Method for determining lifetime for media thermal decay

Details Method for determining lifetime for media thermal decay Method for determining lifetime for media thermal decay

2000-05-24

2004-02-24

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Monitoring or testing the progress of recording

C360S053000

Reexamination Certificate

active

06697203

ABSTRACT:

RESERVATION OF COPYRIGHT
This patent document contains material subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document, as it pears in the U.S. Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of the Invention
Aspects of the invention relate to a method for estimating media thermal decay based on error rate failure criteria.
2. Description of Background Information
One of the biggest problems for high density recording media is media thermal decay. Until now, no one has proposed da feasible method to quantitatively predict media thermal decay lifetime based on real drive level failure criteria. Much of the published literature has discussed how to determine whether a medium is stable or unstable using a media stability factor, KuV/kT, where Ku is anisotropic energy of a media alloy, V is a switching volume, k is a Boltzmann constant, and T is a media temperature. However, no method has been reported that quantitatively determines the media thermal decay lifetime. Some of the reasons for this may be that the previously used failure criteria for media thermal decay is not well defined or directly related to drive performance, lifetime determination was based mostly on modeled results, and simple test acceleration and straightforward extrapolation from accelerated to non-accelerated conditions were never demonstrated.
Other approaches that have been proposed have included:
a) using critical current to detect noise peaks where the magnetic moment reaches zero. See “Thermal Effects & Recording Performance at High Recording Densities”, by M. Alex & D. Wachenschwanz, IEEE Trans. Mag., Vol 35, page 2796 (1999); and
b) using the time dependence of Hc based on the Sharrock equation to estimate decay time. See “Time Dependence of Switching Fields in Magnetic Recording Media”, by M. P. Sharrock, J. Appl. Phys., vol 15, page 6413 (1994).
SUMMARY
An embodiment of the invention is a method for determining a thermal decay lifetime of a machine-readable medium at a given temperature. A test pattern is written to a portion of the medium. An initial amiplitude of signals on the portion of the medium is measured, A first stress magnetic field is applied to the portion of the medium. After applying the first stress magnetic field, a first amplitude of signals on the portion of the medium is measured. The test pattern is rewritten to the portion of the medium. A second stress magnetic field is applied to the portion of the medium. After the applying of the second stress magnetic field, a second amplitude of signals on the portion of the medium is measured. A time to failure is determined corresponding to the first and the second stress, magnetic fields, respectively, the time to failure being an amount of time, measured from a corresponding reference time, for a respective amplitude of the signals on the medium to degrade, in relation to the initial amplitude, beyond a predetermined failure criteria. A time to failure without applying a stress magnetic field is determined based on a relationship between the corresponding times to failure determined for each of the applied stress magnetic fields and Ln(the corresponding times to failure).


REFERENCES:
patent: 5889784 (1999-03-01), Rogers
patent: 6266199 (2001-07-01), Gillis et al.
patent: 6429984 (2002-08-01), Alex
“Thermal Effects & Recording Performance at High Recording Densities”, M. Alex and D. Wachenschwanz, IEE Trans. Mag., V. 35, pp. 2796-2801 (1999).
“Time Dependence of Switching Fields in Magnetic Recording Media”, M.P. Sharrock, J. Appl. Phys., v. 76 (10), pp. 6413-6418 (1994).

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