1. Components content, wt. %
Barium Titanate Thin Films Obtained by Screen Printing Technology I.O. Dulina1, S.O. Umerova2, A.V. Ragulya Frantsevich Institute for Problems of Materials Science of NASU, 3, Krzhyzhanovsky St., Kyiv, 03142, Ukraine.
INTRODUCTION
The miniaturization tendency of electronic devices leads to the necessity of downsizing of multilayered ceramic capacitors simultaneously with their capacity increasing. The specific capacity of the multilayered ceramic capacitors can be increased by thickness decreasing of ceramic and electrode layers and electrodes number increasing. Thickness of metallic and dielectric layers can be decreased to nm by using of nanosize particles and new techniques of layer manufacturing. Screen printing technology is more promising one for thin dielectric layers obtaining, but roughness, evenness and thickness of films and deposit pattern geometry are determinated by the viscosity and rheological behavior of pastes and screen printing process parameters. Thus, investigation of film characteristics dependence on screen printing pastes based on BaTiO3 nanopowder composition, rheology and viscosity and screen printing process parameters of are of great importance.
MATERIALS AND METHODS
Screen printing pastes have been prepared by using of BaTiO3 nanopowder with mean particles size 20 nm, ethyl cellulose with viscosity of 5 wt. % toluene-ethanol solution 350 and 10 mPa·s as binder, terpineol as solvent and dibutyl phthalate as plasticizer.
Paste have been characterized by rheologycal viscosity analysis and printed through nylon screen with 1.5x2 mm patterns. Squeegee pressure range was – MPa, print and flood rates range was – m/s. Obtained films have been characterized by optical microscopy for the purpose of pattern geometry fidelity investigation and pattern relative area determination. Films thickness and roughness parameters Ra and Rz have been identified by optical profilometry.
RESULTS a b
Fig. 5 – Print rate influence on films thickness (a) and roughness (b) for paste P1 a b
Fig. 6 – Flood rate influence on films thickness (a) and roughness (b) for paste P1
Table 1 – Composition and rheological properties of BaTiO3 pastes based on nanopowder (ethyl cellulose 350 mPa·s)
Fig. 8 – Influence of BaTiO3 content on roughness
Fig. 7 – Influence of BaTiO3 content on films thickness
Paste
Components content, wt. %
Viscosity, Pa·s
Thixotropy degree,
kPa/s
BaTiO3
Ethyl
cellulose
Terpineol
0.1 s-1
500 s-1 P1 10 3 87
37.5
2.11
58.00 P2
12.5
84.5
408
5.01
4.64 P3
16.57
2.31
81.12
2780
5.94
rheopexic P4
15.07
1.99
82.94
425
0.52
86.27 P5
18.06
1.91
80.03
1140
0.87 P6
22.56
1.83
75.60
55.2
0.69
74.38
Table 2 – Composition and rheological properties of BaTiO3 pastes based on nanopowder with addition of plasticizer (ethyl cellulose 10 mPa·s)
Paste
Plasticizer
content, wt. %
Viscosity,
Pa·s (0.1 s-1)
Thixotropy
degree, MPa/s
Dilatancy
degree, a.u.
Plastification
effect P7
2.11
-0.112
0.0050
0.0000 P8 5
1.7
0.0038
0.0013
0.0016 P9 10
2.12
0.0003
0.0025
P10 15
2.58
0.01
0.0012
0.0007
P11 20
4.36
0.028
0.0017
P12
22.5
0.34
0.139
0.0009
P13 25
1.68
0.003
0.0014
0.0005
P14 30
4.13
0.0027
0.0002
P15 40
4.33
0.0026 a b
Table 3 – Thickness and roughness of BaTiO3 pastes films based on nanopowder with addition of plasticizer (ethyl cellulose 10 mPa·s)
Fig. 1 – Influence of squeegee pressure on patterns number with good geometry
Fig. 2 – Appearance of patterns with good (a) and bad (b) geometry
Paste
Plasticizer
content, wt. %
Thickness, μm
Ra, nm
Rz, nm P7
1.35
35.56
172.58 P8 5
0.76
26.61
72.77 P9 10
0.97
21.09
56.59
P10 15
0.83
28.93
70.89
P11 20
1.15
26.91
70.73
P12
22.5
0.87
26.47
75.86
P13 25
0.79
23.55
65.01
P14 30
1.29
25.43
64.61
P15 40
1.08
25.99
69.89
Fig. 3 – Squeegee pressure influence on films thickness and roughness for pastes with different composition P2 P4 P1 P6 P5 P3
CONCLUSIONS
1. Ethyl cellulose considerable affinity to BaTiO3 nanopowder led to sizeable paste densifing and owing to this paste solid content decreasing of nanopowder from 50 – 70 % wt. that are typical for submicron powders to 10 – 15 % wt.
2. Rheological behavior changing was associated with solid-binder structure changing in paste.
3. Films thickness and roughness dependence from screen printing parameters was identified by paste rheology only in the case of paste binder content less than 3 wt. %.
4. Paste viscosity 2 – 4 Pa·s at shear rate 500 s-1 and thixotropy degree 58 – 75 kPa/s were considered as optimal ones for obtaining screen printed BaTiO3 film with the highest quality of deposit pattern geometry and the least roughness parameters Ra and Rz.
5. Plastificizer addition has a complicated effect on pastes viscosity and rheological properties. In all cases films thickness and roughness decrease with plastificizer addition.
Fig. 4 – Squeegee pressure influence on films roughness for pastes with different composition