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Browse Prior Art Database

Corrosion Protection Methods for Thin Film Heads in DASD

IP.com Disclosure Number: IPCOM000108817D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 104K

Publishing Venue

IBM

Related People

Billings, RA: AUTHOR [+6]

Abstract

Methods for controlling the electrical potential between an inductive thin film recording head pole piece and a thin film disk in a direct access storage device (DASD) and for minimizing the positive electrical potential difference between the thin film head pole pieces and the thin film disk are disclosed. This is done to counteract electrical corrosion and electrostatic discharge on the pole piece, which is accelerated by having a positive electrical potential on the thin film head pole relative to the disk.

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This is the abbreviated version, containing approximately 52% of the total text.

Corrosion Protection Methods for Thin Film Heads in DASD

       Methods for controlling the electrical potential between
an inductive thin film recording head pole piece and a thin film disk
in a direct access storage device (DASD) and for minimizing the
positive electrical potential difference between the thin film head
pole pieces and the thin film disk are disclosed.  This is done to
counteract electrical corrosion and electrostatic discharge on the
pole piece, which is accelerated by having a positive electrical
potential on the thin film head pole relative to the disk.

      Typical construction of a thin film inductive head includes a
pancake coil 1 surrounded by an insulator 2 and two pole pieces 3
which form the gap used to magnetically interact with the disk media.
Although the insulating material between the coil and pole piece has
typically high resistance, 10s to 100s of megohms, the pole piece
will float to the same potential as the coil because the leakage
resistance 4 to the conductive slider body 5 has much greater
resistance than that from the coil to the pole piece (see Fig. 1).

      For small DASD, the industry standard power supply inputs are 5
volts and 12 volts.  DASD internal circuits are typically powered
from these potentials.  The coil of the thin film head is biased with
a current driven by a circuit powered from the 5- or 12-volt source
which results in the coil being biased above ground.  In the typical
application, the disk is electrically connected to ground through a
spindle-bearing contact or a conductive ferrofluid to prevent
electrostatic charging. For a driver circuit using pull-up resistors,
in a half bridge configuration, the coil will float to the supply
voltage when the coil bias current is inactive (turned off).

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