Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2000-12-27
2002-08-27
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C338S03200R, C360S119050, C360S324000, C428S900000
Reexamination Certificate
active
06441611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic sensor.
The magnetic sensor is used primarily as a magnetic head for a hard disk drive serving as a recording device in a computer. Conventional hard disk drive magnetic heads sense magnetic fields by an induction current generated in a coil. However, with recent demands for higher recording density and higher speed, magnetic sensors that directly sense magnetic fields themselves have begun to be used in magnetic heads. Due to the higher recording density of hard disk drives, the reduction in the 1 bit recording area results in a smaller generated magnetic field. Thus, magnetic sensors that are small and can sense small changes in external magnetic fields are desirable.
2. Description of the Related Art
The magnetic heads that are currently in wide use are magnetic sensors that utilize a magnetoresistance effect (hereunder referred to as “MR effect”). The MR effect is a change in the magnetoresistance according to the strength of the external magnetic field, when the external magnetic field direction and the current direction are different for a magnetic material. Recording density is vastly improved with a magnetic head utilizing the MR effect. However, there is high demand for further improvement in recording density, and a trend is underway toward the use of magnetic heads utilizing giant magnetoresistance effect (hereunder referred to as “GMR effect”), which involves a greater resistance change than the MR effect and is expected to provide even better recording density in the latest generation of magnetic heads.
The magnetic head uses spin-valve GMR. This is an MR ratio of about 7%, and is thought to be applicable up to a recording density of 10-20 Gbit/in
2
.
However, recent improvements in hard disk drive recording density have been drastic, and a recording density of 40 Gbit/in
2
has been set as a goal for 2002. With this level of recording density, the MR ratio must be at least 10%. The recording bit size will have a track width of 0.3 &mgr;m or smaller and a bit length of 0.07 &mgr;m or smaller. Consequently, it will be desirable to have a GMR film thickness of no greater than 0.07 &mgr;m (700 Å), and assuming insulation layer thicknesses of 200 Å each for the upper and lower magnetic shields, it must be no greater than 0.03 &mgr;m (300 Å).
GMR films with a multilayer structure are expected to be used to meet this demand. In multilayer GMR films, the external magnetic field required for resistance change is as large as a few kOe or more for the “first peak, ” i.e., the thickness of a non-magnetic layer of the GMR film of about 1 nm, which gives the largest MR ratio (30-50%). On the other hand, the MR ratio a “second peak,” ie., the thickness of the non-magnetic layer of about 2 nm, is 10-20%, but the external magnetic field required for a resistance change is as small as about 100 Oe, so that it is believed to be suitable for use in magnetic heads.
Furthermore, multilayer GMR films are known to have an MR ratio, when the current flows perpendicular to the film surface (CPP, Current Perpendicular to the Plane), which is about twice that compared to when the current flows parallel to the film surface (CIP, Current In Plane), at room temperature. In this case, the element structure is generally as shown in FIG.
1
. The element has greater resistance and a greater degree of resistance change, with a smaller cross-sectional area of the element. That is, while it offers the advantage of suitability for narrower track widths, its disadvantages include a greater thickness due to the upper and lower element layers and greater difficulty in forming the insulation layer and element member (greater alignment precision is necessary).
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to overcome these problems of the prior art by providing a magnetic sensor which is easy to manufacture and is compact, and which has a high degree of resistance change.
In order to achieve this object, the invention provides a magnetic sensor utilizing GMR effect, wherein an insulation layer with a contact hole is formed on a lower terminal layer, a GMR layer is formed thereover on the region including the entire contact hole and at least the surrounding insulation layer, and an upper terminal layer is formed thereover.
According to another aspect of the invention, the upper terminal layer and the lower terminal layer simultaneously provide magnetic shield layer functions.
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patent: 5351158 (1994-09-01), Shibata
patent: 5675459 (1997-10-01), Sato et al.
patent: 5822158 (1998-10-01), Matsuzono
patent: 6114719 (2000-09-01), Dill et al.
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patent: 7-262520 (1995-10-01), None
patent: 09128719 (1997-05-01), None
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patent: 10-209521 (1998-08-01), None
Fujitsu Limited
Greer Burns & Crain Ltd.
Strecker Gerard R.
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