1. Field of the Invention
The present invention relates to CPP (current perpendicular to plane) magnetic sensing elements. In particular, the present invention relates to a CPP magnetic sensing element that does not cause short-circuiting between thin layers constituting the magnetic sensing element and a method for making the same.
2. Description of the Related Art
FIGS. 16 to 19 are partial cross-sectional view of a known magnetic sensing element and a method for making the same. These drawings are cross-sectional views when viewed from a face opposing a recording medium (hereinafter referred to as merely “opposing face”). Referring to FIG. 16, a lower shield layer 1, a lower electrode layer 2, an underlayer 3, a seed layer 4, an antiferromagnetic layer 5, a pinned magnetic layer 6, a nonmagnetic layer 7, a free magnetic layer 8, and a protective layer 9 are continuously formed on a substrate (not shown) in that order by sputtering. The pinned magnetic layer 6 includes a first pinned magnetic sublayer 6a, a nonmagnetic interlayer 6b, and a second pinned magnetic sublayer 6c. The free magnetic layer 8 includes a first free magnetic sublayer 8a , a nonmagnetic interlayer 8b , and a second free magnetic sublayer 8c . Layers from the underlayer 3 to the protective layer 9 constitute a composite film T.
The lower shield 1 is composed of NiFe, and the lower electrode layer 2 is composed of Cu. The underlayer 3 is composed of Ta, and the seed layer 4 is composed of NiFe. The antiferromagnetic layer 5 is composed of PtMn. The first pinned magnetic sublayer 6a, the second pinned magnetic sublayer 6c, the first free magnetic sublayer 8a , and the second free magnetic sublayer 8c are composed of CoFe. The nonmagnetic interlayers 6b and 8b are composed of Ru. The nonmagnetic layer 7 is composed of Cu, and the protective layer 9 is composed of Ta.
A resist layer R1 is formed on the composite film T. The width of the resist layer R1 in the track width direction (X direction in the drawing) is substantially the same as the track width of the magnetic sensing element.
Referring to FIG. 17, both uncovered portions of the composite film T are removed by ion milling at angle θ from the normal line such that the composite film T has a trapezoidal cross-sectional shape. The angle θ of ion milling is about 5°.
Referring to FIG. 18, on each side of the composite film T, an insulating layer 10 of alumina, a CoPt hard bias layer 11, and an insulating layer 12 of alumina are formed by sputtering. The resist layer R1 is removed, and a Cu upper electrode layer 13 and a NiFe upper shield layer 14 are formed on the composite. A magnetic sensing element shown in FIG. 19 is thereby obtained.
The magnetic sensing element shown in FIG. 19 is of spin-valve type. In the spin-valve type, the magnetization of the pinned magnetic layer is adequately pinned in a direction parallel to the Y direction in the drawing while the magnetization of the free magnetic layer is adequately oriented in the X direction, the pinned magnetic layer and the free magnetic layer having an orthogonal magnetization relationship. In response to a leakage magnetic field from a recording medium, the magnetization direction of the free magnetic layer sensitively changes. Such a change of the magnetization direction causes a change in electrical resistance of the magnetic sensing element. As a result, the leakage magnetic field from the recording medium can be detected as a change in voltage due to a change in electrical resistance.
The magnetic sensing element shown in FIG. 19 is of a CPP type in which a sensing current flows perpendicularly to the composite film T, for example, from the upper electrode layer 13 to the lower electrode layer 2.
In the known magnetic sensing element shown in FIG. 19, the upper face of each insulating layer 12 is curved downward near the corresponding side face Ts of the composite film T in the track width direction to form a dent A on the side face Ts. This is because the materials for the insulating layer 10, the hard bias layer 11, and the insulating layer 12 are not sufficiently deposited near the side faces Ts of the composite film T by the hindrance of the resist layer R1, in the step shown in FIG. 18. Furthermore, the alumina insulating layer 12 is etched by an alkaline material used in patterning of the upper electrode layer 13, and the dents A at the side faces Ts become larger.
The dents A cause short-circuiting between the side faces Ts of the composite film T and the Cu upper electrode layers 13 that formed in the dents A. The short-circuiting decreases sensitivity of the magnetic sensing element. In particular, in a bottom spin-valve magnetic sensing element shown in FIG. 19 of which the free magnetic layer 8 is formed above the antiferromagnetic layer 5, short-circuiting causing a decrease in output easily occurs between the sides of the free magnetic layer 8 and the upper electrode layer 13.
If the dents A reach positions B depicted by dot lines in FIG. 19, the upper electrode layer 13 comes into contact with all sides of the free magnetic layer 8, nonmagnetic layer 7, and pinned magnetic layer 6. In such a case, the free magnetic layer 8 and the pinned magnetic layer 6 are short-circuited and the magnetic sensing element is not sensitive to an external magnetic field.
If thick insulating layers 12 are formed to prevent short-circuiting between the side faces Ts of the composite film T and the upper electrode layer 13 as shown in FIG. 20, layers S corresponding to the insulating layers 10, the hard bias layers 11, and the insulating layers 12 formed on the sides and top of the resist layer R1 connect to the insulating layers 12. After the resist layer R1 is removed, the layers S remain as fins C on the insulating layers 12 as shown in FIG. 21. An upper electrode layer 13 formed on the insulating layers 12 with fins C cannot have a reproducible shape; hence, the connection resistance between the composite film T and the upper electrode layer 13 varies.
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