Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2000-06-16
2002-08-20
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S336000, C428S692100, C428S690000, C428S690000, C428S690000, C428S690000, C428S900000, C360S112000, C360S125330, C338S03200R, C324S252000
Reexamination Certificate
active
06436526
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microscopic magneto-resistive effect element and a microscopic magneto-resistive effect memory cell, an MRAM including a plurality of such magneto-resistive effect elements or a plurality of magneto-resistive effect memory cells integrated at a high density, and a method for performing information write or read to or from the microscopic magneto-resistive effect memory cell.
2. Description of the Related Art
A magnetic random access memory (MRAM) using a magneto-resistive (MR) film was proposed by L. J. Schwee, Proc. INTERMAG Conf. IEEE Trans. on Magn. Kyoto (1972) pp. 405. Various types of MRAMs including word lines as current lines for generating a magnetic field and sense lines using MR films for reading data have been studied. One of such studies is described in A. V. Pohm et al., IEEE Trans. on Magn. 28 (1992) pp. 2356. Such memory devices generally use an NiFe film or the like exhibiting an anisotropic MR effect (AMR) having an MR change ratio of about 2%, and thus the level of an output signal needs to be improved.
M. N. Baibich et al., Phys. Rev. Lett. 61 (1988) pp. 2472 describes that an artificial lattice film formed of magnetic films exchange-coupled through a nonmagnetic film to each other shows a giant MR effect (GMR). K. T. M. Ranmuthu et al., IEEE Trans. on Magn. 29 (1993) pp. 2593 proposes an MRAM using a GM film formed of magnetic films antiferromagnetically exchanged-coupled to each other. The GMR film exhibits a relatively large MR change ratio, but disadvantageously requires a larger magnetic field to be applied and thus requires a larger current for writing and reading information than an AMR film.
One exemplary type of non-coupling GMR film is a spin valve film. B. Dieny et al., J. Magn. Magn. Mater. 93 (1991) pp. 101 describes a spin valve film using an antiferromagnetia film. H. Sakakima et al., Jpn. J. Appl. Phys. 33 (1994) pp. L1668 describes a spin valve film using a semi-hard magnetic film. These spin valve films require a magnetic field as small as that required by the AMR films and still exhibit a larger MR change ratio than the AMP films. Y. Irie et al., Jpn. J. Appl. Phys. 34 (1995) pp. L415 describes an MRAM, formed of a spin valve film using an antiferromagnetic film or a hard magnetic film, which performs a non-destructive read out (NDRO).
The nonmagnetic film used for the above-described GMR films is a conductive film formed of Cu or the like. Tunneling GMR films (TMR) using Al
2
O
3
, MgO or the like as the nonmagnetic film have actively been studied, and MRAMs using the TMR film have been proposed.
It is known that the MR effect provided when a current flows perpendicular to the surface of a GMR film (CPPMR) is larger than the MR effect provided when a current flows parallel to the surface of the GMR film (CIPMR). A TMR film, which has a relatively high impedance, is expected to provide a sufficiently large output.
However, reduction in the size of an MRAM generates the following problems. A magnetic film usually has a thickness of about 1 nm to about 10 nm. In an MRAM having a width of on the order of submicrometers, the strength of an anti-magnetic field component is not negligible, and thus a relatively large magnetic field is required to magnetize the magnetic film. A relatively large magnetic coercive force is also required to maintain the magnetized state of the magnetic film. Thus, it is difficult to invert the magnetization by a magnetic field which is generated by a current flowing in word lines.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a magneto-resistive effect element includes a first ferromagnetia film; a second ferromagnetic film; and a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film has an effective magnetic thickness of about 2 nm or less.
In one embodiment of the invention, at least one of the first ferromagnetic film and the second ferromagnetic ad film has a magnetization direction in a planar direction thereof.
In one embodiment of the invention, the second ferromagnetic film is formed of XMnsb, where X is at least one element selected from the group consisting of Ni, Pt, Pd and Cu.
In one embodiment of the invention, the first ferromagnetic film includes an amorphous magnetic film, and a third ferromagnetic film in contact with the first nonmagnetic film and interposed between the amorphous magnetic film and the first nonmagnetic film.
In one embodiment of the invention, the third ferromagnetic film has a thickness of about 0.2 nm or more and about 2 nm or less.
In one embodiment of the invention, the third ferromagnetic film has a thickness of about 0.8 nm or more and about 1.2 nm or less.
In one embodiment of the invention, the amorphous magnetic film includes at least one selected from the group consisting of CoFeB and CoMnB.
In one embodiment of the invention, the first ferromagnetic film includes a second nonmagnetic film, a fourth ferromagnetic film, and a fifth ferromagnetic film. The fourth ferromagnetic film and the fifth ferromagnetic film are antiferromagnetically exchange-coupled with each other through the second nonmagnetic film.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have different strengths of saturated magnetization from each other.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have different thicknesses from each other.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film have a thickness difference of about 2 nm or less.
In one embodiment of the invention, the second nonmagnetic film is formed of Ru.
In one embodiment of the invention, the second nonmagnetic film is formed of one of Rh, Ir and Re.
In one embodiment of the invention, the second nonmagnetic film has a thickness of about 0.6 nm or more and about 0.8 nm or less.
In one embodiment of the invention, at least one of the fourth ferromagnetic film and the fifth ferromagnetic film contains at least one element selected from the group consisting of Ni, Co and Fe as a main component.
In one embodiment of the invention, the fourth ferromagnetic film and the fifth ferromagnetic film are magnetization-rotated while being kept anti-parallel to each other.
In one embodiment of the invention, the second ferromagnetic film includes a third nonmagnetic film, a sixth ferromagnetic film, and a seventh ferromagnetic film. The sixth ferromagnetic film and the seventh ferromagnetic film are antiferromagnetically exchange-coupled with each other through the third nonmagnetic film.
In one embodiment of the invention. the third nonmagnetic film it formed of Ru.
In one embodiment of the invention, the third nonmagnetic film is formed of one of Rh, Ir and Re.
In one embodiment of the invention, the third nonmagnetic film has a thickness of about 0.6 nm or more and about 0.8 nm or less.
In one embodiment of the invention, at least one of the sixth ferromagnetic film and the seventh ferromagnetic film contains at least one element selected from the group consisting of Ni, Co and Fe as a main component.
In one embodiment of the invention, the first nonmagnetic film is an insulating film.
In one embodiment of the invention, the insulating film contains at least one selected from the group consisting of Al
2
O
3
, MgO, a carbide and a nitride.
According to another aspect of the invention, a magneto-resistive effect memory cell includes a first ferromagnetic film; a second ferromagnetic film; a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film; and at least one conductive film for causing a magnetization rotation of at least the first ferromagnetic film. The first ferromagnetic film has a magnetization more
Hiramoto Masayoshi
Matsukawa Nozomu
Odagawa Akihiro
Sakakima Hiroshi
Kiliman Leszek
Renner , Otto, Boisselle & Sklar, LLP
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