Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-07-24
2001-04-03
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S900000, C204S192200
Reexamination Certificate
active
06210819
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a longitudinal magnetic recording medium for use in a computer disk drive.
BACKGROUND OF THE INVENTION
Thin-film magnetic recording media formed on a rigid disc substrate are widely used in read/write memory devices in computers. The demand for data storage capacity in such devices has increased dramatically in recent years and disc drives using inductive head technology have a storage capacity, i.e., areal density, on the order of 400 Mb/in
2
, and those using magnetoresistive heads are over 600 Mb/in
2
(Russak, M. R., et al.,
Proc. Electrochem. Soc.,
95(18):143-156 (1996)).
The storage capacity of magnetic media can be improved in several ways, including increasing media coercivity, reducing the magnetic remanence-thickness product, reducing media noise and decreasing the flying height.
A high coercivity is one factor important in achieving a high recording density in a magnetic disc. Coercivity, defined as the magnetic flux required to reduce the remanence magnetic flux to zero, i.e., the field required to erase a stored bit of information. A higher coercivity in a medium allows adjacent recorded bits to be placed more closely together without mutual cancellation. Thus, higher coercivity is associated with higher information storage density.
Magnetic remanence, M
r
, provides a measure of the signal amplitude which can be read from an isolated pulse stored in a magnetic medium. The greater the remanence, or moment, the greater the signal amplitude which can be detected in a reading operation.
Signal-to-noise ratio (SNR) is the ratio of signal amplitude, or peak-to-peak amplitude of a single pulse, as a function of recording frequency, to recording noise at that frequency. A high SNR, due to sinal amplitude and/or low noise, is necessary for high density recording.
Widely used commercial thin-film media are prepared by sputtering a magnetic thin film on a substrate, such as a textured, plated aluminum substrate. The disc is typically prepared by sputtering a chromium underlayer onto the substrate surface, then sputtering the magnetic thin film recording layer over the underlayer.
One approach to improving disc storage density by increasing the coercivity has been to vary the composition and method of preparing the underlayer. For example, an increase in the thickness of the chromium underlayer results in an increased coercivity. (Fisher, R. D. et al.,
IEEE Trans. on Magn.,
22:352 (1986); Johnson, K. E.,
J. Appl. Phys,
67:4686 (1990)).
Another approach to improving coercivity, and hence storage capacity, is to employ certain magnetic alloys which result in improved coercivity, for example, by including platinum in a CoCr-based magnetic recording film.
Another approach to increasing media coercivity is to apply a negative voltage bias to the substrate during sputtering. Typically, an improvement in coercivity is observed when the bias is applied to the substrate during sputtering of the magnetic recording layer, with no improvement, or a reduction in coercivity, achieved with the bias is applied during sputtering of the chromium underlayer (Lal, B. B. and Russak, M. A.,
J. Appl. Phys.,
81(8):3934 (1997)). A voltage bias during sputtering of both the chromium-based underlayer and the magnetic layer can also improve coercivity (Lal, B. B. and Russak, M. A.,
J. Appl. Phys.,
81(8):3934 (1997); U.S. Pat. No. 5,069,983). Others have reported modest increases in coercivity when a bias is applied to the substrate during sputtering of the chromium underlayer (U.S. Pat. No. 5,147,734).
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a magnetic recording medium having an improved coercivity for improved storage capacity.
In one aspect, the invention includes a magnetic recording medium for longitudinal recording, comprising an underlayer film composed of 5-50 atomic percent titanium, balance chromium, deposited on a rigid disc substrate by sputtering in the presence of a negative voltage bias. Sputter deposited directly on the underlayer film is a magnetic recording film composed of an alloy including cobalt and chromium.
In one embodiment, the underlayer film is composed of 15-25 atomic percent titanium, balance chromium. In a preferred embodiment the underlayer is a chromium-titanium alloy composed of 80 atomic percent chromium and 20 atomic percent titanium.
The negative voltage bias applied to the substrate during deposition of the underlayer, in one embodiment, is between 50-750 volts. In another embodiment, the voltage bias is between 50-500 volts.
In another aspect, the invention includes a method of preparing a magnetic recording medium for longitudinal recording. The method includes depositing under a negative voltage bias an underlayer film composed of 5-50 atomic percent titanium, balance chromium, the underlayer being deposited on a rigid disc substrate. Deposited directly on the underlayer film is a magnetic recording film composed of an alloy including cobalt and chromium.
In one embodiment of the method, the underlayer film is composed of 15-25 atomic percent titanium, balance chromium. In a preferred embodiment of the method, the underlayer is a chromium-titanium alloy composed of 80 atomic percent chromium and 20 atomic percent titanium.
The negative voltage bias applied to the substrate during sputtering of the chromium-titanium underlayer is between typically between −50 to −750 volts, more preferably between −50 to −500 volts.
In another aspect, the invention includes an improvement in a method of preparing a longitudinal magnetic recording medium having an underlayer composed of an alloy of chromium and titanium and magnetic recording layer composed of a cobalt-chromium alloy. The improvement is effective to increase the magnetic remanence thickness product by at least about 10%, and includes sputter depositing the underlayer under a negative voltage bias.
These and other objects and features of the invention will be more fully appreciated when the following detailed description of the invention is read in conjunction with the accompanying drawings.
REFERENCES:
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patent: 4743491 (1988-05-01), Asada et al.
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patent: 5456978 (1995-10-01), Lal et al.
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Lal, Brij B. and Michael Russak, “Effects of Cr and magnetic bias on read/write and noise characteristics of CoCrTa/Cr longitudinal thin-film media,” J. Appl. Phys. 81(8) :3934-3936 (1997).
Matsuda, Y., et al., “Reduction of Co-Cr-Pt media noise by addition of Ti to Cr underlayer,” J. Appl. Phys. 79(8) :5351-5353 (1996).
Lal Brij Bihari
Zhang Lan
HMT Technology Corporation
Iota Pi Law Group
Kiliman Leszek
Mohr Judy M.
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