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Read/ Write Magneto-optic Structure With Improved Reflective/ Capping Layer

IP.com Disclosure Number: IPCOM000121777D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 96K

Publishing Venue

IBM

Related People

Brusic, VA: AUTHOR [+4]

Abstract

Disclosed is a read-write magneto-optic (MO) structure with an aluminum alloy reflector/capping layer. The aluminum is alloyed with 3-30% of Ta, Nb, Ti, Cr, or Mo. These alloys are super-saturated solid solutions containing solute far in excess of the equilibrium solid solubility and have far superior resistance to attack by chlorides than pure Al, the material most commonly used for this application.

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Read/ Write Magneto-optic Structure With Improved Reflective/ Capping
Layer

      Disclosed is a read-write magneto-optic (MO) structure
with an aluminum alloy reflector/capping layer.  The aluminum is
alloyed with 3-30% of Ta, Nb, Ti, Cr, or Mo.  These alloys are
super-saturated solid solutions containing solute far in excess of
the equilibrium solid solubility and have far superior resistance to
attack by chlorides than pure Al, the material most commonly used for
this application.

      There are two types of MO effects which are utilized in
storage:  the Kerr effect, in which polarized light is simply
reflected off the surface of an MO film and the rotation of the
reflected beam is measured, and the Faraday effect, in which the
rotation of polarized light passing through the MO film is measured.
A slight variation of the second method utilizes a reflecting layer
behind the MO layer to allow for multiple passes of light through the
MO layer, thereby enhancing the Faraday signal.

      On either side of the MO layer are dielectric layers that
minimize reflection loss off the MO layer and provide thermal and
environmental isolation as well.  MO materials typically contain a
large concentration of a rare earth element that is very susceptible
to environmental interaction and degradation.  While the dielectric
layers are somewhat protective, a metal layer, such as aluminum, is
typically deposited on top of the second dielectric layer as a cap
for additional protection.  In the transmission (Faraday) storage
mode, the capping layer also acts as a mirror layer to allow a second
pass of light through the media.  In this mode, the MO and second
dielectric layers are thinner than in the Kerr effect mode as the
beam must pass through them.  The metal capping/reflector layer must
also be thinner to prevent excessive heat loss.  As a result, it it
especially important for the capping/ reflector layer to be corrosion
resistant and to provide environmental protection for the MO layer.

      In practice the aluminum layers employed in these applications
have been shown to be susceptible to pitting corrosion.  Once pitting
corrosion has occurred, the MO layer is vulnerable to corrosion
attack as well and the functionality of the storage disk can be
compromised.  By alloying Al with several other elements, including
but not limited to Mo, Ta, Nb, Ti and Cr, a...