Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-03-22
2004-05-04
Wojciechowicz, Edward (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S298000, C257S301000, C365S158000, C365S171000, C365S173000
Reexamination Certificate
active
06730949
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority from Japanese Patent Applications Nos. 2001-082107 and 2001-083877, filed on Mar. 22, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistance effect device including first and second ferromagnetic material layers, whose magnetization directions change under an applied magnetic field, and a non-magnetic material layer inserted between the first and the second ferromagnetic material layers.
2. Discussion of the Background
A Tunnel MagnetoResistance or a Tunnel MagnetoResistive (TMR) device basically includes a three-layered film of a first ferromagnetic material layer, a dielectric material layer formed on the first ferromagnetic material layer, and a second ferromagnetic material layer formed on the dielectric material layer. A tunnel junction is formed and tunnel current flows between the first and the second ferromagnetic material layers via the dielectric material layer by applying voltage to both the ferromagnetic material layers. The tunnel junction's electrical resistance changes in proportion to cosine of relative angle of magnetization directions of the first and the second ferromagnetic material layers. The junction resistance takes a minimum value when magnetizations of the first and the second ferromagnetic material layers are substantially in parallel and a maximum value when the magnetizations of the first and the second ferromagnetic material layers are substantially anti-parallel. Such a change in the resistance is referred to as a Tunnel MagnetoResistance (TMR) effect and the device utilizing the TMR effect is called a TMR device.
It is reported that the change in the resistance by the TMR effect is as large as 49.7% at room temperature (Appl. Phys. Lett. 77, 283 (2000)).
A TMR device can be used as a memory cell of a memory device, such as a magnetic random access memory (MRAM) of magnetic information.
One of the first and second ferromagnetic material layers may usually have a fixed or pinned magnetization in a predetermined direction and the fixed magnetization does not rotate/invert even when a magnetic field is applied. Another one of the first and second ferromagnetic material layers has a magnetization free to rotate/invert under the applied magnetic field, referred as a magnetization free layer. When the TMR device is applied to a memory device, such as the MRAM, the ferromagnetic material layer having the magnetization free to rotate/invert may also be referred to as a memory layer, because it retains in memory written magnetic information as a state of magnetization of the magnetization free layer, while the ferromagnetic material layer having a pinned magnetization may be referred as a reference layer.
By corresponding each state of parallel and anti-parallel directions of magnetization of the reference layer and the memory layer to the binary information of “0” or “1,” a TMR device can be used as the memory device.
Writing of the magnetic information can be achieved by providing an electrical current flow to a conductive line formed at a vicinity of the memory cell and inverting magnetization of the memory layer by a magnetic field generated by the electrical current.
The written magnetic information can be read by flowing tunnel current as a sense current to the TMR device and current detector or a voltage detector can sense the electrical resistance of the TMR device.
An integrated magnetic memory apparatus includes a number of memory cells each having the TMR device and a switching transistor, which is coupled to the respective TMR device of the same memory cell, and with a large number of memory cells aligned in a matrix. An arbitrary cell can be selected in known methods, for example, as employed in DRAM addressing. The integrated magnetic memory apparatus also includes bit lines extended in row directions and word lines extended in column directions. Each of the bit lines is coupled to a series of memory cells which are aligned in the same direction as the bit line extends. Each of the word lines is also coupled to a series of the memory cells aligned in the same direction as the word line extends. Peripheral circuits for controlling current or voltage of the bit and word lines are also provided at ends in row and column directions of the memory cell region.
A memory apparatus having the TMR devices and diodes in place of the switching transistors has also been reported (U.S. Pat. Nos. 5,640,343 and 5,650,958).
It is necessary to reduce the memory cell region for a highly integrated magnetic memory apparatus. Therefore, an area of ferromagnetic material layer is necessarily reduced, however, when the area of the ferromagnetic material layer is reduced, its coercive force increases. A magnitude of a switching magnetic field that is necessary for inversion of magnetization of the memory layer increases as the coercive force increases, and accordingly, a reduction in the plan area results to an increase in the switching magnetic field. In writing magnetic information, larger current flow is needed to write information with the increased switching magnetic filed, whereby power consumption of the apparatus increases. Therefore, the reduction in the coercive force of the memory layer is important in reducing the highly integrated magnetic memory apparatus into practice.
A multi-layered memory film is proposed in order to resolve the large power consumption. The multi-layered memory film including two ferromagnetic material layers and a nonmagnetic layer formed between the two ferromagnetic material layers, in which the two ferromagnetic material layers are antiferromagnetically coupled (Japanese Patent Laid-Open No. 9-251621, U.S. Pat. No. 5,953,248).
The two ferromagnetic material layers of multi-layered film differ from each other in magnetic moment or thickness. Directions of magnetization of the ferromagnetic material layers are in opposite directions by the antiferromagnetic interlayer coupling. Therefore, the magnetizations of the two ferromagnetic material layers are cancelled and the multi-layered film as a whole can be regarded as one ferromagnetic material layer having a small amount of magnetization.
When a magnetic field directed opposite to the direction of the magnetization of the multi-layered film is applied, magnetization of the two ferromagnetic material layers invert, while maintaining the antiferromagnetic coupling. In this case, its small coercive force determines a switching magnetic field of multi-layered film and inversion of magnetization can be carried out by a small amount of switching magnetic field. While having such advantage, the multi-layered film fabricated into a very small size for a highly integrated magnetic memory apparatus exhibits an effect of enlargement of “edge magnetic domain” such that a change in a magnetic structure pattern during magnetization inversion becomes complicated. As a result, the coercive force and the switching magnetic field increase. The edge domain appears as a magnetic structure, when a width of a short axis of small ferromagnetic material layer becomes about several micrometers to sub micrometer, at film end portions of a magnetic material layer owing to influence of a demagnetization field (J. App. Phys. 81, 5471 (1997)).
To prevent generation of edge domains, a method of fixing magnetization of the edge domain was proposed (U.S. Pat. No. 5,748,524, and Japanese Patent Laid-Open No. 2000-100153).
When magnetization of an edge domain is fixed, a behavior in magnetization inversion can be controlled. However, it becomes difficult to reduce the switching magnetic field. A new composition added to fix the magnetization for preventing the edge domains is not suitable for high-density integration.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a magnetoresistance effect device having a stable magnetization structure of a magnetic layer having a m
Amano Minoru
Kishi Tatsuya
Nakajima Kentaro
Sagoi Masayuki
Saito Yoshiaki
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wojciechowicz Edward
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