Crystalline/Amorphous Regions – CD-RW Technology
(Phase Change Technology)
 Phase change is a type of compact disk (CD) recording technology
that enables the disks to be written, erased, and rewritten through
the use of a layer of a special material (called the phase change layer)
that can be changed repeatedly from an amorphous (formless) to a
crystalline state, or phase-through exposure to variably-powered
laser beams.
 Like CD-Recordable (CD-R), CD-RW has a polycarbonate
substrate, which is preformed with a spiral groove to guide the
laser.
 The alloy phase-change recording layer, which is commonly a mix
of silver, indium, antimony and tellurium, is sandwiched between
two dielectric layers that draw excess heat from the recording layer.
 After heating to one particular temperature, the alloy will become
crystalline when it is cooled; after heating to a higher temperature, it
will become amorphous when it is cooled.
 By controlling the temperature of the laser, crystalline areas and
non-crystalline areas are formed.
 The crystalline areas will reflect the laser, while the other areas will
absorb it.
 The differences will register as binary data that can be unencoded
for playback.
 To erase or write over recorded data, the higher temperature laser is
used, which results in the amorphous form, which can then be
reformed by the lower temperature laser.
 According to Sony, the process can be repeated up to 1000 times.