Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2001-08-22
2004-08-17
Elms, Richard (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000
Reexamination Certificate
active
06778425
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magneto-resistive effect element (hereinafter, referred to as “MR”), in particular to a microscopic magneto-resistive effect element, a magneto-resistive effect magnetic head, a microscopic magneto-resistive effect memory element, and a high density magneto-resistive effect memory device including such magneto-resistive effect memory elements in a matrix.
BACKGROUND 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 exhibits a giant MR effect (GMR). K. T. M. Ranmuthu et al., IEEE Trans. on Magn. 29 (1993) pp. 2593 proposes an MRAM using a GMR 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 antiferromagnetic 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 AMR 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, the tunnel junction of a TMR film has a problem in that the junction impedance gradually increases as the size of the element is reduced.
When the size of a memory cell including the tunnel junction is small to the order of submicrons, the junction impedance becomes excessively high such that the signals cannot be read. Accordingly, a tunnel insulating body capable of providing a desirable junction resistance is demanded.
When the scattering of electrons at the tunnel junction interface of the tunnel junction element is excessively strong, desirable element characteristics are not obtained. Thus, the state of the tunnel junction interface significantly influences the junction characteristics.
In a conventional TMR films it is common to form the tunnel junction using Al
2
O
3
as a nonmagnetic insulating layer. In order to obtain satisfactory insulating characteristics, such a nonmagnetic insulating layer is formed of spontaneous oxidation or plasma oxidation of a metal Al film.
However, such production methods have a possibility that a metal layer and an insulating layer are mixed in a nonmagnetic layer and a possibility that a ferromagnetic layer is also oxidized resulting in formation of an unnecessary insulating layer. These defects cause deterioration in the tunnel characteristics.
As the size of a tunnel junction element is reduced, the resistance (impedance) of the tunnel junction element is required to be decreased. It is very difficult to form a tunnel junction having a tunnel junction resistance of 10 &OHgr;&mgr;m
2
or less using Al
2
O
3
as a nonmagnetic layer.
In light of the above-described problems, the present invention has an objective of providing a magneto-resistive element, a magneto-resistive effect magnetic head, and a magneto-resistive effect memory element having a reduced tunnel junction resistance and an ideal tunnel junction interface; and a magneto-resistive effect memory device including such magneto-resistive effect memory elements in a matrix.
DISCLOSURE OF THE INVENTION
A magneto-resistive effect memory element according to the present invention includes a first ferromagnetic film; a second ferromagnetic film: a first nonmagnetic film provided between the first ferromagnetic film and the second ferromagnetic film; a first conductive film for generating a magnetic field for causing magnetization inversion in at least one of the first ferromagnetic film and the second ferromagnetic film, the first conductive film not being electrically in contact with the first ferromagnetic film or the second ferromagnetic film; and a second conductive film and a third conductive film for supplying an electric current to the first ferromagnetic film, the first nonmagnetic film, and the second ferromagnetic film. The first ferromagnetic film and the second ferromagnetic film have different magnetization inversion characteristics with respect to the magnetic field, and the first nonmagnetic film contains at least a nitride. Thus, the above-described objective is achieved.
At least one of the first ferromagnetic film and the second ferromagnetic film may contain a nitride.
At least one of the first ferromagnetic film and the second ferromagnetic film may contain a nitride which contains at least one of Fe and Co as a main component.
At least one of the second conductive film and the third conductive film may contain a nitride.
At least one of the second conductive film and the third conductive film may contain TiN.
The first nonmagnetic film may have a thickness of 0.5 nm to 4 nm.
The first nonmagnetic film may contain AlN.
The first nonmagnetic film may contain BN.
The first nonmagnetic film may contain InN.
The first nonmagnetic film may contain at least M—N—(O) where M is at least one metal element of Al, B and In, N is a nitrogen element, and (O) is an oxygen element contained in the nitride.
The first nonmagnetic film may be formed by nitriding a nonmagnetic metal material.
The first nonmagnetic film may further contain an oxide.
A method, according to the present invention, for producing the above-described magneto-resistive effect memory element includes a first step of forming the first nonmagnetic film by nitriding a nonmagnetic metal material in a nitrogen atmosphere; and a second step of oxidizing the first nonmagnetic film in an oxygen atmosphere.
At least one of the first step and the second step may be performed a plurality of times.
The method according to the present invention may further include a third step of forming the first ferromagnetic film: and a fourth step of forming the second ferromagnetic film.
The first nonmagnetic film mainly may contain M—N, and may mainly contain M—O in a grain boundary thereof.
A method, according to the present invention, for producing the above-described magneto-resistive effect memory element includes a first step of forming the first nonmagnetic film by nitriding the metal element in a nitrogen atmosphere; and a second step of oxidizing the first nonmagnetic film in an oxygen atmosphere.
At least one of the first step and the second step may be performed a plurality of times.
The method according to the present invention may further inclu
Adachi Hideaki
Hiramoto Masayoshi
Matsukawa Nozomu
Odagawa Akihiro
Sakakima Hiroshi
Elms Richard
Matsushita Electric - Industrial Co., Ltd.
Nguyen Hien
Snell & Wilmer LLP
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