Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-03-16
2004-09-21
Tugbang, A. Dexter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S603160, C029S603180, C360S321000, C360S316000, C216S022000, C216S048000
Reexamination Certificate
active
06792670
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive device substructure including magnetoresistive elements, a magnetoresistive device including a magnetoresistive element, and a micro device including a first patterned thin film and a second patterned thin film that covers the first thin film, and to methods of manufacturing such a magnetoresistive device substructure, a magnetoresistive device and a micro device.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as 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 recording head having an induction-type electromagnetic transducer for writing and a reproducing head having a magnetoresistive element for reading.
Reproducing heads that exhibit high sensitivity and produce high outputs have been required. In response to such demands, attention has been focused on tunnel magnetoresistive elements (that may be hereinafter called TMR elements) that detect a magnetic field through the use of the tunnel magnetoresistive effect.
As shown in
FIG. 21
, the TMR element has a structure in which a lower magnetic layer
102
, a tunnel barrier layer
103
and an upper magnetic layer
104
are stacked on a substrate
101
. Each of the lower magnetic layer
102
and the upper magnetic layer
104
includes a ferromagnetic substance. In general, the magnetic layer closer to the substrate is called the lower magnetic layer and the magnetic layer farther from the substrate is called the upper magnetic layer. Therefore, the terms ‘upper’ and ‘lower’ of the upper and lower magnetic layers do not always correspond to the position in the arrangement of an actual TMR element.
The tunnel barrier layer is a layer made of a thin nonmagnetic insulating film through which electrons are capable of passing while maintaining spins thereof by means of the tunnel effect, that is, through which a tunnel current is allowed to pass. The tunnel magnetoresistive effect is a phenomenon that, when a current is fed to a pair of magnetic layers sandwiching the tunnel barrier layer, a tunnel current passing through the tunnel barrier layer changes, depending on the relative angle between magnetizations of the two magnetic layers. If the relative angle between magnetizations of the magnetic layers is small, the tunneling rate is high. As a result, the resistance to the current passing across the magnetic layers is reduced. If the relative angle between magnetizations of the magnetic layers is large, the tunneling rate is low. The resistance to the current passing across the magnetic layers is therefore increased.
With regard to the structure of a thin-film magnetic head incorporating a TMR element, if the tunnel barrier layer made up of a thin insulating layer is exposed from the medium facing surface that faces toward a recording medium, a short circuit may occur during or after lapping of the medium facing surface. Such a structure is therefore not preferred.
To cope with such a problem, a thin-film magnetic head is disclosed in U.S. patent application Ser. No. 09/517,580. This head has a structure in which a TMR element retreats from the medium facing surface. FIG.
22
and
FIG. 23
illustrate a front-flux-probe-type head as an example of the head having such a structure.
FIG. 22
is a cross section of the main part of the head.
FIG. 23
is a top view thereof This head comprises a pinning layer
105
, a pinned layer
106
, a tunnel barrier layer
107
and a free layer
108
that are stacked one by one. These layers make up the TMR element. The TMR element is located at a distance from the medium facing surface.
The head further comprises a front flux probe (FFP) layer
109
formed on the free layer
108
. The FFP layer
109
is T-shaped and includes two portions one of which extends from the medium facing surface to a portion above the free layer
108
, and the other of which is located in the portion above the free layer
108
and extends from side to side along the direction parallel to the medium facing surface. The FFP layer
109
is a soft magnetic layer that directly touches the TMR element. As shown in FIG.
22
and
FIG. 23
, the FFP layer
109
may be formed by adding a soft magnetic layer different from the TMR element in size. Alternatively, the FFP layer
109
may be made of a part of the free layer
108
of the TMR films.
The portion
109
a
of the FFP layer
109
that extends to the medium facing surface has the function of introducing a signal magnetic flux from the medium facing surface to the TMR element. The length of the portion
109
a
is called the front flux probe length (FFP length of FIG.
23
).
The head further comprises a pair of hard magnet layers
110
located on the portion of the FFP layer
109
extending from side to side.
Another function of the FFP layer
109
is to effectively give the free layer of the TMR element a bias magnetic field in the horizontal direction obtained from the bias field applying layers such as the hard magnet layers and antiferromagnetic substances. In the case of the TMR element, as in the cases of an anisotropic magnetoresistive (AMR) element and a giant magnetoresistive (GMR) element, a short circuit occurs if the bias field applying layer touches an end of the element. As a result, no rate of change in resistance is detected. If the bias field applying layer directly touches a top portion or a bottom portion of the TMR element, no short circuit occurs. However, the problem is that, if the direction of magnetization of the pinned layer and the direction of magnetization of the free layer are antiparallel with respect to each other, a greater current flows through a portion of the tunnel barrier layer in which the bias field applying layer is located. As a result, the rate of change in resistance is reduced.
To solve the above-described problem, a technique is disclosed in U.S. patent application Ser. No. 09/517,455. According to this technique, a soft magnetic layer greater than a TMR element in width along the track width is formed. The soft magnetic layer has a portion located outside the TMR element. A bias field applying layer is located in this portion. This soft magnetic layer has the function of effectively inducing a bias field from the bias field applying layer to the free layer of the TMR element. The FFP layer
109
of FIG.
22
and
FIG. 23
corresponds to this soft magnetic layer.
As described above, the FFP layer
109
having the functions of introducing a signal flux and inducing a bias field is T-shaped.
If the conventional photolithography technique is employed, the problem is that corners of a pattern reduced in size are rounded. The above-described front-flux-probe-type head has a reproducing track width which is defined by the width of the front flux probe layer measured in the medium facing surface. Therefore, it should be avoided that corners of the front flux probe layer formed through the photolithography technique are rounded, since such rounded corners cause variations in track width. To avoid this problem, an electron beam exposure technique may be employed. In this case, however, the throughput is reduced while manufacturing costs increase since the apparatus required for electron beam exposure is expensive.
To reduce roundness of corners of the pattern, it is possible to provide the front flux probe layer having the shape of a rectangle greater than the TMR element, in place of the T-shaped front flux probe layer. However, this solution is not preferred since it is impossible that the track width is made smaller than the width of the TMR element.
To precisely control the dimensions and shape of the T-shaped soft magnetic layer having the functions of introducing a signal flux and inducing a bias field, it is possible to make the T-shaped soft magnetic layer in two steps by dividing it into two rectangular layer
Kasahara Noriaki
Sato Kazuki
Shimazawa Koji
Oliff & Berridg,e PLC
TDK Corporation
Tugbang A. Dexter
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