Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1999-06-17
2002-03-05
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C338S03200R, C360S313000, C360S317000, C360S327300
Reexamination Certificate
active
06353316
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive element utilizing the magnetoresistive effect (hereinafter also called MR element), and also relates to a thin film magnetic head comprising the MR element.
2. Explanation of the Related Art
In accordance with the miniaturization of a magnetic disc drive, a thin film magnetic head including a MR element as a reading element has been known as a magnetic converting device which is suitable for reading information recorded on a magnetic record medium with a high density, because an output from the MR element is not related to a relative velocity of the MR element and the magnetic disc. Furthermore, there has been widely used a combination type thin film magnetic head having a magnetoresistive type thin film magnetic head for reading and an inductive type thin film magnetic head for writing, which are stacked one on the other on a substrate.
A MR element used as the reading magnetoresistive element is disclosed in, for instance Japanese Patent Application Laid-open Publication Kokai Hei 3-125311. The magnetoresistive element described in this publication includes a central active region and passive end portions arranged on either sides thereof. The central active region comprises a magnetoresistive film (hereinafter referred to as a MR film), a magnetic isolation film (non-magnetic spacer film) and a soft magnetic film. The soft magnetic film has a function to apply a lateral magnetic bias (lateral bias) to the MR film.
Each of a pair of the passive end portions comprises longitudinal bias films applying a longitudinal magnetic bias to the MR film, and lead conductive films. The longitudinal bias films serve to apply the longitudinal magnetic bias to the MR film, and are arranged on opposite sides of the central active region. The lead conductive films are provided on these longitudinal bias films.
When a sense current is flowed through the MR film to generate a magnetic flux, the soft magnetic film is magnetized in an axis of easy magnetization by the thus generated magnetic flux, and a magnetic field is generated by this magnetization. The MR film is magnetized laterally by the thus generated magnetic field. A direction in which the MR film is magnetized is rotated from the longitudinal direction to the lateral direction by a certain angle in accordance with the lateral bias. In this manner, a linear operation can be performed upon reading data recorded on the magnetic disc and so on.
The longitudinal bias films serve to apply a longitudinal magnetic bias (longitudinal bias) to the MR film to suppress Barkhausen noise. U.S. Pat. No. 4,024,489 discloses a MR sensor using a hard magnetic bias film as the longitudinal bias film.
When a magnetic field produced by data magnetically recorded on a magnetic record medium is applied to the MR film such that this magnetic field intersects the direction of the magnetization of the MR film, the direction of the magnetization of the MR film is changed. This results in that a resistance of the MR film is changed, and the sense current flowing through the MR film is changed accordingly. When the direction of the magnetic field produced by data magnetically recorded on the magnetic record medium is coincided with the direction of the magnetization of the MR film, the direction of the magnetization is not changed, and therefore the resistance of the MR film is not substantially changed.
In this specification, the longitudinal direction is a direction in which the sense current flows in the MR film and the lateral direction means a direction which crosses the longitudinal direction. It should be noted that the longitudinal direction is not always perpendicular to the lateral direction.
As stated above, in the known thin film magnetic head, the soft magnetic film is magnetized in the direction of the axis of easy magnetization by the magnetic field induced by the sense current flowing through the MR film, and the lateral magnetic bias is applied to the MR film with the aid of the magnetic field induced by said magnetization in the soft magnetic film. Therefore, a direction and a magnitude of the lateral bias (referred to as a lateral bias amount) are liable to be different from respective thin film magnetic heads and an output signal is liable to be asymmetrical and fluctuate. This results in a decrease in a manufacturing yield of the thin film magnetic head. Causes by which the lateral bias amount fluctuate may be summarized as follows.
(a) The lateral bias amount is sensitive to thickness of the MR film, magnetic isolation film and soft magnetic layer, and therefore the lateral bias amount fluctuates in accordance with a variation in thickness of these films.
(b) The lateral bias amount is influenced by external magnetic fields under the using condition, and is liable to fluctuate.
(c) Since the MR element is constructed such that the soft magnetic layer is magnetized in the direction of the axis of easy magnetization by the magnetic field induced by the sense current and the lateral bias to the MR film is produced by the magnetic field induced by said magnetization in the soft magnetic layer, the lateral bias amount is liable to be affected by a magnetic anisotropic dispersion of the soft magnetic layer. Therefore, the lateral bias amount becomes non-uniform.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetoresistive element, in which a constant lateral bias can be applied without being affected by the sense current and external disturbing magnetic fields, and thus a very small change in magnetization can be detected stably.
Another object of the present invention is to provide a magnetoresistive element, in which a fluctuation in characteristics for respective elements can be reduced, and elements can be manufactured with a high yield.
Another object of the present invention is to provide a magnetoresistive element having small noise and high performance.
The present invention also relates to a thin film magnetic head including an MR element, and has for its object to provide a thin film magnetic head in which a surface recording density on a magnetic record medium can be increased by providing a magnetoresistive element which can detect stably a very small change in magnetization.
According to the present invention, a magnetoresistive element comprises:
a magnetoresistive film through which a sense current for detecting a change in resistance due to a magnetization to be detected flows in a longitudinal direction;
a pair of lead conductive films coupled with both end portions of the magnetoresistive film viewed in the longitudinal direction in an electrically conductive manner and conducting the sense current in the longitudinal direction;
a lateral bias film magnetized in a fixed direction by a constant magnitude to apply a lateral bias in a lateral direction which crosses said longitudinal direction, said lateral bias being not influenced by said sense current and external magnetic fields; and
a substrate supporting said magnetoresistive film, lead conductive layers and lateral bias film.
In the magnetoresistive element according to the present invention, the lateral bias film serves to apply the lateral bias to the magnetoresistive film. Therefore, when the direction of the magnetization of the MR film due to a magnetic field induced by data recorded on a magnetic record medium is changed, a resistance of the magnetoresistive film is varied. Thus, by conducting the constant sense current through the magnetoresistive film, the variation in the resistance can be detected as a variation in a voltage across the magnetoresistive film, and the recorded data can be read out.
In the magnetoresistive element according to the invention, said lateral bias film is magnetized such that the constant lateral bias which is not affected by the sense current flowing through the MR film and external magnetic fields can be applied to the magnetoresistive film in the fixed lateral direction. That is to say, a direction an
Andersen Henry S.
Oliff & Berridg,e PLC
TDK Corporation
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