the millipede, a very dense, highly parallel …... the millipede, a very dense, highly parallel...
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The Millipede, a Very Dense, Highly Parallel The Millipede, a Very Dense, Highly Parallel Scanning-Probe Data-Storage SystemScanning-Probe Data-Storage System
August 26, 2002August 26, 2002
G. Cherubini, T. Antonakopoulos, P. Baechtold, G. Binnig, G. Cherubini, T. Antonakopoulos, P. Baechtold, G. Binnig, M. Despont, U. Drechsler, A. Dholakia, U. Dürig, E. Eleftheriou, M. Despont, U. Drechsler, A. Dholakia, U. Dürig, E. Eleftheriou, B. Gotsmann, W. Haeberle, M. Lantz, T. Loeliger, H. Pozidis, B. Gotsmann, W. Haeberle, M. Lantz, T. Loeliger, H. Pozidis,
H. Rothuizen, R. Stutz, and P. VettigerH. Rothuizen, R. Stutz, and P. Vettiger
IBM Research DivisionIBM Research DivisionZurich Research Laboratory, SwitzerlandZurich Research Laboratory, Switzerland
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OutlineOutline
Vision and motivationVision and motivation
The "Millipede" conceptThe "Millipede" concept
Thermomechanical writing/reading/erasingThermomechanical writing/reading/erasing
System aspectsSystem aspects
Modeling thermomechanical processModeling thermomechanical process
Summary Summary
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8 10 12 14 16SNR [dB]
1E-3
1E-2
1E-1
1E+0
Sect
or e
rror p
roba
bilit
y RS-MTR96/104LDPC (4095/4376)
PW50/Tu=3.0
> 4.7 dB2.0 dB
Information Theoretic LimitsInformation Theoretic Limits
Millipede
1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Year
0.1
1
10
100
1000
Area
l Den
sity
(Gbi
ts/s
q. in
ch)
PRML
NPMLMTR/parity
Turbo?
Superparamagnetic Effect
Areal Density LimitsAreal Density Limits
Limits of Magnetic StorageLimits of Magnetic Storage
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Probe Storage TechnologyProbe Storage Technology
Zurich Research LaboratoryMicro- and Nanomechanics GroupZurich Research LaboratoryMicro- and Nanomechanics Grouplow cost
high density (> 1011-1012 bits/in2)
Objectives:Objectives:
Atomic Force Microscopy-based, thermomechanical write/read/erase in thin polymer
parallel operation with 1000 levers or more
batch fabrication VLSI MEMS/NEMS
Concept:Concept:
high data rate (> 100 Mb/sec)
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The "Millipede" ConceptThe "Millipede" Concept
Storage mediaon X/Y/Z/Tilt scanner
Multiplex-Driver
x
z 2
z3
z1y
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Thermomechanical Read/Write ResultsThermomechanical Read/Write Results
72 nm pitch125 Gbit/in.2
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Thermomechanical Read/Write Results (cont.)Thermomechanical Read/Write Results (cont.)
200 nm
120 nm
0.5 1 Tb/in.2
Uniform pitch
Ultrahigh density
Variable pitch
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-0.5 0.0 0.5 1.0
1. 2..
Erasing MechanismErasing Mechanism
sample: PMMAµm
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Thermomechanical Erasing at Line Level Thermomechanical Erasing at Line Level
erasing two lines erasing two lines
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Thermomechanical Erasing at Line Level Thermomechanical Erasing at Line Level
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Thermomechanical Erasing at Subfield Level Thermomechanical Erasing at Subfield Level
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Parallel Write/Read with 32x32 Array ChipParallel Write/Read with 32x32 Array Chip
32 columns
32 ro
ws
Individual fields
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Readback Channel CharacteristicsReadback Channel Characteristics
!∏(t) + 1R!(1+"x )C!
(!(t) −!0) = 1C!
Vp2(t)Re(!(t))
Evolution of temperature in Evolution of temperature in response to applied pulse response to applied pulse
R!
C!
"x
Thermal resistance to heat conduction:
Thermal capacitance of cantilever:
Relative change of thermal resistance due to topographic variations ("pit", "no pit"):
Vo∏ (t)+ 1RlpfClpf V0(t) = 1
Re(!(t))ClpfVp(t)
Vp(t)
Applied pulseApplied pulse
Evolution of filtered Evolution of filtered read back signal read back signal
Re(!(t))Temperature dependent cantilever electrical resistance:
∆R/R ~ 10-5
per nm
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Read-back Signal ModelingRead-back Signal Modeling
2-D image of stored bits (experimental data) 2-D image of stored bits (synthetic model)
0 0 0 1 1 1 1 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 1 0 0
Readback signal along a data track (experimental data)
0 1 1 1 1 0 1 1 1 0 1 1 1 1 1 0 1 1 1 0 0 0 1 0 0 0 0 0 0 1 1
Readback signal along a data track (synthetic model)
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Channel Modeling: 2-DimensionalChannel Modeling: 2-Dimensional
Experimental Synthetic
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Channel Modeling: 3-Dimensional Channel Modeling: 3-Dimensional
3-D model of "indentation" in the polymer medium based on simple thermomechanical model
Optimization of SNR for detectionDevelopment of timing and PES (position error signal) algorithmsSimulation of overall system performance under various conditions
Experimental Synthetic
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"Millipede"-based Storage System Architecture"Millipede"-based Storage System Architecture
MILLIPEDECHIP
MICROSCANNER
REC MEDIUM
WRITE DRIVER
INTERLEAVER/DEINTERLEAVERDETECTOR (d,k) ENCODER/
DECODER
ECC
BUFFER RAMSERVO & TIMING
ANALOG SCANNER DRIVER
HOST INTERFACE
MICRO-CONTROLLER
orHARD-WIRED
LOGIC(servo compensator,
defect mapping, power mgmt, temp control,
special commands)
HOST DEVICEINSTRUCTIONROM or FLASH(for ucontroller)
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Layout of Data and Servo/Timing FieldsLayout of Data and Servo/Timing Fields
...
...
...
... ... ... ...Servo/Timing fields are elongated to provide extra information for acquisition purposes Fine position information provided by servo bursts in the servo fields
Servo/Timing FieldData Field
Every lever "sees" its own field: Dedicated fields for Servo and Timing
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Data DetectionData Detection
Readback channelOffset compensation needed to reduce dynamic range of readback signalLow-pass-filter limits bandwidth of high frequency noise
Thresholddecision
Clock rate 1/T
Sensorcantilever
Referencecantilever
Vp(t)
Vp(t)
Rlpf
Clpf
Expe
rimen
tal s
igna
l
Synt
hetic
sig
nal
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Timing RecoveryTiming Recovery
Timing pattern
SYNC (start of data)
Timing recovery based on dedicated clock field
Over-sampling mode of operationFast initial phase/gain acquisitionSecond-order PLL
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PES GenerationPES Generation
Track pitch = 84 nm, Bit pitch = 42 nmTrack pitch = 84 nm, Bit pitch = 42 nmVertical offset between A-B and C-D bursts = 42 nmVertical offset between A-B and C-D bursts = 42 nm
A-burst D-burstC-burstB-burst
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PES Generation Experiment (cont.)PES Generation Experiment (cont.)
Servo demodulation similar to data detectionPES zero-crossings at track centerlinesAlmost linear shape between zeros (unique decodability)
Experimental PES
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(d,k) Coding for "Millipede" (d,k) Coding for "Millipede"
(d,k) codes increase linear density(d,k) codes increase linear densityd=1 and k>6 guarantees existence of code with rate R=2/3d=1 and k>6 guarantees existence of code with rate R=2/3Use of (1,k) codes reduces bit distance by half while maintaining Use of (1,k) codes reduces bit distance by half while maintaining the pitch between 1's, increasing linear density by (4/3)the pitch between 1's, increasing linear density by (4/3)d=2 and k>6 guarantees existence of code with rate R=1/2d=2 and k>6 guarantees existence of code with rate R=1/2Use of (2,k) codes reduces bit distance by a third while maintainingUse of (2,k) codes reduces bit distance by a third while maintainingthe pitch between 1's, increasing linear density by (3/2) the pitch between 1's, increasing linear density by (3/2)
(d,k) codes reduce "interaction" between adjacent 1's (pits) (d,k) codes reduce "interaction" between adjacent 1's (pits) enabling more reliable detectionenabling more reliable detection
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ConclusionsConclusions
Millipede has potential to achieve densities well beyond 500 Gbit/in.Millipede has potential to achieve densities well beyond 500 Gbit/in.22
Attractive as candidate future storage technology due to:Attractive as candidate future storage technology due to:ultrahigh areal densityultrahigh areal densitysmall form factorsmall form factorlow power conslow power consuumption mption
Full overwrite and erase capabilty at subfield level and even at bit level Full overwrite and erase capabilty at subfield level and even at bit level
Reliable operation with small overhead via dedicated servo and timing fieldsReliable operation with small overhead via dedicated servo and timing fields