outline introduction basics of chemical solution deposition (csd) of functional–oxide thin films...
TRANSCRIPT
Outline
Introduction
Basics of Chemical Solution Deposition (CSD) of functional–oxide thin films
Solutions for CSD: overview of synthetic approaches
Sol-gel (Alkoxide – based)
MOD
Inorganic routes
Stages of CSD
Ink-jet printing: parameters to control
Solutions for ink-jet-printing
Introduction
- History
Optical coatings on glass
TiO2/Pd, SiO2/TiO2
-Schott: Geffcken, Berger (1939)
Dislich (1971)
Electronic ceramic films
PT/PZT/PLZT
- S. R. Gurkovich, J. B. Blum, (1984).- K. D. Budd, S. K. Dey, D. A. Payne, (1985).
1985
Applications of Films and Coatings
Optical (antireflective, absorbing, ...)
SiO2, SiO2/TiO2, TiO2/Pd (IROX)
Protective (corrosion or abbrasion resistance, adhesion passivation, planarization,..)
SiO2, ... ORMOSIL (Schmidt, 1986)⇨
Electronic
Dielectric: (Ba,Sr)TiO3 - BST
Ferroelectric: (Pb(Zr,Ti)O3-PZT, SrBi2Ta2O9 - SBT)
Piezoelectric: ZnO, PZT
Pyroelectric: PbTiO3, Ti-rich PZT
Sensors: TiO2
HTSC: YBa2Cu3O7 - YBCO
Conductive / semiconductive : LaNiO3, (La,Sr)CoO3, La-ruthentates, RuO2,
ITO (90% In2O3, 10% SnO2 by weight), In2O3–ZnO, …
...
• Chemical homogeneity• Crystallinity (if
crystalline: phase and orientation
• Microstructure • Functional response
Chemical Solution Deposition (CSD) routes
⇨Organic routes
⇨Sol-gel (pure) alkoxide-based
alkoxide + salt/oxide
⇨Metalloorganic decomposition (MOD)
⇨Routes involving polymers: in-situ polymerisation (‘Pechini’), polymer precursor route
Metal ions are homogeneously distributed in the organic network and coordinatively bonded by polymer’s functional groups.
⇨ Inorganic routes (nitrates, citrates, peroxo- compounds)
Stability of water based solutions of different metal ions.
REACTIVE
NON-REACTIVE
CSD processing steps:
Synthesis ofprecursor solution (‘Sol’)
Coating
‘Gel’ film
Drying, pyrolysis
Amorphous oxide film
Crystallization
Crystalline film
20 30 40 500
20
40
60
80
100
120
Int.
(p
.e.)
2-theta(o)
substrate
substrate
substrate
Alkoxide based sol-gel route
Precursors:
• Metal alkoxides M(OR)n
For M = transition metal
• High reactivity of TM(OR)n towards water
• Tendency to increase the coordination number oligomerization⇨
• Metal - acetates - nitrates - oxides (problem of solubility)
Ti(OR)4, R: n-Pr, n-Bu
Z = 4
N = 5
Babbonneau et al., 1988.
Reactive solvents:
alkyl-alcohols (R-OH)
ether-alcohols: R-O-(CH2)n-OH
poly-alcohols (diols, triols): 1,3 propanediol
methanol/acetic acid
CH2-OH
CH2
CH2-OH
CH3-O-C2H4-OH
Turova, Turevskaya, Kessler, Yanovskaya, 2002.
2-methoxyethanol
Two major reactions (shown for one alkoxide group):
Hydrolysis: M-OR + HOH M-OH + ROH
Polycondensation: M-OR + M-OH M-O-M + ROH
M-OH + M-OH M-O-M + HOH
Building blocks of the inorganic network.
Oxo-bridge
Heterometallic systems:
Reaction between: two alkoxides
TM alkoxide and a metal salt (acetate, nitrate).
Ester elimination:
-[Pb-CH3COO] + [RO-TM] -[Pb-O-TM] + R-OOC-CH3
oxo bridge
PZT: S. R. Gurkovich, J. B. Blum, 1984. K. D. Budd, S. K. Dey, D. A. Payne, 1985.
Alkoxide based sol-gel route
+: starting compounds for a wide range of metals
possibility to tailor the reactivity of the starting compounds
effective solvents
easy synthesis of different heterometallic solutions
solutions are suitable for film deposition (viscosity, wettability)
-: reactive starting materials
inert atmosphere (dry-box, Schlenk glassware)
toxic solvents
syntheses require some knowledge of chemistry
sometimes products with stoichiometries ≠ target material
MOD route
Precursors: large metal carboxylates R-COO- or b-diketonates R-CO-CH2-CO-R’
Ba, Pb ethylhexanoate (CH3-(CH2)6-COO-)
Zr neodecanoate (CH3-(CH2)8-COO-), Zr acetylacetonate (CH3COCHCOCH3-)
Ti di-methoxydineodecanoate (Ti(CH3C2H4O)2(CH3-(CH2)6-COO)2
Zn naphtenate (= salt of cyclic carboxylic acid obtained from petroleum, MW ~200)
Solvents: Non-polar: toluene (methyl-benzene), xylene (di-methyl-benzene),...
Polar: alcohols, alcohol/carboxylic acid, ...
Mixing at RT.
No reaction between the starting chemicals.
No reactive reagents (no need for protective atmosphere).
Variables: chemicals, solution concentration.
R. W. Vest, J. Xu, 1988 Hoffman, Klee, Waser, 1995
Water – based solutions for CSD
Heterometallic systems: problems with common solubility of different metal species.
To overcome such problems, water-based heterometallic solutions often contain coordinating ligands, such as:
-acetato
-nitrato
-carboxylato
-peroxo.
Depending on the pH of the solution the equilibrium between three types of solvated species is established (hydrolysis of metal ions – shown for one group):
[M-(OH2)] z+ [M-(OH)] (z-1)+ + H+ [M=O] (z-2)+ + 2H+
Aquo- Hydroxo- Oxo- ligands
The type of the complex depends on:
Z
CN
pH
Z = 4
(Ti, Zr)
0 2 4 6 8 10 12 140
2
4
6
8
O2-
H2O
Z
pH
OH-Z = 4
(Ti, Zr)
0 2 4 6 8 10 12 140
2
4
6
8
O2-
H2O
Z
pH
OH-
Transition metal ions (La3+, Ti4+, Zr4+, Nb5+, etc.) in water are solvated by water molecules:
H H z+
Mz+ + :O M O
H H
H H z+
Mz+ + :O M O
H H
Aquo-ligand
(H2O)n-1 - (H2O)n-1- Z: oxidation number
CN: coordination number
Thin film deposition methods:
Dip coating Spin coating Spray coating
Substrates:• Single crystals: sapphire (A, C, R), SrTiO3 (100), ...• Ceramics (Al2O3)
• Pt (/TiO2)/SiO2/Si -
Pt typically strongly (111) oriented • Metal foils (Cu)• Glass
Variables:• Solution concentration• Viscosity• Volatility• Surface tension• Wetting
• Deposition• Spin-up• Spin-off• Evaporation
Four stages:
Processes/reactions taking place in the as-deposited ‘gel’ film
Solvent evaporation strong ⇨concentration of solute species ⇨viscosity increases.
‘Physical’ aggregation: = concentrating of solute species. (MOD)
‘Chemical’ aggregation: Promoted polymerisation or polycondensation (= more cross-linking) leads to a gel. (Alkoxide sol-gel)
Viscosity increases
Efficiency of ‘packing’ depends on branching of solute species (linear or branched).
Thickness of a deposited film depends on solution properties and deposition conditions. Typically it is in the range a few 10 nm - 100 nm.
Processes taking place upon heating
Drying Pyrolysis Crystallization
100- 200 oC 350 – 450 oC 400 – 800 oC
Evaporation of the trapped solvents
Dehydroxylation: removal of –OH groups from the network (continued polycondensation – alkoxide route)
Thermolysis/pyrolysis: decomposition/oxidation of functional (organic/carbonate) groups
Structural rearrangement: - film shrinkage- change of coordination environment- long-range ordering
Two-step:
One-step:
(Ba,Sr)TiO3 (BST): Pb(Zr,Ti)O3 (PZT) Homogeneous nucleation Heterogeneous nucleation- Granular micorstructure - Columnar microstructure
Crystallization and evolution of microstructure:
Nucleation and growth from the amorphous phase
100 nmAl2O3
BST
100 nmAl2O3
BST
DIMATIX ink-jet printer
http://www.dimatix.com
Requirements for the ink (given by the producer):
• Viscosity = 10 to 12 m Pas• Surface tension = 28 to 32 mN/m
How to adapt the CSD-solution for ink-jet printing?How to adapt the CSD-solution for ink-jet printing?
To realise the ink-jet printing and to obtain uniform and
crack-free 1D/2D structure.
Ink stability
Viscosity
Surface tension
Concentration of the solution
Wettability on the substrate
Deposition parameters
- Temperature of the cartridge
- Temperature of the substrate
- Drop spacing
- Cleaning of the substrate
Heating
Des
ign
of t
he in
kP
rintin
g pr
oced
ure
Parameters to controlParameters to control
In2O3/ZnO(IZO) CSD-solutionIn2O3/ZnO(IZO) CSD-solution
2MOE
Dissolution
In isopropoxide
Zn acetate
dissolution
Clear and stable solution
C=0.25M
Alkoxide and acetate based solution in 2-methoxyethanol
J. Tellier et al., submitted.
Polymer
IZO, 4 deposited layers, 1h at 150°C in air after each deposition
0.5 mm
Silicon
Printing the CSD-solutionPrinting the CSD-solution
OMInk-jet printing of IZO designed for spin coating1 layer, annealing at 150oC 10 minutes
Low viscosityBad coverageCracks (too thick)
Solution of IZO in 2-methoxyethanol, C=0.25M
How to modify the solution ?
• Increase of the viscosity by adding a viscous solvent in the right proportion (1,3
propanediol) and also modify the surface tension• Decrease the thickness by diluting• Keep the stability of the original solution
Fluid parametersFluid parameters
R. Noguera et al, Journal of the European Ceramic Society (2005)
Range 5-20 mPas and 35-40 mJ/NWeber numberAdimentional number, related to surface tension
v: speedr: distancer: volume weights: surface tension
Reynolds numberAdimentional number, related to viscosity
v: speedr: distancer: volume weightn: cinematic viscosityh: dynamic viscosity
rv
We** 2
rrv ***
Re
r
We
**Re
r: nozzle diameterr: ink densityh: dynamic viscositys: surface tension
Proper formation of drops
Increase of viscosityIncrease of viscosity
0
5
10
15
20
25
30
35
40
45
0 0,2 0,4 0,6 0,8 1
1,3-propanediol
Vis
cosi
ty (
mP
as)
2022242628303234363840
0 0,2 0,4 0,6 0,8 1
1,3-propanediol
Su
rfac
e te
nsi
on
(m
N/m
)
Properties of the solvent have a strong influence on the ink properties
Different 2-metoxyethanol
(2MOE) / 1,3-propanediol
(13PD) volume ratios
Stalagmometer
Room temperature measurements
Design of IZO ink viscosityDesign of IZO ink viscosity
Optimum : 2MOE / 13PD: 45 / 55
(x) 13PD - (1-x) 2MOE
25
20
15
10
0 0.2 0.4 0.6 0.8 1
Vis
cosi
ty (
mP
as)
0
5S
urf
ace
tens
ion
(mN
/m)
(x) 13PD - (1-x) 2MOE
40
36
32
28
0 0.2 0.4 0.6 0.8 120
24
Solvent Viscosity (mPas)2MOE 3.413PD 41.5
Solvent system: 2-methoxyethanol (2MOE) / 1,3-propanediol (13PD)
Printing the modified solution (ink)Printing the modified solution (ink)
C=0.5M t=150 nm C=0.25M t=50 nm
Decrease of concentration
C=0.25M t=400 nm C=0.05M t=50 nm
PZT thin films obtained by spin coating
500µm
• Cracks (measured thickness 400 nm)• Random nozzles clog• Film not continuous
150°C
Possibility to form a single drop
Solution of IZO in 2-methoxyethanol + 1,3-propanediol (45/55), C=0.25M
Decrease concentration
IZO thin films obtained by ink jet printing
Decrease of concentration
Wettability of IZO inkWettability of IZO ink
Contact angle:
Glass = 42.5°
SiOx/Si = 27.6°
PEN = 24.1°
Viscosity h = 9.6 mPas
Surface tension g = 34.5 mN/m
Solution of IZO in 2-methoxyethanol
+ 1,3-propanediol
Contact angle : high enough to ensure a good resolutionContact angle : high enough to ensure a good resolution
ImageJ software: drop_analysis (Drop Snake)
References (and source of the majority of figures): :
C. J. Brinker, G. W. Scherer, Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing, Academic Press, San Diego, 1990.
M. Ohring, Materials Science of Thin Films, 2nd ed., Academic Press, San Diego, 2002.
R. Waser (Ed.), Nanoelectronics and Information Technology, Wiley-VCH, Weinheim, 2003, P. Erhart, Film Deposition Methods, pp. 201 – 221.
R.C. Buchanan (Ed.), Ceramic Materials for Electronics, 3rd ed. Marcel Dekker, New York, 2004, A. I. Kingon, P. Muralt, N. Setter and R. Waser, Electroceramic Thin Films for Microelectronics and Microsystems, pp. 465 – 526.
G. Cao, Nanostructures and Nanomaterials, Imperial College Press, London, 2004.
C. N. R. Rao, A. Mueller, A. K. Cheetham, The Chemistry of Nanomaterials (Vol. 1), Wiley, Weinheim, 2004.
Acknowledgements
Colleagues from Electronic Ceramics Department, Jožef Stefan Institute.
Slovenian Research Agency (P2-0105)
EU 6FP project MULTIFLEXIOXIDES (NMP3-CT-2006-032231).