Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-06-30
2001-02-06
Heinz, A. J. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06185081
ABSTRACT:
TECHNICAL FIELD
The present invention relates to transducers that employ magnetoresistive sensing mechanisms.
BACKGROUND OF THE INVENTION
The use of magnetoresistive (MR) sensing mechanisms is well known. Such sensors can be used in information storage systems such as disk or tape drives, or as measurement devices for test equipment, among other things.
A transducer for reading and writing information on a medium such as a disk or tape, for example, may have a MR mechanism for sensing magnetic signals from the medium, as well as an inductive mechanism for writing magnetic signals to the medium. MR sensors or transducers that are known for disk drive heads include anisotropic magnetoresistive (AMR) sensors, canted current sensors, spin valve (SV) sensors, giant magnetoresistive (GMR) sensors, etc. To optimize sensor performance it is conventional to provide magnetic fields that bias the magnetoresistive layer or layers within the sensor, in order to remove noise that can occur due to boundary domains as well as to provide more easily interpreted signals.
Ravipati et al., in U.S. Pat. No. 5,434,826, discuss various mechanisms for providing a longitudinal bias to a MR sensor. As pointed out in that patent, it is important that the MR sensing layer has a magnetic direction that will change at a lower coercive force than that required to change the magnetic direction of the bias layers. Unfortunately, if the magnetization provided by the bias layers to the MR sensing layer is too strong, the sensing layer will not change magnetic direction under the influence of changing fields from the media. Even for the case where the MR sensing layer is able to change magnetic direction under the influence of media fields, the sensitivity of the sensing layer may be reduced by the longitudinal bias provided by the bias layers.
Moreover, bias layers abutting ends of MR sensor layers are constrained to a thickness approximating that of the sensor layers, which may be less than 1000 Å. Stated differently, a primary determinant of sensor linear resolution is the spacing between shield layers surrounding the sensor, within which bias, lead, gap and any seed layers must also fit. Unfortunately, the quest for higher sensor resolution and reduced thickness may exacerbate these difficulties.
This need for thinner sensor layers differs from the thickness requirements for media layers, for which a primary determinant of resolution is head to media spacing. Thus reducing the thickness of any overcoat that separates a media layer from the head may be important whereas the thickness of layers formed under the media layer may be immaterial, except for the extra time needed to create thicker underlayers. For example, in U.S. Pat. Nos. 5,693,426 and 5,800,931, Lee et al. teach that media coercivity may be enhanced by forming a relatively thick NiAl underlayer, but that such coercivity is dramatically reduced when the NiAl underlayers are less than 100 nm in thickness.
SUMMARY OF THE INVENTION
The present invention provides improved bias layers for MR sensors. The bias layers formed according to the present invention have an in-plane easy axis of magnetization that can used to provide a desired longitudinal bias. The bias layers may also have increased coercivity, which can help to maintain the magnetization of the bias layers in the presence of applied fields from the head or media.
Further, such bias layers may have a fine grain structure, which can be used to provide a magnetic field at a border between a bias layer and an MR sense layer that rapidly diminishes in strength with distance from that border. This border localized bias field can essentially pin border domains of the MR sense layer while leaving the remainder of the MR sense layer free to rotate under the influence of media fields, reducing noise in the sensor while increasing sensitivity to media fields.
Increases in coercivity and in-plane orientation of the easy axis of magnetization allow the bias layers to be made thinner, allowing other sensor layers to be thinner and sensor resolution to be increased. The increased coercivity and preferred in-plane crystalline orientation also increase the stability of the bias layers. An increase in a ratio of in-plane versus out-of-plane crystalline orientation of the bias layers also corresponds with decreased noise for the sensor.
REFERENCES:
patent: 5434826 (1995-07-01), Ravipati et al.
patent: 5583727 (1996-12-01), Parkin
patent: 5693426 (1997-12-01), Lee et al.
patent: 5789056 (1998-08-01), Bian et al.
patent: 5800931 (1998-09-01), Lee et al.
patent: 5846648 (1998-12-01), Chen et al.
patent: 5858566 (1999-01-01), Zhang
Chen Yingjian
Miller Mark S.
Simion Bogdan M.
Heinz A. J.
Lauer Mark
Read-Rite Corporation
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