Transcript Memory Devices

ERD Memory Discussion
Victor Zhirnov
July 10, 2011
San Francisco, CA
Outline
u
u
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ERD Memory Tables/Text Updates
Memory Select Device Section
Storage Class Memory Section
2
ERD Memory Tables
2011 Memory Transition Table
IN/OUT (Table ERD5)
Emerging Ferroelectric
Memory
IN
Redox memory
IN
Mott Memory
IN
FeFET Memory
OUT
Electronic effects memory
OUT
Nanothermal memory
OUT
Nanoionic memory
OUT
Spin Torque Transfer MRAM
OUT
Reason for IN/OUT
Replaces former FeFET
category and the
ferroelectric
polarization/electronc effects
memory categories
Comment
Replaces former
nanothermal and Ionic
memory categories
Separated from the
electronic effects memory
Merged with FeFET and the
ferroelectric
polarization/electronc effects
memory
Replaced by EFM and Mott
Merged with Ionic Memory to
form Redox Memory
Category
Merged with Nanothermal
Memory to form Redox
Memory Category
Became a prototypical
technology
Spin Torque Tranfer MRAM is
already included in PIDS chapter
since 2009 (Tables PIDS5 and
PIDS 5A)
4
2011 ERD Memory Table
Emerging
Ferroelectric
memory
Storage Mechanism
Nanomechanical Redox
Memory
Memory
Remnant polarization on Electrostaticallya ferroelectric gate
controlled mechanical
dielectric
switch
Mott Macromolecular Molecular
Memory
Memory
Memories
Ion transport
and
Multiple
Multiple
Multiple mechanisms
mechanisms
mechanisms
redox reaction
Cell Elements
Device Types
1T or 1T1R
1T1R or 1D1R
1T1R or 1D1R
1) nanobridge
1) cation
migration
2) telescoping CNT
2) anion
migration
FET with FE gate
insulator
FTJ
1T1R or
1D1R
Mott
transition
1T1R or 1D1R
1T1R or 1D1R
M-I-M (nc)-I-M
Bi-stable
switch
3) Nanoparticle
5
Emerging Ferroelectric Memory
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Combines two subcategories:
v
v
u
Should not be confused with conventional ferroelectric
memory or FeRAM
v
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Ferroelectric FET
Ferroelectric tunnel junction
Based on FE capacitor
Is currently in PIDS
Temporary working name:
v
v
Emerging Ferroelectric Memory
Suggestions are welcome
6
Emerging Ferroelectric Memory
u
Text update: completed
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Table ERD5 update: Work in progress
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References update: Work in progress
7
Nanomechanical Memory
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Text update: completed
v
De-emphasized CNT-based nanomechanical memory
(earlier Nantero concept)
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Table ERD5 update: Work in progress
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References update: Work in progress
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RedOx Memory
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Replaces former nanothermal and Ionic memory
categories
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New text based on the materials from Barsa Workshop
(white papers and presentations)
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Numbers in Table ERD5 updated
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References update: Work in progress
9
Macromolecular Memory
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Text update: Work in progress
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Table ERD5 update: Work in progress
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References update: Work in progress
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Molecular Memory
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Text update: Work in progress
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Table ERD5 update: Work in progress
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References update: Work in progress
11
Input Received
Alex Bratkovski (HP)
Table ERD5/Redox Memory
Curt Richter (NIST)
Table ERD5/Redox Memory
Eric Pop (U Illinois)
Table ERD4/PCM
An Chen (GLOBALFOUNDRIES) Table ERD5/Mott Memory
Rainer Waser (U Aachen)
Text / References
Hiro Akinaga (AIST)
Text / References
12
Memory Select Device
Wei Lu (U Michigan)
An Chen (GLOBALFND)
Dirk Wouters (IMEC)
Kwok Ng (SRC)
Victor Zhirnov (SRC)
Memory Select Device TWG:
Wei Lu (U Michigan)
An Chen (GLOBALFND)
Dirk Wouters (IMEC)
Kwok Ng (SRC)
Victor Zhirnov (SRC)
The fundamental study team
Rainer Waser (U Aachen)
Thomas Vogelsang (RAMBUS)
Zoran Krivokapic(GLOBALFND)
Al Fazio (Intel)
Kyu Min (Intel)
U-In Chung (Samsung)
Matthew Marinella (Sandia Labs)
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Memory Select Device: Intro
•A memory cell in array can be viewed as being composed of two
fundamental components: the ‘Storage node’, and the ‘Select
device’ to minimize sneak current through unselected cells.
•Both components impact scaling limits for memory.
•Several advanced concepts of resistance-based memories offer
storage node scaling down below 10 nm, and the memory density
will be limited by the select device.
•The select device thus represents a serious bottleneck for
memory scaling to 10 nm and beyond.
15
Suggested select device categories
Select
devices
Transistor
Switchbased
selector
Diode
Planar
p-n junction
Vertical
Schottky
junction
Heterojunction
Mott
transition
switch
Threshold
switch
Resistive
switch
Mixed ionic
electronic
conduction
(MIEC)
Complementary
resistive switch
structure
Planar FET select device
(8-9)F2
L. Li, K. Lu, B. Rajendran, T. D. Happ, H-L. Lung, C. Lam, and M. Chan, “Driving Device Comparison for PhaseChange Memory”, IEEE Trans. Electron. Dev. 58 (2011) 664-671
17
Vertical Select Devices
Vertical diode
Vertical FET
L. Li, K. Lu, B. Rajendran, T. D. Happ, H-L. Lung, C. Lam, and M. Chan, “Driving Device Comparison for PhaseChange Memory”, IEEE Trans. Electron. Dev. 58 (2011) 664-671
18
Vertical Select Devices
Vertical diode
4F2
Vertical FET
5.3F2
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Vertical Transistor Select Devices
Experimental demonstrations of vertical transistors in memory arrays.
Technology Memory Type
Infineon (2004)1
Samsung (2010)2
170 nm
80 nm
DRAM
DRAM
Array
size
1 Mb
50 Mb
Hynix&Innovative
Silicon (2010)3
Numonix (2009)4
54 nm
Z-RAM
-
45 nm
PCM
1Gb
5.5F2
BJT
NTHY&ITRI
(2010)4
A*STAR (2008)5 **
180 nm
ReRAM
-
4F2*
BJT
25 nm
(NW dia)
-
-
-
NWGA
A FET
*
Cell size Transist
Ion
Von Ion/Iof
or
f
2
8F
DG FET 50mA 1.8V 1010
4F2
GAA
30mA 1.2V 1011
FET
DG FET
0.5V
300m 2V
A
100m 1.2V
A
25mA 1.2V
107
projected cell size
potential as a select device (not demonstrated)
**has
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Two-terminal selector devices
u
External 2-terminal structure with non-linear characteristics
n
n
u
e.g. switching diode-type behavior for unipolar memory cells
for bipolar cells, selectors with two-way switching behavior are
needed, e.g. Zener diode, avalanche diode etc.
Storage element with inherent rectifying/isolation properties
I
ION1
ON2
ION
OFF
OFF
unipolar
ON1
V
bipolar
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Benchmark Select Device Parameters
Parameter
Value
Driver
Compatibility with logic; low-power operation
ON Voltage, Vr
~1 V
ON current, Ir
~10-6 A
ON/OFF ratio*
>106
Sufficiently low ‘sneak’ currents **
Operating
85°C
The top end spec for servers.
temperature
50°C
NAND spec (the very embodiment of non- volatile
Sensing of memory state (fast read)
memory for the current state-of-the-art),
*ON/OFF
current ratio at ~(1V) supply
alternative schemes of array biasing could result in relaxed requirements on the select device ON/OFF ratio [5]
**Proposed
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Diode-type Select Devices
u
u
u
u
u
u
pn-diode,
Schottky diode
Heterojunction diode
Unipolar cell
BARITT diode
Zener diode
Reverse breakdown Schottky diode
Bipolar cell
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Diode-type Select Devices
Selector type
pn-diode
Schottky diode
Heterojunction
diode
Material
System
Von1
Poly-Si (E)
1
n-ZnO (E)
1
Ge NW (E)
1
a-Si (I)
1
p-Si (E)
1
Pt/TiO2
1
n-ZnO/p-Si
3
CuO/InZnO
1
Ion1
Von2
Unipolar cell
20 mA
4
2
2×10 A/cm
Ion2
ON/OFF
F
REF
-
105
0.3 mm
van Duuren
2007
45 mA
500 A/cm2
1 mA
500 A/cm2
100 nA
1000 A/cm2
10 mA
1000 A/cm2
6 mA
10 A/cm2
-
-
105
3 mm
Huby 2008
-
-
102
0.5 mm
Wong 2008
-
-
106
100 nm
Lu 2010
-
-
103
1 mm
Lee 2010
-
-
109
245 mm
Hwang
2010
25 mA
250 A/cm2
2.5 mA
1000 A/cm2
-
-
103
100mm
Choi 2010
-
-
103
0.5 mm
Park 2009
2 mm
Toda 2009
Kozicky
2010
Bipolar cell
Zener diode
Reverse
breakdown
Schottky diode
(E)
Cu/n-Si
1
10 mA
-3
10 mA
103
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Switch-type select devices
u
u
u
Innovative device concepts that exhibit resistive switching behavior.
In some of these concepts the device structure/physics of operation
is similar to the structure of the storage node.
A modified memory element could act as select device!
v
v
a ‘nonvolatile’ switch is required for the storage node, while for select
device depending on the approaches non-volatility may not be necessary
and can sometimes be detrimental.
Knowledge gained from studying new memory phenomena can be used
for select device!
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Resistive-Switch-type select devices I
u
Mott-transition switch
v
v
v
is based on the Mott Metal-Insulator transition
a volatile resistive switch,
A VO2-based Mott-transition device has been demonstrated as a selection
device for NiOx RRAM element [Ref: M.J. Lee, “Two Series Oxide Resistors Applicable to High
Speed and High Density Nonvolatile Memory,” Adv. Mater. 19, 3919 (2007).].
v
u
The feasibility of the Mott-transition switch as selection devices still needs
further research.
Threshold switch
v
v
is based the threshold switching in MIM structures caused by electronic
charge injection/trapping
Significant resistance reduction can occur at a threshold voltage and this
low-resistance state quickly recovers to the original high-resistance state
when the applied voltage falls below a holding voltage.
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Resistive-Switch-type select devices II
MIEC switch
observed in materials that conduct both ions and electronic charges – so
called mixed ionic electronic conduction materials (MIEC).
The resistive switching mechanism is similar to the ionic memories.
Complementary resistive switch
the memory cell is composed of two identical non-volatile ReRAM
switches connected back-to-back.
Example: Pt/GeSe/Cu/GeSe/Pt structure
During idle conditions one of the ReRAM switch is off so sneak current is
reduced.
Read involves turning on both ReRAM devices and is destructive.
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Mott-Switch as Select Device
Combined device switching
Threshold Switching
Resistive Switching
Lee 2007
- demonstrated very fast writing and erasing process, 1.5V; 10ns.
- read operation at 0.6V also doesn’t seem to be degraded by switch element
- on/off ratio ~ 103, Ion ~ 400 A/cm2
Threshold switch as Select Device
Current
Current
VReset
VSet
Vread
Voltage
Schematic I-V characteristics of
threshold switch
Voltage
Schematic I-V characteristics of
combined unipolar RRAM devices with
threshold switch as the select device
-Similar to Mott switch, but not restricted by the transition temperature
- Organic Threshold Switch as select device integrated with PCM (Kau 2009)
- 9ns switching speed and 106 endurance demonstrated
- Array data not available. Arrays based on MOS select devices presented
MIEC-Switch as Select Device
Switch device characteristics
Gopalakrishnan 2010
- MIEC switching due to redistribution of Cu ions and associated hole diff. current
- Current scales with BEC area. Needs very thin (~ 13nm) dielectric for high current
- Combined MIEC/PCM device demonstrated with endurance of > 3x104 cycles.
Complementary ReRAM cell
Two identical RRAM devices
connected back-to-back
(1,1)
C-ReRAM 0 = (0,1)
C-ReRAM 1 = (1,0)
(1,0) (1,0)
(0,1)
(1,1)
Vc,set
(0,1)
Vc,reset
Vread
Waser 2010
VT,set<Vread<2VT,reset
(1,0) -> (1,1), -> high read current
(0,1) -> (0,1), -> low read current
Complementary ReRAM cell
CRRAM cell
C-ReRAM based on back-toback Pt/ZrOx/HfOx/BE devices
Read endurance is limited to 105
Lee 2010
Resistive-Switch-type select devices
Source: Philip Wong / Stanford
Select Device
Material System
Mott transition
switch
Pt/VO2/Pt
Threshold
switch
Von1
Ion1
(Jon1)
0.4/0 (400 A/cm2)
.6V
Chalcogenide alloy
(undisclosed)
MIEC switch
~1
Complementary Pt/GeSe/Cu/GeSe/Pt
resistive switch
1
ON/OFF
F
REF
103
Lee 2007
106
Kau 2009
40 nm Gopalakrishnan
2010
600 mA
2400 A/cm2
5 mm
Waser 2010
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Criteria for the evaluation of
selection devices
Parameters
Explanations
Blocking state
resistance
• Measure the resistance from the selection devices in the blocking state; it is
generally a voltage-dependent value
• The higher the blocking state resistance the better
Conductive state
resistance
• Measure the resistance from the selection devices in the conductive state; it is
generally a voltage-dependent value
• The smaller the conductive state resistance the better
Turn-on voltage
• The voltage where the selection devices become sufficiently conductive
Turn-on speed
• How fast the selection devices turn on, which affect switching dynamics
Turn-off voltage
• The voltage where the selection devices become nonconductive (high resistance)
Turn-off speed
• How fast the selection devices turn off, which affect switching dynamics
Operation polarity
• Blocking/conductive states exist in both polarities (suitable for bipolar switching
devices) or each in different polarity (suitable for unipolar switching devices)
Scalability
• How scalable is the selection devices
Linearity
• Linear or nonlinear I-V characteristics in blocking and conductive states
Processing temperature
• Low processing temperature is preferred
Materials
• What materials are required? How available are they? Are they compatible with
the processing of the resistive switching devices?
Structures
• Two terminal or three terminal
Fundamental Issues
For scaled diode-type select devices two fundamental
challenges are:
Contact resistance
Lateral depletion effects
Very high concentration of dopants are needed to minimize
both effects.
high dopant concentrations result in increase reverse currents
in classical diode structures and therefore in reduced ON/OFF
ratio.
For switch-type select devices the main challenges are:
identifying the right material
and the switching mechanism to achieve the required drive
current density, ON/OFF ratio and reliability.
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Selection Devices Summary
Experimental two-terminal select devices have yet to
meet the benchmark specifications
Hence, outstanding research issues persist
2011 MSD tables and text reflects both target parameters
and experimental status
More detailed benchmarking and further analysis is
currently underway
Currently no data from functional arrays based on twoterminal select devices are available
36
Solid-State Storage Class Memory
SCM Team:
Barry Schechtman (INSIC)
Rod Bowman (Seagate)
Geoff Burr (IBM)
Bob Fontana (IBM)
Michele Franceschini (IBM)
Rich Freitas (IBM)
Kevin Gomez (Seagate)
Mark Kryder (CMU)
Antoine Khroueir (Seagate)
Kroum Stoev (Western Digital)
Winfried Wilcke (IBM)
Thomas Vogelsang (RAMBUS)
Matthew Marinella (Sandia Labs)
Jim Hutchby (SRC)
Victor Zhirnov (SRC)
38
Storage-class memory (SCM)
Research and development efforts are underway
worldwide on several nonvolatile memory technologies
that not only complement the existing memory but also
reduce the distinction between memory and storage1
Memory: fast, evanescent, random-access, expensive
Storage: slow, permanent, sequential-access, inexpensive
Storage-class memory (SCM): Emerging solid-state
technologies with (some) attributes of both memory and
storage devices
May eventually replace discs and (perhaps) DRAM1
1 “Storage-class
memory: The next storage system technology”, by
R. F. Freitas and W. W. Wilcke, IBM J. Res. & Dev. 52 (2008)
439
Draft Section on SCM is Completed
Storage-class memory (SCM) describes a device category that
combines the benefits of solid-state memory, such as high
performance and robustness, with the archival capabilities and
low cost of conventional hard-disk magnetic storage.
Such a device requires a nonvolatile memory technology that could
be manufactured at a very low cost per bit.
As the scalability of flash is approaching its limit, emerging
technologies for non-volatile memories need to be investigated
for a potential “take over” of the scaling roadmap for flash.
In principle, such new SCM technology could engender two
entirely new and distinct levels within the memory and storage
hierarchy, located below off-chip DRAM and above mechanical
storage, and differentiated from each other by access time.
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Hard-disk Drive
Conventionally, magnetic hard-disk drives are used for
nonvolatile data storage.
The cost of HDD storage (in $/GB) is extremely low and
continues to decrease.
Issues:
poor random access time
relatively high energy consumption,
large form factor,
limited reliability.
41
Flash memory: Device Challenges
NAND flash has recently become an alternative storage technology
faster access times,
smaller size and potentially lower energy consumption, as compared to
HDD.
The NAND-based solid state drive (SSD) market has flourished recently.
There are several serious limitations of NAND flash for storage
applications
poor endurance (104 – 105 erase cycles),
modest retention (typically 10 years on the new device, but only 1 year at
the end of rated endurance lifetime),
long erase time (~ms), and high operation voltage (~15V).
42
Flash SSD: Architectural Challenges
Page/block-based architecture,
doesn’t allow for a direct overwrite of data,
requiring sophisticated garbage collection
bulk erase procedures,
Computation-intensive data management
Takes extra memory space,
Limits performance
Accelerates the wearing out of memory cells.
Lower power potential compromised in current SSD
implementations
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Flash Scaling Challenges
Flash memory scaling doesn’t improve (and sometimes
degrades) the basic performance characteristics
read, write and erase latencies have been nearly constant for
over a decade
Extreme scaling results in the degradation of retention time
and endurance,
critical for storage applications!
There are opportunities for prototypical and emerging
memory technologies to enter the non-volatile solid state
memory space.
44
Prototypical and emerging memory
technologies for SCM applications
As the scalability of flash is approaching its limit,
emerging technologies for non-volatile memories need to
be investigated for a potential “take over” of the scaling
roadmap for flash.
It appears that storage applications could be the primary
driver for the new memory technologies,
may help to overcome the fundamental shortcomings of
flash technology.
In principle, such new SCM technology could engender
two entirely new and distinct levels within the memory
and storage hierarchy, located below off-chip DRAM and
above mechanical storage, which are differentiated from
each other by access time.
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I. S-type storage-class memory
The first new level, identified as S-type storage-class
memory (S-SCM), would serve as a high-performance
solid-state drive
accessed by the system I/O controller much like an HDD.
S-SCM would need to provide at least the same data retention as
flash,
offering new direct overwrite and random access capabilities
(which can lead to improved performance and simpler systems)
However, it would be absolutely critical that the device cost for SSCM be no more than 1.5-2x(1-1.5x? IN THE MATURE STATE))
higher than NAND flash
If the cost per bit could be driven low enough through ultrahigh
memory density, ultimately such an S-SCM device could potentially
replace magnetic hard-disk drives in enterprise storage server
systems.
46
II. M-type storage-class memory
M-SCM:
should offer a read/write latency of less than 1 ms.
would allow it to remain synchronous with a memory system,
allowing direct connection from a memory controller and
bypassing the inefficiencies of access through the I/O
controller.
Would be to augment a small amount of DRAM to provide the
same overall system performance as a DRAM-only system,
while providing
Moderate retention,
Lower power-per-GB and lower cost-per-GB than DRAM.
Endurance is particularly critical
the time available for wear-leveling, error-correction, and other similar
techniques is limited

> 109 cycles
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Target device and system
specifications for SCM
Parameter
Benchmark
Target
HDD*
NAND flash**
DRAM
Read/Write
latency
3-5 ms
~100ms
(block erase ~1
ms)
Endurance
(cycles)
Retention
ON power
(W/GB)
unlimited
Standby power
Areal density
Cost ($/GB)
* enterprise
<10 ns
Memory-type
SCM
<0.3ms
Storage-type
SCM
1-10ms
105
unlimited
>109
108
>10 years
~0.04
~10 years
~0.01-0.04
64 ms
0.4
~10 years
Lower (per
GB) than HDD
~20% ON
power
~ 1011 bit/cm2
0.1
<10% ON
power
~ 1010 bit/cm2
2
~25% ON
power
~ 109 bit/cm2
10
>5 days
Lower (per
GB) than
DRAM
<1% ON
power
>109 bit/cm2
Lower than
DRAM
class
**single-level cell (SLC)
<1% ON
power
>109 bit/cm2
Within (1.5-2x?)
of NAND
Flash
48
Prototypical and emerging memory
technologies for SCM applications
Necessary attributes of a memory device for the storageclass memory applications are:
Scalability
Multilevel Cell - MLC (MLC vs extreme scaling dilemma)
3D integration (stacking)
Fabrications costs
Endurance (for M-SCM)
Retention (for S-SCM)
The driving issue is to minimize the cost per bit
49
Potential of the current prototypical research
memory candidates for SCM applications
Parameter
FeRAM
STT-MRAM
PCRAM
Scalability
low
medium
good
MLC
no
difficult
yes
good
excellent
average
3D integration
Fabrication cost
Endurance
A likely introduction of these new memory devices to the market is by the
hybrid solid-state discs, where the new memory technology
complements the traditional flash memory to boost the SSD
performance.
Experimental implementations of FeRAM/flash and PCRAM/flash have
recently been explored. It was shown that the PCRAM/Flash hybrid
improves SSD operations by decreasing the energy consumption
and increasing the lifetime of flash memory.
50
Potential of the current emerging research
memory candidates for SCM applications
Parameter
Ferroelectric Nanomechanical
memory
memory
Redox
memory
Mott
Memory
Macromolecular
memory
Molecular
Memory
Scalability
MLC
3D integration
Fabrication cost
Endurance
51
“Traffic Light” indicators
Green: this entry has good progress; there are no or few issues.
Yellow: this entry’s potential is not clear; there is a number of issues.
Red: this entry’s potential is questionable; there is a list of issues.
Message might be softer, a bit more proactively positive (or at least hopeful).
52
Proposal from Toshiba
Table 1 (current version)
Parameter
Benchmark
Target
HDD*
NAND flash**
DRAM
Read/Write
latency
3-5 ms
~100ms
(block erase ~1
ms)
Endurance
(cycles)
Retention
ON power
(W/GB)
unlimited
>10 years
~0.04
Standby power
~20% ON
power
Areal density
Cost ($/GB)
~ 1011 bit/cm2
0.1
* enterprise
class
**single-level cell (SLC)
<10 ns
Memory-type
SCM
<0.3ms
Storage-type
SCM
1-10ms
105
unlimited
>109
108
~10 years
~0.01-0.04
64 ms
0.4
>5 days
Lower (per
GB) than
DRAM
<1% ON
power
~10 years
Lower (per
GB) than HDD
>109 bit/cm2
Lower than
DRAM
>1010 bit/cm2
Within (1.5-2x?)
of NAND
Flash
<10% ON
power
~ 1010 bit/cm2
2
~25% ON
power
~ 109 bit/cm2
10
<1% ON
power
54
Table 1 (proposed)
Parameter
Memory-type SCM
Target
Benchmark
STT(DRAM)
MRAM
Read/Write
latency
<0.3ms
Endurance
(cycles)
Retention
ON power
(W/GB)
>10
Standby
power
Areal
density
<10 ns
30ns
<10 ns
9
unlimited
10
15
>5 days
64 ms
20 years
Lower (per
0.4
0.01
GB) than
DRAM
<1% ON
~25% ON
<1% ON
power
power
power
9
2
8
2
~109 bit/cm2 ~ 10 bit/cm ~ 10 bit/cm
Cost ($/GB) Lower than
DRAM
10
50,000
Storage-type SCM
Target
Benchmark Benchmark
*
(NAND
(HDD )
Flash)
3-5 ms
1-10ms
~100ms
(block erase
~1 ms)
8
4
5
unlimited
10
10 -10
>106
~10 years
>10 years
~10 years
Lower (per
~0.04
~0.01-0.04
GB) than
HDD
<1% ON
~20% ON <10% ON
power
power
power
>109 bit/cm2
~ 1011
~ 1010
Within 2-3x
of NAND
Flash
bit/cm2
0.1
bit/cm2
2
Other proposals
How about to mention about emerging NVM
technologies? Such as FusionIO, NVM express, and so
on.
How about to merge Table 2 and 3?
Architectural Implications
Advances in SCM could drive the emerging data-centric chip
architectures
Nanostores
Nanostores architectures could be an important direction for the future
of information processing.
Addressed in the ERA section
Computer, Jan. 2011
57
Input Received
Atsuhiro Kinoshita (Toshiba)
Dirk Wouters (IMEC)
Rainer Waser (U Aachen)
Thomas Vogelsang (RAMBUS)
Matthew Marinella (Sandia Labs)
Geoff Burr (IBM)
Bob Fontana (IBM)
Kevin Gomez (Seagate)
Mark Kryder (CMU)
Paul Frank (INSIC)
58