Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-05-14
2004-06-01
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06744608
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic memory systems, and more particularly to a method and system for providing tunneling magnetoresistive sensors that could be used in magnetic memory systems.
BACKGROUND OF THE INVENTION
Magnetic memories are often used in storing data. One type of memory currently of interest utilizes tunneling magnetoresistive (“TMR”) sensors in the memory cells. A TMR sensor typically includes two ferromagnetic layers separated by a thin insulating layer. The insulating layer is thin enough to allow charge carriers to tunnel between the ferromagnetic layers. One ferromagnetic layer has its magnetization fixed, or pinned, in place. This is typically accomplished using an antiferromagnetic layer. The other ferromagnetic layer has a magnetization that can rotate in response to an applied magnetic field. The resistance of the TMR sensor depends upon the orientation of the magnetic tunneling junctions. Thus in order to store data in the TMR sensor or MRAM, one or two magnetic fields are applied to rotate the magnetization of one of the layers. Typically, the magnetization of one ferromagnetic layer will be rotated to be parallel or anti-parallel relative to the magnetization of the other ferromagnetic layer. The TMR sensor will thus be in either a low resistance (magnetizations parallel) or a high resistance (magnetizations antiparallel) state. The TMR sensor can thus be used to store data. A signal corresponding to the resistance is developed in order to indicate the type of data stored.
FIG. 1
is a flow chart depicting a conventional method
10
for fabricating the TMR sensor.
FIGS. 2A-2E
depict a conventional TMR sensor during fabrication. Referring to FIGS.
1
and
2
A-
2
E, the method
10
commences after the layers for the TMR sensor have been deposited. Thus, the method
10
starts after the free layer, the tunneling barrier and the pinned layer and antiferromagnetic layer which pins the magnetization of the pinned layer, have been provided on a bottom lead layer. A conventional bilayer structure is provided, via step
12
.
FIG. 2A
depicts the conventional TMR structure
50
after step
12
has been performed. The TMR layers
54
reside on a bottom lead
52
. The TMR layers include an antiferromagnetic layer, a ferromagnetic pinned layer, a tunneling barrier (a thin insulating layer) and a ferromagnetic free layer. Also depicted is the conventional bilayer structure
56
that includes a PMGI layer
55
and a larger photoresist layer
57
.
Using the conventional bilayer structure
56
as a mask, the TMR sensor is defined, via step
14
.
FIG. 2B
depicts the conventional TMR structure
50
after the conventional TMR sensor
60
has been defined. A dielectric layer is provided, via step
16
.
FIG. 2C
depicts the TMR structure
50
after the dielectric layer has been deposited. The dielectric layer includes regions
62
A and
62
B on either side of the conventional TMR sensor
60
as well as a region
62
C that lies on the conventional bilayer structure
56
. The conventional bilayer structure
56
is lifted off, via step
18
.
FIG. 2D
depicts the conventional TMR structure
50
after the conventional bilayer structure
56
has been removed. A top lead is provided, via step
20
.
FIG. 2E
depicts the conventional TMR structure
50
after the top lead
64
has been provided.
Although the conventional method
10
provide the conventional TMR sensor
60
, one of ordinary skill in the art will readily recognize that the conventional bilayer structure
56
may limit the size of the TMR sensor that can be provided. The bilayer photoresist structure
56
requires an undercut of approximately 0.05 &mgr;m on each edge. The undercut is utilized to ensure that the conventional bilayer structure
56
can be lifted off. For smaller TMR sensors, the conventional bilayer structure
56
may easily be inadvertently removed before steps
16
and
18
are completed. This is particularly true for TMR sensors
60
which have aminimum dimension of 0.2 &mgr;m in length or less. Thus, it becomes difficult to fabricate smaller devices having a minimum dimension of approximately 0.2 &mgr;m or less. For such devices, the yield decreases. In addition, electrostatic discharge damage and particle contamination also become an issue for device made using the conventional method
10
. Consequently, it is difficult to fabricate smaller TMR sensor
60
.
Accordingly, what is needed is a system and method for providing a shorter TMR sensor. The present invention addresses such a need.
SUMMARY OF THE INVENTION
A method and system for providing a tunneling magnetoresistive sensor is disclosed. The method and system include providing a pinned layer, a free layer and an insulating layer between the pinned and free layers. The pinned and free layers are ferromagnetic. The method and system also include providing a hard mask layer to be used in defining the sensor at the top of the tunneling magnetoresistive sensor. The method and system also include using the hard mask layer to define the tunneling magnetoresistive sensor. Thus, the pinned layer, the free layer and the insulating layer are capable of being less than 0.2 &mgr;m in length.
According to the system and method disclosed herein, the present invention provides a smaller tunneling magnetoresistive sensor.
REFERENCES:
patent: 5768071 (1998-06-01), Lin
patent: 5898548 (1999-04-01), Dill et al.
patent: 6529353 (2003-03-01), Shimazawa
Bjelland Kristian M.
Chen Benjamin
Hiner Hugh C.
Shi Xizeng
Sin Kyusik
Letscher George J.
Sawyer Law Group LLP
Western Digital (Fremont) Inc.
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