Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-11-03
2001-02-06
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192200, C204S192220, C075S230000, C075S244000, C075S245000, C075S246000, C428S065100, C428S411100, C428S432000, C428S433000, C428S690000, C428S692100, C428S900000, C428S698000, C420S466000, C420S128000, C420S008000
Reexamination Certificate
active
06183606
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention includes the method for producing high coercivity FePt—Si
3
N
4
granular composite thin films that may be used for high-density magnetic recording media.
2. Description of the Prior Art
For a long time now, the most important problem in magnetic recording medium has been how to increase its recording density. A high recording density medium needs high coercivity Hc and optimum remnant magnetization Mr for giant magnetic resistance (GMR) and MR read-heads.
At present, the CoCrPtM (M=Ni, Ta, W) alloy thin films are the most widely used magnetic recording materials for hard disk drive, due to their high coercivity (Hc>2800 Oe). However, these alloy thin films have two disadvantages for high recording density applications: (1) media noise is too high, and (2) coercivity is not enough, therefore the recording density can not be increased. For these metallic films, the most significant problem is the noise that results from magnetic exchange coupling between the grains located at the domain transition region (Jian-Gang Zhu, “Transition Noise Properties in Longitudinal Thin Film Media”, IEEE Trans. Magn. Vol. 29, no.1, pp.195-200, 1993). On the other hand, if the areal recording density of the metallic film is to be increased, the grain size of the film must be reduced (D. N. Lambeth, E. M. T. Velu, G. H. Bellesis, L. L. Lee, and D. E. Laughlin, “Media for 10 Gb/in
2
Hard Disk Storage: Issues and Status”, J. Appl. Phys., 78(8), pp.4496-4501, 1996). However, due to the lack of enough space among grains to reduce the magnetic exchange coupling between the grains, even the grain size of the continuous metallic film is decreased to single-domain size, the high media noise will lead to read-write error and system instability. (E. I. Kondorsky, “On the stability of certain magnetic modes in fine ferromagnetic particles”, IEEE Trans. Magn. Vol. 15, no.5, pp.1209-1214, 1986).
To improve the disadvantages of cobalt-based alloy thin films described above, the present inventors have invented high coercivity granular thin films with FePt particles dispersed in a non-magnetically amorphous Si
3
N
4
matrix, for use as a recording media for higher density magnetic recording. Since the magnetic FePt particles in these granular films are isolated, the media noise of the films can be largely reduced. In addition, by using high magnetocrystalline anisotropy FePt particles as recording material, the recording bits of this granular film can be reduced and recording density of the film will be increased, provided that the write ability of magnetic head is strong enough. These granular films for recording media has many other good properties such as oxidization resistance, corrosion resistance and wear resistance due to the magnetic particles being surrounded by an insulator material Si
3
N
4
.
SUMMARY OF THE INVENTION
The object of the present invention is to fabricate high coercivity FePt—Si
3
N
4
granular thin films for high-density magnetic recording media.
A granular FePt—Si
3
N
4
thin film with soft magnetic &ggr;-FePt particles dispersed in amorphous Si
3
N
4
matrix was prepared by the co-sputtering of a FePt target and Si
3
N
4
target on a low temperature substrate. After an optimum heat treatment, a high coercivity FePt—Si
3
N
4
granular thin film with magnetic hard &ggr;
1
-FePt particles dispersed in amorphous Si
3
N
4
matrix is obtained. The granular thin film has a magnetic easy-axis parallel to the film plane.
Magnetic granular thin film has an especially artificial structure. Usually, the magnetic properties of granular thin film are different from that of continuous metal thin film due to the fact that the magnetic particles of granular film are isolated by non-magnetic material. Changing the non-magnetic material content of the film will change the magnetic particles' inter-particle distance, particle size, and particle shape. These parameters all directly affect the magnetic properties of the film.
The present inventors use FePt alloy as the magnetic particles of granular film media due to its high magnetocrystalline anisotropy constant (K
u
{tilde over (=)}7×10
7
erg/cm
3
), high curie temperature, and good stability. (M. Watanabe, T. Nakayama, K. Watanabe, T. Hirayama and A. Tonomura, “Microstructure and magnetic properties of high-coercive Fe—Pt alloy thin films”, Mater. Trans., JIM. 37, pp.489-493, 1996). The high coercivity granular FePt—Si
3
N
4
thin films produced by the method of the invention may be one of the most promising candidates for future high-density magnetic recording media. The method of the present invention includes using magnetron co-sputtering of a FePt and a Si
3
N
4
target at a controlled sputtering power and argon gas pressure to form a selective composition of granular FePt—Si
3
N
4
thin films on a low temperature substrate. The as-deposited film has a granular structure and soft magnetic properties. After annealing in a vacuum, the soft magnetic &ggr;-FePt particles of as-deposited film are transformed into hard magnetic &ggr;
1
-FePt phase with a very high coercivity. These annealed films can be used for magnetic recording media.
REFERENCES:
patent: 5824409 (1998-10-01), Sellmyer et al.
patent: 6007623 (1999-12-01), Thiele et al.
Han et al, IEEE Trans. Magnetics, 33(5), pp. 3610-3612, Sep. 1997.
Kuo et al, J. Appl. Phys. 87(1), pp. 419-426, Jan. 2000.
Kuo Chih-Ming
Kuo Po-Cheng
Birch & Stewart Kolasch & Birch, LLP
Diamond Alan
National Science Council of Republic of China
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