Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-01-31
2003-12-30
Watko, Julie Anne (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06671139
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to magnetoresistive read heads. More particularly, it relates to magnetoresistive read heads having in-stack longitudinal bias structures.
BACKGROUND ART
Thin film magnetoresistive (MR) sensors or heads have been used in magnetic data storage devices for several years. Physically distinct forms of magnetoresistance such as anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) and spin tunneling magnetoresistance (TMR) are well known in the art. Magnetic readback sensor designs have been built using these principles and other effects to produce devices capable of reading high density data. In particular, three general types of magnetic read heads or magnetic readback sensors have been developed: the anisotropic magnetoresistive (AMR) sensor, the giant magnetoresistive (GMR) sensor or GMR spin valve, and the magnetic tunnel junction (MTJ) sensor.
A magnetoresistive (MR) read head typically includes a top and bottom shield layers, top and bottom gap layers, a read sensor, such as a spin valve, and the first and second leads that are connected to the read sensor for conducting a sense current through the read sensor. The top and bottom gap layers are located between the top and bottom shield layers, and the read sensor and the first and second leads are located between the top and bottom gap layers. Accordingly, the top and bottom gap layers are constructed as thin as possible without shorting the top and bottom shield layers to the read sensor and the first and second leads.
The first and second leads abut the first and second side edges of the read sensor in a connection referred to in the art as a contiguous junction. A spin valve read sensor typically includes a spacer layer sandwiched between a free layer and a pinned layer, and a pinning layer adjacent to the pinned layer for pinning the magnetic moment of the pinned layer. The free layer has a magnetic moment that is free to rotate relative to the fixed magnetic moment of the pinned layer in the presence of an applied magnetic field.
Typically, magnetic spins of the free layer are unstable in small sensor geometries and produce magnetic noise in response to magnetic fields. Therefore, the free layer must be stabilized by longitudinal biasing so that the magnetic spins of the free layer are in a single domain configuration.
There are two stabilization schemes for longitudinal biasing of the free layer. One stabilization scheme is to provide a longitudinal bias field from the lead regions at the side edges of the read sensor. The most common technique of the prior art includes the fabrication of tail stabilization at the physical track edges of the sensor. The efficacy of the method of stabilization depends critically on the precise details of the tail stabilization, which is difficult to accurately control using present fabrication methods.
The other stabilization scheme is to provide an in-stack longitudinal bias structure including a soft ferromagnetic bias layer and an anti-ferromagnetic (AFM) bias layer.
FIG. 1
shows an in-stack bias scheme for stabilizing a spin valve of the prior art. A MR sensing head
100
includes a spin valve
102
and an in-stack longitudinal bias structure
104
. The spin valve
102
includes a free layer
112
, a pinned layer
108
, a spacer layer
110
located between the free layer
112
and the pinned layer
108
, and an AFM layer
106
adjacent to the pinned layer
108
. The in-stack longitudinal bias structure
104
includes a ferromagnetic bias layer
116
and an AFM bias layer
118
. The MR sensing head also includes a non-magnetic spacer layer
114
disposed between the spin valve
102
and the in-stack longitudinal bias structure
104
. The ferromagnetic bias layer
116
and the AFM bias layer
118
exchange couple to each other, resulting in dominant edge magnetostatic coupling field that stabilize the magnetization of the free layer
112
. However, in the prior art in-stack bias scheme, the sense current will be shunted by the bias stack. In addition, the prior art in-stack bias scheme utilizes mainly the edge magnetostatic coupling field that requires self-aligned edges to produce a maximum edge magnetostatic coupling field that is opposite to the interlayer magnetostatic coupling field. It implies a requirement of minimizing the positive interlayer magnetostatic coupling field in order to maximize the longitudinal bias field.
U.S. Pat. No. 6,023,395 issued Feb. 8, 2000 to Dill et al. discloses a magnetic tunnel junction (MTJ) magnetoresistive (MR) read head with an in-stack biasing scheme. The MTJ head includes a MTJ stack, which contains a pinned layer, a free layer and an insulating tunnel barrier layer between the pinned layer and the free layer, a biasing ferromagnetic layer and a non-magnetic electrically conductive spacer layer separating the biasing ferromagnetic layer from the layers in the MTJ stack. The biasing ferromagnetic layer is magnetostatically coupled with the free layer to provide either longitudinal bias or transverse bias or a combination of longitudinal and transverse bias fields to the free layer. However, the in-stack biasing scheme of Dill is not optimal for a spin valve sensor read head since the read current and readback signal will be shunted by the biasing ferromagnetic layer.
There is a need, therefore, for an improved MR sensing head having a spin valve with a magnetically stabilized free layer and without significant shunting of the sense current by the longitudinal bias stack.
SUMMARY
A magnetoresistive (MR) sensing head according to a first embodiment of the present invention includes a current-in-plane CIP) sensor, an in-stack longitudinal bias structure, and an electrically insulating layer separating the CIP sensor and the in-stack longitudinal bias structure. The CIP sensor typically includes a ferromagnetic free layer, a ferromagnetic pinned layer, a spacer layer located between the ferromagnetic free layer and the ferromagnetic pinned layer, and an anti-ferromagnetic (AFM) layer adjacent to the ferromagnetic pinned layer for pinning the magnetic moment of the ferromagnetic pinned layer. The width along the off-track direction of the in-stack longitudinal bias structure is greater than the track-width of the CIP sensor such that the edge magnetostatic coupling field H
D
acting on the ferromagnetic free layer from the track-width edges of the longitudinal bias structure is reduced to approximately zero. Typically, the track-width of the CIP sensor is between 0.1 &mgr;m and 0.4 &mgr;m, and the width of the in-stack longitudinal bias structure is greater than 0.5 &mgr;m.
The in-stack longitudinal bias structure preferably includes a ferromagnetic bias layer adjacent to the electrically insulating layer and an AFM bias layer. The longitudinal stabilization is achieved by an interlayer magnetostatic coupling (H
F
) acting on the free layer from the ferromagnetic bias layer across the electrically insulating layer.
In a preferred configuration of the first embodiment, the MR sensing head includes a CIP sensor with the ferromagnetic free layer on the top. The MR sensing head also includes abutted leads located on both sides of the CIP sensor. In this case, the electrically insulating layer includes a first insulating portion located on top of the CIP sensor and second insulating portions located on top of the abutted leads. The first insulating portion is thinner than the second insulating portion. Typically, the thickness of the first insulating portion is between 2 Å and 100 Å, and the thickness of the second insulating portion is between 30 Å and 600 Å. The MR sensing head further includes a bottom gap between a bottom shield and the AFM layer of the CIP sensor and a top gap located on top of the in-stack longitudinal bias structure. Since the second insulating portions are thick, these portions can serves as part of the top gap, therefore, the thickness of the top gap can be reduced significantly or eliminated. The thickness of the second gap is typica
Carey Kashmira J.
Childress Jeffrey R.
Fontana, Jr. Robert E.
Ho Kuok San
Tsang Ching Hwa
Lumen Intellectual Property Services Inc.
Watko Julie Anne
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