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!