Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
2001-01-24
2003-03-04
Pham, Long (Department: 2823)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S048000, C257S421000, C257S422000, C257S426000, C257S295000, C257S427000
Reexamination Certificate
active
06528326
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetoresistive device and a method for producing the same, and a magnetic component.
BACKGROUND ART
A TMR (tunnel magnetic resistance) device is a device in which a very thin insulating layer is inserted between two ferromagnetic layers. A TMR device uses the phenomenon that the tunneling current flowing through the insulating layer is changed by the relative angle of magnetization of each metal element M.
It has been expected in theory that when using a ferromagnetic metal element M having a high spin polarizability such as Fe or FeCO for the ferromagnetic layers, a high rate of change in magnetic resistance of at least 35% is obtained (M. Jullier, Phs. Lett. 54A (1975) 225). However, a high MR (magneto resistance) has not been possible to realize.
Recently, Miyazaki et al. reported that they produced an insulating layer of alumina by natural oxidation in the air, and obtained a high rate of change in MR (T. Miyazaki and N. Tezuka, J. Magn. Magn. Mater. 139 (1995) L231). With this report, active development of TMR materials and TMR devices has started.
The recently reported methods for producing insulating layers showing a high MR are classified largely into two methods. One is a natural oxidation method in which an aluminum film formed on a ferromagnetic film is oxidized in the air or in pure oxygen (Tsuge et al., Document of the 103rd Workshop by the Society of Applied Magnetics of Japan, p. 119, (1998)). The other is a plasma oxidation method in which an aluminum film formed on a ferromagnetic film is oxidized in an oxygen plasma (J. S. Moodera et al. Phy. Rev. Lett., 74, 3273 (1995)).
To obtain a high MR, these TMR devices use a transition metal showing a high spin polarizability such as Fe or CoFe for the lower ferromagnetic layer on which the aluminum film is formed.
Because the current flowing in a TMR device is mainly a tunneling current through an insulating layer, the resistance of the device is substantially high. Thus, when a TMR device is used as a reproducing head or MRAM, S/N ratio decreases due to thermal noise, and threshold frequency of a readout circuit decreases during a fast response.
To lower the resistance of the device, reducing the film thickness of the alumina insulating layer could be considered. However, with a conventional process for oxidizing an aluminum film, the lower ferromagnetic film is likely to be oxidized beyond the aluminum film when the aluminum film is thin. As a result, when antiferromagnetic materials such as Fe
2
O
3
and CoO are formed at the interface with the aluminum oxide film by an excess oxidation reaction, for example, due to the interaction with these antiferromagnetic oxides, tunneling electrons lose information of magnetization direction with an external magnetic field.
On the other hand, when the aluminum film is not oxidized completely and a portion of the aluminum film remains, the spin memory of the tunneling electrons passing through the remaining aluminum film is lost, and MR is reduced.
Furthermore, in conventional TMR devices, when a large bias is applied, the rate of change in MR is decreased greatly due to generation of magnon, etc.
Furthermore, conventional MR devices do not have a sufficient thermal stability, and for example, when using them as MRAM, heat deterioration such as decreased MR property is caused during post-annealing of CMOS (at about 250 to 400° C.) or heating in the production of MR heads (at about 250° C.), or during its use.
DISCLOSURE OF THE INVENTION
In view of the above-mentioned problems, it is an object of the present invention to provide a new magnetoresistive device having a low junction resistance and a high MR and a method for producing the same, and a magnetic component.
To achieve the above object, the present invention provides a magnetoresistive device including a high-resistivity layer, a first magnetic layer and a second magnetic layer, the first magnetic layer and the second magnetic layer being arranged so as to sandwich the high-resistivity layer, wherein the high-resistivity layer is a barrier for passing tunneling electrons between the first magnetic layer and the second magnetic layer, and contains at least one element L
ONC
selected from oxygen, nitrogen and carbon; at least one layer A selected from the first magnetic layer and the second magnetic layer contains at least one metal element M selected from Fe, Ni and Co, and an element R
CP
different from the metal element M; and the element R
CP
combines with the element L
ONC
more easily in terms of energy than the metal element M. In the magnetoresistive device of the present invention, the element R
CP
contained in the layer A combines selectively with the element L
ONC
diffusing from the high-resistivity layer to form a compound. Thus, in the magnetoresistive device of the present invention, oxidation, nitriding or carbonization of the metal element M can be inhibited, thereby preventing generation of a localized spin resulting in spin inversion. Furthermore, when the element R
CP
in the layer A combines with the element L
ONC
to form a compound, the compound itself functions as a part of the high-resistivity layer. In addition, because the diffusion velocity of oxygen ions or nitrogen ions in the compound of the element R
CP
and the element L
ONC
is substantially lower than in the magnetic films, the compound of the element R
CP
and the element L
ONC
acts as a layer to inhibit diffusion of excess oxygen or nitrogen. Therefore, in the magnetoresistive device of the present invention, formation of a high-resistivity layer having a larger thickness than necessary, resulting in an increase in the resistance of the device, is inhibited. Thus, according to the magnetoresistive device of the present invention, a device having a low junction resistance and a high MR is obtained.
In the magnetoresistive device of the present invention, it is preferable that the layer A contains the element R
CP
so that a concentration of the element R
CP
is high on the side of the high-resistivity layer. When the element R
CP
is in a solid solution state with a metal composed of the metal element M, its spin polarizability is generally lower than that of the single metal composed of the metal element M. However, by making the concentration of the element R
CP
high on the side of the high-resistivity layer in the layer A, the element R
CP
forms a compound, and the element R
CP
and the metal element M are separated in phase. As a result, high spin polarizability is obtained in the vicinity of the high-resistivity layer, which has the greatest influence on the rate of change in magnetoresistance. The spin polarizability can be increased by decreasing the concentration of the element R
CP
as it is farther from the high-resistivity layer. The layer A may have a two-layered structure such as an element R
CP
—containing Fe layer/Fe layer from the side of the high-resistivity layer. The layer A also may have a structure such as an element R
CP
—containing FeCo layer/FeCo layer from the side of the high-resistivity layer.
In the magnetoresistive device of the present invention, it is preferable that the element R
CP
is at least one element selected from Si, Ge, Al, Ga, Cr, V, Nb, Ta, Ti, Zr, Hf, Mg and Ca. These elements have a larger free energy in negative for forming oxides than the metal element M, and selectively capture oxygen ions or nitrogen ions diffusing from the high-resistivity layer. Among these elements, Si, Al, Cr and Ti have particularly large diffusion constants in metal elements. Thus, these four elements diffuse toward the side of the high-resistivity layer so that their concentrations are high on the side of the high-resistivity layer, using as a driving force the chemical potential gradient of the oxygen or nitrogen ions generated when forming the high-resistivity layer. Therefore, a desirable concentration gradient of the element R
CP
can be formed easily by using these four elements. This self-diffusion of elements tends to appear more remarkably when t
Adachi Hideaki
Hiramoto Masayoshi
Matsukawa Nozomu
Odagawa Akihiro
Sakakima Hiroshi
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Nguyen Khiem
Pham Long
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