Etching a substrate: processes – Forming or treating article containing magnetically...
Reexamination Certificate
2000-04-04
2002-09-17
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Forming or treating article containing magnetically...
C216S075000, C438S003000, C438S720000, C134S001100, C134S002000, C360S313000, C360S324200, C427S059000
Reexamination Certificate
active
06451215
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a magneto-resistive tunnel junction head for reading the magnetic field intensity from a magnetic recording medium or the like as a signal. In particular, the present invention relates to a method of producing a magneto-resistive tunnel junction head in which a higher output can be obtained for allowing the application of the head to ultra-high density magnetic recording.
2. Description of the Related Art
MR sensors based on the anisotropic magneto-resistance (AMR) or spin-valve (SV) effect are widely known and extensively used as read transducers in magnetic recording. MR sensors can probe the magnetic stray field coming out from transitions recorded on a recording medium by the resistance changes of a reading portion formed of magnetic materials. AMR sensors have quite a low resistance change ratio &Dgr;R/R, typically from 1 to 3%, whereas the SV sensors have a &Dgr;R/R ranging from 2 to 7% for the same magnetic field excursion. The SV magnetic read heads showing such high sensitivity are progressively supplanting the AMR read heads to achieve very high recording density, namely over several Giga bits per square inch (Gbits/in
2
).
Recently, a new MR sensor has attracted attention for its application potential in ultra-high density recording. Magneto-resistive tunnel junctions (MRJT, or synonymously referred to as TMR) are reported to have shown a resistance change ratio &Dgr;R/R over 12%. Although it has been expected that TMR sensors replace SV sensors in the near future as the demand for ultra-high density is ever growing, an application to the field of the magnetic heads has just started, and one of the outstanding objects is to develop a new head structure which can maximize the TMR properties. Great efforts of developments are still needed to design a new head structure since TMR sensors operate in CPP (Current Perpendicular to the Plane) geometry, which means that TMR sensors requires the current to flow in a thickness direction of a laminate film.
In a basic SV sensor which has been developed for practical applications, two ferromagnetic layers are separated by a non-magnetic layer, as described in U.S. Pat. No. 5,159,513. An exchange layer (FeMn) is further provided so as to be adjacent to one of the ferromagnetic layers. The exchange layer and the adjacent ferromagnetic layer are exchange-coupled so that the magnetization of the ferromagnetic layer is strongly pinned (fixed) in one direction. The other ferromagnetic layer has its magnetization which is free to rotate in response to a small external magnetic field. When the magnetization of the ferromagnetic layers are changed from a parallel to an antiparallel configuration, the sensor resistance increases and a &Dgr;R/R in the range of 2 to 7% is observed.
In comparison between the SV sensor and the TMR sensor, the structure of the TMR is similar to the SV sensor except that the non-magnetic layer separating the two ferromagnetic layers is replaced by a tunnel barrier layer being an insulating layer and that the sense current flows perpendicular to the surfaces of the ferromagnetic layers. In the TMR sensor, the sense current flowing through the tunnel barrier layer is strongly dependent upon a spin-polarization state of the two ferromagnetic layers. When the magnetization of the two ferromagnetic layers are antiparallel to each other, the probability of the tunnel current is lowered, so that a high junction resistance is obtained. On the contrary, when the magnetization of the two ferromagnetic layers are parallel to each other, the probability of the tunnel current is heightened and thus a low junction resistance is obtained. The inventors of the present invention have attempted to design TMR heads the constructions of which are similar to those of SV heads. One of these head constructions is shown in FIG.
5
. The TMR head
100
shown in
FIG. 5
comprises a TMR element
200
having a laminate structure composed of a ferromagnetic free layer
120
, a tunnel barrier layer
130
, a ferromagnetic pinned layer
140
, and an antiferromagnetic pinning layer
150
. Insulating layers
191
and
191
are externally formed on the opposite ends (left and right directions of the drawing paper) of the TMR element
200
. The ferromagnetic pinned layer
140
is pinned such that its magnetization direction is fixed in one direction (a depth direction of the drawing sheet), and the ferromagnetic free layer
120
can change its magnetization direction freely in response to an external signal magnetic field.
Biasing layers
161
and
161
, for applying a bias magnetic field in the direction of the arrow (&agr;), are formed on the upper surface of both ends of the ferromagnetic free layer
120
, which is disposed at an upper portion of the TMR element
200
. The biasing layers
161
and
161
are composed of permanent magnet, for example. Thus, at portions where the biasing layers
161
contact with the upper surface of the ferromagnetic free layer
120
, the magnetization direction of the ferromagnetic free layer
120
is pinned in the direction of the arrow (&agr;) by the exchange coupling magnetic field. In
FIG. 5
, numerals
171
,
175
represent a pair of upper and the lower electrodes, and numerals
181
,
185
represent a pair of upper and the lower shield layers.
It was confirmed that an effective bias magnetic field was applied to the ferromagnetic free layer
120
by employing the head construction shown in FIG.
5
. However, the present inventors found that the following problems to be solved were raised in the head construction shown in FIG.
5
.
Specifically, the TMR effect is a phenomenon that when a current is applied in a laminate direction between a pair of ferromagnetic layers (a ferromagnetic pinned layer and a ferromagnetic free layer) sandwiching a tunnel barrier layer therebetween, a tunnel current flowing in the tunnel barrier layer changes depending on a relative angle of magnetization between the ferromagnetic layers. The tunnel barrier layer is a thin insulation film which allows electrons to pass therethrough while keeping spin due to the magneto-resistive tunnel junction effect.
Therefore, as shown in
FIG. 4A
, when the ferromagnetic pinned layer and the ferromagnetic free layer are parallel in magnetization to each other, the tunneling probability is increased so that the resistance to current flowing therebetween is decreased (resistance value Rp).
In contrast, as shown in
FIG. 4C
, when both ferromagnetic layers are antiparallel in magnetization to each other, the tunneling probability is lowered, thus, the resistance to current flowing therebetween is increased (resistance value Rap).
In the intermediate state between the state shown in FIG.
4
A and the state shown in
FIG. 4C
, i.e. when both ferromagnetic layers are orthogonal in magnetization to each other, a resistance value Rm takes a value between the resistance value Rp and the resistance value Rap so that a relation of Rp<Rm<Rap is satisfied.
It was found through experiments implemented by the present inventors that an unfavorable phenomenon as shown in
FIGS. 6A and 6B
was generated between the ferromagnetic pinned layer and the ferromagnetic free layer in the head structure shown in FIG.
5
. Specifically, as shown in
FIG. 6A
, when the magnetization directions of the ferromagnetic pinned layer
140
and the free layer
120
are basically parallel to each other, magnetization in both end portions
120
a
and
120
a
of the free layer
120
is fixed in the direction of arrow &agr; due to the exchange-coupling relative to the bias layers as described above. If a sense current i is caused to flow in the laminate direction in this state, the current mainly flows at the center portions of the layers where the magnetization directions are parallel to each other and thus the resistance is small. The total resistance value at this time is given by R′p. On the other hand, as shown in
FIG. 6B
, when the magnetization direc
Araki Satoru
Morita Haruyuki
Shimazawa Koji
Gulakowski Randy
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Smetana J.
TDK Corporation
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