Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Method for Improving Reliability of Magnetoresistive Heads Used in a Sector Servo Application

IP.com Disclosure Number: IPCOM000103236D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 165K

Publishing Venue

IBM

Related People

Ottesen, HH: AUTHOR [+2]

Abstract

The sector servo method is an effective means for positioning the recording head, especially in situations where thermal stress is a problem. In applications with few disks it is preferable to a dedicated servo because it uses less disk area.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 45% of the total text.

Method for Improving Reliability of Magnetoresistive Heads Used in a Sector Servo Application

      The sector servo method is an effective means for positioning
the recording head, especially in situations where thermal stress is
a problem.  In applications with few disks it is preferable to a
dedicated servo because it uses less disk area.

      The relevant aspect of the sector servo scheme is the presence
of the sector data fields on the same surfaces as the data so that
the data heads, not a dedicated servo head, perform the servo
function.

      The MagnetoResistive (MR) head represents a new recording head
technology which has enormous potential in disk drives, primarily due
to the large signal available. The MR head operates on the principle
that certain materials exhibit a change in resistance in the presence
of a changing magnetic field.  This change in resistance can be
transformed into a voltage signal by passing a constant current
through the MR element.  In this sense, it is a parametric device and
so the output signal will be larger if the sense current is
increased.  An upper limit on the sense current arises because of
reliability concerns. Electromigration of the alloy constituents
within the MR layer is a function of the current density and the
temperature.  Eventually this process leads to catastrophic failure
of the device.

      Increasing the sense current past the normal operating point
will drastically decrease the expected lifetime of the device.  Even
at the normal sense current, the lifetime of the device is limited
and is usually less than the lifetime of the disk drive in which it
is used.  This is not a problem in most applications because the
readback duty cycle for any given head is low enough, and the sense
current is applied only during the read operation.

      A problem does arise when MR heads are used in a sector servo
application.  In the usual sector servo implementation one head could
be active during the entire time that the disk driver functions
performing the servo function. Present MR heads do not have a long
enough lifetime for such usage.

      Disclosed is a modification of the sector servo scheme for
lengthening the life of an MR head by minimizing power on hours for
on MR head.  The servo system exists in one of several states of
readiness each of which differs in the level of performance and in
the degradation imposed by electromigration.  The states change
automatically to provide the least active mode, and thus the least
degradation of the MR head, consistent with the needs of the system.
In the most active mode, system performance is the same as usual.  In
the least active mode, the integrated current through all heads is
kept low enough so that the reliability is maintained.  The
integrated current is reduced through a combination of duty cycle and
current reductions.

      Host 1 sends a command to File Data Controller 2 for either a
read o...