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