Static information storage and retrieval – Systems using particular element – Magnetic thin film
Reexamination Certificate
2001-03-19
2002-06-11
Nelms, David (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetic thin film
C365S171000, C365S232000, C365S158000
Reexamination Certificate
active
06404673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention relates to a magnetic memory device capable of writing and reading data (information) by utilizing a magnetoresistive effect in each of a plurality of magnetic memory cells that are disposed in a matrix form, each magnetic memory cell having a plurality of magnetic layers laminated in a state that these magnetic layers are partitioned by a non-magnetic layers. The present invention also relates to a method of reading data in this magnetic memory device.
In recent years, the above-described magnetic memory device has come to attract attention as a nonvolatile high-density memory. Each of the plurality of magnetic memory cells that constitute a main part of the magnetic memory device is generally formed by having a plurality of magnetic layers laminated in a state that the magnetic layers are partitioned by non-magnetic layers. For example, each magnetic memory cell is formed by two ferromagnetic layers made of thin films of ferromagnetic material that are partitioned by a non-magnetic layer. This magnetic memory device has a function of writing data into a memory cell at an operational position (an address) and reading data from this memory cell, like a DRAM (dynamic random access memory) that has a plurality of memory cells. Thus, this magnetic memory device is also called an MRAM (magnetic random access memory).
In more detail, a resistance due to the magnetoresistive effect of the magnetic memory cell is different depending on whether magnetic moments of the two ferromagnetic layers included in the magnetic memory cell are mutually in parallel directions or in anti-parallel directions. Data of either “0” or “1” is stored in the magnetic memory cell according to the value of the resistance.
The operation of writing data into the magnetic memory cell is executed by first passing a current through a current line (for example, a word line or a bit line) provided near one of the two ferromagnetic layers. Then, an inversion or a non-inversion of a direction of a magnetic moment of this ferromagnetic layer is controlled based on a magnetic field generated by this current. On the other hand, the operation of reading data from the magnetic memory cell is executed by utilizing the fact that the resistance of the magnetic memory cell is smaller when the magnetic moments of the two ferromagnetic layers are mutually in parallel directions than when the magnetic moments of the two ferromagnetic layers are mutually in anti-parallel directions. In other words, the data read operation is executed by first detecting a relative resistance of the magnetic memory cell based on a flow of a very small current (or fine current) in a direction horizontal to the two ferromagnetic layers, or a flow of a very small current in a direction vertical to the two ferromagnetic layers. Next, a result of this detection is amplified by a sense amplifier, and a decision is made on the data “0” or “1”.
2. Description of the Related Art
In order to facilitate understanding of problems of a conventional magnetic memory device, the principle of the operation of a magnetic memory device generally used and conventional examples of a magnetic memory device having a layout of a plurality of magnetic memory cells will be explained below, with reference to
FIG. 1
to
FIG. 3
that will be described later in “BRIEF DESCRIPTION OF THE DRAWINGS”.
A schematic diagram showing the principle of the operation of a magnetic memory cell that utilizes a general magnetoresistive effect, is illustrated in
FIG. 1. A
perspective view showing a structure of a first example of a conventional magnetic memory device is illustrated in
FIG. 2. A
perspective view showing a structure of a second example of a conventional magnetic memory device is illustrated in FIG.
2
. FIG.
2
and
FIG. 3
show structures of a main part of the magnetic memory device, respectively.
Portion (a) to portion (c) of
FIG. 1
show a sequence of executing a data write operation to a magnetic memory cell
200
having a structure that two ferromagnetic layers made of thin films of a ferromagnetic material are partitioned by a non-magnetic layer. In general, a thin film of ferromagnetic material is manufactured of Permalloy (usually expressed as Ni-Fe/Co) added with a small volume of cobalt, and a non-magnetic layer is manufactured of aluminum oxide (usually expressed as Al
2
O
3
). The magnetic memory cell
200
that includes the two ferromagnetic layers and one non-magnetic layer has such a structure that, on a first magnetic layer
201
at a lower-layer portion within the two ferromagnetic layers, a second magnetic layer
202
at an upper-layer portion is laminated via a non-magnetic layer
203
.
As shown in portion (d) and portion (e) of
FIG. 1
, there arises a difference in the magnetoresistive effect due to the magnetic mutual operation between the first magnetic layer
201
and the second magnetic layer
202
, depending on whether the magnetic moments of the first magnetic layer
201
and the second magnetic layer
202
are mutually in parallel directions or in anti-parallel directions. As a result, there arises a difference in the resistance of the magnetic memory cell
200
. More specifically, when the magnetic moments of the first magnetic layer
201
and the second magnetic layer
202
are mutually in parallel directions ((d) in FIG.
1
), this resistance becomes smaller than when the first magnetic layer
201
and the second magnetic layer
202
are mutually in anti-parallel directions ((e) in FIG.
1
). Data “0” or “1” is stored in the magnetic memory cell corresponding to the value of this resistance.
Assume a state that the magnetic moments of the first magnetic layer
201
and the second magnetic layer
202
are mutually in parallel directions. For example, assume a state that the data of “0”has been stored in advance, before data is written into the magnetic memory cell
200
, as shown in portion (a) of FIG.
1
. The operation of writing data “1” into the magnetic memory cell
200
in this state is executed by first passing a current through a current line (for example, a word line or a bit line)
204
provided near the second magnetic layer
202
. Then, a direction of the magnetic moment of the second magnetic layer
202
is inverted based on a magnetic field B generated by this current, as shown in portion (b) of FIG.
1
. Thereafter, the direction of the magnetic moment of the second magnetic layer
202
maintains the invented state even after the current of the current line
204
has been set to be zero and the magnetic field B has been removed, as shown in portion (c) of FIG.
1
. Therefore, the data of “1” is stored in the magnetic memory cell. In this case, a component ratio of each element (iron, nickel, cobalt, etc.) of the magnetic material for the first magnetic layer
201
and the second magnetic layer
202
is changed in advance so that the magnetic moment of the second magnetic layer
202
is inverted in a magnetic field smaller than that of the first magnetic layer
201
. Based on this arrangement, it becomes easy to invert only the magnetic moment of the upper-layer second magnetic layer
202
, without influencing the magnetic moment of the lower-layer first magnetic layer
201
.
On the other hand, for executing the operation of reading data stored in the magnetic memory cell
200
, a fine current is supplied to the magnetic memory cell
200
from a power source Vd via a current line
204
, as shown in portions (d) and (e) of FIG.
1
. Based on this current supply, a difference between two resistances is detected as follows. That is, a difference is detected between the resistance of the magnetic memory cell
200
when the magnetic movements of the first magnetic layer
201
and the second magnetic layer
202
are mutually in parallel directions and the resistance of the magnetic memory cell
200
when these magnetic moments are mutually in anti-parallel directions. Based on this, a decision is made as to whether the data in “0” or “1”.
In a spin-valve ty
Fujitsu Limited
Lam David
Nelms David
Staas & Halsey , LLP
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