Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-03-27
2004-06-22
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06754052
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive head for use in a magnetic recording device such as a magnetic disk drive and a magnetic tape drive.
2. Description of the Related Art
In association with a reduction in size and an increase in recording density of a magnetic disk drive in recent years, the flying height of a head slider has become smaller and it has been desired to realize contact recording/reproduction such that the head slider flies a very small height above a recording medium or comes into contact with the recording medium. Further, a conventional magnetic induction head has a disadvantage such that its reproduction output decreases with a decrease in peripheral speed of a magnetic disk as the recording medium (relative speed between the head and the medium) caused by a reduction in diameter of the magnetic disk. To cope with this disadvantage, there has recently extensively been developed a magnetoresistive head (MR head) whose reproduction output does not depend on the peripheral speed and capable of obtaining a large output even at a low peripheral speed. Such a magnetoresistive head is now a dominating magnetic head. Further, a magnetic head utilizing a giant magnetoresistive (GMR) effect is also commercially available at present.
With higher-density recording in a magnetic disk drive, a recording area of one bit decreases and a magnetic field generated from the medium accordingly becomes smaller. The recording density of a magnetic disk drive currently on the market is about 10 Gbit/in2, and it is rising at an annual rate of about 200%. It is therefore desired to develop a magnetoresistive sensor and a magnetoresistive head which can support a minute magnetic field range and can sense a change in small external magnetic field.
At present, a spin valve magnetoresistive sensor utilizing a spin valve GMR effect is widely used in a magnetic head. In such a magnetoresistive sensor having a spin valve structure, a magnetization direction in a free ferromagnetic layer (free layer) is changed by a signal magnetic field from a recording medium, so that a relative angle of this magnetization direction to a magnetization direction in a pinned ferromagnetic layer (pinned layer) is changed, causing a change in resistance of the magnetoresistive sensor.
In the case of using this magnetoresistive sensor in a magnetic head, the magnetization direction in the pinned layer is fixed to a direction along the height of a magnetoresistive element, and the magnetization direction in the free layer in the condition where no external magnetic field is applied is generally designed to a direction along the width of the magnetoresistive element, the direction which is perpendicular to the pinned layer.
Accordingly, the resistance of the magnetoresistive sensor can be linearly increased or decreased according to whether the direction of the signal magnetic field from the magnetic recording medium is parallel or antiparallel to the magnetization direction of the pinned layer. Such a linear resistance change facilitates signal processing in the magnetic disk drive.
In the conventional magnetoresistive sensor, a sense current is passed in a direction parallel to the film surface of the magnetoresistive element to read a resistance change according to an external magnetic field. In such a case of a CIP (Current In the Plane) structure that a current is passed in a direction parallel to the GMR film surface, the output from the sensor decreases with a decrease in sense region defined by a pair of electrode terminals. Further, in the spin valve magnetoresistive sensor having the CIP structure, insulating films are required between the GMR film and an upper magnetic shield and between the GMR film and a lower magnetic shield.
That is, the distance between the upper and lower magnetic shields is equal to the sum of the thickness of the GMR film and a value twice the thickness of each insulating film. At present, the thickness of the insulating film is about 20 nm at the minimum. Accordingly, the distance between the upper and lower magnetic shields becomes equal to the sum of the thickness of the GMR film and about 40 nm.
However, with this distance, it is difficult to support a reduction in length of a recording bit on the recording medium, and the current CIP spin valve magnetoresistive sensor cannot meet the requirement that the distance between the magnetic shields is to be reduced to 40 nm or less. In these circumstances, it is considered that a magnetic head having a CIP structure utilizing a spin valve GMR effect can support a recording density of 20 to 40 Gbit/in
2
at the maximum. Even by applying specular scattering as a latest technique, the maximum recording density is considered to be 60 Gbit/in
2
.
As mentioned above, the increase in recording density of a magnetic disk drive is rapid, and it is expected that a recording density of 80 Gbit/in
2
will be desired by 2002. When the recording density becomes 80 Gbit/in
2
or higher, it is very difficult to support such a high recording density even by using a CIP spin valve GMR magnetic head to which the latest specular scattering is applied, from the viewpoints of output and the distance between the magnetic shields. As a post spin valve GMR intended to cope with the above problem, there have been proposed a tunnel MR (TMR) and a GMR having a CPP (Current Perpendicular to the Plane) structure such that a current is passed in a direction perpendicular to the GMR film surface.
The TMR has a structure that a thin insulating layer is sandwiched between two ferromagnetic layers. The amount of a tunnel current passing across the insulating layer is changed according to the magnetization directions in the two ferromagnetic layers. The TMR shows a very large resistance change and has a good sensitivity, so that it is expected as a promising post spin valve GMR. On the other hand, in the case of the GMR having the CPP structure, the output increases with a decrease in sectional area of a portion of the GMR film where a sense current is passed. This feature of the CPP structure is a large advantage over the CIP structure.
The TMR is also considered to be a kind of CPP structure, because a current is passed across the insulating layer from one of the ferromagnetic layers to the other ferromagnetic layer. Therefore, the TMR also has the above advantage. For the purpose of higher sensitivity in the GMR having the CPP structure, it has been proposed to make the sizes of two electrode terminals sandwiching the GMR film smaller than the size of the GMR film (Japanese Patent Laid-open No. 10-55512).
In a manufacturing method for the magnetoresistive head described in the above publication, one of the two electrode terminals is first formed, the GMR film is next formed, and the other electrode terminal is next formed. However, in fabricating a microstructural GMR element at present, it is very difficult to make the sizes of the two electrode terminals smaller than the size of the GMR film and to suppress misalignment by adopting the above conventional manufacturing method.
In a conventional MR head manufacturing method (the term of MR in this specification including GMR), an MR head is manufactured by a contact hole process or a lift-off process. In the contact hole process, an MR film is formed into a desired shape, and a magnetic domain control film and an insulating film are next laminated. Thereafter, a contact hole is formed to electrically connect an upper electrode terminal and the MR film. In the lift-off process, a photoresist for patterning an MR film is left, and a magnetic domain control film and an insulating film are laminated. Thereafter, the photoresist is removed to thereby form a contact hole for electrically connecting an upper electrode terminal and the MR film.
The MR film at present has a width of about 0.1 &mgr;m. On the other hand, the photolithography technique at present has an error of about 0.06 &mgr;m. Accordingly, as the MR film becomes more microscopic, alig
Asida Hiroshi
Eguchi Shin
Kondo Reiko
Shimizu Yutaka
Tanaka Atsushi
Cao Allen
Fujitsu Limited
Greer Burns & Crain Ltd.
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