Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-11-18
2002-09-17
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06452765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to magneto-resistive heads and more particularly to a soft adjacent layer made from a ternary alloy material and an anisotropic magneto-resistive sensor that utilizes this soft adjacent layer. The soft adjacent layer of the present invention is a ternary alloy material including CoXY, where Co is cobalt, X is a first transition metal and Y is a second transition metal. In a preferred embodiment, the first transition metal is niobium (Nb) and the second transition metal is titanium (Ti) so that resulting ternary alloy material is cobalt-niobium-titanium (CoNbTi). Alternatively, X and Y may be any transition metals such that the resulting ternary alloy CoXY exhibits properties similar to CoNbTi.
2. Background Art
Anisotropic magneto-resistive (MR) sensors are used in numerous devices for reading signals recorded on a magnetic storage medium. For example, MR sensors are widely used in computers as read sensors in high-capacity hard drives and other types of magnetic storage media. Even though current hard drives can store large amounts of data, there are in development hard drives with even greater storage capabilities. Existing MR sensors, however, are inadequate to read the higher-density storage media of these next generation hard drives. Therefore, as more data is packed onto these magnetic storage media, there is a need for higher-density anisotropic MR sensors capable of reading this data.
Anisotropic MR sensors utilize the anisotropic magneto-resistive (AMR) effect to detect signals recorded on a magnetic storage medium through the resistance change in a material as a function of the amount and direction of magnetic flux. The basic AMR effect states that the electrical resistance of a MR material changes in the presence of a magnetic field. FIG.
1
. illustrates the AMR effect in a thin-film strip of MR material. Typically, this thin-film strip, known as a MR layer
100
, is contained on a MR sensor. The thickness of the MR layer
100
is thin enough that the resistance of the MR layer
100
varies as cos
2
&thgr;, where &thgr; is known as the magnetization angle. As shown in
FIG. 1
, &thgr; is the angle between the magnetization vector M of the MR layer
100
and the direction of the current I flowing through the MR layer
100
. The resistance of the MR layer
100
is given as:
R=R
0
+&Dgr;R
cos
2
&thgr;
where R
0
is the fixed part of the resistance and &Dgr;R is the maximum value of the variable part of the resistance.
The fundamental idea behind the MR sensor is that the signal produced by the tape, disk, or other magnetic storage media rotates the magnetization vector M of the MR layer
100
. When the magnetization angle &thgr; is properly biased with a bias field, any small changes in resistance are almost directly proportional to the signal produced by the storage medium. In turn, this resistance change is transformed into a voltage signal by passing the current I through the MR layer
100
. In order to have a nearly linear response from the MR layer
100
, it is important that the magnetization vector M be properly biased so that the magnetization angle &thgr; is 45 degrees.
In general, the magnetization angle &thgr; is biased at 45 degrees by using two bias fields, longitudinal and transverse bias. The preferred technique for transverse biasing MR sensors is by soft adjacent layer (SAL) biasing. One reason SAL biasing for MR sensors is the preferred technique is that SAL biasing is relatively easy to fabricate and work with and uses well-known thin-film techniques. Another reason is that efforts to increase recording density require that the recording tracks be narrower and the linear recording density along each track be increased. The small MR layers that are necessary to achieve these requirements are particularly well-suited for SAL biasing.
FIG. 2
illustrates a conventional SAL biasing arrangement. In particular, the tri-layer thin-film stacked structure
200
includes the MR layer
205
, a spacer
210
and the SAL
220
. The spacer
210
is made of a non-magnetic material of high-resistivity and is sandwiched between the MR layer
205
and the SAL
220
to prevent magnetic exchange coupling. In addition, the spacer
210
electrically insulates the MR layer
205
from the SAL
220
. In a typical tri-layer structure, the spacer
210
is made from tantalum (Ta), the MR layer is any one of various types of permalloy consisting generally of 81% nickel (Ni) and 19% iron (Fe), and the SAL
220
is made from one of several materials including permalloy and ternary alloys containing nickel-iron (NiFe) and a third element selected from rhodium (Rh), ruthenium (Ru), titanium (Ti), chromium (Cr), iridium (Ir) or niobium (Nb).
In order to operate the tri-layer structure
200
in a MR sensor a sense current Is is applied to the MR layer
205
from a current source. Due to the SAL sense current shunting effect, however, only of a portion of the sense current I
S
flows through the electrically conductive MR layer
205
, as represented by I
S205
. The SAL sense current shunting effect is a major disadvantage in SAL biasing. This inherent shunting occurs when the fill sense current I
S
is shunted away from the MR layer
205
into the SAL
220
. In existing MR sensors, the sense current I
S
is divided among the tri-layer structure
200
as follows: a great majority of I
S
goes to the MR layer, a considerable amount goes to the SAL and a negligible amount goes to the spacer. Shunting of the sense current I
S
from the MR layer
205
is undesirable because in general the higher the current through the MR layer
205
the higher the amplitude and the magneto-resistive effect of the MR sensor. This, in turn, contributes to higher-density MR sensors. Thus, it is highly desirable to decrease the shunting effect and increase the sense current through the MR layer.
One way to decrease the shunting effect is to increase the resistivity of the SAL material. In particular, the higher the resistivity of the SAL material the less sense current will be shunted through the SAL and the more current will flow through the MR layer. However, simply increasing the resistivity of the SAL is not enough. In order to be useful as a SAL, a SAL material must possess other desirable characteristics besides high resistivity. Specifically, a SAL material exhibit the following properties:
a. high permeability and low coercivity: This permits the SAL material to switch easily to its non-magnetic state and not retain any magnetic field even after be magnetically saturated;
b. low interdiffusion between layers and high stability over time: Because the SAL is in close proximity to other materials and layers in the tri-layer structure, it is important that the SAL material not interdiffuse into the other layers. Moreover, the SAL material should be stable over time to ensure a prolonged existence;
c. low magnetostriction: Magnetostriction is the phenomenon in which a magnetic material changes its size depending on its state of magnetization. Low magnetostriction is desirable in a SAL because with low magnetostriction the SAL does not alter its magnetization properties when the SAL goes through the device fabrication process;
d. high corrosion resistance: Because many chemicals are used in the fabrication process, it is important that the SAL material have high corrosion resistance. In particular, cobalt (Co) has a high tendency to corrode, and therefore it is typically quite difficult to find a SAL material made from a Co alloy that has a high corrosion resistance;
e. high saturation magnetization: This property is needed so that the SAL can properly bias the MR layer. For optimal performance of the MR sensor, the SAL should be operated in a magnetically saturated state, and a high saturation magnetization helps achieve this requirement.
Therefore, there exist a need for a SAL material exhibiting the property of high-resistivity so that the SAL sense current shunting effect will be greatly reduced a
Basi Raman
Mahajan Sukesh
Mahvan Nader
Carr & Ferrell LLP
Castro Angel
Hudspeth David
Read-Rite Corporation
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