Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-10-02
2004-04-06
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324000, C360S327100, C365S158000
Reexamination Certificate
active
06717780
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-resistive element widely used for, for example, a magnetic head for reproducing information recorded on a magnetic medium such as a magnetic disc, an optical magnetic disc, a magnetic tape or the like, for a magnetic sensor used in an automobile or the like, and a magnetic random access memory (MRAM).
2. Description of the Related Art
In accompaniment with recent improvement in the magnetic recording density, a spin valve type GMR (giant magneto-resistive) element has been put into practice. A spin valve type GMR is described as operating on a fundamental principle that a mean free path of electrons flowing in a layer along a direction parallel to a layer surface changes in accordance with a relative magnetization angle between a free layer and a fixed layer. A spin valve type GMR provides an MR ratio (magneto-resistive ratio) of about 10%, which is several times higher than that of a conventional anisotropic MR element.
As elements providing a still higher MR ratio than that of the spin valve type GMR, a TMR element using a TMR (tunneling magneto-resistive) effect and a CPP (current perpendicular to the plane) GMR element using a magnetic metal/transfer metal artificial lattice are now being studied.
A CPP GMR element basically operates on the same principle as that of the above-mentioned spin valve type GMR element. In the CPP GMR element, however, a current flows along a direction perpendicular to the layer surface. A TMR element is a new magneto-resistive element using a tunneling probability of electrons which changes in accordance with the relative magnetization angle between two ferromagnetic layer interposing a tunneling insulating layer, in the TMR element, a current flows in a direction perpendicular to the layer surface, like the above-mentioned CPP GMR element. In this specification, a TMR element and a CPP GMR element in which a current flows in a direction perpendicular to the layer surface will be collectively referred to as a “vertical current type magneto-resistive element”.
Various structures for using a vertical current type magneto-resistive element for a magnetic head have been proposed. Japanese Laid-Open Publication No. 11-213349 proposes a shield type magnetic head including a TMR element, instead of a spin valve type GMR element, and including a flux guide. Japanese Laid-Open Publication No. 11-25425 proposes a magnetic head including a TMR element inside a yoke formed in a direction perpendicular to a surface of a magnetic recording medium.
When a TMR element is used for a magnetic head, there are problems that, due to an essentially high junction impedance of the TMR element, thermal noise is generated and the TMR element does not match an electric circuit for driving the TMR element.
An increase in the area of the TMR element in order to reduce the junction impedance causes another problem that it becomes difficult to reduce the size of the magnetic head. Such an increase in the area of the TMR element also causes a problem that it becomes difficult to improve the sensitivity of the magnetic head because a magnetic flux leaking from a surface of a magnetic recording medium increases as the recording density is improved.
A reduction in the thickness of the tunneling insulating layer of the TMR element in order to reduce the junction impedance also causes the following problem. Such a reduction strengthens the magnetic bonding between the ferromagnetic layers interposing the tunneling insulating layer. Therefore, it becomes difficult to realize an ideal relative magnetization angle, which makes it difficult to provide a high MR ratio.
A reduction in the distance between the TMR element and the magnetic recording medium in order to improve the sensitivity of the magnetic head causes a problem that a contact of the TMR element with the magnetic recording medium generates a thermal spike.
The above-mentioned conventional structures for using a vertical current type magneto-resistive element have problems of pulse amplitude asymmetry and asymmetry of side reading may undesirably occur.
A common problem among magnetic heads and MRAMs, the size of which is now being reduced, is that when the amount of a current flowing in the TMR element increases, a magnetic field generated based on the current causes an unfavorable influence on the magnetization direction of the free layer (or the magnetic field sensing section).
A TMR element has an inherent problem of bias voltage dependence such that when the bias voltage applied on the TMR element is increased, the MR ratio is decreased.
In order to apply a bias magnetic field on a vertical current type magneto-resistive element, it is necessary to provide an anti-ferromagnetic member for generating a bias magnetic field or it is necessary to provide a magnetic body forming the vertical current type magneto-resistive element with anisotropy by heat-treating the magnetic body in a magnetic field.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a magneto-resistive element includes a vertical current type magneto-resistive element; a first conductor for causing a current to flow into the vertical current type magneto-resistive element; and a second conductor for causing the current to flow out of the vertical current type magneto-resistive element. The first conductor generates a first magnetic field based on the current. The second conductor generates a second magnetic field based on the current. The first conductor and the second conductor are located so that the first magnetic field and the second magnetic field act as a bias magnetic field applied on the vertical current type magneto-resistive element.
In one embodiment of the invention, the first conductor and the second conductor are located parallel to each other.
In one embodiment of the invention, the magneto-resistive element is substantially U-shaped.
In one embodiment of the inventions the first conductor and the second conductor are located twisted to each other.
According to another aspect of the invention, a magneto-resistive element includes a vertical current type magneto-resistive element; a first conductor for causing a current to flow into the vertical current type magneto-resistive element; and a second conductor for causing the current to flow out of the vertical current type magneto-resistive element. The first conductor generates a first magnetic field based on the current,
the second conductor generates a second magnetic field based on the current. The first conductor and the second conductor are located so that the second magnetic field cancels at least a part of the first magnetic field.
In one embodiment of the invention, the first conductor and the second conductor are located parallel to each other.
According to still another aspect of the invention, a multiple element magneto-resistive device includes a first vertical current type magneto-resistive element responding to a specific external magnetic field; a second vertical current type magneto-resistive element responding to the specific external magnetic field; and a yoke on which the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are provided.
In one embodiment of the invention, the multiple element magneto-resistive device further includes an adder for adding an output of the first vertical current type magneto-resistive element and an output of the second vertical current type magneto-resistive element so as to detect the specific external magnetic field.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a subtracter for processing an output of the first vertical current type magneto-resistive element and an output of the second vertical current type magneto-resistive element with subtraction so as to detect the specific external magnetic field.
In one embodiment of the invention, each of the first vertical current type magneto-resistive element and the s
Hiramoto Masayoshi
Iijima Kenji
Matsukawa Nozomu
Odagawa Akihiro
Sakakima Hiroshi
Heinz A. J.
Renner Otto Boisselle & Sklar
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