Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-05-17
2004-04-13
Letscher, George J. (Department: 2653)
Metal working
Method of mechanical manufacture
Electrical device making
C029S603180, C360S322000
Reexamination Certificate
active
06718623
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 same, and to a thin-film magnetic head that incorporates a magnetoresistive element and a method of manufacturing same.
2. Description of the Related Art
With recent enhancements in the areal recording density of hard disk drives, improved performance has been sought of thin-film magnetic heads. For the past few years in particular, hard disk drives have been doubling in areal recording density roughly each year. Lately, areal recording densities of 100 Gbit/(inch)
2
or more are required.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads 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 (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.
For reproducing heads, a high sensitivity and a high output are required. Reproducing heads that meet these requirements are GMR heads incorporating spin-valve GMR elements. Such GMR heads have been mass-produced.
In general, a spin-valve GMR element incorporates: a nonmagnetic conductive layer having two surfaces that face toward opposite directions; a free layer that is located adjacent to one of the surfaces of the nonmagnetic conductive layer and has a direction of magnetization that varies in response to a signal magnetic field from a recording medium; a pinned layer that is located adjacent to the other of the surfaces of the nonmagnetic conductive layer and has a fixed direction of magnetization; and an antiferromagnetic layer that is located adjacent to one of surfaces of the pinned layer that is farther from the nonmagnetic conductive layer and fixes the direction of magnetization of the pinned layer. The free layer and the pinned layer are each made of a ferromagnetic layer. An electric resistance value of the free layer varies according to the direction of magnetization of the free layer. The spin-valve GMR element utilizes the variations in the electric resistance value of the free layer to reproduce data that is magnetically recorded on the recording medium.
Another characteristic required of reproducing heads 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 ratio (S/N ratio) and an increase in error rate.
To reduce Barkhausen noise, a bias magnetic field in the longitudinal direction (that may be hereinafter called a longitudinal bias field) is applied to the MR element. 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 laminate of a ferromagnetic layer and an antiferromagnetic layer, or a permanent magnet, for example.
In a reproducing head in which bias field applying layers are provided on both sides of the MR element, in general, a pair of electrode layers for feeding a current used for signal detection (hereinafter called a sense current) to the MR element are located to touch the bias field applying layers.
In general, the MR element is sandwiched between a bottom shield layer and a top shield layer. A bottom shield gap film that is an insulating film is interposed between the MR element and the bottom shield layer. Similarly, a top shield gap film that is an insulating film is interposed between the MR element and the top shield layer. A base layer may be provided between the MR element and the bottom shield gap film for the purpose of attaining better orientation and magnetic properties of magnetic layers that constitute the MR element. For example, a Ta or Cr compound may be used as a material of the base layer. Between the MR element and the top shield gap film, a protection layer may be formed after forming films making up the MR element, for the purpose of protecting those films. The protection layer may be made of Ta, for example.
Reference is now made to FIG.
25
through
FIG. 28
to describe an example of a method of manufacturing a reproducing head. In this manufacturing method, as shown in
FIG. 25
, a bottom shield gap film
104
made of alumina (Al
2
O
3
), for example, is first formed on a bottom shield layer
103
made of NiFe, for example. A base layer
105
is formed on the bottom shield gap film
104
. Then, an MR-element-to-be film
106
P to make the MR element is formed on the base layer
105
. A protection layer
107
is then formed on the MR-element-to-be film
106
P. Then, a mask
108
for patterning the MR-element-to-be film
106
P by etching is formed on the protection layer
107
. The mask
108
is made of a photoresist layer patterned by photolithography. For easy lift-off, the mask
108
is formed to have a T-shaped cross section, i.e., such a shape that a portion close to the bottom is smaller in width than a portion close to the top.
Next, as shown in
FIG. 26
, ion beam etching is performed so that ion beams travel at an angle of 5 to 10° with respect to the direction perpendicular to the top surface of the bottom shield layer
103
, thereby partially etching the protection layer
107
, the MR-element-to-be film
106
P, and the base layer
105
. The protection layer
107
, the MR-element-to-be film
106
P, and the base layer
105
are thus patterned. The MR-element-to-be film
106
P makes an MR element
106
as a result of the patterning.
Next, as shown in
FIG. 27
, a hard magnetic layer
109
P for making bias field applying layers is formed by sputtering on the entire top surface of the laminate obtained by the steps so far, with the mask
108
left unremoved. The hard magnetic layer
109
P is made of CoPt, for example. The mask
108
is then lifted off. Portions of the hard magnetic layer
109
P remaining after the liftoff make a pair of bias field applying layers
109
.
Next, as shown in
FIG. 28
, a pair of electrode layers
110
are formed on the pair of bias field applying layers
109
. The electrode layers
110
are made of a laminate of Au and Ta films, for example. A top shield gap film
111
made of alumina, for example, is then formed on the entire top surface of the laminate. Then, although not shown, a top shield layer is formed on the entire top surface of the laminate.
As disclosed in, e.g., Published Unexamined Japanese Patent Applications (KOKAI) Heisei 11-224411 and 2000-76629, it is known that, when the bias field applying layers are provided on both sides of the MR element, regions that may be hereinafter called lower-sensitivity regions develop 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 limits variations of the direction of magnetization, and the sensitivity is thereby lowered. Consequently, if the electrode layers are located so as not to overlap the MR element, a sense current passes through the lower-sensitivity regions and the output of the reproducing head is thereby lowered. This problem becomes more noticeable as the track width of the reproducing head becomes smaller.
To solve this problem, each of the electrode layers is located such that a portion thereof is laid over part of (hereinafter expressed as “overlap”) the MR element, as disclosed in, e.g., Published Unexamined Japanese Patent Applications (KOKAI) Heisei 11-224411 and 2000-76629. It is possible to reduce Barkhausen noise while preventing a reduction in output of the reproducing head, if the reproducing head has a structure (hereinafter called an overlapping electrode layer structure
Kamigama Takehiro
Sasaki Yoshitaka
Headway Technologies Inc.
Letscher George J.
LandOfFree
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