 
9 5 4 5 5 2 2 1 6 3 2 
5 Rb 
Sr Y Zr Nb 
Mo Tc Ru 
Rh 
Pd 
Ag 
Cd In 
Sn Sb 
Te I 
0 1 -- -- -- 
-- -- 6 -- 
5 2 2 1 1 3 2 
6 Cs 
Ba La Hf Ta 
W Re Os 
Ir 
Pt 
Au 
Hg Tl 
Pb Bi 
Po At 
0 2 series 
-- -- 
7 -- 7 6 4 2 -- 
1 2 
__________________________________________________________________________ 
Indication 
0 0-0.99 
5 5-5.99 
1 1-1.99 
6 6-6.99 
2 2-2.99 
7 7-7.99 
3 3-3.99 
8 8-8.99 
4 4-4.99 
9 9-9.99 
(Good conductor; Ib Cu, Ag, Au IIIb Al) 
TABLE 2 
__________________________________________________________________________ 
Resistivity (.mu..OMEGA.cm) 
Ia IIa 
IIIa IVa 
Va VIa 
VIIa 
VIII Ib IIb 
IIIb 
IVb Vb VIb VIIb 
__________________________________________________________________________ 
2 Li Be B C N O F 
8.47 
5.5 -- 1375 
3 Na Mg Al Si P S Cl 
4.35 
4.0 2.5 
10 10.sup.7 
4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br 
6.29 
4.2 
61 83 24.8-26 
15.4 
90.9 
8.9 
6.25 
6.25 
1.55 
5.5 
40.8 
46 33.3 
12.sup.7 
-- 
5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I 
11.6 
3.0 
57 41.7 
22.7 
4.3 
-- 11.7 
4.5 
10 1.50 
6.7 
8.3 
10 39.sup. 
54 .times. 10.sup.5 
1.3 .times. 
10.sup.15 
6 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At 
17.8 
58.8 
series 
29.4 
13.9 
5.0 
18.8 
9.1 
5.0 
9.8 
2.0 
23 14.1 
19.2 
106.8 
-- -- 
__________________________________________________________________________ 
Metals such as Mo, Ti and W which are relatively hard metals are suitable 
as metal conductors. The front surface of the MR head is made of only hard 
metals, thereby preventing the chipping and damage shown in FIG. 3B. The 
electrodes are electrically connected to the MR element through the 
corresponding metal conductor layers 19, so that incomplete connection 
between the electrodes and the MR element is eliminated. In addition to 
these advantages, the MR head has a sufficiently low resistance for use as 
a magnetic head. 
FIGS. 8A and 8B show an MR head according to a third embodiment of the 
present invention, and FIG. 9 shows a recording medium contact surface 
thereof. The MR head of this embodiment is substantially the same as that 
of the first embodiment, except that parts 20 of a metal conductor layer 
19 comprise an oxide obtained by anodic oxidation or thermal oxidation. 
Unlike the embodiment shown in FIG. 6, a current does not flow in both the 
MR element and the metal conductor layer. As a result, utilization of an 
electric current in the MR element can be improved. In this case, 
relatively hard metals such as Mo, Ti, Cr and W can be selected to form 
the metal conductor layers, thereby providing good wear resistance. In 
addition to this advantage, the MR element requires only a small current, 
thereby decreasing thermal noise inherent to the MR element.