Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-03-10
2002-09-03
Letscher, George J. (Department: 2654)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06445554
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic recording, and more particularly to a method and system for providing a tunneling magnetoresistance recording junction suitable for high areal density magnetic recording.
BACKGROUND OF THE INVENTION
Tunneling magnetoresistive (“TMR”) junctions have recently become of interest for potential use in reading recording media in a magnetoresistive (“MR”) head.
FIG. 1A
depicts diagrams of a conventional TMR sensor
10
as viewed from the side.
FIG. 1A
depicts the shields first and second shields
24
and
26
, first and second gaps
20
and
22
, leads
11
and
19
, and the TMR sensor
10
.
FIG. 1B
depicts the conventional TMR sensor
10
as viewed from the side and from an air-bearing surface or magnetic material with which the TMR sensor
10
is being used. In addition to the TMR sensor
10
,
FIG. 1B
depicts leads
11
and
19
and first and second gaps
20
and
22
, respectively. Not depicted in
FIG. 1B
are conventional shields
24
and
26
, which partially surround the conventional TMR sensor
10
. The conventional TMR sensor
10
includes a conventional antiferromagnetic (“AFM”) layer
12
, a conventional pinned layer
14
, a conventional barrier layer
16
, and a conventional free layer
18
. The TMR junction for the TMR sensor
10
includes the interfaces between the conventional pinned layer
14
, the conventional barrier layer
16
and the conventional free layer
18
. Also depicted are portions of gaps
20
and
22
that surround a portion of the TMR sensor
10
. The conventional pinned layer
14
and conventional free layer
18
are ferromagnetic. The conventional pinned layer
14
has its magnetization fixed, or pinned, in place because the conventional pinned layer
14
is magnetically coupled to the conventional AFM layer
12
. The conventional antiferromagnetic layer
12
is approximately one hundred to three hundred Angstroms thick. The conventional pinned layer
14
is approximately twenty to one hundred Angstroms thick. The conventional barrier layer
16
is typically five to twenty Angstroms thick and the conventional free layer
18
is typically thirty to one hundred Angstroms thick.
The magnetization of the conventional free layer
18
of the TMR sensor
10
is biased in the plane of the page when there is no external magnetic field, but is free to rotate in response to an external magnetic field. The conventional free layer
18
is typically composed of Co, Co
90
Fe
10
, or a bilayer of Co
90
Fe
10
and permalloy. The magnetization of the conventional pinned layer
14
is pinned perpendicular to the plane of the page. The conventional pinned layer
14
is typically composed of Co, Fe, or Ni. The conventional barrier layer
16
is typically composed of aluminum oxide (Al
2
O
3
).
For the conventional TMR sensor
10
to function, a bias current is driven between the leads
11
and
19
, perpendicular to the plane of the layers
12
,
14
,
16
and
18
of the conventional TMR sensor
10
. Thus, the TMR sensor
10
is known as a current perpendicular to the plane (“CPP”) junction. The direction of flow of the bias current is depicted by the arrow
24
. The MR effect in the conventional TMR sensor
10
is believed to be due to spin polarized tunneling of electrons between the conventional free layer
18
and the conventional pinned layer
14
. Thus, spin polarized electrons tunnel through the conventional barrier layer
16
in order to provide the magnetoresistive effect. When the magnetization of the conventional free layer
18
is parallel or antiparallel to the magnetization of the conventional pinned layer
14
, the resistance of the conventional TMR. sensor
10
is minimized or maximized, respectively. In addition, the magnetization of the conventional free layer
18
is biased to be perpendicular to the magnetization of the conventional pinned layer
14
when no external field is applied, as depicted in FIG.
1
B. The magnetoresistance, MR, of a MR sensor is the difference between the maximum resistance and the minimum resistance of the MR sensor. The MR ratio of the MR sensor is typically called &Dgr;R/R, and is typically given as a percent. A typical magnetoresistance of the conventional TMR sensor is approximately twenty percent.
The conventional TMR sensor
10
is of interest for MR sensors for high areal density recording applications. Currently, higher recording densities, for example over 40 gigabits (“Gb”) per square inch, are desired. When the recording density increases, the size of and magnetic field due to the bits decrease. Consequently, the bits provide a lower signal to a read sensor. In order to maintain a sufficiently high signal within a MR read head, the signal from the read sensor for a given magnetic field is desired to be increased. One mechanism for increasing this signal would be to use an MR sensor having an increased MR ratio. The conventional TMR sensor
10
has an MR of approximately twenty percent, which is higher than a conventional giant magnetoresistance (“GMR”) sensor having a nonmagnetic conducting layer separating a free layer and a pinned layer. Furthermore, the conventional TMR sensor
10
has a smaller thickness than a conventional GMR sensor, allowing for a smaller spacing between shields (not shown). The smaller spacing between shields allows for more effective shielding of bits not desired to be read by the TMR sensor
10
. The width of the TMR sensor
10
, shown in
FIG. 1
, can be narrower than a conventional GMR sensor. This also aids in allowing the conventional TMR sensor
10
to read smaller bits at higher recording densities.
Although the conventional TMR sensor
10
is of interest for high-density recording applications, one of ordinary skill in the art will readily realize that there are several drawbacks to the conventional TMR sensor
10
. Some of these drawbacks are due to the area of the conventional TMR sensor
10
. In particular, the conventional TMR sensor
10
often has a nonuniform bias current and may have a reduced MR ratio due to the large area of the TMR sensor
10
. The area of the conventional TMR junction includes the area of the interfaces between the conventional pinned layer
14
, the conventional free layer
18
and the conventional barrier layer
18
. The junction area is defined by the width of the conventional TMR sensor
10
, w, depicted in
FIG. 1B
, and the length of the conventional TMR sensor
10
Into the plane of the page depicted in FIG.
1
B. The length of the conventional TMR sensor
10
is determined by the stripe height, h, of the conventional TMR sensor
10
as depicted in FIG.
1
A. The width w of the conventional TMR sensor
10
is determined by the track width (not shown) of the media desired to be read and is typically approximately half of the track width. Thus, the junction area for the conventional TMR sensor
10
is the width multiplied by the stripe height (w×h). The area of the conventional TMR junction for the conventional TMR sensor
10
is typically on the order of one square micrometer. As discussed above, the conventional barrier layer
16
is typically between five and twenty Angstroms thick. Because the conventional barrier layer
16
has such a large area but is so thin, pinholes (not shown in
FIG. 1
) often exist in the conventional barrier layer
16
. Current more easily flows between the conventional pinned layer
14
and the conventional free layer
18
through these pinholes than through the conventional barrier layer
16
. As a result, the bias current between the leads
11
and
19
is nonuniform. In addition, because electrons pass readily through these pinholes, the electrons do not undergo spin polarized tunneling. As a result, the MR effect for the conventional TMR sensor
10
can be reduced by the electrons which pass through the pinholes instead of tunneling through the conventional barrier layer
16
. Consequently, not only may the bias current lack uniformity, but the MR ratio for the conventional TMR sensor
10
may also be reduced below the intrinsic percent
Dong Zi-Weng
Shi Zhupei
Letscher George J.
Read-Rite Corporation
Sawyer Law Group LLP
LandOfFree
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