1. 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

2. 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

3. 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

4. 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

5. precursor solution (‘Sol’)
CSD processing steps:
Synthesis of
precursor solution (‘Sol’)
Coating
‘Gel’ film
Drying, pyrolysis
Amorphous oxide film
Crystallization
Crystalline film
substrate
substrate
substrate

6. 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.

7. 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
CH3-O-C2H4-OH
2-methoxyethanol
Turova, Turevskaya, Kessler, Yanovskaya, 2002.

8. Building blocks of the inorganic network.
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
Oxo-bridge
Building blocks of the inorganic network.
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, K. D. Budd, S. K. Dey, D. A. Payne, 1985.

9. +: starting compounds for a wide range of metals
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

10. 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.
Neodecanoate = C10H19O2
R. W. Vest, J. Xu, Hoffman, Klee, Waser, 1995

11. 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.

12. [M-(OH2)] z+  [M-(OH)] (z-1)+ + H+  [M=O] (z-2)+ + 2H+
Transition metal ions (La3+, Ti4+, Zr4+, Nb5+, etc.) in water are solvated by water molecules:
Aquo-ligand
(H2O)n-1 -
(H2O)n-1-
Z: oxidation number
CN: coordination number
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

13. Thin film deposition methods: Dip coating Spin coating Spray coating
Spin-up
Spin-off
Evaporation
Four stages:
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

14. 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
Thickness of a deposited film depends on solution properties and deposition conditions. Typically it is in the range a few 10 nm nm.
Efficiency of ‘packing’ depends on branching of solute species (linear or branched).

15. Spin coating of a PZT sol ( solvent: 2-methoxyethanol): influence of the sol concentration, rotation of the spinner on evolution of cracks upon drying at different temperatures.
C=1M, t=400 nm
Temperature
Speed rotation
60°C
100°C
200°C
350°C
500 rpm
wet film
cracks
no film
1000 rpm
1500 rpm
2000 rpm
3000 rpm
Temperature
Speed rotation
60°C
100°C
200°C
350°C
500 rpm
cracks
no film
1000 rpm
no cracks
1500 rpm
2000 rpm
3000 rpm
C=0.5M, t=150 nm
C=0.25M, t=50 nm
Temperature
Speed rotation
60°C
100°C
200°C
350°C
1000 rpm
no cracks
1500 rpm
2000 rpm
3000 rpm

16. Processes taking place upon heating
Drying Pyrolysis Crystallization
oC – 450 oC – 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:

17. Crystallization and evolution of microstructure:
Nucleation and growth from the amorphous phase
(Ba,Sr)TiO3 (BST): Pb(Zr,Ti)O3 (PZT)
Homogeneous nucleation Heterogeneous nucleation
- Granular micorstructure - Columnar microstructure

18. How to adapt the CSD-solution for ink-jet printing?
DIMATIX ink-jet printer
Requirements for the ink (given by the producer):
Viscosity = 10 to 12 m Pas
Surface tension = 28 to 32 mN/m

19. Parameters to control
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
Design of the ink
Printing procedure

20. In2O3/ZnO(IZO) CSD-solution
Alkoxide and acetate based solution in 2-methoxyethanol
2MOE
Dissolution
In isopropoxide
Zn acetate
dissolution
Clear and stable solution
Polymer
IZO, 4 deposited layers, 1h at 150°C in air after each deposition
0.5 mm
Silicon
C=0.25M
J. Tellier et al., submitted.

21. Printing the CSD-solution
Solution of IZO in 2-methoxyethanol, C=0.25M OM
Ink-jet printing of IZO designed for spin coating
1 layer, annealing at 150oC 10 minutes
Low viscosity
Bad coverage
Cracks (too thick)
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

22. Fluid parameters Weber number
Adimentional number, related to surface tension
Range 5-20 mPas and mJ/N
v: speed
r: distance
r: volume weight
s: surface tension
Reynolds number
Adimentional number, related to viscosity
Proper formation of drops
v: speed
r: distance
r: volume weight
n: cinematic viscosity
h: dynamic viscosity
r: nozzle diameter
r: ink density
h: dynamic viscosity
s: surface tension
R. Noguera et al, Journal of the European Ceramic Society (2005)

23. Increase of viscosity
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

24. Design of IZO ink viscosity
Solvent system: 2-methoxyethanol (2MOE) / 1,3-propanediol (13PD)
Solvent Viscosity (mPas)
2MOE 3.4
13PD 41.5
Optimum : 2MOE / 13PD: 45 / 55

25. Printing the modified solution (ink)
Solution of IZO in 2-methoxyethanol + 1,3-propanediol (45/55), C=0.25M
150°C
Cracks (measured thickness 400 nm)
Random nozzles clog
Film not continuous
Decrease concentration
Possibility to form a single drop
PZT thin films obtained by spin coating
IZO thin films obtained by ink jet printing
C=0.5M t=150 nm
C=0.25M t=50 nm
C=0.25M t=400 nm
C=0.05M t=50 nm
Decrease of concentration
Decrease of concentration
500µm

26. Wettability of IZO ink Contact angle:
Contact angle : high enough to ensure a good resolution
Contact angle:
Glass = 42.5°
SiOx/Si = 27.6°
PEN = 24.1°
Solution of IZO in 2-methoxyethanol
+ 1,3-propanediol
Viscosity h = 9.6 mPas
Surface tension g = 34.5 mN/m
ImageJ software: drop_analysis (Drop Snake)

27. Acknowledgements
Colleagues from Electronic Ceramics Department, Jožef Stefan Institute.
Slovenian Research Agency (P2-0105)
EU 6FP project MULTIFLEXIOXIDES (NMP3-CT ).
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.