Writable and Rewritable CD’s

By

Thomas Szychowski

The CD

Written from inside out TOC is written first Last two mm left open Three types

– Pressed– CD-R– CD-RW

Pressed CD

Data is pressed on an aluminum layer

Physical Pits and Lands

Data is seen through the transition from one depth to another

Differences from Pressed and “burned” CDs

Pressed– Metallic layer with different heights

Burned– Everything is generally at the same height– Reflection is manipulated using lasers to create

differences– Compounds are dyes that are responsive to

localized heat

CD-R

CD – Recordable Data kept on an organic dye compound

– Normally reflective

Laser “burns” areas in the die to represent a bump– Heats the dye to a critical point to change the materials

properties– Burned areas are far less reflective than non-burned ones

Permanent and irreversible

CD-RW

CD – Rewritable Phase changing data layer Data is kept on a special combination of antimony, indium, silver and tellurium

– Reflective originally Three laser powers

– Read power Lowest power setting

– Erase power More powerful than Read-power Sets the compound from Dull back to original state when cooled

– Write power most powerful Creates a non-reflected area

– Heated area is non-crystalline when cooled

Laser Power – CD-R

cyanine dye – 6.5 mW at burn-speed of 1x– Faster burn speed means more powerful laser.

Phthalocyanine– Alternative to cyanine dye– Excellent longevity– Lower powered laser at 1x – 5.5mW

Laser Power – CD-RW

Power levels– Read State

Low power– Low enough to not affect the chemical compound

– Erase State Medium power

– Temperature is below the melting point, but above the crystalline temp (~200ºC)

– Atoms revert to crystalline form– Write State

Highest power– Temperature rises to 500ºC to 700ºC – creates an amorphous state

Questions

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