Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Reexamination Certificate
2001-07-31
2004-03-23
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
C428S629000, C428S632000, C428S637000, C428S675000, C428S676000, C428S678000, C428S215000, C428S336000, C428S692100, C428S702000, C427S539000, C427S294000, C427S419300, C204S192200, C360S324100, C360S119050, C360S125330, C360S121000, C148S277000
Reexamination Certificate
active
06709767
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to spin-valve sensors for reading information signals from a magnetic medium and more particularly to novel structures for spin-valve sensors and magnetic recording systems which incorporate such sensors.
2. The Relevant Art
Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device, such as a disk drive, incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data are recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic recording heads carrying read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, a giant magnetoresistance (GMR) head carrying a spin-valve sensor is now extensively used to read data from the tracks on the disk surfaces. This spin-valve sensor typically comprises two ferromagnetic films separated by an electrically conducting nonmagnetic film. The resistance of this spin-valve sensor varies as a function of the spin-dependent transmission of conduction electrons between the two ferromagnetic films and the accompanying spin-dependent scattering which takes place at interfaces of the ferromagnetic and nonmagnetic films.
In the spin-valve sensor, one of the ferromagnetic films, referred to as a pinned layer, typically has its magnetization pinned by exchange coupling with an antiferromagnetic film, referred to as a pinning layer.
The magnetization of the other ferromagnetic film, referred to as a “sensing” or “free” layer is not fixed, however, and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In the spin-valve sensors, the GMR effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the sensing layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium causes a change in the direction of magnetization in the sensing layer, which in turn causes a change in the resistance of the spin-valve sensor and a corresponding change in the sensed voltage.
FIG. 1
shows a typical prior art spin-valve sensor
100
comprising a pair of end regions
103
and
105
separated by a central region
102
. The central region
102
is formed by depositing various layers onto a bottom gap layer
118
, which is previously deposited on a bottom shield layer
120
, which is, in turn, deposited on a substrate. Two end regions
103
,
105
abut the edges of the central region
102
. A ferromagnetic sensing layer
106
is separated from a ferromagnetic pinned layer
108
by an electrically conducting nonmagnetic spacer layer
110
. The magnetization of the pinned layer
108
is fixed through exchange coupling with an antiferromagnetic pinning layer
114
. This spin-valve sensor is sputtered onto seed layers
116
, on which the pinning, pinned, spacer and sensing layers of the spin-valve sensor grow with preferred crystalline textures during sputtering so that desired improved GMR properties are attained.
The end regions
103
and
105
are also formed by a suitable deposition method such as sputtering of various layers onto the bottom gap layer
118
. Longitudinal bias (LB) and conducting lead layers
126
abut the spin-valve sensor. The central and end regions are sandwiched between electrically insulating nonmagmetic films, one referred as a bottom gap layer
118
and the other referred as a top gap layer
124
.
The disk drive industry has been engaged in an ongoing effort to increase the recording density of hard disk drives, and correspondingly to increase the overall signal sensitivity to permit the GMR head of the hard disk drives to read smaller changes in magnetic flux. The major property relevant to the signal sensitivity of a spin-valve sensor is its GMR coefficient. A higher GMR coefficients leads to higher signal sensitivity and enables the storage of more bits of information on a disk surface of a given size. The GMR coefficient of the spin-valve sensor is expressed as &Dgr;R
G
/R
ll
where R
ll
is a resistance measured when magnetizations of the free and pinned layers are parallel to each other, and ARG is the maximum giant magnetoresistance (GMR) measured when magnetizations of the free and pinned layers are antiparallel to each other.
Other properties relevant to the signal sensitivity of the spin-valve sensor include exchange coupling between the antiferromagnetic pinning and ferromagnetic pinned layers. This exchange coupling must be high in order to keep the magnetization of the pinned layer at a direction perpendicular to an air bearing surface for optimal sensor operation. An inadequate exchange coupling may cause canting of the magnetization of the pinned layer from the preferred direction, thereby reducing the signal sensitivity of the spin-valve sensor.
It is also vital that the sensing current flowing in the spin-valve sensor be confined to the pinned
108
, spacer
110
and sensing
106
layers of the spin-valve sensor. If the sensing current is permitted to shunt through the pinning
114
or other layers, the resistance of the spin-valve sensor will be low, thus producing a low GMR coefficient. Accordingly, the material selected for the pinning layer must possess a high electrical resistivity in order to prevent the current shunting.
In certain spin-valve sensors, particularly those with a Ni-Fe sensing layer, a cap layer
112
is often formed over the sensing layer. The cap layer
112
serves several purposes, and plays a crucial role in attaining a high GMR coefficient. For instance, a Cu cap layers is thought to induce spin filtering, while a NiO cap layer is thought to induce specular scattering. Both spin filtering and specular scattering are believed to increase the GMR coefficient of a spin-valve sensor. In addition, a cap layer may be employed to prevent the underlying sensing layer from interface mixing occurring immediately during depositions and oxygen diffusion occurring during subsequent annealing, thereby maintaining suitably soft magnetic properties of the sensing layer and improving the thermal stability of the spin-valve sensor. The term “soft magnetic property” refers to the capability of a spin-valve sensor to sense very small magnetic fields.
Currently, a Ta cap layer is used in many conventional spin-valve sensors. However, the Ta cap layer does not exhibit desired specular scattering, and is considered inadequate in preventing the sensing layer from interface mixing and oxygen diffusion. Interface mixing originates from direct contact between the sensing layer and the Ta cap layers, and causes a substantial loss in the magnetic moment of the sensing layer. For one currently used spin-valve sensor with a 0.32 memu/cm
2
sensing layer, this magnetic moment loss accounts for 25% of the magnetic moment of the sensing layer. Oxygen diffusion originates from low passivity of the Ta cap layer, which oxidizes continuously and entirely during annealing, such that oxygen eventually penetrates into the sensing layer, causing more losses in the magnetic moment of the sensing layer.
Thus, it can be seen from the above discussion that there is a need existing in the art for an improved spin-valve sensor with an increased GMR coefficient and improved thermal stability. Particularly, it would be advantageous to provide a spin-valve sensor with a suitable cap layer to achieve the increased GMR coefficient and improved thermal stability through decreases in the occurrence of interface mixing and oxygen diffusion.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available spin-valve sensors. Accordingly, it is an overall object of the pr
Lin Tsann
Mauri Daniele
Bernatz Kevin M.
Hitachi Global Storage Technologies - Netherlands B.V.
Kunzler & Associates
Thibodeau Paul
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