Ion Elena-Daniela

FE nanostructures

Processing issues

Potential applications

Ferroelectricity, Ferroelectric materials FE nanostructure, Size limit in ferroelectricity

Invasive and Non-invasive approachCharacterization of FE nanostructure

Outline

Important Events

1921 Discovery of ferroelectricity in Rochelle Salt

40’s Barium titanate era

60’s Age of high science

80’s Age of integration

1990-present Age of miniaturization

def = reversibility of the direction of the electric dipole by means of an applied electric field in a polar crystal

Materials which exhibit ferroelectricity are called ferroelectric materials

Ferroelectricity

32 Symmetry Points groups

21 Noncentrosymetric

20 PiezoelectricPolarized under stress

10 PyroelectricSpontaneously polarized

SubgroupFerroelectric

Spontaneously polarizedPolarization reversible

TungstenBronze

Oxygen OctahedralABO3

Pyrochlore Layer structure

11 Centrosymetric

Non-piezoelectric

Ceramic Perovskite

Pi = dijk jk

(Direct Effect)

ijdkijCo

nverse Effect

Ps = T

Ferroelectric materials

e.g. Perovskite oxide – ABO3 BaTiO3, PbTiO3, Pb(ZrxTi1-x)O3,

Reversible spontaneous polarization-1 or 0 data bits (binary data storage media)

Piezoelectric effect-Piezoelectric actuators, sonar detectors

Pyroelectric effectPyroelectric detectorsfor infrared detection, imaging, thermometry, ...

Applications

• 3D→2D transition : bulk to thin film• 2D→1D transition : thin film to wire• 2D→0D transition : thin film to nanostructures

F. D. Morrison et al. Rev. Adv. Mater. Sci. 4 (2003) 114

Alexe et al.APL- 75, 1793, (1999)Ma et al.

APL, 83, 3770 (2003)

Luo et al.APL, 83, 3, 440, (2003)

Yun et. al. Nano Letters, S1530, (2002)

Ferroelectric nanostructures

• Switching @ nanoscale

• P=10 µC/cm2, ε = 200

• a = 10 nm Q = P·S ≈ 60 e

• a = 2 nm Q = P·S ≈ 3 e

Size limit in ferroelectricity

Rudinger et. al. Appl. Phys. A, 80, 1247 (2005)

2

2

2

1

o

C

VPW

Factors that influence the ferroelectric properties in nanostructure:Grain size,Mechanical bondary conditions,...

Wc > kBT

Electron Beam Direct Writing

Focussed Ion Beam Patterning

LithographyMethods

NANOSTRUCTURES

Focussed Ion Beam Patterning Electron Beam

Direct Writing

LithographyMethods

Self-PatterningChemical Routes

Self-PatterningPhysical RoutesSelf-Patterning

Physical Routes

Self-PatterningChemical Routes

Invasive and Non-invasive approach

Focussed Ion Beam Patterning

FIB equipment• similar to SEM• a highly focussed beam of gallium ions

• purposes: imaging, and micromachining

• nanopatterning - resolution ~ 20 nm

•gallium doping, damaged surface layer

C.S. Ganpule et.al. APL 75, 409 (1999)

Electron Beam Direct Writing

Alexe, Harnagea and Hesse, J. Electroceram. 12, 69 (2004)

• solution: metalorganic compounds (Sr-, Bi-, Pb-ethylhexanoate, Ti-, Zr-isopropylene and Ta-methoxide ) or metal colloids and solvent: xylene and 2-methoxiethanol• patterning by scanning an electron beam

•Powerful method to prepare arrays of ferroelectric cells with lateral sizes down to 75nm

•Expensive equipment and time

LithographyMethods

• Photolithography• Soft lithography Nanoimprint

Alexe, Harnagea and Hesse, J. Electroceram. 12, 69 (2004)

Large-area and low-cost ferroelectric cells below 100nm in lateral size

Self-PatterningPhysical Routes

Pulsed Laser Deposition

Met.Org. Chem.Vap. Deposition

Chemical Solution Deposition

Pulsed Laser Deposition

1. Laser radiation interaction with the target 2. Dynamic of the ablation 3. Transport of the ablated material to a charger and a furnace 4. Nucleation and growth

Seol et al. - Appl. Phys. Lett., 81, 1894, 2002

Crystalline nanoparticles ~ 4-20nm

Complex experimental set-up, low yield

Met.Org. Chem.Vap. Deposition

Large surface coating areaUsed in combination with FIB, EBDW

Expensive equipement

Metal organic precursor:Tetraethyl lead - Pb(C2H5)4

Titanium isopropoxide: Ti(i-OC3H7)4

Zirconium tert-butoxide: Zr (t-OC4H9)4

M. Shimizu et.al.-Jpn. J. Apl. Phys, 33, 5168 (1994)

R.W. Schwartz et al. / C. R. Chimie 7 (2004) 433–461

Metal carboxylate:R-COOMM: PbR: CH3-, C2H5-

Metal alkoxide: M(OR)x

M: Ti, Zr, (OR): (OC3H7), (OC4H9)

Solvent: CH3OC2H5OH

Chemical Solution

Deposition(Sol-gel)

Self-PatterningChemical Routes

Pb(O2C2H3)2 R= [H2O]/ [Pb]Zr(OC4H9)4 pH=11Ti(OC4H9)4

C4H10O

11-PT-15

11-PZ-15

11- PZT-15

BET: 58nm

BET: 109nm

BET: 144nm

Cost-effective, various shapes

Agglomeration

(Sol-gel)

Self-PatterningChemical Routes

Synthesis, Functionalization and surface treatment of NanoparticlesMarie-Isabelle Baraton/ ASP 2003

Alexe, Harnagea and Hesse, J. Electroceram. 12, 69 (2004)

Microemulsion

Removal of the surfactant

Uniforme particles in nm range

Characterization of ferroelectric nanostructures

• Piezoresponse Scanning Force Microscopy (PFM)

M. Alexe, C. Harnagea and D. Hesse, J. Electroceram. 12, 69 (2004)

C.H. Ahn, K.M. Rabe, J.M. Tiscone, Science, 303, 488, (2004)

Potential applications

Many others to come!!!

Thank you for your attention!