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Browse Prior Art Database

Optical Storage System With a Beam Addressable Switch

IP.com Disclosure Number: IPCOM000121668D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 3 page(s) / 105K

Publishing Venue

IBM

Related People

Brady, MJ: AUTHOR [+3]

Abstract

Disclosed is an optical storage system with a bit cell consisting of a photovoltaic (PV) cell and a light-emitting diode (LED) connected by a beam-addressable persistent switch. This switch can be left in the conductive (on or "1" state) by a laser pulse of appropriate length, duration, power and wavelength. The persistent switch can be reset to the nonconductive (off or "0" state) by a different laser pulse. Fig. 1 shows a circuit diagram of the bit cell. Fig. 2 shows a cross section and a plane view of the storage cell as used in a beam-addressable storage disk. The disk can be fabricated by the usual deposition techniques on a single crystal silicon substrate. With suitable buffer layers, it is possible to grow GaAs LEDs epitaxially on silicon.

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Optical Storage System With a Beam Addressable Switch

      Disclosed is an optical storage system with a bit cell
consisting of a photovoltaic (PV) cell and a light-emitting diode
(LED) connected by a beam-addressable persistent switch.  This switch
can be left in the conductive (on or "1" state) by a laser pulse of
appropriate length, duration, power and wavelength.  The persistent
switch can be reset to the nonconductive (off or "0" state) by a
different laser pulse.  Fig.  1 shows a circuit diagram of the bit
cell. Fig. 2 shows a cross section and a plane view of the storage
cell as used in a beam-addressable storage disk.  The disk can be
fabricated by the usual deposition techniques on a single crystal
silicon substrate.  With suitable buffer layers, it is possible to
grow GaAs LEDs epitaxially on silicon.  The PV can be made in the Si
by suitable doping or in the epitaxial GaAs layer.

      One example of a class of materials suitable as a beam
addressable persistent switch are materials that show persistent
photoconductivity.  For example, Indium (In)-doped cadmium manganese
telluride, Cd1-xMnxTe, becomes conductive when exposed to light of
about 1 eV at low temperatures.  This "conductive" state will persist
for long periods after the 1 eV light is turned off, as long as the
material is not heated above a critical temperature, Tcr, e.g., about
100oK for the CdMnTe type materials.  This temperature is determined
by the activation barrier necessary to release the trapped
photoexcited carriers.  If the sample is heated above Tcr, it is
reset to the nonconductive initial state.

      An example of a material which can be thermally switched from a
semiconductor to a metal is VO2 .  It undergoes a phase transition at
around 68oC from a semiconductor to a metal.  There are two important
changes in physical properties at the transition temperature.  One,
the index of refraction, undergoes a reasonably large change, WnZ0.5.
There is also a large change in resistivity, typically about 4 orders
of magnitude, from a high resistance (semiconductor) to a low
resistance metal regime.  It has a reasonably large hysteresis range
where the change in resistance approaches 100% of the maximum change.
A ty...