Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Reexamination Certificate
2002-02-04
2004-08-24
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
C428S623000, C428S632000, C428S640000, C428S675000, C428S676000, C428S678000, C428S679000, C428S215000, C428S336000, C428S692100, C428S702000, C360S324000, C360S324200, C360S125330, C360S121000
Reexamination Certificate
active
06780524
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 magnetic 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 magnetic medium (the signal field). In the spin-valve sensor, 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 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 GMR head
100
comprising a pair of end regions
103
and
105
separated by a central region
102
. The central region
102
is formed by depositing a spin-valve sensor
128
onto a bottom gap layer
118
, which is previously deposited on a bottom shield layer
120
, which is, in turn, previously deposited on a substrate. Two end regions
103
and
105
abut the edges of the central region
102
. In the spin-valve sensor
128
, 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 includes seed layers
116
, on which the pinning, pinned, spacer and sensing layers of the spin-valve sensor
128
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 depositing longitudinal bias (LB) and conducting lead layers
126
on the bottom gap layer
118
and at the spin-valve sensor
128
. The end regions
103
,
105
abut the central region
102
. The central and end regions are sandwiched between electrically insulating nonmagnetic 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 the hard disk drive, and correspondingly to increase the overall signal sensitivity to permit the GMR head of the hard disk drive to read smaller changes in magnetic fluxes. The major property relevant to the signal sensitivity of a spin-valve sensor in the GMR head is its GMR coefficient. A higher GMR coefficient 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
H
, where R
H
is a resistance measured when the magnetizations of the free and pinned layers are parallel to each other, and &Dgr;R
G
is the maximum giant magnetoresistance (GMR) measured when the magnetizations of the free and pinned layers are antiparallel to each other.
In certain spin-valve sensors, particularly those with Co—Fe/Ni—Fe films as sensing layers
106
, a cap layer
112
is often formed over the sensing layers. 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 Cu—O 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 layers 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 layers from interface mixing and oxygen diffusion. Interface mixing originates from direct contact between the sensing layers and the Ta cap layer, and causes a substantial loss in the magnetic moment of the sensing layers. For one currently used spin-valve sensor with 0.32 memu/cm
2
sensing layers, this magnetic moment loss accounts for 25% of the magnetic moment of the sensing layers. 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 layers, causing more losses in the magnetic moment of the sensing layers.
Another limiting factor of the disk drive recording density is the dimensions of the GMR head. The recording density of the disk drive is inversely proportional to the total thickness of the spin-valve sensor, the gap layers
118
and
124
. In other words, in order to increase the disk drive recording density the thicknesses of the spin-valve sensor, the gap layers
118
and
124
must be decreased. Several challenges have arisen in the miniaturization of the gap layers
118
and
124
.
The primary duties of the gap layers
118
and
124
are to prevent electrical shorting between the spin-valve sensor
128
and the shield layers
120
and
130
, and thus to ensure the functionality of the spin-valve sensor
128
. In order to prevent this electrical shorting, a spin-valve sensor must be sandwiched between gap layers
118
and
124
of substantial thicknesses. The gap layers
118
and
124
have been a limiting factor in the miniaturization of the GMR head
100
, because as the thicknesses of the gap layers
118
and
124
decreases, the possibility of electrical shorting increases, causing the GMR head to be non-functional.
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 for improved gap layers with decreased thicknesses.
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 GMR heads. Accordingly, it is an overall object of the present inventi
Lin Tsann
Mauri Daniele
Bernatz Kevin M
Hitachi Global Storage Technologies - Netherlands B.V.
Kunzler & Associates
Thibodeau Paul
LandOfFree
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