Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-11-15
2004-04-13
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S320000
Reexamination Certificate
active
06721140
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive device that incorporates a magnetoresistive element and a method of manufacturing such a magnetoresistive device, and to a thin-film magnetic head that incorporates a magnetoresistive element and a method of manufacturing such a thin-film magnetic head.
2. Description of the Related Art
In recent years, performance improvements in thin-film magnetic heads have been sought as areal recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite thin-film magnetic head is made of a layered structure including a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
MR elements include: an AMR element that utilizes the anisotropic magnetoresistive effect; a GMR element that utilizes the giant magnetoresistive effect; and a TMR element that utilizes the tunnel magnetoresistive effect.
The read head comprises: an MR element; two electrode layers that are connected to the MR element in order to feed a current used for detecting a signal magnetic field (that may be hereinafter called a sense current) to the MR element; and two shield layers, i.e., top and bottom shield layers disposed to sandwich the MR element and the electrode layers to thereby shield them.
Insulating layers are interposed between the MR element/electrode layers and the top and bottom shield layers, respectively, to electrically isolate the MR element/the electrode layers from the shield layers. For example, these insulating layers are each made of a thin alumina film formed through sputtering.
When a GMR element is used as the MR element, for usual read operations, a voltage of about 200 mV is required to be applied from the electrode layers to the GMR element in order to feed a sense current to the GMR element. Conventional insulating layers have an insulating property sufficient to withstand a voltage of this magnitude.
However, the conventional insulating layers cannot withstand an electric field of several volts to tens of volts established by static electric charges that are built up in the process from integration to machine processing of the read head, which can result in electrostatic damage to the insulating layers. This problem becomes more serious when the insulating layers are required to be 10 to 20 nm in thickness or even thinner than this range from the viewpoint of recording density.
Conventionally, a variety of methods have been suggested for preventing damage to the MR element related to electrostatic discharge. Now, four of the methods are described below.
According to a first method, the top and bottom shield layers are electrically connected to each other as disclosed in Published Unexamined Japanese Patent Application (KOKAI) Nos. Sho 61-77114 and Hei 7-65324.
According to a second method, the shield layers are electrically connected to the electrode layers as disclosed in Published Unexamined Japanese Patent Application (KOKAI) No. Hei 10-11717.
According to a third method, two electrode layers are short-circuited between their terminals when processing the head and then the short-circuited portion between the terminals are cut off after the head has been processed, as disclosed in Published Unexamined Japanese Patent Application (KOKAI) Nos. Hei 8-315321, Hei 11-316915, Hei 11-45423, and Hei 6-60338.
A fourth method uses diodes, as disclosed in Published Unexamined Japanese Patent Application (KOKAI) Nos. Hei 7-85422, Hei 10-269534, Hei 10-255235, and 2000-76626. Published Unexamined Japanese Patent Application (KOKAI) No. Hei 7-85422 discloses a technique of connecting two diodes that are opposite in polarity in parallel between the terminals of two electrode layers. Published Unexamined Japanese Patent Application (KOKAI) No. Hei 10-269534 discloses a technique of connecting two diodes that are opposite in polarity in parallel between two electrode layers. Published Unexamined Japanese Patent Application (KOKAI) No. Hei 10-255235 discloses a technique of connecting two diodes that are opposite in polarity in parallel between two electrode layers, and also a technique of connecting two diodes that are opposite in polarity in parallel between an electrode layer and a shield layer. Published Unexamined Japanese Patent Application (KOKAI) No. 2000-76626 discloses techniques of connecting two diodes that are opposite in polarity in parallel between two electrode layers, connecting two diodes that are opposite in polarity in series between two shield layers, and connecting two diodes that are opposite in polarity in series between an electrode layer and a shield layer.
Any of these methods, however, present the following problems with regard to prevention of electrostatic damage to the insulating layers disposed between the electrode layers and the shield layers.
In the first method, when a large potential difference occurs between the shield layers and the electrode layers, it is impossible to prevent the electrostatic damage to the insulating layers disposed between the shield layers and the electrode layers.
In the second method, since the MR element and the shield layers are electrically connected via the electrode layers, the shielding function of the shield layers would be degraded.
In the third method, when a large potential difference occurs between the shield layers and the electrode layers, it is impossible to prevent the electrostatic damage to the insulating layers disposed between the shield layers and the electrode layers. Furthermore, in the third method, since the short-circuited portion between the terminals is cut off after the head has been processed, it is impossible to prevent electrostatic damage in post-processing steps, for example, in the step of fixing the head to a suspension after the head has been processed.
In the fourth method, it is necessary to form at least a total of four layers of n-type and p-type semiconductors, which makes the structure and manufacturing steps of the head complicated.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a magnetoresistive device and a method of manufacturing the same, and a thin-film magnetic head and a method of manufacturing the same, which make it possible to prevent electrostatic damage to the insulating layers disposed between the shield layer and the electrode layer connected to the magnetoresistive element, with a simple structure and simple manufacturing steps.
A magnetoresistive device of the invention comprises:
a magnetoresistive element that detects a magnetic field;
an electrode layer for feeding a current for detecting the magnetic field to the magnetoresistive element;
a first shield layer and a second shield layer that sandwich and shield the magnetoresistive element and the electrode layer;
a first insulating layer disposed between the magnetoresistive element/the electrode layer and the first shield layer;
a second insulating layer disposed between the magnetoresistive element/the electrode layer and the second shield layer; and
a semiconductor layer that is made up of a single layer and disposed between the electrode layer and at least one of the shield layers, for connecting the electrode layer and the at least one of the shield layers.
According to the magnetoresistive device of the invention, the electrode layer and at least one of the shield layers are connected via the semiconductor layer. The semiconductor layer functions as an insulator for a voltage of such a level as is needed for feeding a current for detecting a magnetic field to the magnetoresistive element, whereas functioning as a conductor for a voltage of such a level as causes a dielectric breakdown of the insulating layer disposed between the electrode layer and the shield layer.
A method of the invention is provided for manufacturing a magnetoresistive
Inoue Tohru
Tanemura Shigeki
Terunuma Koichi
Klimowicz William
Oliff & Berridg,e PLC
TDK Corporation
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