Magnetic memory device and manufacturing method thereof

Details Magnetic memory device and manufacturing method thereof Magnetic memory device and manufacturing method thereof

2002-12-12

2004-12-07

Elms, Richard (Department: 2824)

Static information storage and retrieval

Systems using particular element

Magnetic thin film

C365S158000

Reexamination Certificate

active

06829162

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-380321, filed Dec. 13, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic memory device and a manufacturing method thereof, and more particularly, to a magnetic memory device and a manufacturing method thereof for writing data by use of a current magnetic field in each bit, and reading out information of “1”, “0” according to the resistance change caused by the change in the cell magnetization state.
2. Description of the Related Art
Recently, an MRAM (Magnetic Random Access Memory) utilizing a tunneling magneto resistive (TMR) effect is proposed as a memory element. MRAMs have been developed to have non-volatility, high-density integration, high reliability and high operation speed thus have great potential in the memory market.
FIG. 26
is a cross sectional view showing part of an MRAM according to the prior art technique. As shown in
FIG. 26
, first and second wirings
13
,
23
are arranged to cross at right angles and an MTJ (Magnetic Tunneling Junction) element
16
is arranged in the cross point portion between the first wiring
13
and the second wiring
23
. The MTJ element
16
is connected to the second wiring
23
via an upper electrode (not shown) and connected to a source/drain diffusion layer
52
of a MOS transistor
53
via a lower electrode
55
and contact
54
. Further, a gate electrode
51
of the MOS transistor
53
is used as a readout wiring.
The MTJ element
16
is configured by a magnetically fixed layer
31
which is a ferromagnetic layer and connected to the lower electrode
55
, a magnetic recording layer
33
which is a ferromagnetic layer and connected to the second wiring
23
via the upper electrode and a tunnel junction layer
32
which is a non-magnetic layer and sandwiched between the magnetically fixed layer
31
and the magnetic recording layer
33
.
In the above MRAM, the data write and readout operations are performed as follows.
First, when data is written into a desired selected cell, the state of “1” or “0” data is written into the MTJ element
16
of a selected cell by inverting the magnetization direction of the magnetic recording layer
33
. As a result, the resistance of the tunnel junction layer
32
becomes the lowest when the magnetization direction of the magnetic recording layer
33
become the same as the magnetization direction of the magnetically fixed layer
31
. In contrast, when the magnetization directions become opposite to each other, the resistance of the tunnel junction layer
32
becomes the highest. A change in the resistance of the tunnel junction layer
32
is read by causing a current to flow in a direction through the MTJ element
16
from the two wirings
23
,
13
arranged above and below the MTJ element
16
with the upper electrode and lower electrode
55
which sandwich the MTJ element
16
disposed therebetween. Thus, the storage state of “1”, “0” can be determined and information can be read out.
As described above, in the MRAM of the prior art technique, two-value data can be stored for each bit, but it is impossible to store data having a larger value.
BRIEF SUMMARY OF THE INVENTION
A magnetic memory device according to a first aspect of the present invention, comprises magneto resistive elements which are laminated in each cell with the easy axes of magnetization (easy axes) set in different directions, each magneto resistive elements having at least two resistance values, and first and second wirings which sandwich the magneto resistive elements and arranged to extend in different directions.
A magnetic memory device manufacturing method according to a second aspect of the present invention, comprises forming a first wiring which extends in a first direction, laminating magneto resistive elements above the first wiring, the magneto resistive elements respectively having magnetically fixed layers and each having two resistance values, forming a second wiring which extends in a second direction different from the first direction on the magneto resistive elements, and sequentially performing heat treatments in a magnetic field at different temperatures with respect to the magneto resistive elements and fixing magnetization directions of the magnetically fixed layers of the magneto resistive elements in different directions.


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V. N. Samofalov, et al., Journal of Magnetism and Magnetic Materials, vol. 128, No. 3, pp. 354-360, “Features of Remagnetization Processes in Stripes of Multilayer Films with Crossed Easy Axes of Magnetization and Prospects of Their Applications”, Dec. 1, 1993.

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