Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1999-11-24
2003-12-16
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C360S313000
Reexamination Certificate
active
06664784
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a magneto-resistive sensor detecting magnetically recorded data out of a medium having magnetically stored data therein, a method of fabricating the same, and an apparatus for magnetically reproducing data, including the same.
2. Description of the Related Art
There have been known a magneto-resistive sensor (hereinafter, referred to simply as “MR sensor”) and a magneto-resistive head (hereinafter, referred to simply as “MR head”) for detecting a magnetic field. These sensor and head read magnetically recorded data out of a medium in which data have been magnetically stored, with a high linear density.
On detecting a magnetic field, MR sensor varies its electrical resistance in accordance with intensity and direction of the detected magnetic field. That is, MR sensor detects fluctuation in electrical resistance therein to thereby detect a magnetic field.
MR sensor having the above-mentioned function can be grouped into a sensor which operates on the basis of anisotropic magneto-resistive effect (hereinafter, referred to simply as “AMR”) and a sensor which operates on the basis of giant magneto-resistive effect (hereinafter, referred to simply as “GMR”). Among GMR, spin-valve effect magneto-resistive effect is well known to those skilled in the art.
An example of AMR type MR sensor is described, for instance, in D. A. Thomson et al., “Memory, Storage, and Related Applications”, IEEE Trans. on Mag. MAG-11, pp. 1039, 1975.
In AMR type MR sensor, electrical resistance is varied in proportion to Cos
2
&thgr; wherein &thgr; indicates an angle between an orientation of magnetization in a magnetic layer (MR layer) which orientation is varied in accordance with a magnetic field of a signal, and a direction in which a sense current flows in the MR sensor. AMR type MR sensor is generally designed to include a magnetization-bias layer for applying magnetization-bias to MR layer, in order to suppress Barkhausen noise by suppressing formation of magnetic domain in MR layer. The magnetization-bias layer is formed at opposite sides of a sense region of MR layer, and applies magnetization-bias to MR layer in a direction in which a sense current flows. Such magnetization-bias layer is composed of anti-ferromagnetic material such as FeMn, NiMn and nickel oxide, for instance.
A spin-valve effect type MR sensor, which is one of GMR type MR sensors, is generally designed to include MR layer comprised of a multi-layered structure including two magnetic layers, and a non-magnetic layer sandwiched between the magnetic layers. Since fluctuation in resistance in MR layer is dependent on spin-dependent transmission of conduction electrons between the two magnetic layers sandwiching the non-magnetic layer therebetween, and spin-dependent scattering which occurs at interfacial planes among the layers in association with the spin-dependent transmission, MR layer generates significant magneto-resistive effect. Specifically, electrical resistance in MR layer is varied in proportion to cos &thgr; wherein &thgr; indicates an angle between magnetization orientations of the two magnetic layers.
The spin-valve effect type MR sensor having such a structure as mentioned above has higher sensitivity than that of AMR type MR sensor, and hence, exhibits greater fluctuation in electrical resistance than that of AMR type MR sensor.
Examples of the above-mentioned spin-valve effect type MR sensor are suggested as follows.
Japanese Unexamined Patent Publication No. 2-61572 has suggested a magneto-resistive sensor including a multi-layered structure having a non-magnetic layer, two ferromagnetic layers sandwiching the non-magnetic layer therebetween, an anti-ferromagnetic layer making contact with one of the ferromagnetic layers. The ferromagnetic layers are composed of ferromagnetic transition metals or alloy thereof, and the anti-ferromagnetic layer is composed of FeMn.
Japanese Unexamined Patent Publication No. 4-358310 has suggested a magneto-resistive sensor including a multi-layered structure having a non-magnetic metal layer, and two ferromagnetic layers sandwiching the non-magnetic metal layer therein. The two ferromagnetic layers are designed to have magnetization orientations which are perpendicular to each other when a magnetic field applied thereto has an intensity of zero. Since magnetization orientations are perpendicular to each other when an applied magnetic field is zero in intensity, the suggested magneto-resistive sensor has superior linearity in fluctuation in electrical resistance.
Japanese Unexamined Patent Publication No. 6-203340 has suggested a magneto-resistive sensor including a multi-layered structure having a non-magnetic metal layer, two ferromagnetic layers separated from each other by the non-magnetic metal layer, and an anti-ferromagnetic layer making contact with one of the ferromagnetic layers. The two ferromagnetic layers are designed to have magnetization orientations which are perpendicular to each other when a magnetic field of a signal has an intensity of zero.
Japanese Unexamined Patent Publication No. 7-262529 has suggested a magneto-resistive sensor including a multi-layered structure comprised of a first magnetic layer, a non-magnetic layer, a second magnetic layer, and an anti-ferromagnetic layer. The first and second magnetic layers are composed of CoZrNb, CoZrMo, FeSiAl, FeSi, NiFe alone or in combination of Cr, Mn, Pt, Ni, Cu, Ag, Al, Ti, Fe, Co or Zn.
Japanese Unexamined Patent Publication No. 10-92638 has suggested a magneto-resistive sensor including a multi-layered structure comprised of a non-magnetic substrate, a non-magnetic base layer, a magnetic layer, and a protection film. The non-magnetic base layer is comprised of a multi-layered structure including a first base layer composed of Ta, Ag or Al and a second base layer formed on the first base layer and composed of Cr or alloy of Cr. The magnetic layer is composed of an alloy predominantly containing Co.
In the above-mentioned MR sensors, a base layer is composed of Ta in order to enhance crystallinity of MR layer.
For instance, an example of MR sensor having a base layer composed of Ta is suggested in Abstract of 21st Japan Applied Magnetic Academy Conference, 1997, pp.26.
FIG. 1
is a cross-sectional view of a multi-layered structure of the spin-valve effect type MR sensor suggested in the Abstract. As illustrated in
FIG. 1
, the suggested MR sensor has a multi-layered structure including a base layer
2
, a non-fixed magnetic layer
3
, a non-magnetic layer
4
, a fixed magnetic layer
5
, a magnetization-bias layer
6
, and a protection layer
7
, deposited on a substrate
1
in this order. The base layer
2
is composed of Ta in order to enhance crystallinity of a portion of the multi-layered structure, comprised of the non-fixed magnetic layer
3
, the non-magnetic layer
4
, the fixed magnetic layer
5
, and the magnetization-bias layer
6
.
An apparatus for magnetically reproducing data, including such MR sensor as mentioned above, has been recently required to enhance reproduction output and improve a signal
oise ratio (S/N ratio). To this end, MR sensor has to be designed to have an enhanced resistance-change ratio and enhanced sensitivity.
However, if a base layer is composed of Ta, it is impossible to enhance a resistance-change ratio or MR rate. Hence, a base layer has to be composed of a material other than Ta. However, crystallinity of MR layer would be degraded, if a base layer were composed of a material other than Ta.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem, it is an object of the present invention to provide a magneto-resistive sensor including MR layer having crystallinity which is superior to almost the same degree as crystallinity obtained when a base layer is composed of Ta, and enhancing a resistance-change rate (MR rate), even though MR layer is composed of a material other than Ta.
It is also an object of the present invention to provide a method of fabricating such MR sensor, and an app
NEC Corporation
Patidar Jay
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