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Adjustable Read Bias Current for Enhanced Head Reliability

IP.com Disclosure Number: IPCOM000102126D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 92K

Publishing Venue

IBM

Related People

Kerwin, GJ: AUTHOR

Abstract

Long term reliability of a Magneto-Resistive (MR) is effected by the amplitude of the current used to bias the read transducer. This is due to the current density dependency of the long term failure mode of this type of head, material migrating from the read element. Within the operating range of the bias current, a significant difference in the rate of migration can be realized. The graph in Fig. 1 shows a curve of the read hours versus the probability of failure (excessive metal migration). A significant increase in the operation time can be realized for the same reliability if the bias current is reduced.

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Adjustable Read Bias Current for Enhanced Head Reliability

       Long term reliability of a Magneto-Resistive (MR) is
effected by the amplitude of the current used to bias the read
transducer.  This is due to the current density dependency of the
long term failure mode of this type of head, material migrating from
the read element.  Within the operating range of the bias current, a
significant difference in the rate of migration can be realized.  The
graph in Fig. 1 shows a curve of the read hours versus the
probability of failure (excessive metal migration).  A significant
increase in the operation time can be realized for the same
reliability if the bias current is reduced.

      The signal-to-noise ratio (S/N) of the read signal is also
effected by the amplitude of the bias current such that a lower value
of bias current lowers the S/N of the read signal.  For the purpose
of maintaining the best possible longevity to the transducer, a
method of lowering the MR bias current when read operations with
reduced S/N are permissible, and returning the bias current to a
nominal level for normal read operations has been achieved.

      One of these operations that can perform adequately when the
S/N is at a less than optimal value is reading the servo signal.
Since the servo head, used in a dedicated servo file, reads full
time, it could represent a problem running at a high level of read
bias current.  A way to get around this would be to use either
ferrite or thin film heads for the dedicated servo head.  This option
is not available for a fil...