Methods and apparatus to fabricate soft magnetic film with preferred uniaxial anisotropy for perpendicular recording

1. Technical Field

The present invention relates in general to perpendicular recording media for hard disk drives and, in particular, to an improved system, method, and apparatus for fabricating soft magnetic film with preferred uniaxial anisotropy for perpendicular recording.

2. Description of the Related Art

In perpendicular recording media, the soft magnetic underlayer (SUL) film gets thinner as the write pole head gets smaller with increasing areal density. An anti-parallel (AP) coupled SUL structure (e.g., two SULs separated by an Ru spacer) is widely used in disk drives because of its remnant state of cancelled magnetic moments between the two SULs. Uniaxial anisotropy of the SUL is induced by a radial cathode magnetic field during sputter deposition. The cathode field strength should be higher than the AP exchange field, Hex, in order to induce radial anisotropy.

As for the second SUL deposited onto the Ru spacer, the initial deposited layer experiences a very high AP exchange field having a direction opposite to the cathode field direction. Moreover, its anisotropy direction (i.e., the magnetic easy axis) can be tilted out of the radial direction or rotated into a circumferential direction if the Hex is strong enough to exceed the radial cathode field. As the layer gets thicker, the Hex decreases sharply and then the cathode field can readily overcome the Hex to align the anisotropy to the radial direction. Inducing radial anisotropy in an AP-coupled SUL becomes an issue as the SUL thickness decreases.

As shown in FIG. 1 , for a SUL (Bs=1.2 T) thickness below about 12 nm, the Hex 11 is higher than the cathode field (e.g., about 60 Oe), which makes it difficult to align the radial anisotropy of the top SUL. In this case, the dispersion of the second SUL anisotropy is observed due to interference between the cathode field and the Hex. However, as a result of this, the saturation field 21 ( FIG. 2 ) of the SUL in the circumferential direction is reduced. Thus, an improved solution for fabricating soft magnetic film with preferred uniaxial anisotropy for perpendicular recording would be desirable.

Embodiments of a system, method, and apparatus for fabricating AP-coupled SUL film with good radial anisotropy are disclosed. For example, one type of cathode design has a field direction that is parallel to the direction of the Hex of the second SUL with a magnetically-pinned first SUL. In addition, an SUL structure having a low AP exchange energy also is disclosed.

In one embodiment, the SUL structure combines the cathode field direction of the SUL 2 with the pinned SUL 1 . The SUL 1 is magnetically pinned to the pinning layer and the pinning direction is parallel to the direction of the cathode field applied during deposition of the SUL 1 . High Hc ferro-magnetic materials may be deposited onto a heated substrate that is magnetized along the radial direction by the cathode field. For an SUL thickness below 18 nm, the pinning field is higher than the cathode field, indicating that the cathode field during deposition of the SUL 2 cannot disturb the magnetic state of the SUL 1 pinned to pinning layer.

The cathode field direction of the SUL 2 may be opposite to the cathode field direction of the SUL 1 . With this method, the cathode field direction is in the same direction as the AP exchange field. Applying Hex to the SUL 2 results in strong uniaxial anisotropy along the radial direction during deposition of the SUL 2 layer.

In another embodiment, an SUL structure reduces the AP exchange energy, Jex which results in lower Hex. With lower Jex, the Hex over a wide range of SUL thicknesses is decreased, resulting in the condition, H(cathode)>Hex, even at SUL thicknesses below 10 nm. The Hex may be significantly reduced, leading to the required condition, H(cathode)>Hex. By controlling Ru thickness at different SUL thickness, the Hex can be adjusted to satisfy the condition of H(cathode)>Hex.

In another embodiment, Jex is reduced to change and optimize the magnetization (Bs) of the SUL. Because of the interfacial nature of Jex, lower Bs of the SUL results in lower Jex. The Hex as well as Jex can be reduced by a factor of 2 as Bs changes from 1.2 T to 0.8 T. A low-Bs SUL can shift down the Hex at every SUL thickness level, which leads to the condition: H(cathode)>Hex. Moreover, by employing a low-Bs SUL only at the Ru interface (which reduces Jex but with a majority of high-Bs SUL in the SUL structure), average magnetization of the SUL can be maintained at a high level, but the Hex can be reduced to meet the requirement: H(cathode)>Hex. In this composite SUL structure, low-Bs at the Ru interface may be in the range of 0.3 to 0.8 T, and high-Bs may be in the range of 1.0 to 2.4 T.

The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.

So that the manner in which the features and advantages of the present invention, which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings which form a part of this specification. It is to be noted, however, that the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.

FIG. 1 is a plot of the exchange field performance of a conventional soft underlayer (SUL) structure;

FIG. 2 is a plot of the saturation field performance of the SUL structure of FIG. 1 ;

FIG. 3 is a schematic sectional side view of one embodiment of a SUL structure constructed in accordance with the invention;

FIG. 4 is a plot of the pinning field performance of the SUL structure of FIG. 3 as a function of SUL thickness;

FIG. 5 is a schematic sectional side view of another embodiment of a SUL structure constructed in accordance with the invention;

FIG. 6 is a plot of the exchange field performance of the SUL structure of FIG. 5 as a function of SUL thickness;

FIG. 7 is a plot of the performance of another embodiment of a SUL structure constructed in accordance with the invention;

FIG. 8 is a plot of performance for SUL structures having different thicknesses constructed in accordance with the invention;

FIG. 9 is a plot of performance for another embodiment of a SUL structure constructed in accordance with the invention; and

FIG. 10 is a schematic sectional side view of still another embodiment of a SUL structure constructed in accordance with the invention.

Referring to FIGS. 3-10 , embodiments of a system, method and apparatus for fabricating anti-parallel (AP) coupled soft magnetic underlayer (SUL) film with good radial (e.g., preferred uniaxial) anisotropy are disclosed. The invention is particularly well suited for applications at SUL thicknesses below 15 nm. For example, one type of cathode design has a field direction that is parallel to the direction of the Hex of the second SUL with a magnetically-pinned first SUL. In addition, a SUL structure having a low AP exchange energy also is disclosed.

In one embodiment ( FIG. 3 ), the SUL structure 31 combines the cathode field direction 33 of the SUL 2 with the pinned SUL 1 . The SUL 1 is magnetically pinned to the pinning layer 35 and the pinning direction 37 is parallel to the direction of the cathode field 39 applied during deposition of the SUL 1 . The pinning layer 35 may be formed from, for example, CoPt, CoPtCr, CoPtCrTa, CoPtCrB, etc., with high coercivity, Hc. For example, the pinning layer may be provided with a coercivity in a range of 1 kOe to 5 kOe. The high Hc ferro-magnetic materials may be deposited onto a heated substrate that is magnetized along the radial direction by the cathode field 39 .

Referring now to FIG. 4 , the pinning field 37 as a function of SUL thickness (e.g., Bs=1.2 T) is shown. For an SUL thickness below 18 nm, the pinning field is higher than the cathode field 39 . This indicates that the cathode field 33 during deposition of the SUL 2 cannot disturb the magnetic state of the SUL 1 pinned to pinning layer 35 .

As shown in FIG. 3 , the cathode field direction 33 of the SUL 2 may be opposite to the cathode field direction 39 of the SUL 1 . With this embodiment, the cathode field direction 33 is in the same direction as the AP exchange field (Hex) 41 . Applying Hex 41 to the SUL 2 during deposition of the SUL 2 layer results in strong uniaxial anisotropy along the radial direction. The polarity of the cathode field 33 in the SUL 2 station can be changed by, for example, either (1) rotating the poles of permanent magnets by 180 degrees away from those in the SUL 1 station, or (2) changing the current direction of the cathode electromagnets in the SUL 2 vs. SUL 1 when the cathode utilizes electromagnets.

In another embodiment ( FIG. 5 ), an SUL structure 51 reduces the AP exchange energy, Jex, which results in lower Hex 53 ( FIG. 6 ). For example, the SUL structure may be provided with an AP exchange energy in a range of 0.01 to 0.20 erg/cm 2 . With lower Jex, the Hex over a wide range of SUL thicknesses is decreased, resulting in the condition, H(cathode)>Hex, even at SUL thicknesses below 10 nm.

For example, the Jex may be reduced by one of two methods: (1) increasing Ru spacer thickness, or (2) decreasing magnetization (Bs) of the SUL. In addition, the Jex may be provided in a range of 0.01 to 0.1 erg/cm 2 . The change 71 in Hex with Ru spacer thickness is shown in FIG. 7 for SUL layers (e.g., Bs=1.2 T) for thickness of about 8 nm. By increasing Ru thickness from 0.45 nm to up to about 0.7 nm, the Hex is significantly reduced as shown, leading to the required condition, H(cathode)>Hex. By controlling Ru thickness at different SUL thicknesses, the Hex can be adjusted to satisfy the condition of H(cathode)>Hex. FIG. 8 illustrates the suggested Ru thickness 81 for different SUL thickness (e.g., Bs about 1.2 T) to meet the condition: H(cathode)>Hex by about 20 Oe.

In another embodiment, Jex is reduced to decrease and optimize the magnetization (Bs) of the SUL. Because of the interfacial nature of Jex, lower Bs of the SUL results in lower Jex. As shown in FIG. 9 , the Hex 91 as well as Jex 93 can be reduced by a factor of 2 as Bs changes from about 1.2 T to 0.8 T. A low-Bs SUL can shift down the Hex at every SUL thickness level, which leads to the condition: H(cathode)>Hex.

Moreover, by employing a low-Bs SUL only at the Ru interface (which reduces Jex but with a majority of high-Bs SUL in the SUL structure), average magnetization of the SUL can be maintained at a high level, but the Hex can be reduced to meet the requirement: H(cathode)>Hex. In this composite SUL structure (see, e.g., schematic example shown in FIG. 10 ), low-Bs layers 101 , 101 at the Ru interface 105 may be in the range of 0.3 to 0.8 T, and high-Bs layers 107 , 109 may be in the range of 1.0 to 2.4 T. Low-Bs materials may comprise, for example, FeCoTaZr, FeCoTaZrB, FeCoTaZrBSi, FeCoTaZrMoB, CoB, CoFeSiB, CoFeB, CoZrTa, CoZrNb, or CoZrTaNb; and high-Bs materials may comprise FeCoTaZr, FeCoB, FeCoBCr, FeCoTaB, FeCoTa, FeCoTaCr, etc.

While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, the invention also is suitable for magnetic media applications such as magnetic tape.