Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-08-03
2003-07-15
Ciric, Ljiljana (Department: 3743)
Metal working
Method of mechanical manufacture
Electrical device making
C029S603160, C029S603150, C029S603070, C216S022000
Reexamination Certificate
active
06591481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a magnetoresistive device that incorporates a magnetoresistive element, and a method of manufacturing a thin-film magnetic head that incorporates a magnetoresistive element.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as the 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 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 (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.
Read heads that exhibit a high sensitivity and a high output are required. An example of read heads that meet these requirements are GMR heads incorporating spin valve GMR elements. Such GMR heads have been mass-produced.
In general, the spin valve GMR element incorporates: a nonmagnetic layer having two surfaces that face toward opposite directions; a soft magnetic layer located adjacent to one of the surfaces of the nonmagnetic layer; a ferromagnetic layer located adjacent to the other one of the surfaces of the nonmagnetic layer; and an antiferromagnetic layer located adjacent to one of the surfaces of the ferromagnetic layer that is farther from the nonmagnetic layer. The soft magnetic layer is a layer in which the direction of magnetization changes in response to the signal magnetic field and is called a free layer. The ferromagnetic layer is a layer in which the direction of magnetization is fixed by the field supplied from the antiferromagnetic layer and is called a pinned layer.
Another characteristic required for the read head is a small Barkhausen noise. Barkhausen noise results from transition of a domain wall of a magnetic domain of an MR element. If Barkhausen noise occurs, an abrupt variation in output results, which induces a reduction in signal-to-noise (S/N) ratio and an increase in error rate.
To reduce Barkhausen noise, a bias magnetic field (that may be hereinafter called a longitudinal bias field) is applied to the MR element along the longitudinal direction. To apply the longitudinal bias field to the MR element, bias field applying layers may be provided on both sides of the MR element, for example. Each of the bias field applying layers is made of a hard magnetic layer or a laminate of a ferromagnetic layer and an antiferromagnetic layer, for example.
In the read head, in which the bias field applying layers are provided on both sides of the MR element, two electrode layers for feeding a current used for magnetic signal detection (that may be hereinafter called a sense current) to the MR element are located to touch the bias field applying layers.
As disclosed in Published Unexamined Japanese Patent Application Heisei 11-31313 (1999), it is known that, when the bias field applying layers are located on both sides of the MR element, regions that may be hereinafter called dead regions are created near ends of the MR element that are adjacent to the bias field applying layers. In these regions the magnetic field produced from the bias field applying layers fixes the direction of magnetization, and sensing of a signal magnetic field is thereby prevented. Such dead regions are created in the free layer of the spin valve GMR element.
Consequently, if the electrode layers are located so as not to overlap the MR element, a sense current passes through the dead regions. The output of the read head is thereby reduced.
To solve this problem, the electrode layers are located to overlap the MR element, as disclosed in Published Unexamined Japanese Patent Application Heisei 8-45037 (1996), Published Unexamined Japanese Patent Application Heisei 9-282618 (1997), Published Unexamined Japanese Patent Application Heisei 11-31313 (1999), and Published Unexamined Japanese Patent Application 2000-76629, for example.
It is possible to reduce Barkhausen noise while a reduction in output of the read head is prevented, if the read head has a structure such that the bias field applying layers are located on both sides of the MR element, and the electrode layers overlap the MR element, as described above. Such a structure is hereinafter called an overlapping electrode layer structure.
To improve the sensitivity of the read head incorporating the spin valve GMR element, a variety of improvements in spin valve film that make up the spin valve GMR element have been proposed. One of such next-generation spin valve films is a spin valve film in which a high resistance layer is located adjacent to one of the surfaces of the free layer that is farther from the nonmagnetic layer. (See Atsushi Tanaka et al., ‘Microstructure Process Techniques and Development of Prototype Head with Reduced Read Core Width’. The 9
th
Research Workshop of The Second Research Division of Association of Super-Advanced Electronics Technologies, Aug. 29, 2000, pp. 65-76.) The high resistance layer of the specular spin valve film reflects electrons and thereby increases the rate of change in resistance of the spin valve GMR element. The read output of the read head is thereby increased. The high resistance layer maybe made of an oxide of a metal such as Fe, Al, Ni, or Ta.
Consideration is now given to the read head having the overlapping electrode layer structure in which the GMR element incorporating the above-described specular spin valve film is located such that the pinned layer is closer to the substrate and the free layer is farther from the substrate. To fabricate this read head, if the electrode layers are formed after the high resistance layer is formed on the free layer, the high resistance layer is located between the free layer and the electrode layers. As a result, a sense current flows from the bias field applying layers to an end of the GMR element, which results in a reduction in output of the read head and unstable operations. Therefore, to fabricate the read head that has both specular spin valve film and overlapping electrode layer structure as described above, it is necessary to adopt some method to form the high resistance layer adjacent to the free layer after the electrode layers are formed.
The following method may be taken to fabricate the read head that has both specular spin valve film and overlapping electrode layer structure.
Reference is now made to
FIG. 20
to
FIG. 28
to describe this method. In the method, as shown in
FIG. 20
, a base layer
121
, an antiferromagnetic layer
122
, a pinned layer
123
, a nonmagnetic layer
124
, a soft magnetic layer (a free layer)
125
, and a protection layer
126
are formed in this order through sputtering, for example, and stacked. Each of the base layer
121
and the protection layer
126
is made of a metal material.
Next, as shown in
FIG. 21
, after the protection layer
126
is formed, the layers of
FIG. 20
are exposed to the atmosphere, so that part of the top surface thereof is natural-oxidized and an oxide layer
140
is thereby formed.
Next, as shown in
FIG. 22
, a resist mask
141
is formed on the oxide layer
140
through photolithography. The resist mask
141
is used for patterning the layers from the oxide layer
140
to the pinned layer
123
. Next, these layers are selectively etched through ion milling, for example, using the resist mask
141
, and thereby patterned. Through this etching, part of the top surface of the antiferromagnetic layer
122
is etched, too.
Next, as shown in
FIG. 23
, on the antiferromagnetic layer
122
, two bias field applying layers
127
are formed on both sides of the layers from the oxide layer
140
to the pinned layer
123
while the resist mask
141
is left unremoved. Each of the bias field applying
Ito Noriyuki
Shimazawa Koji
Terunuma Koichi
Ciric Ljiljana
Oliff & Berridg,e PLC
TDK Corporation
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