KR20020090451A - MRAM cell using exchange biasing of strong ferromagnetic dipole - Google Patents

Abstract

PURPOSE: A magnetic random access memory cell using a ferromagnetic dipole is provided to remarkably improve magnetoresistive ratio by increasing spin polarity of a ferromagnetic layer. CONSTITUTION: A magnetic random access memory cell using a ferromagnetic dipole includes a ferromagnetic dipole layer(110) formed on a silicon substrate(100), a ferromagnetic layer(120) laminated on the ferromagnetic dipole layer, a ferromagnetic free layer(140) formed above the ferromagnetic layer, and an oxide tunneling barrier(130) formed between the ferromagnetic layer and the free layer. The magnetizing direction of the ferromagnetic layer is fixed according to exchange bias with the ferromagnetic dipole layer. When magnetic field is applied, tunneling current flows through the oxide tunneling barrier.

Description

Magnetic random access memory cell using ferromagnetic dipoles {MRAM cell using exchange biasing of strong ferromagnetic dipole}

The present invention relates to a magnetic random access memory cell using a ferromagnetic dipole, and more particularly, to a magnetic random access memory cell using the ferromagnetic dipole to achieve a fixed magnetization through an exchange bias with a fixed layer.

The basic structure of a conventional magnetic random access memory (MRAM) cell is a ferromagnetic material in which magnetization is fixed by an exchange bias coupling with an antiferromagnetic layer (AFM) 10 as shown in the schematic structure of FIG. A fixed layer (Ferromagnetic: FM) 20 formed of phosphorus CoFe or NiFe, a free layer 40 which is a ferromagnetic material freely rotating in response to a magnetic field from a medium (signal field) in which magnetization is not fixed, and It is formed of an oxide tunneling barrier 30 that is an insulating layer separating the pinned layer 20 and the free layer 40.

When the magnetization spins of the pinned layer 20 and the free layer 40 are in opposite directions, when the current is applied, little current flows through the tunnel barrier due to the high magnetoresistance. Conversely, if the direction of spin of the pinned layer 20 and the free layer 40 is the same, and the magnetic resistance is low, a large amount of current flows when a current is applied. The magnetoresistive ratio (MR ratio) is expressed by the following equation.

In this case, a high MR ratio makes it easier to determine the direction of spin of the pinned layer 20 and the free layer 40, thereby making it possible to make an excellent MRAM for reading and writing information of " 1 " and " 0 ".

The conventional MRAM cell structure induces magnetic polarity in the pinned layer 20 by using an exchange bias field between the antiferromagnetic layer 10 and the pinned layer 20. The recording state is maintained in the free layer 40 through electrostatic interaction (magnetostatic exchange-coupling) and magnetic anisotropy of the free layer 40. In this case, since the strength of the exchange bias field is determined by the sharpness of the contact surface between the antiferromagnetic layer 10 and the pinned layer 20 and the cleanliness, it is necessary to improve the sharpness and cleanliness. The equipment for high vacuum becomes complicated and the deposition process becomes difficult, and the fixed layer is impossible to induce complete magnetic polarity due to the material limitations generated in the magnetic properties. In addition, many magnetic spin-polar filter layers are used to increase the spin-polarity that influences the MR ratio, which causes a problem of complicated MRAM fabrication process and inability to guarantee uniform characteristics of cells.

SUMMARY OF THE INVENTION The present invention was created to solve the above problems, and an object of the present invention is to provide a magnetic random access memory using ferromagnetic dipoles, which is easy to manufacture an MRAM cell, stabilizes a cell, and greatly improves MR ratio by increasing spin polarity of a fixed layer. To provide a cell.

1 is a schematic cross-sectional view of a conventional MRAM cell,

2 is a schematic cross-sectional view of an MRAM cell according to the present invention;

3 illustrates writing and reading using magnetoresistance of MRAM cells in accordance with the present invention.

Explanation of symbols on the main parts of the drawings

10: antiferromagnetic layer 20, 120: fixed layer

30, 130: oxide film tunnel barrier 40, 140: free layer

100: substrate 110: ferromagnetic dipole layer

In order to achieve the above object, a magnetic random access memory cell using a ferromagnetic dipole according to the present invention, a ferromagnetic dipole layer formed on a silicon substrate; A pinned layer laminated on the ferromagnetic dipole layer to fix the magnetization direction by an exchange bias with the ferromagnetic dipole layer; A free layer of ferromagnetic material formed above the pinned layer; And an oxide film tunnel barrier formed between the pinned layer and the free layer to allow a tunneling current to flow when the magnetic field is caught.

The ferromagnetic dipole layer is made of an amorphous rare earth transition metal alloy, and the ferromagnetic dipole layer preferably has magnetic properties in which the saturation magnetization is close to " 0 " and the coercivity is infinity near the compensation composition.

Hereinafter, embodiments of a magnetic random access memory cell using the ferromagnetic dipole of the present invention will be described in detail with reference to the accompanying drawings.

2 is a view schematically showing the structure of an MRAM cell according to the present invention. Referring to the drawings, the ferromagnetic dipole layer 110, the pinned layer 120, the oxide barrier tunnel 130, and the free layer 140 are sequentially formed on the silicon substrate 100.

The ferromagnetic dipole layer 110 has an amorphous rare earth transition metal alloy (amorphous rare-) having a magnetic property of near saturation magnetization near the compensation composition and having an infinite coercivity. earth transition-metal alloy). This magnetic property forms a dipole layer having a complete magnetization direction in one direction.

The pinned layer 120 and the free layer 140 are formed of a ferromagnetic material CoFe or NiFe, and the oxide tunnel barrier 130 is formed of an insulating layer.

The dipole layer 110 acts as a pinning layer to form a strong ferromagnetic exchange coupling with the pinned layer 120, which has a magnetization direction of the pinned layer 120 in the direction of the dipole layer 110. Arrange them along the lines. The magnetization direction of the strong pinned layer 120 arranged in this way is strongly opposite to the magnetization direction of the free layer 140 by performing a magnetostatic interaction with the free layer 140 through the oxide tunnel barrier 130. To guide.

3 is a view for explaining the writing and reading using the magnetoresistance of the MRAM cell according to the present invention according to the present invention.

Referring to the drawing, when there is no magnetic field, as shown in FIG. 3A, the magnetization direction (arrow direction) between the pinned layer 120 and the free layer 140 is parallel to the opposite direction. Record the state of time as "0". When the magnetic field is hung, as shown in FIG. 3B, the magnetization between the pinned layer 120 and the free layer 140 may be paralleled in the same direction, thereby recording “1”.

When a current flows perpendicularly to the cell, when the magnetization direction is different between the pinned layer 120 and the free layer 140 (FIG. In the case where the magnetization directions between the pinned layer 120 and the free layer 140 are the same (FIG. 3B), since the magnetization direction is low, it is read as "1".

As described above, the magnetic random access memory cell using the ferromagnetic dipole according to the present invention forms a multilayer without a buffer layer as compared to a conventional MRAM cell by strongly pinning the magnetization direction of the fixed layer. This facilitates and increases the spin polarization of the pinned and free layers, greatly improving the MR ratio.

Although the present invention has been described with reference to the embodiments with reference to the drawings, this is merely exemplary, it will be understood by those skilled in the art that various modifications and equivalent embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined only by the appended claims.

Claims (3)

A ferromagnetic dipole layer formed on the silicon substrate; A pinned layer laminated on the ferromagnetic dipole layer to fix the magnetization direction by an exchange bias with the ferromagnetic dipole layer; A free layer of ferromagnetic material formed above the pinned layer; And And an oxide tunnel tunnel barrier formed between the pinned layer and the free layer to allow a tunneling current to flow when a magnetic field is applied to the magnetic layer. The method of claim 1, And the ferromagnetic dipole layer is formed of an amorphous rare earth transition metal alloy. The method according to claim 1 or 2, And the ferromagnetic dipole layer has a magnetic property of saturation magnetization close to zero and a coercive force of infinity near a compensation composition.