Recording Mechanism For Cd-Rs And Cd-Rws; Disc; Overwrite Recording Of Cd-Rw - Pioneer PDR-555RW Service Manual

5. RECORDING MECHANISM FOR CD-Rs AND CD-RWs

5.1 DISC

The PDR-555RW is capable of recording on CD-R discs and of
recording and overwriting on CD-RW discs.
A CD-R has a triple-layered structure (from the bottom, the pigment
recording layer, reflective layer, and protective layer) on a
polycarbonate substrate, as shown in Fig. 5-1.
There are three kinds of pigments: cyanic pigments, phthalocyanin
pigments, and azo pigments. And there are two kinds of reflective
layer: gold and silver.
To record on the disc, a laser beam is shot at the pigment recording
layer to form pits by transforming the pigments by heat.
When the disc is played, the difference in reflectivity between areas
with converted pigments and unconverted pigments is read as a
signal.
Fig. 5-1 CD-R disc
The more complex CD-RW has a five-layered structure (from the
bottom, a dielectric layer, phase-change recording layer, another
dielectric layer, reflective layer, and protective layer) on a
polycarbonate board, as shown in Fig. 5-2.
The phase-change recording layer is a colloid of chalcogen
substances. such as AG-In-Sb-Te4 and Ge-Sb-Te. It becomes a
liquid layer when heated to a high temperature (about 500°C to
700°C), with its atomic structure chaotic. And after being cooled
rapidly, it becomes solid, with its atomic structure still chaotic> It
is non-crystal (in an amorphous state).
It reaches a crystalline state after being heated to a lower temperature
(about 200°C) and being cooled gradually. Lands and pits are made
on the disc by repeating this procedure.
The reflectance is small when the layer is noncrystalline (in an
amorphous state), and it is large when the layer is crystalline. This
difference in reflectivity is read as a signal when the disc is played.
Fig. 5-2 CD-RW disc
PDR-555RW, PDR-V500, PDR-19RW, PDR-509
Transformation of CD-RW
Crystal
Reflectance = Large
Label
Protective coating
Reflective layer
5.2 OVERWRITE RECORDING OF
(gold or silver)
Pigment layer
Polycarbonate
CD-RWs adopt overwriting. New recording can be made in an area
with previous recording as shown in Fig. 5-4.
Previous
recording
New
recording
Label
Protective coating
Reflective layer
(aluminum)
Dielectric layer
Phase-change layer
Dielectric layer
Polycarbonate
Recording
Erasing
Fig. 5-3 Transformation of CD-RW
CD-RW
Record Record
Erase Erase Erase
Fig. 5-4 Overwrite recording of CD-RW
State of amorphous
Reflectance = Small
Record
Record
Erase Erase
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