Will Phase Change Memory (PCM) Replace DRAM or NAND Flash? Dr. Mostafa Abdulla High-Speed Engineering Sr. Manager, Micron Marc Greenberg Product Marketing Director, Cadence August 19, 2010 Flash Memory Summit 1
Phase Change Memory (PCM) New memory motivation (recognized ~1999) Current NVM (and DRAM) are becoming electrostatics limited MOS transistor based cell Charge storage memory effect Starting to encounter physical scaling limitations Limitations manifesting first as degradation in reliability (endurance/retention)
Phase Change Memory (PCM) Realization Next-generation NVM will exploit new storage physics Significant innovation will take time (history says ~10 year gestation ) Response PCM identified as the best candidate Research efforts validated the assumptions and initiated development PCM moving into production today We believe features of PCM will enable new usage models
Current [ma] PCM Mechanisms Storage GST: germanium-antimony-tellurium chalcogenide glass Cell states varying from amorphous (high resistance) to crystalline (low resistance) states Read operation Measure resistance of the GST Write operation Heat GST via current flow (Joule effect) Time at critical temperature determines cell state Temperature during write 0.75 0.50 0.25 Crystal Amorphous 0.00 0.0 0.5 1.0 1.5 V th Voltage [V] Crystalline Temperature I T m m T x V Amorphous Reset (amorphization) Set (crystallization) Time
Summary of Key PCM Reliability Metrics Retention decoupled from endurance No issue with READ DISTURB PCM PCM Retention Time NAND Read Endurance NAND P/E Cycles P/E Cycles Result: Management greatly simplified; no software overhead for some apps Post-stress shelf life problem solved Endurance can be increased significantly through management of bit errors; data is stable when successfully written Write Error Rate Wearout is well behaved NAND PCM P/E Cycles
PCM Key Attributes Attribute PCM EEPROM NOR NAND DRAM Nonvolatile Yes Yes Yes Yes No Granularity Small/Byte Small/Byte Large Large Small/Byte Erase No No Yes Yes No Software Easy Easy Moderate Hard Easy Power ~Flash ~Flash ~Flash ~Flash High Write Bandwidth 1 15+ MB/s 13 30 KB/s 0.5 2 MB/s 10+ MB/s 100+ MB/s Read Latency 50 100ns 200 200ns 70 100ns 15 50µs 20 80ns Endurance 10 6+ 10 5 10 6 10 5 10 4-5 Unlimited PCM provides an new set of features combining components of NVM with DRAM
PCM Application Opportunities Wireless systems Direct code execution, semi-static data and file storage Bit alterability allows direct-write memory Solid state storage subsystems Frequently accessed pages and elements easily managed when manipulated in place Caching with PCM will improve performance and reliability Computing platforms Taking advantage of nonvolatility to reduce the power PCM offers endurance and write latency that are compelling for a number of novel solutions
Wireless Systems: LPDDR2-PCM Architecture Evolution Paged SnD Solution Code stored in NVM Code shadowed or paged to DRAM to execute Reliability is a significant concern Significant performance variability PCM/XiP Solution Code stored in PCM Code executed from PCM No reliability concerns for code Limited or no performance variability Paged SnD Solution Code 2Gb NAND Code 2Gb PCM PCM/XiP Solution Processor Code 2Gb+ DRAM 1Gb DRAM Processor
System Benefits of LPDDR2-PCM LPDDR2-PCM system architecture saves DRAM and power Performance mostly equivalent to DRAM PCM system architecture simplifies software Endurance and data retention are fundamentally decoupled, improving TTM PCM opens new usage models Persistent-RAM model (NV + bit alterability) changes application operation
System Benefits of LPDDR2-PCM PCM file system performance close to spec (NAND/NOR lose performance due to erase) PCM user improvements Instant on Boot time Application launch Application concurrency Power PCM reliability improvements PCM overcomes DRAM scaling and NAND reliability concerns
Memory Hierarchy in Servers and Storage Where PCM Can Fit Network Clients Storage Controllers Network Attached Storage Storage Area Networks Local and Remote Memory Servers Direct Attached Storage ns/gb us/gb ms/tb s/pb CPU RAM SSD DISK TAPE PCM replaces battery backed up RAMcache at cabinet and rack levels PCM PCM improves reliability and performance in HDD/SSD PCM for performance-high IOPs and low latency PCM enables improved endurance for logging applications
Memory Hierarchy 1.E+07 Cost/Performance Levels in the Memory Hierarchy 1.E+06 L1 Bandwidth (MB/s) 1.E+05 1.E+04 1.E+03 1.E+02 HDD NAND PCM DRAM L3 L2 1.E+01 Tape 1.E+00 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 Sources: Jim Handy, Objective Analysis Oct 2009, Micron Price per Gigabyte
Summary Phase change memory (PCM) technology is demonstrating the capability to enter the broad memory market and to become a mainstream memory PCM provides a new set of features for novel applications, combining components of NVM and DRAM, while at the same time being a sustaining and a disruptive technology Our prediction is that with PCM achieving technology maturity, having a scaling perspective, and having a broad application range, it will play a key role in the memory market for the next decade