Static information storage and retrieval – Systems using particular element – Magnetic thin film
Reexamination Certificate
1999-02-12
2001-01-23
Hoang, Huan (Department: 2818)
Static information storage and retrieval
Systems using particular element
Magnetic thin film
C365S171000, C365S174000
Reexamination Certificate
active
06178112
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for controlling magnetization of a magnetic material. More particularly, it relates to an element exploiting a magnetic material, such as an information recording element for recording the information by controlling the magnetization of the magnetic material, or a variable resistance element for controlling electrical resistance by controlling magnetization of the magnetic material, and to an addressing method in an appliance employing such element.
2. Description of the Related Art
An element employing a magnetic material is attractive for two reasons as compared to a semiconductor device. First, since electrically conductive metals can be used as device elements, high carrier density and low resistance can be achieved. Therefore, an element exploiting a magnetic material is expected to be suited to design rule minuting and high integration. Second, bistable magnetization direction proper to a magnetic material can be used in a non-volatile memory. That is, if bistable magnetization direction proper to a magnetic material is utilized, a solid non-volatile memory, in which the recorded information is not lost even on interruption of the circuit power source, is expected to be realized.
Meanwhile, a solid non-volatile memory, in which the recorded information is not lost even on interruption of the circuit power source, is expected to be useful in many fields of application. Specifically, a solid non-volatile memory does not consume power during periods of non-use, and hence is expected to be in reducing the capacity and the weight of batteries in portable electronic information equipment. On the other hand, the solid non-volatile memory finds wide use, on the background of the advent of the age of satellite media business, to support the activity of a satellite while under the shade of the earth, a time when a solar battery becomes unusable.
The element exploiting the magnetic material has advantages such as i) nonvolatility; ii) no deterioration due to repeated usage; iii) possibility of high-speed writing; iv) small size and adaptability for high recording density; and v) superior resistance against radiation. These merits are discussed hereinbelow in detail.
i) non-volatility
Thanks to the bistability of the direction of magnetization proper to the magnetic material, the information written as the direction of magnetization is maintained unchanged in the absence of the driving power,
ii) no deterioration due to repeated usage
There is also proposed a memory employing a dielectric material exhibiting bistability as does a magnetic material (ferroelectric random access memory F-RAM). In this F-RAM, the memory state is rewritten by reversing the spontaneous dielectric polarization. However, since the inversion of spontaneous dielectric polarization corresponding to rewriting of the memory state is accompanied by ionic movement in a crystal lattice, repetition of rewriting over one million times leads to development of crystal defects. Thus, with F-RAM, the service life of the element, that cannot be surpassed due to fatigue of the material, poses a problem. On the other hand, since the inversion of magnetization of the magnetic material is not accompanied by ionic movement, an element exploiting the magnetic material can be used almost limitlessly for re-writing without limitation due to fatigue of the material.
iii) possibility of high-speed writing
The speed of inversion of magnetization of the magnetic material is as fast as approximately one ns, so that, by exploiting this high switching rate, high-speed writing becomes possible.
iv) small size and adaptability to high recording density
The magnetic properties of a magnetic alloy can be varied extensively subject to selection of the composition or structure. Thus, an element utilizing a magnetic material has an extremely high degree of freedom in deigning. With the element exploiting a magnetic material, it is possible to utilize electrically conductive magnetic alloy. If the electrically conductive magnetic alloy is used, the current density in the element higher than with the use of a semiconductor is assured, thus enabling further minution and higher recording density than is possible with the use of the semiconductor element.
As an element exploiting these properties, a spin transistor, as described in Journal of Society of Applied Magnetic Science of Japan, vol.19,684 (1995), has been proposed. A spin transistor has its emitter constituted by a magnetic material E, while having its collector and base constituted by a magnetic material C and a non-magnetic material B, respectively, as shown in FIG.
1
. With this spin transistor, an output voltage dependent on the direction of magnetization of the magnetic materials C, E is generated by the polarization density which seeps from the magnetic materials C, E towards the non-magnetic material B. Meanwhile, the structure of the spin transistor shown in
FIG. 1
is such that an output voltage depends on the direction of magnetization of the magnetic materials C and E. The direction of magnetization is changed by furnishing the current pulses for magnetization to a current line for magnetization
500
and by applying the magnetic field generated by the current pulses for magnetization P to the magnetic materials C and E.
v) superior resistance against radiations
If ionized radiations traverse an element, the memory state of which is created by charging into electrical capacitance, such as a dynamic random access memory (DRAM), electrical discharging is produced, so that the store information is lost. Conversely, the direction of magnetization of the magnetic material is not disturbed by the ionized radiations. Thus, the element exploiting a magnetic material is superior in resistance against radiation. Therefore, the element exploiting a magnetic material is particularly useful for application in need of high resistance against radiations, such as communication satellite. In actuality, a magnetic bubble memory, among the memories exploiting the magnetic material, is already finding use asa memory loaded on a communication satellite.
The device exploiting the magnetic material has many advantages, as discussed above. As a device for taking advantage of these merits, a solid magnetic memory has been proposed. The solid magnetic memory is a magnetic storage device employing an array of magnetic materials asa storage medium and, in distinction from a magnetic tape or a magnetic disc, performs the storage operation without being accompanied by movement of a storage medium.
In the conventional solid magnetic memory, a simple addressing method, exploiting the properties of the magnetic material, is used. The addressing method in the conventional solid magnetic memory is now explained.
In the solid magnetic memory, a magnetic thin film, exhibiting uniaxial magnetic anisotropy, is used. The magnitude of the magnetic field, required for inducing inversion of magnetization in the magnetic thin film, depends on the direction of application of the magnetic field. That is, inversion of magnetization can be induced with a smaller strength of the magnetic field if the magnetic field is applied in a direction inclined by approximately 45° from the easy axis than if the magnetic field is applied in a direction parallel to the easy axis. In the conventional solid magnetic memory, these properties can be utilized for addressing of recording bits to enable the use of an extremely simple addressing system.
That is, in the conventional solid magnetic memory, word lines W
1
, W
2
, W
3
, . . . and bit lines B
1
, B
2
, B
3
, . . . are arrayed at right angles to one another, and storage carriers A-
1
, A-
2
, . . . , B-
1
, B-
2
, . . . , C-
1
, C-
2
, . . . are arranged at the points of intersections, as shown in FIG.
2
. That is, in the conventional solid magnetic memory, storage carriers are arrayed in an x-y matrix configuration to constitute a memory chip. The easy axis of each storage carrier is aligned a
Bessho Kazuhiro
Iwasaki Yoh
Hoang Huan
Sonnenschein Nath & Rosenthal
Sony Corporation
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