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Contents Introduction Opportunities and Reality of New Types of Memories Technology Scaling and Technology Barriers of New Memories 1) FRAM 2) MRAM 3) PRAM 4. Summary
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Future Memory Technologies in Nano Era
Kinam Kim, Hongsik Jeong* Semiconductor R&D Center Samsung
Electronics Co. Ltd. Contents Introduction
Opportunities and Reality of New Types of Memories Technology
Scaling and Technology Barriers of New Memories 1)FRAM 2)MRAM
3)PRAM 4.Summary History of Memory Device
1947 : The invention of Transistor - William B. Shockley, John
Bardeen and Walter H. Brattain at The Bell Laboratories - Nobel
Prize, 1956 1951 : The invention ofBJT 1955 : The invention of FET
1958-9: First Integrated Circuit - Jack Kilby at Texas Instruments
( 2000, Nobel Prize ) Robert Noyce at Fairchild Camera 1966 :
Invention of DRAM Paper Clip, Ge 1970 : Intel, 1Kb DRAM D/R = 8 m
World First Transistor : Point Contact Memory Density : X 1,000,000
Feature Size : X 1/100 2004 : Samsung, 1Gb DRAM D/R = 0.08 m Memory
Scaling Trend Growing technical complexity, fabrication cost,
physical limit What are showstoppers? ? 2000 2005 2010 2015 2020 20
40 60 80 100 1 10 Design Rule [nm] Density [Gb] FLASH DRAM 25nm
10nm 55nm 100nm 1Gb 8Gb 64Gb 512Gb 256Gb 32Gb 4Gb 512Mb 3rd Node
1st Node 2nd Node -5nm / year 1.41 / year Year Scaling Limit of
DRAM Cell transistor scaling
Gate contact Electric field distribution ( V/cm ) Maximum electric
field Channel length decrease Channel doping increase Electric
field increase Junction leakage currentincrease Retention time
decrease Cell Transistor Technology
3D Cell Structure reducing E-Field Planar Transistor RCAT (
Recessed Cell TR.) FINFETTr. Scaling Limit of NAND Flash
Cell-to-cell coupling CTUN CONO CFGX CFGY CFGXY CFGCG V1 V2 V3 V4
V6 V5 VFG VCG Control gate ONO Floating gate Tunnel oxide Silicon
substrate STI Narrower word-line space Cell-to-cell capacitance
increase Wide distribution of Vth Over-program / under-erase
Scaling Limit of NAND Flash
Cell-to-cell coupling estimation Steep increase of coupling below
40 nm Improvement : - Low-k dielectric - Floating gate height scale
down. Cell transistor scaling Cell to cell interference
Scaling Limit of Memories Lifetimes of conventional memories are
far shorter than that of CMOS Need new memories with longer
lifetime, less technical barriers and betterfunctional properties
Memory & Device Fundamental limiting factor Limit of technology
node DRAM Cell transistor scaling 50 nm NAND Flash Cell to cell
interference 20 nm NOR Flash Si-SiO2 barrier height SRAM CMOS 10 nm
Electron wave length Contents Introduction
Opportunities and Reality of New Types of Memories Technology
Scaling and Technology Barriers of New Memories 1)FRAM 2)MRAM
3)PRAM 4.Summary Characteristics of Emerging New Memories
New Paradigm of IT World requires Ideal Memory - New Materials and
New Function Devices New Function Non-volatility :> 10 years
Fast random access :tRead = 10ns tWrite = 5ns ~ 100ns Virtually
unlimited usage :> 10^12 cycles New Material FRAM: Ferroelectric
Material PZT, SBT, BLT MRAM: Ferromagnetic Material NiFe, CoFe,
PRAM: Chalcogenide GeSbTe, Opportunities of New Memories
Memory management in systems complicated multiple memory simplified
single memory Reduce power consumption mobile system High Speed
Data Storage Merge code and data storage memory Simplify data
changing process Block write (flash) bit-by-bit write enhance
system performance Virtually unlimited endurance No need for
complicated software New applications Instant on PC, Simplified
Data Process / No Buffer Memory
New Memory Applications Mobile Devices Simplified Data Process / No
Buffer Memory Flash + RAM Solution New Memory Solution The
Reduction of Data Storage Time (7sec 7ms)
New Memory Applications High Speed Data Storage The Reduction of
Data Storage Time (7sec 7ms) The Comparison of 2Mb PixelPicture
Storage Time - VGA, 640x480, 420KB Block Erase Program:7000ms NOR
Flash NAND Flash New Memory 1x 245ms 35x 7ms 1,000x The possibility
of Motion Picture or Continuous Taking Photos Emerging Memory
Devices
MRAM ( Magnetic RAM ) FRAM ( Ferroelectric RAM ) PRAM (
Phase-Change RAM ) CellSw. Speed High Speed (~10ns) High
Speed(~10ns) Moderate Speed (>100ns ) Density Low Density Very
Low Density High Density Potential Tunnel Ox. Control ( 1015 105
>1013 Read time 10 ns 2 ns 25 s 70 ns Write time 300 s 10 s 5 ns
200 ns Commercially available memories
DRAM SRAM NAND Flash NOR FRAM Memory capacity 1Gb 64 Mb 2 Gb 128 Mb
256 Kb Tech. node 90 nm 100 nm 120nm 350 nm Cell Area Factor (F2) 8
90 5.3 11 80 New types of memories are only at the early stage of
verification or creating niche market, despite its great potentials
FRAM passed the criteria of commercial product but its density is
still very low Contents Introduction
Opportunities and Reality of New Types of Memories Technology
Scaling and Technology Barriers of New Memories 1)FRAM 2)MRAM
3)PRAM 4.Summary Technology Scaling of FRAM
Cell area scaling WL BL F-Cap. 1.Larger capacitor area for given
footprint 2.Larger remnantpolarization 3.Thinner ferroelectric film
Nonvolatile loose constraint on array transistor Cell Area Scaling
of FRAM
3-mask etch Separate via & plate 700nm cap stack 1-mask etch
Common via & plate 300nm cap stack 3D capacitor Etchless
capacitor Technology Barriers of FRAM
Ferroelectric film thickness scale down Degradation of electrical
and physical properties Lower thickness limit few nm ? Need new
growth technique! Technology Barriers of FRAM
Reliability requirement -Endurance > 1014 cycles -Retention time
> 10 85C 50nm thick MOCVD PZTon Ir Deposition Temp. : 530o C
Fatigue stress : 125oC Bake Contents Introduction
Opportunities and Reality of New Types of Memories Technology
Scaling and Technology Barriers of New Memories 1)FRAM 2)MRAM
3)PRAM 4.Summary MRAM Operations Magnetic tunneling resistance
variation
depending onrelative magnetization directions of electrode Rap Rp
Al2O3 NiFe CoFe Rp Rap Requirements for proper operations
2. Immunity to writing disturbance Resistance uniformity R
Distribution Hard axis field (Oe) Easy axis field Write Window
Reference 1.0 Sensing noise PDF 0.5 0 1 0.0 8 10 R ( k W ) 12 14 16
Only MTJs at the crosspoint of bit-line and digit-line should be
switched - Small ditribution of switching field - Asteroid curve
close to L-shape Large MR ratio Small distribution of resistance
Technology Barriers of MRAM
Small sensing signal TMR ratio = Rap Rp Rp Maximum TMR ratio ?60%
so far. Resistance variation Exponential dependence on Al2O3
thickness Technology Barriers of MRAM
Writing Disturbance Operating condition Possible fail with
Disturbance Need to decrease switching field distribution -
Roughness - MTJ shape - MTJ aspect ratio - Free layer magnetization
- Free layer thickness Technology Barriers of MRAM
Scaling trend ofwritingcurrent Smaller MTJ size Higher switching
field Higher writing current - Power consumption increase - Chip
size increase - Reliability issues Improved by flux concentrating
layer DL BL 0.45 m 0.2 m -100 -50 50 100 -200 200 Bit line field
(Oe) Digit line field (Oe) 1.2x0.6 m 2 0.8x0.4 0.4x0.2 NiFe
Prospects for MRAM Nearly ideal memory
-Non-volatile, fast read and write, unlimited endurance Many
technical barriers Scaling issues large cell size - SOC chip
application is more suitable than stand-alone memory application
Contents Introduction
Opportunities and Reality of New Types of Memories Technology
Scaling and Technology Barriers of New Memories 1)FRAM 2)MRAM
3)PRAM 4.Summary PRAM Operations Reversible phase change of
chalcogenide (Ge2Sb2Te5)
Phase change by heating current control Amorphizing RESET Pulse
(~few ns) Crystallizing SET Pulse ~50ns Tm Tx Time Temp BEC
Crystalline Top Electrode Bottom Electrode Low resistance SET state
: 0 High resistance RESET state : 1 BEC Top Electrode Bottom
Electrode Amorphous Cell area scaling PRAM density vs writing
current
(NMOS Cell Tr) Need enough cell transistor width to flow required
writing current Cell area is mainly determined by cell transistor
width Technology Barriers of PRAM
Large writing current - Require large cell transistor Cell area
increase - Reliability degradation - Current scales down with
contact and GST size ! 0.66x1.28 0.72x0.72 0.66x0.66 0.62x0.62
0.56x0.56 0.48x0.48 0.40x0.40 1.5 2.0 2.5 3.0 3.5 Reset Current (
mA ) GST Size PRAM Writing Current Reduction
Edge contact cell M0 BEC BE GST TEC M1 Contact area is controlled
by BE thickness & width more small and uniform contact area
Reset current reduction by more than 80% Prospects for PRAM Writing
current reduction new structure, new material Intrinsic advantage
for size scaling -High density Feasibility -Stand-alone memory with
moderate speed (Possibility of NOR flash replacement) Contents
Introduction
Opportunities and Reality of New Types of Memories Technology
Scaling and Technology Barriers of New Memories 1)FRAM 2)MRAM
3)PRAM 4.Summary Summary Assessment of memory products
- We needto consider functional and cost aspects at the same time -
Functional aspect : random access, speed, non-volatility,
endurance, - Cost aspect : technical complexity, technical barrier,
technology scaling Prospects for Conventional memories - Non-ideal
functional aspects - Excellent cost aspects - Will be dominant
players down to 30~50nm technology node Summary Prospects for New
types of memory
- Manufacturing and cost aspects are not properly evaluated yet 1)
FRAM : No serious limitations in theory except ferroelectric film
thickness 2) MRAM : Excellent device characteristics, Scaling
difficulty Suitable for SOC chip application 3) PRAM : Less
technical barriers compared to FRAM and MRAM Intrinsic advantage
for size scaling - Future of emerging memory depend on how far we
can keep its key attributes ( ferroelectric cap in FRAM, MTJ in
MRAM, reset current in PRAM)