Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-02-11
2004-04-13
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06721149
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic recording technology, and more particularly to a tunneling magnetoresistive read head which is capable of being used in high density magnetic recording and can be easily manufactured.
BACKGROUND OF THE INVENTION
Recently, tunneling magnetoresistive (“TMR”) junctions have become of interest for potential use in reading recording media in a magnetoresistive (“MR”) head.
FIG. 1
is a diagram of a conventional TMR junction
10
. Also depicted in
FIG. 1
are leads
11
and
19
. Not depicted are conventional shields and gaps which would surround the conventional TMR junction
10
if the TMR junction
10
is used as a sensor. The conventional TMR junction
10
includes a conventional antiferromagnetic (“AFM”) layer
12
, a conventional pinned layer
14
, a conventional insulating spacer layer
16
and a conventional free layer
18
. 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 magnetization of the conventional free layer
18
may be free to rotate in response to an external magnetic field. The conventional pinned layer
14
is typically composed of Co, Fe, or Ni. 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 conventional insulating spacer layer
16
is typically composed of aluminum oxide (Al
2
O
3
).
For the conventional TMR junction
10
to function, 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 junction
10
. The MR effect in the conventional TMR junction
10
is believed to be due to spin polarized tunneling of electrons between the conventional free layer
18
and the conventional pinned layer
14
. 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 junction
10
is minimized or maximized. When the magnetization of the conventional free layer
18
is perpendicular to the magnetization of the conventional pinned layer
14
, the bias point for the TMR junction
10
is set. The magnetoresistance, MR, of a MR sensor is the difference between the maximum and minimum resistances of the MR sensor. The MR ratio of the MR sensor is typically called &Dgr;R/R, and is typically given as a percent. The intrinsic magnetoresistance of such a conventional TMR junction
10
is approximately seventeen percent.
TMR junctions, such as the conventional TMR junction
10
, are of interest for MR sensors for high 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.
Although the conventional TMR junction
10
is approximately seventeen percent, a higher MR ratio is desired. Some conventional TMR junctions
10
have an increased MR ratio due to the resistance effect of the leads
11
and
19
. In such conventional TMR junctions
10
, an MR ratio of up to forty percent has been reported. However, the high MR ratio for such conventional TMR junctions
10
is due to lead resistance. The resistance of the leads
11
and
19
is much higher than the resistance of the conventional TMR junction itself of the conventional TMR sensor
10
, which is on the order of sixty ohms per micrometer squared. Consequently, the resistance of the combination of the TMR junction
10
and the leads
11
and
19
is high.
One of ordinary skill in the art will readily realize that a high resistance for the conventional TMR sensor
10
and leads
11
and
19
results in a slow response. Because the combination of the conventional TMR junction
10
and leads
11
and
19
have a high resistance, the time constant for the combination is large. As a result, the response time for the conventional TMR junction
10
is long. The large response time results in a low data transfer rate, which is undesirable.
FIG. 2A
depicts another conventional TMR junction
20
disclosed in “Inverse Tunnel Magnetoresistance in Co/SrTiO
3
/La
0.7
Sr
0.3
MnO
3
: New Ideas on Spin-Polarized Tunneling” J. M. De Teresa, A. Barthelemy, A. Fert, J. P. Contour, R. Lyonnet, F. Montaigne, P. Seneor, and A. Vaures, Phys. Rev. Lett., Vol. 82, No. 21, 4288-4291 (1999). Also depicted in
FIG. 1B
are leads
21
and
29
, which are used to carry current to and from the conventional TRM junction
20
. The conventional TMR sensor
20
includes an antiferromagnetic layer
22
. Above the antiferromagnetic layer is a conventional La
0.7
Sr
0.3
MnO
3
(LSMO) pinned layer
24
. Above the LSMO pinned layer
24
is a SrTiO
3
(STO) insulating layer
26
. On the side of the STO insulating layer
26
is a conventional free layer
28
composed of Co or LSMO. The MR ratio of the conventional TMR junction
20
is higher than that of the conventional TMR junction
10
.
FIG. 2B
depicts a conventional method
40
for forming the conventional TMR junction
20
. The LSMO pinned layer
24
is provided using pulsed laser deposition at seven hundred degrees Celsius and an oxygen pressure of three hundred and fifty millitorr, via step
42
. The STO insulating layer
26
is then provided using pulsed laser deposition at seven hundred degrees Celsius and an oxygen pressure of three hundred and fifty millitorr, via step
44
. The conventional pinned layer
28
of Co is then provided using molecular beam epitaxy or sputtering, via step
46
.
Referring to
FIGS. 2A and 2B
, the conventional TMR junction
20
utilizes the STO insulating layer
26
in order to improve the MR for the conventional TMR junction
20
. It is believed that d-shell electrons can tunnel more readily through the STO insulating layer
26
than through an insulating layer such as the aluminum oxide insulating spacer layer
16
used in the conventional TMR junction
10
. Ferromagnetic materials, such as Co, have d-shell electrons in their unfilled shell. Moreover, the magnetic properties of many ferromagnetic materials are dominated by the d-shell electrons. The STO insulating layer
26
more readily forms d electron bonds with the conventional free layer
28
at the interface between the STO insulating layer
26
and the conventional free layer
28
. As a result, it is believed that the d-shell electrons from the conventional free layer
28
can more readily tunnel through the STO insulating layer
26
. The same is true for the STO insulating layer
26
and the conventional LSMO pinned layer
24
. As a result, tunneling of spin polarized electrons is more likely to take place in the conventional TMR junction
20
than in the conventional TMR junction
10
, which has an insulating spacer layer
16
of aluminum oxide through which s-shell electrons are more likely to tunnel. Therefore, the MR ratio of the conventional TMR junction
20
is higher.
In addition, the LSMO pinned layer
24
is what is known as a half metallic ferromagnet. A half metallic ferromagnet has electrons of only one spin type in its unfilled shells. The spin polarization of a material is proportional to the number of spin up electrons in the material's unfilled shell minus the number of spin down electrons in the material's unfilled shell. The spin polarization is typically expressed as a percentage. Thus, a half metallic ferromagnet has a spin polarization of one hundred percent. It has been postulated that the MR ratio for a TMR junction is 2*P
1
*P
2
/
Dong Zi-Weng
Leng Qun Wen
Shi Zhupei
Chen Tianjie
Miller Brian E.
Sawyer Law Group LLP
Western Digital (Fremont) Inc.
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