Sintering of screen-printed platinum thick films for electrode applications
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electrodes with a 6–8-m thickness were produced on alumina substrates by a double-print Pt screen-printing process that included a sequential heat treatment at 600 °C and 1300 °C. This process improved the final sintered double-print film because the first printed layer acted as a sintering template for the second printed layer. The sintered Pt films have a 95% coverage of the alumina surface, 92% density, 0.73-m average surface roughness, and 16.10−5 ⍀ cm resistivity. The sintering behavior of Pt films exhibited three stages of densification: Stage I (T °C < 700 °C), exhibiting neck growth, and Stage II (700 < T °C < 1300 °C), exhibiting grain growth, have activation energies of 64 kJ/mol and 125 kJ/mol, respectively. Stage III exhibits a decrease in shrinkage due to Pt coalescence and island formation. The transition temperature, 700 °C, between Stages I and II corresponds to an anomalous increase in surface roughness and resistivity. The thickness of Pt films was a critical parameter for achieving alumina surface coverage. Uniaxial pressing of dried Pt films increased densification and reduced the surface roughness of double-print Pt films.
I. INTRODUCTION
Piezoelectric PbZrxTi1−xO3 (PZT) thick films prepared by screen printing are increasingly being studied to realize microelectromechanical devices for a variety of sensor and actuator applications.1–5 Examples of such devices include micromotors,6,7 ultrasonic transducers,8,9 pressure sensors,10 –15 and micropositioners. Screenprinting technology for the fabrication of PZT thick films is of industrial interest due to its possibility for production of relatively low-cost films with thickness between 5 and 100 m.16–19 Many microelectromechanical devices require thin piezoelectric layers 1300 °C, there is an obvious decrease in shrinkage (Stage III). Assuming that the sintering and associated shrinkage is controlled by lattice diffusion31–34 as described by Eq. (1),35 activation energies (Ea) for Stages I and II can be calculated from the slope of a plot of ln(T 2/5⌬t/tp) versus 1/T (Fig. 2).
冉 冊
D*2 Ⲑ 5 Ea ⌬t = A × 2 Ⲑ 5 where D* = D0 × exp − tp RT T
(1) where A ⳱ constant; ⌬t ⳱ change in thickness, tp ⳱ pressed thickness, D0 ⳱ diffusion coefficient, and T ⳱ absolute temperature.
J. Mater. Res., Vol. 16, No. 4, Apr 2001 Downloaded: 16 Aug 2014
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J.B. Ve´chembre et al.: Sintering of screen-printed platinum thick films for electrode applications
Stages I and II exhibit activation energies of 64 ± 4 and 125 ± 13 kJ/mol, respectively. In comparison, the densification of bulk pure metal powder compacts can be represented by a single straight-line plot from which a single activation energy of 270 kJ/mol is obtained.29,36,37 The two distinct stages of densification for Pt thick films may arise because of the influence of carbon impurities on Pt diffusion at low temperatures or changes in the dominant diffusion mechanisms for the two temperature ranges. The platinum ink contains organic solvents and binders that evaporate and burn o
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