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: h.h.kohlstedt@fz-juelich.de

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