Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2003-06-25
2004-12-14
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S298000, C257S303000, C257S306000, C257S324000, C438S003000, C438S240000
Reexamination Certificate
active
06831314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive effect element having an arrangement for obtaining a magnetoresistive change by causing a current to flow in the direction perpendicular to the layer surface and a magnetic memory device including this magnetoresistive effect element.
2. Description of the Related Art
As information communication devices, in particular, personal small information communication devices such as portable terminal devices (e.g. personal digital assistants) are widely spreading, it is requested that devices such as memories and logic devices comprising these information communication devices or portable terminal devices should become higher in performance, such as they should become higher in integration degree, they can operate at higher speed and they can consume lesser electric power. Particularly, technologies that can make nonvolatile memories become higher in density and larger in storage capacity are becoming more and more important as complementary technologies for replacing hard disk devices and optical disk devices with nonvolatile memories because it is essentially difficult to miniaturize hard disk devices and optical disk devices because they have their movable portions (e.g. head seek mechanism and head rotation mechanism).
Flash memories using semiconductors, an FRAM (ferro electric random-access memory) using a ferro dielectric material and so on are known as nonvolatile memories.
However, flash memories have a defect that the information writing speed thereof is slow as the order of microseconds. On the other hand, it has been pointed out that the FRAM cannot be rewritten so many times.
A magnetic memory device called an MRAM (magnetic random-access memory) device that had been described in “Wang et al., IEEE Trans. Magn. 33 (1997), 4498”, receives a remarkable attention as a nonvolatile memory that can overcome these defects. This MRAM is simple in structure and therefore can be easily integrated at high integration degree and since the MRAM is able to record by rotation of magnetic moment, it can be rewritten a large number of times. Further, it is expected that the MRAM has very high access time and it has already been confirmed that the MRAM can be operated at speed in the order of nanoseconds.
A magnetoresistive effect element used in this MRAM and especially ferromagnetic tunnel junction (MTJ (magnetic tunnel junction)) is essentially composed of a laminated layer construction of a ferromagnetic material layer, a tunnel barrier layer and a ferromagnetic material layer. In this element, when an external magnetic field is applied to the ferromagnetic material layers under the condition in which a constant current flows through the ferromagnetic material layers, magnetoresistive effect appears in response to a relative angle of the magnetizations of the two ferromagnetic material layers. When the magnetization directions of the two ferromagnetic material layers are anti-parallel, a resistance value becomes the maximum. When the magnetization directions of the two ferromagnetic material layers are parallel to each other, a resistance value becomes the minimum. Functions of the memory element can be achieved when anti-parallel and parallel states are produced with application of external magnetic fields.
In particular, in a spin-valve type TMR element, one ferromagnetic material layer is coupled to an adjacent antiferromagnetic material layer in an antiferromagnetic fashion and thereby formed as a magnetization fixed layer whose magnetization direction is constantly made constant. The other ferromagnetic material layer is formed as a magnetization free layer whose magnetization direction is easily inverted with application of external magnetic fields and the like. Then, this magnetization free layer is formed as an information recording layer in a magnetic memory.
For the TMR element of a spin-valve structure, a changing ratio of a resistance value in the TMR element is expressed as the following equation (A) where P1, P2 represent spin polarizabilities of the respective ferromagnetic material layers:
2
P
1
P
2/(1
−P
1
P
2) (A)
Accordingly, the changing ratio of the resistance value increases as the respective spin polarizabilities increase. With respect to a relationship between materials for use with the ferromagnetic material layers and this resistance change ratio, ferromagnetic elements of Fe group, such as Fe, Co, Ni and alloys of these three kinds of elements have been reported so far.
Fundamentally, the MRAM comprises a plurality of bit write lines (so-called bit lines), a plurality of word write lines (so-called word lines) and TMR elements disposed at intersection points between these bit write lines and word write lines as magnetic memory elements as shown in Japanese laid-open patent application No. 10-116490, for example. When information is to be written in such MRAM, information is selectively written in the TMR elements by using asteroid characteristics.
Bit write lines and word write lines for use with the MRAM are made of Cu or Al conductive thin films which are generally used in semiconductors. When information is written in the element by a write line having a width of 0.25 &mgr;m with application of inverted magnetic fields, for example, a current of approximately 2 mA was required. When the thickness of the write line is the same as the line width, a current density obtained at that time reaches 3.2×10
6
A/cm
2
and which is a limit value in breaking wires due to electro-migration. From a problem of heat generated by a write current and from a standpoint for decreasing power consumption, it is necessary to decrease this write current.
As a method for realizing decrease of the write current in the MRAM, there may be enumerated a method for decreasing coercive force of the TMR element. The coercive force of the TMR element is properly determined based upon suitable factors such as size and shape of element, film arrangement and selection of materials.
However, when the TMR element is microminiaturized in order to increase the recording density of the MRAM, for example, there arises a disadvantage in which the coercive force of the TMR element increases.
Accordingly, in order to microminiaturize the MRAM (to integrate the MRAM with high integration degree) and to decrease the write current at the same time, the coercive force of the TMR element should be decreased from a standpoint. of materials.
In the MRAM, when magnetic characteristics of the TMR elements fluctuate at every element or magnetic characteristics fluctuate when the same element is repeatedly used, there arises a problem in which it becomes difficult to selectively write information by using asteroid characteristics.
Accordingly, the TMR element is requested to have magnetic characteristics that can draw an ideal asteroid curve.
To draw an ideal asteroid curve, an R-H (resistance-magnetic field) loop obtained when magnetic characteristic of the TMR element are measured is free from noises such as a Barkhausen noise, a waveform should have an excellent rectangle property, the magnetization state should be stable and the coercive force Hc should be prevented from being fluctuated.
In order to read out information from the TMR element of the MRAM, information is read out from the TMR element by a difference current at a constant bias voltage and by a difference voltage at a constant bias current obtained in the condition in which the state of “1”, for example, is presented when the directions of the magnetic moments of one ferromagnetic material layer and the other ferromagnetic material layer sandwiching the tunnel barrier layer are anti-parallel and resistance values are high and in which the state of “0” is presented when the directions of the magnetic moments are parallel to each other.
Accordingly, when the fluctuations of the resistance values between the elements are the same, a higher TMR ratio (magnetoresistive changing ratio) is advantageous so that a memory whi
Bessho Kazuhiro
Higo Yutaka
Hosomi Masanori
Kano Hiroshi
Mizuguchi Tetsuya
Huynh Andy
Nelms David
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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