Emerging non-volatile memory (NVM) technologies like MRAM and PCRAM combine the speed of SRAM, density of DRAM, and non-volatility of flash memory. While they have attractive features like high density and non-volatility, they also have undesirable features like long write latency and low endurance. Replacing SRAM caches with MRAM can reduce cache misses but harm performance when write intensity is high due to MRAM's slow writes. A hybrid SRAM-MRAM cache can improve this by reducing MRAM write intensities. Emerging NVM also enables unique applications and new memory hierarchies using technologies like hybrid cache/memory architectures.

1. EMERGINIG
MEMORY
TECHNOLOGY
BY
VIDYA REDDY

2. Position Statement
Emerging NVM are very attractive
 Combing the speed of SRAM, the density of DRAM,
and the non-volatility of Flash memory.
Attractive features
 high density, low leakage, non-volatile.
Undesirable features:
 Write-related: long write-latency, high write-energy.
 low endurance (e.g. PCRAM).
 Cost (Needs large volume production).
Solution: Hybrid cache/mem/storage + 3D?
Enabling unique applications.

3. OUTLINE
 Introduction
 Modelling
-
MRAM/PCRAM modelling
 Architecture
-
MRAM/PCRAM stacking
HCA: Hybrid Cache Architecture
Hybrid storage system
 Application
-
Exascale computing
 Conclusion

4. Memories principles

5. Emerging Memory Technologies
 FeRAM (Ferroelectric RAM)
 MRAM (Magnetic RAM)
 Memristor (Resistive RAM)
 PCRAM (Phase-Change RAM)
Toshba - iFeRAM(2009)
Ever Spin - MRAM(2008)
HP Labs - Memristor (2009)
Samsung - PCRAM(2008)

6. Traditional Memory Hierarchies

7. NVRAM Comparison
 FeRAM, MRAM, or
PCRAM, combines
the advantages of
SRAM, DRAM and
Flash.
 Good opportunity
to rethink the
memory hierarchy
design.

8. Emerging Non-volatile Memory
(NVM)
Magnetic RAM (MRAM)
Phase-change RAM (PCRAM)

9. SRAM vs. MRAM
Area(65nm)
3.66mm2SRAM
3.30mm^2MRAM
Capacity
128KB
512KB
Read latency
2.25ns
2.32ns
Write latency
2.26ns
11.02ns
Read energy
0.90ns
0.86ns
Write energy
0.80ns
5.0ns
Cache configuration
Leakage power
2MB(16*128KB)SRAM Cache
2.09W
8MB(16*512KB)MRAM Cache
0.20W
Pros: Low leakage power, high density.
Cons: Long write latency and large write energy.

10. Cont……..
 High Density
 Low Leakage power and high dynamic power
 Fast Read
 Slow Write
 Low Read Energy High Write Energy
 Reduce cache miss rate and increase hit latency
Replace SRAM caches with MRAM ?

11. Direct Replacement
 Replace SRAM with MRAM of same area.
 The number of banks are kept the same.
 The capacity of L2 cache increases by 4X.

12. Observation 1
Replacing SRAM L2 caches directly with MRAM
can reduce the access miss rate of L2caches.
However, the long access latency to MRAM
cache has a negative impact on the performance.
When the write intensity is high, it even results in
performance degradation.
Direct MRAM replacement may harm performance.
How is power consumption?

13. Power Analysis (Direct Replacement)
1
0.8
0.6
0.4
0.2
0
Total Power (SRAM vs. MRAM)

14. Observation 2
Replacing SRAM L2 caches directly with MRAM
can greatly reduce the leakage power.
When the write intensity is high, the dynamic
power increases significantly because of the high
write energy of MRAM cache.
How to improve the performance and further reduce power of
MRAM?

15. SRAM-MRAM Hybrid L2 Cache
Using hybrid L2 cache,
MRAM write intensities are reduced

16. Comparisons
Feature
SRAM
eRAM
STTRAM/MRAM
PCRAM
Density
Low(1)
High(4)
High(4)
Very High(16)
Speed
Very fast
Fast
Fast for read,
Slow for write
Slow for read,
very slow for
write
Dynamic
power
Low
Medium
Low for read,
Very high for
write
Medium for
read,
high for write
Leakage
power
High
Medium
Low
Low
no volatility
no
Yes
Yes
Yes

17. HCA: Hybrid Cache Architecture

18. HCA: Hybrid Cache Architecture
 A hybrid cache/memory architecture can be used.
 Two possibilities for this are
- an STT-RAM or SRAM hybrid on-chip cache.
- A PCRAM or DRAM hybrid main memory.
 In such a hybrid architecture, instead of building a pure STT-RAMbased cache ,a pure PCRAM-based main memory.
 We could replace a portion of the MRAM or PCRAM cells with
SRAM or DRAM elements, respectively.

19. Emerging NVM Applications

20. General Conclusions
 The emerging NVM business will be very dynamic over the next five
years, thanks to improvements in scalability/cost and density of
emerging NVM chips:
- PCM devices, the densest NVM in 2012 at 1GB, will reach 8GB by
2018 -> could replace NOR Flash Memory in mobile phones and will
also be used as Storage Class Memory in Enterprise Storage.
- MRAM/STTMRAM chips will reach 8 - 16 GB in 2018 -> It will be
widely sold as a Storage Class Memory, and possibly as a DRAM
successor in Enterprise Storage after 2018.

21. Cont……..
-
RRAM will reach between 32GB – 2TB in 2018 thanks to 3D
capability -> gradually be adopted in the Mass Storage market
dominated by NAND technology, in addition to limited market
adoption in lower-density applications like Industrial and Enterprise
Storage.
- FRAM will be more stable in terms of scalability, with 8 – 16MB chips
available by 2018 -> development of new FRAM material could raise
scalability, but we don’t expect it to be widely industrialized and
commercialized before 2018.