Writable and Rewritable CD’s

1. Writable and Rewritable CD’s By Thomas Szychowski

2. The CD • Written from inside out • TOC is written first • Last two mm left open • Three types • Pressed • CD-R • CD-RW

3. Pressed CD • Data is pressed on an aluminum layer • Physical Pits and Lands • Data is seen through the transition from one depth to another

4. 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

5. 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

6. 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

7. 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

8. 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

9. Questions ?