Semiconductor Memories (Yu xiang).ppt
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Semiconductor Memories (Yu xiang).ppt Presentation Transcript

  • 1. Semiconductor Memories ECE423 Xiang Yu 12.16.06
  • 2. RAM vs. ROM
    • Volatile
    • RAM (random access)
      • SRAM (static)
        • Synchronous
        • Asynchronous
      • DRAM (dynamic)
        • FPM DRAM
        • EDO DRAM
        • SDRAM
        • DDR SDRAM
        • DDR2 SDRAM
        • Etc..
    • Non-volatile
    • ROM (read only)
      • System/Video BIOS
    • PROM
      • OTP with fuses/anti-fuses
    • EPROM
      • UV light for erasure
    • EEPROM
      • Reprogrammable with software and hardware
      •  Flash Memory
  • 3. SRAM & DRAM
    • SRAM
      • Pros
        • Extremely Fast
        • No refresh cycle
      • Cons
        • Large area - 6T/bit
        • Expensive
      • Applications
        • Memory caches L1 & L2
    • DRAM
      • Pros
        • Cheaper
        • Higher density - 1T/bit
      • Cons
        • Slower in speed
        • Needs refresh cycle
      • Applications
        • Computer memory
  • 4. Flash Memory
    • Pros
    • Non-volatile
    • Portability
    • High Density
      • Floating gate transistor
        • CG and FG
        • MLC technology
    • High Isolation
    • Cons
    • Oxide layers near min. limit
    • High voltage required
    • Slow WRITE cycle
    • Capacitance Coupling
    • Limited Use
  • 5. Focus For Improvement
    • Non-volatility
    • Portability
    • Small Area
    • High Density
    • Faster WRITE/ERASE cycles
    • Lower Power
    • Lower Costs
    • Longevity
  • 6. FRAM
    • FeRAM (Ferroelectric RAM)
      • Uses ferroelectric characteristics of the capacitor
        • lead (Pb) zirconate (Zr) titanate (Ti) - PZT
    • Pros
    • Non-volatile
    • Small size
    • Fast WRITE cycles
    • Cons
    • A potential WRITE after each READ
    • Longevity
    • Polarization degradation
    • Requires high temperatures
    • Want higher densities
  • 7. MRAM
    • Magnetoresistive RAM
      • Uses properties of magnetism and the development of the MTJ
      • Uses STT technology (Spin Torque Transfer)
    • Pros
    • Non-volatile
    • Small size
    • Fast WRITE cycles
    • Longevity
    • Cons
    • Requires high temperatures
    • Want higher densities
  • 8. PRAM
    • Phase-change RAM, PCM, C-RAM (chalcogenide RAM)
      • Uses the special property of chalcogenide alloy
        • Germanium (Ge), antimony (Sb) and tellurium (Te) – GST
        • Switches between amorphous (0) and crystallized (1) states with heat from current
    • Pros
    • Non-volatile
    • Small size
    • High density
    • Fast switching times
    • Cons
    • Requires high current (heat)
    • Longevity
  • 9. Comparisons
    • Overall View
    5 ns 5 ns 20 ns 10 μ s 10 ns 2 ns Write Time > 10 12 > 10 15 > 10 12 10 5 > 10 15 > 10 15 Write cycles No No No No ms No Refresh 1T1R 1TCMTJ 1T1C 1T 1T1C 6T Cell Size 10ns Yes MRAM 10ns 10ns 70ns 10 ns 2 ns Read Time Yes Yes Yes No No Non-volatile PRAM FRAM Flash DRAM SRAM Parameters