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24 August 2004
Magnetic Random Access Memory (MRAM)Magnetic Random Access Memory (MRAM)
Jimmy ZhuABB Professor in Engineering
Department of Electrical and Computer EngineeringCarnegie Mellon University
J. Zhu, 18-200 Lecture, Fall 2004 2
Computer SystemComputer System
DRAM
SRAM
Disk Drive
CPU
SRAM
TLB
SRAM
DRAM
L1 Cache
L2 Cache
Main Memory
Archival Memory
Volatile Memory
Non-Volatile Memory
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J. Zhu, 18-200 Lecture, Fall 2004 3
Static RAM (SRAM)
6-Transistor CMOS SRAM Access time: < 1 ns
Expensive:
Fast:
Cache Memory
$100 / MByte
Low Density:
>120 F2
F -- minimum fabrication feature size
= 10-9 second
J. Zhu, 18-200 Lecture, Fall 2004 4
Field Effect Transistor (FET)
symbol
D
S
G Source
Gate
Drain n+n+ p
n-channel FET
Conducting metal plate
Insulating oxide layer
Semiconductor
Conducting ground
MOSFET: Metal-Oxide-semiconductor-FET
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J. Zhu, 18-200 Lecture, Fall 2004 5
electron with charge –e
http://www.pbs.org/transistor/science/info/transmodern.html
TGG VV >
Source
Gate
Drain
n+n+
++ + + + + + +
DI
p
DDV
GGV
n-channel FET
S D
G
Active condition:
TGS VV >i.e.
S
D
GDR
DDV
Drain current will be a function of gate voltage.
Di
How a FET Works: Transistor On
J. Zhu, 18-200 Lecture, Fall 2004 6
How a FET Works: Transistor Off
Source
Gate
Drain n+n+ p
electron with charge –e
No current
S
DG
DDD VV =
DR
DDV
TGS VV <
S
D
Gthreshold voltage TV
Cutoff condition:
Zero Drain current.
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J. Zhu, 18-200 Lecture, Fall 2004 7
A Modern CMOS ProcessA Modern CMOS Process
p-well n-well
p+
p-epi
SiO2
AlCu
poly
n+
SiO2
p+
gate-oxide
Tungsten
TiSi2
DualDual--Well TrenchWell Trench--Isolated CMOS ProcessIsolated CMOS Process
VDD
Vin Vout
M1
M2
J. Zhu, 18-200 Lecture, Fall 2004 8
Dynamic RAM Dynamic RAM
Individual access time 60 ns+++ + ++ +
−−−−−−−
CQV =
0=V
State “1”
State “0”
Main Computer Memory
All “1”s need to be refreshed every 1 ms.
$4 /MByte
10 F2
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J. Zhu, 18-200 Lecture, Fall 2004 9
Rotational Latency
7,500 – 15,000 rpm
sector
track
• Average latency: 3 – 6 ms
• Wait until desired sector passes under head
Rotational Latency
• Worst case: a complete rotation 7,500 rpm = 8 ms
15,000 rpm = 4 ms
Inexpensive: $0.001/1MByte
J. Zhu, 18-200 Lecture, Fall 2004 10
Hard Disk Drives
Magnetic Force Microscopy Image of A Disk Surface
18-316 Introduction to Data Storage
18-517 Data Storage Systems Design
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J. Zhu, 18-200 Lecture, Fall 2004 11
1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3
1E-3
0.01
0.1
1
10
100
HDD
DRAMPr
ice
Per M
Byte
($)
Access Time (second)
SRAM
Price vs. Speed Price vs. Speed
J. Zhu, 18-200 Lecture, Fall 2004 12
Computer System on a Chip?Computer System on a Chip?
Can one change the disk drive into a high speed memory chip?
DRAM
SRAM
Disk Drive
CPU
SRAM
TLB
SRAM
DRAM
If one can, one can put the entire computer system on a single chip:
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J. Zhu, 18-200 Lecture, Fall 2004 13
Control Data Corp. 1Kbits Ferrite Core Memory
1965
Motorola4Mbits MRAM Chip
Magnetic tunnel junction 2003
Magnetic RAM: Historical Perspective
Honeywell 16Kbits MRAM ChipAMR Technology 1994
J. Zhu, 18-200 Lecture, Fall 2004 14
Remember Magnet !Remember Magnet !
Magnetic moment can maintain its direction without power !
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J. Zhu, 18-200 Lecture, Fall 2004 15
Tunnel barrier
CoFe/Al2O3 (7-20Å) /Co
Magnetic electrode
m1
m2
Magnetic electrode
Magnetic Tunnel Junction (MTJ)
Memory Element
0 20 40 60 80 1000.0
0.5
1.0
1.5
2.0
2.5
Res
ista
nce
(kΩ
)
Data Bits
State “0” State “1”
J. Zhu, 18-200 Lecture, Fall 2004 16
Memory ArrayMemory Array
“L” “L” “L” “L”
“L”
“H”
“H”
“L”
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J. Zhu, 18-200 Lecture, Fall 2004 17
Detailed Structure
Magnetic moments are fixed.
State “0” State “1”
Only the magnetic moment of a storage layer is switched back and forth.
J. Zhu, 18-200 Lecture, Fall 2004 18
Writing Bits Writing Bits
I
Hr
I IState “0” State “1”
H
M
Mr
Mr
State “0”
State “1”
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J. Zhu, 18-200 Lecture, Fall 2004 19
X-Point Addressing X-Point Addressing
I
half-select elements
x
y
I
-1.0 -0.5 0.0 0.5 1.0
-1.0
-0.5
0.0
0.5
1.0
Y-C
ompo
nent
Fie
ld (H
k)X-Compone Field (Hk)
3/23/23/2yxk HHH +=
J. Zhu, 18-200 Lecture, Fall 2004 20
MRAM Cell
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J. Zhu, 18-200 Lecture, Fall 2004 21
4 Mbits MRAM Chip4 Mbits MRAM Chip
Freescale 4Mbits MRAM Chip
J. Zhu, 18-200 Lecture, Fall 2004 22
MRAM: Dream Memory?MRAM: Dream Memory?
Advantages of MRAM:
Nonvolatile (No power needed to maintain memory states)
SRAM Speed (~ 1 nanosecond )
DRAM Density (~ 20 F2 )
Endurance (Infinitely rewritable)
MRAM has the potential to be an universal memory to replace SRAM, DRAM, FLASH, and disk drives in some applications to become the
Universal Solid-State Memory!
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J. Zhu, 18-200 Lecture, Fall 2004 23
A Potential Game ChangerA Potential Game Changer
If MRAM replaces SRAM, DRAM or even disk drives:
Instant on systems: No booting from disk drive
Minimum stand-by power (Turn it off!)
Enable computer system to be integrated on a single chip!
J. Zhu, 18-200 Lecture, Fall 2004 24
Applications
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J. Zhu, 18-200 Lecture, Fall 2004 25
System on Chip (SoC)System on Chip (SoC)
Function Module
Computing (processing)
Memory
NV Memory
Example:
RF Module
Data Processing
Memory
SoC
J. Zhu, 18-200 Lecture, Fall 2004 26
MRAM: Dream Memory?MRAM: Dream Memory?
Present MRAM Technology Shortfalls:
Relatively high power dissipation (high current)
Down-size scaling not clear (thermal magnetic stability)
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J. Zhu, 18-200 Lecture, Fall 2004 27
X-Point Addressing X-Point Addressing
I
half-select elements
x
y
I
-1.0 -0.5 0.0 0.5 1.0
-1.0
-0.5
0.0
0.5
1.0
Y-C
ompo
nent
Fie
ld (H
k)X-Compone Field (Hk)
3/23/23/2yxk HHH +=
99.999% of power is dissipated as I2R on the write lines!
J. Zhu, 18-200 Lecture, Fall 2004 28
Digital Line with cladding
Word Line with Cladding
Read Transistor
Magnetic Cladding (18-303 Electromagnetics)
x 5
The main power consumption arises from the ohmic dissipation, I2R, in word/digital lines.
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J. Zhu, 18-200 Lecture, Fall 2004 29
Thermally Activated Reversal
08.0 xx HH =
Hx
t2 ns
τrise= 0.3 ns
0.2 µm
0.1 µm
E
Angle
J. Zhu, 18-200 Lecture, Fall 2004 30
The Potential Universal Memory
SRAM DRAM Disk Drive FLASH
Speed
MRAM
Cost
Density
Cyclability
Non-volatility
Power consumption
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J. Zhu, 18-200 Lecture, Fall 2004 31
MRAM: The enabling technology for computer systems on a single chip!
Only Continued Innovation Will Ensure Future Competitiveness of MRAM
Conclusions
J. Zhu, 18-200 Lecture, Fall 2004 32
Data Storage Systems Track
18-220
18-30318-316
18-517
18-396
Eng. ElectromagneticsIntro. to Data Storage Tech.
Data Storage Sys. Design18-715
18-716
Signal & Sys.
Physics of Appl. Magn.
Advanced Appl. Magn.
Fundamentals of E.E.
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J. Zhu, 18-200 Lecture, Fall 2004 33
Building a Virtual Disk Drive using MATLAB/SIMULINKBuilding a Virtual Disk Drive using MATLAB/SIMULINK
Equalizer
Detector
Data to be recorded Retrieved signal
Recovered data
18-517 Data Storage Systems Design
J. Zhu, 18-200 Lecture, Fall 2004 34
18-315 Fall 2004
Introduction to Optical Communication Systems
Professor Jimmy Zhu
Course Objective:Provide a basic understanding of present optical communication systems and components, as well as future engineering challenges.
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J. Zhu, 18-200 Lecture, Fall 2004 35
1 8 5 0 1 9 0 0 1 9 5 0 2 0 0 0 2 0 5 011 01 0 01 k1 0 k1 0 0 k1 M1 0 M1 0 0 M
1 G1 0 G1 0 0 G1 T1 0 T1 0 0 T1 P
Bandwidth Explosion
Dat
a R
ate
Cap
acity
(bi
ts/s
econ
d)
Year
Voice-centric Network
Doubles every 4.7 years
Doubles every 9 months
Data-centric Network(Optical)
Fiber
WDM
DWDM
Coax
Telephone
Telegraph
Video on demand
World wide web
O.S.
Source: Agilent Technologies
J. Zhu, 18-200 Lecture, Fall 2004 36
FactsA single optical fiber is capable of transmiting 2x1012 bits of data per second, which is equivalent to
simultaneously carry more than 30,000,000 phone conversations, or
200,000 users download (upload) information at 10 Mbits/second data rate at same time, or
download all 380 CDs (each with 1 hour long music) in 1 second , or
download 30 DVD movies in 1 second .
Present dense wavelength division multiplexing (DWDM) technology is realizing the full potential of a single optical fiber !
A optical fiber cable may contain up to 200 fibers.
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J. Zhu, 18-200 Lecture, Fall 2004 37
Fiber-Optical Long-Haul Routes Source: KMI
J. Zhu, 18-200 Lecture, Fall 2004 38
Metro Optical NetworkSource: Nortel Networks e.g. 10 Gbits Ethernet
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J. Zhu, 18-200 Lecture, Fall 2004 39
Course Coverage
How light carries information Generation of lightLight traveling in a fiber Amplification of Light
FiberLEDSemiconductor lasersFiber AmplifiersOptical receiversOptical modulatorsOptical couplers and switches
Time Division Multiplexing (TDM)Wavelength Division Multiplexing (WDM)Optical networks
Light
Systems
Devices and Components
18-315 Introduction to Optical Communication Systems
Encoder Laser driver Amp. Decoder
Fiber receiverlaser
J. Zhu, 18-200 Lecture, Fall 2004 40
prepare students with up-to-date education ready for the optical communication and network industry.
Provide students sufficient background knowledge for further career development in optical communication systems and networks.
Stimulate students’ ability for innovation.
Train students’ problem analyzing and problem solving abilities.
This course is designed to: