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Ferroelektrische Schichten und Heterostrukturen: Deposition, Anwendung und „Interface Engineering“*p , g „ g g
H. Kohlstedt
Forschungszentrum Jülich, Institut für Festkörperforschung, IFF
Forschungszentrum Forschungszentrum Jülich *pdf file of this talk: [email protected]
Ferroelectric Materials
(PVDF)PbZrxTi1-xO3 (PVDF)BaTiO3
Polyvinylidene fluoride: [C2H2F2] nBa or Pb
FC+PTi
H
H+P -P
O
CH
-Pc
F
Effects related to Ferroelectric Materials
Piezo electric effect Polarization switch
+/-PF P
P VE
Pyro electric effectC i l t i ff t Pyro electric effect
ΔT
ΔIConverse piezo electric effect
S
P AΔTPL = L ± ΔL
S
E
Technological applicationsFerroelectric RAM’sFerroelectric RAM s Smart cards Portable electronic devices
Ferroelectric
PiezoelectricPiezoelectric
PyroelectricPyroelectric
SAW devices for mobileThermal IR pyroelectric detectors
SAW devices for mobile technology and gas sensing
Ferroelectric Random Access MemoryFerroelectric Random Access MemoryFeRAM
BasicsNanoscale Characterization of Ferroelectric Materials, M. Alexe and A. GruvermanNanoscience and Technology, Spinger-Verlag 2004
Ferroelectric Memories, J. F. Scott, Springer Series in Advanced Microelectronics, (Springer-Verlag Berlin Heidelberg New York 2000)
gy, p g g
Ferroelectric Random Access Memories: H. Ishiwara, M. Okuyama, eds., Topics in Applied Physics, Vol. 93 (Springer-Verlag, Berlin Heidelberg 2004).
(Springer-Verlag, Berlin Heidelberg, New York 2000).
Nanoscale Phenomena in Ferroelectric Thin Films, S. Hong, Kluwer Academic Pub. 2004
Matrix Architecture: Random Access Memory
1T1C ll
DRAM: Dynamic Random Access Memory
Bit line decoder
1T1C cell
TBit line decoder
Sense amplifier
tro
lc
Data
C
ne
de
co
de
r
co
nt
log
ic
Address
C
Wo
rdli
n
DRAM Cell
Word line
Bit line1T1C cell
Word line
TransistorTransistor
DRAM it
Sense Amplifier
DRAM capacitor“1” charged Cap.“0” non charged Cap.CBL
Cmin ≅ 30 fF
Linear dielectric:SiO2, Si3N4, HfO2, etc.
Ferroelectric Capacitor
Electrode
Ferroelectric V∼
ElectrodeElectrode
FeRAM Cell
Word line
Bit line1T1C cell
Word line
TransistorTransistorSense Amplifier
CBLFerroelectric Capacitor
Hysteretic dielectric:PZT, SBT etc.
Ferroelectric Hysteresis
“1”Pr
PbZr Ti O
Metal
P
1
zatio
n Curr
PbZrxTi1-xO3
Metal
P
E“0”
Pola
ri
rent
Electric Field or Voltage
Ec0
Electric Field or VoltagePr = 10 – 80 µC/cm2
Ec = 50 – 300 kV/cm
Thin Film Capacitor: t = 100 nm
VC = 0.5 V - 2 V
Ferroeletric Random Access Memory (FeRAM) Principle
cm2 )P “1”
0 5
1.0 switching
nsity
(kA
/c1
0.0
0.5non-switching
urre
nt d
en
Vc
V
“0”0 10 20 30
C
Time (ns)Vbias
0
Different remanent polarization states
diff t t i t t b h i t li d lt⇒ different transient current behavior to an applied voltage pulse
Integrating the current ⇒ switched charge QS and non-switched charge QNS (distinction between the two logic states)
Non-volatile memory but destructive readout
Smart Card
Low-density FeRAM A li tiApplication
Fujitsu 2000
(www fujitsu fme com/products)(www.fujitsu-fme.com/products)
Smart Card: Block Diagram
RF-Energyde
r
RF-Receiver/Transmitter
Data
EnergyStorage DC
Voltage control
Rectifier
rdRe
ad
Data
Processor&
Logic Inte
rface
MemoryModulator/
Demodulator
mar
tCar
Sm
Failure Mechanisms of FeRAMs
Fatigue: Retention loss: Imprint:
Polarization loss upon cycling
Time dependentpolarization loss
Shift of the hysteresis loop
Decrease of Pr and / or PS
N i ifi t h diff b t th⇒ No significant charge difference between the switching and the non-switching case
⇒ read failure
Failure mmechanisms are reasonable well understood –Mb Chips are in pproduction
Ferroelectric Random Access MemoryFeRAMFeRAM
TechnologyTechnology
Thin film Deposition of Complex Oxides for Research
High-Pressure Sputtering Molecular Beam Epitaxy Pulsed Laser Deposition
SrRuO3, PbZr0.52Ti0.48O3 BaTiO3, (Ba,Sr)TiO3BaTiO3, SrRuO3
Oxygen pressure: 2.5 - 3.5 mbarmean free pathatoms have low kinetic energy
Oxygen pressure: 10-3
mbar
SrRuO3/Pt
atoms have low kinetic energy
BaTiOSrRuO3
O2/O3 gas mixture: 10-6-10-7
mbar
SrRuO3
SrTiO3
PbZr0.52Ti0.48O3SrRuO3
SrTiO3
BaTiO3in-situ characterization: RHEED
Darrell SchlomDarrell SchlomPenn State Jürgen Schubert,
JülichUlrich Poppe, Jülich
FeRAM Cell
Word line
Bit line1T1C cell
Word line
TransistorTransistorSense Amplifier
CBLFerroelectric Capacitor
Hysteretic dielectric:PZT, SBT (SrBi2Ta2O9), etc.
Integration Aspects Real Memories
Si-Technology vs. Complex Oxides
Thin Film and Interface Issues
Bit LineDrive LineEtching of refractory and oxide materials:
Reactive dry etching of Pt, Ir etc.very difficult,
Drive Line
Ferro-
Pt-SrRuO3/PZTInterface
y ,
CMOS compatibility/H-backend annealing:Encapsulation wit AlOx
PZTelectric Down scaling of Fe
Thickness (smaller Vc)
Oxygen Barrier/Plug:W or Ti/Al etc.
W 3D conformal coverage
CMOS
It`s a challenge to combine both technologies!!
Scaling and 3D conformal Coverage
Transition from 2D to 3D technology
Minimum capacitance for sensing: 30 fFPt
2D planar
Minimum capacitance for sensing: 30 fFOperation voltage 1 V3 x 10-14C needed for sensing: approx. 20.000 e-
Q=CU n=Q/ePZT
Q=CU n=Q/e
Capacitor:A = 100 nm x 100 nmA 100 nm x 100 nm P = 10µC/cm2
10-15 Ccorresponds to 6000 e-
not sufficient for data sensing!corresponds to 6000 eQ = P A
not sufficient for data sensing!
3D approach necessary!PZT
Conformal coverage/MOCVD mandatory
Pt PZT
Supposed to be implemented in 2007-09for 100 nm FeRAM node technology
Pt
Metal Organic Chemical Vapor Deposition (MOCVD)
Ar (pushing gas)
Vaporizer (Tri-jet)
A PPrecursors
Ar PurgeExhaust Substrate (240ºC)
Reactor
ExhaustExhaust
Reactor H2O
Reservoir
CVD of complex oxides on 3D structures -> non-uniformity
PZT@ TITec
A. Nagai et al. Electrochem. Solid State Lett. 9, C15 (2006).
BST@ SNU
C.S. Hwang et al. J. Electrochem. Soc. 10, G585 (2002).
Principle of Atomic Layer Deposition: ALD
Chem
Chemisorption Purge of Oxidation Purge of residual
Chem.
Chemisorption of source A
gphysisorbed precursors
(H2O,O2,O3 etc)g
oxidant
)(Å
/cyc
le)
Mono-layer thickness
tion
rate
Self regulated growth behavior, saturated growth rate with increasing precursor input!
Dep
osi
Phys. (to be purged)Chem.
Source gas supply
Uniformity of an ALD grown amorphous PZT film in a 3D trench structure T. Watanabe, S. Hoffmann-Eifert, et al., J. Electrochem. Society 154, G262 (2007)
200
250
5
6Pb
Ti (-
)
Diameter: 180 nmLS1LS1
LS3
100
150
2
3
4
nsity
(Cou
nt)
TiZr
ity ra
tio, P
b/T
0 50 100 150 200 250 3000
50
0
1
2
Inte
n
Inte
ns
LS2 0 50 100 150 200 250 300Distance (nm)
200
250
5
6
Pb -) 200
250
5
6Pb
-)LS2 LS3
40 nmLS2
100
150
200
3
4
5
ity (C
ount
)
TiZr ra
tio, P
b/Ti
(-
100
150
200
3
4
5
ity (C
ount
)Ti
Zr ratio
, Pb/
Ti (-LS2 LS3
0
50
100
0
1
2
Inte
ns
Zr
Inte
nsity
0
50
100
0
1
2
Inte
nsi
Inte
nsity
0 50 1000 0
Distance (nm)0 50 100 150 200
0 0
Distance (nm)
3D technology indeed possible with homogenous PZT composition!
Vertical Capacitor Concept
2D planar Toshiba/Infineon
Hysteresis
Electrodes separated
F l t iFerroelectric material
New concept has potential for high density applications/small cell sizes:
• Shrinkability beyond 70 nm• 4F2 cell size possible, comparable to NAND Flash Toshiba/Infineon
Summary for FeRAMs I
H. Ishiwara “Current Satus of Ferroelectric Random –Access MemoryMRS Bulletin, 29, No.1, 823 (2004).and Int. Techn. Roadmap for Semic. Ed. ITRS, San Jose 2003p ,
For standard FeRAMs
2007: 512 Mb2010: 1Gb2015: 10 Gb
Summary for FeRAMs II
Example: Texas Instrument for 64 Mbit mobile Applications:
1T-1C stacked Cell(TE)Ir/IrO2-PZT-Ir (BE) CapacitorDesign rule: 0 13µmDesign rule: 0.13µmCell area: 0.54 µm2
Capacitor area: 0.25 µm2
TiAlN diffusion BarrierTiAlN diffusion BarrierMOCVD PZT depositionSidewall protection by AlOx
Operation voltage: 1.3VAccess time: 30 nsPower Consumption: 0.57mW/MHZ
Future: 3D 1T-1C Cells in Productions with 20 nm thin PZT!
If this obstacle will be overcome ULSI FeRAM chips are visiblepVery competitive with other Non-volatile RAMs
Ferroelectric Field Effect Transistor
FeFET
Ferroelectric Field Effect Transistor
GateP
D iCh lSource DrainChannel
Si
FeFET: Readout
FeFETFloating gate Transistor
FlashLogic Device
n-MOSFETNon-volatile Memory Device
DSG
Pn+ n+
Ferroelectric gate oxideG t id
p SiB
Channel
Ferroelectric gate oxideFloating gate
e- in the floating gateshift the threshold
Gate oxide
polarizationshifts the threshold
Ids
IIon
Read Voltage
VTH“0” “1”
Ioff
Memory Window
Write Voltage“1”
“0”
VGB
Stacked FeRAM Cell vs. FeFET
Stacked cell FeFETFe
Bit LineDrive Line
P
PZT
Si
PZT
W
WordLine • Ferroelectric in direct contact with Si
Fe-Si interface
• Capacitor and transistor
Fe Si interfaceA single device
• Capacitor and transistor separated by appr. 100 nm
• Diffusion barriers
!
Two individual devices
The History of FeFETs
F FET P t t (1957 1973)
• 1st FeFET Publication (1963) TGS on CdS (J. L. Moll)
• FeFET Patents (1957, 1973)
• 1st FeFET Publication on Si (1974) BixTiyO3 (S. Wu)
• MFMIS with a retention time >106 s reported BLT (2003)
• FeFET still elusive (2002) (T. P. Ma)
• MFMIS with a retention time >10 s reported BLT (2003)
No products with FeFETs up to now!
Where are the show stoppers?
p p
Where are the show stoppers?
Short Rentention Times
Reason(s) not yet clear!
30-day-long Retention in an FeFET
Si-HfO2-SBT Gate Stack
K. Takahashi et al.,Abs. Int. Conf. Solid State Devices and Materials,,Tokyo. Paper D1-2 (2004).
Si- Fe Interface
PLD: Pulse Laser Deposition
Interdiffusion:
aus: T. Yamaguchi et al.: Jpn. J. Appl. Phys. Vol. 39, 2058 (2000).
Summary for FeFET
• FeFET are still in the research State• Performance improvement from Year to Year (small Steps)• Performance improvement from Year to Year (small Steps)• FeFETs in production not visible for the next five years
Uncon entional approaches are ell come!Unconventional approaches are well come!Separate ferroelectricity from source-drain channel
GateStray Field
For example:
Strain Effect of Fe Transfer to Channel,Change of Carrier Mobility
Source Drain Source Drain
Change of Carrier Mobility
n n
p-Si
n n
p-Si
New and unconventional approaches:Lead-freeness
St i i iStrain-engineering, FerroResistive RAM
Millipede –Scanning Probe MemoryOrganic FeFETOrganic FeFET
Millipede with Ferroelectrics I
Photo detectorx,y,z Deformation signals
J M T i d k2 lock-in`s
Feedback
Laser
ence
J. M. Triscone and coworkersPhys. Rev. Lett. 89, 097601 (2002)
Polarized regions
Ref
ere
Electrode e g SrRuO or Pt
Ferroelectric
Electrode, e.g. SrRuO3 or Pt
Nanoscale Characterization of Ferroelectric Materials, M. Alexe and A. GruvermanNanoscience and Technology, Spinger-Verlag 2004
Epitaxial films and substrates
Millipede with Ferroelectrics IIelectrical contactsfrom sensor Tbit/inch2 is possible
sensor region, e.g.:single-electron transistorfield-effect transistorsemiconductor resistor
+ - +
ferroelectric
semiconductor resistor
PZT
SrRuO3 SrRuO3
Seagate: System in advanced development state
H. Shin in:Nanoscale Phenomena in Ferroelectric Thin Films, S. Hong, Kluwer Academic Pub. 2004
Entire Organic-FeFET
R S h d L M j ki d MR. Schroeder, L. Majewski, and M. Grell, Adv. Mat. 16 (2004) 633.
Ronal C G Naber et alRonal C.G. Naber et al., Nature Materials, February 2005
University of Groningen and Philips Research
Flexible substrates, cheap but slow
Need for New Non-volatile Memory Technology
Needs:– Low power (low voltage)– Fast write/read times– Near infinite number of write/read cycles– Compatible with Si logic processp g p– Minimum added process cost– Small cell size (for high density applications)
Limitations of Flash / EEPROM Technologies:– Slow write, large added process cost, large voltages
Possible Technologies:– Ferroelectric RAM – Ferroelectric FET
Nice overview:MRS Bulletin 29, November 2004Emerging Solid-State Memory TechnologiesFerroelectric FET
– Ferromagnetic (tunnel junction)– PCM/Ovonics
M l l C t
g g y g
– Molecular Concepts– Electrochemical (resistiv) Switches– ...
Charge and Resistance for RAMs
MRAMFlash FeFET
DRAM/SRAM+-
Computational “1”
Binary FeRAM
MIM Junction(Resistive Switch)
“Write” “Read”
Computational “0”
yLogic
FeRAM
Carbon nano Computational 0Carbon nanotubes
Ovonic Molecular Memory(single molecule)
Conductive bridge(Solid State Electrolyte)
+
-
Summary: Ferroelectric Memories
Recent Improvements in FeRAMs are encouraging (3D)
Current FeFETs performance still far from production:(new approaches necessary)
New materials and concepts are developed:Multi-Probe PFM memories and FRRAMs are
interesting alternatives
Still a large ? for plastic ferroelectric electronicsStill a large ? for plastic ferroelectric electronics
?How strong are the competitors and how fast is their progress?
Forschungs entrum Forschungszentrum Jülich
Scaling and Interface EngineeringScaling and Interface Engineering
Ferroelectric Thickness Limit
T)
O)
O)
S)nm
)
100
nase
(PZT
neda
(BTO
Li (B
TO
PZT
)ye
r (PZ
T)
man
(TG
S
Lim
it (n
10
Ya Yo
J. S
cott
(P
PZT
)
Sa y
and
Silv
er
ness
L
10 J
Sym
etrix
(P
Batra
a
Thic
k
1970 1975 1980 1985 1990 1995 2000
1S
PTO: PbTiO31970 1975 1980 1985 1990 1995 2000
Year of PublicationPZT: Pb(Zr,Ti)O3
BTO: BaTiO3
TGS: tryglycine sulphate
Ultra thin Ferroelectric Oxide Films
5 nm12
(BTO
)an
(PZT
)
TO)
8
10
ger (
PTO
)
Kim
N
agar
aja
O)PTO
)
ev (P
TO)
(PZT
)
Rab
e (P
T
it ce
lls
on d
irect
ng re
gim
e
6
hten
stei
g
O)
iffer
(PTO
nd
TO)
Stre
iffer
(P
Per
tse
Tybe
ll
sez
and
R
er o
f un
ra (B
TO)
Elec
tro
tunn
eli
2
4 Lic
appe
(PTO
Stre
i
nque
ra a
nho
sez
(BTS
Gho
s
Num
be
Ger
r
1 0.4 nm
1999 2000 2001 2002 2003 2004 2005 20060
2 Ra
Ju Gh
1999 2000 2001 2002 2003 2004 2005 2006
Year
Ferroelectric Tunnel Junctions
H. Kohlstedt et al., Phys. Rev. B 72, 125341 (2005).
Polarization Decay at the Surface
Interface region FerroelectricP
Pinner part outer part
Ferroelectric
P∞
correlationcorrelation length ξ
extrapolation lengthxr
extrapolation length
R. Kretschmer and K. Binder, Ph R B20 1065 (1979)Phys. Rev. B20, 1065 (1979).
Unit-cell scalemapping of Ferroelectricity
N t M t 6 64 (2007)Nature Mat. 6, 64 (2007)C. Jia et al.
Today ξ and λ can be measured
Strain enhanced Ferroelectricity
N.A. Pertsev, et al., Phys. Rev. Lett. 80, 1988 (1998)
Film
Substrate:side view E h f P iblside view Enhancement of P possible
Sm = (b – a0)/bc
out-of-plane
Sm (b a0)/b
b = Substrate lattice parametera0 = Equiv. cubic cell constant of
ab
in planefree film, Prototypic cell
Sm: Misfit strain
in-plane
Utrathin Ferroelectrics
&SrRuO3
BaTiO3 2.1 nm
SrRuO3
Darrel Schlom & ChambersPenn StatePenn StateMBE grown oxidesJulio Rodriguez
20nm
Epitaktische Heterostruktur
SrRuO 3SrRuO 3
BaTiOBaTiOBaTiO 3BaTiO 3
SrRuOSrRuOSrRuO 3SrRuO 3
END