Interactions between lead oxide and ceramic substrates for thick film technology
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Interactions between lead oxide and ceramic substrates for thick film technology Massimo Bersani,a) Bruno Morten, and Maria Prudenziati Istituto Nazionale per la Fisica della Materia (INFM) and Department of Physics, University of Modena, 41100 Modena, Italy
Alessandro Gualtieri Department of Earth Sciences, University of Modena, 41100 Modena, Italy (Received 1 July 1996; accepted 22 August 1996)
This paper deals with the mechanisms and kinetics of interactions between screen printed and fired PbO layers and ceramic substrates: alumina and beryllia. The interaction with alumina occurs via two main processes: (i) a reaction between PbO and Al2 O3 grains, which induces the formation of a crystalline phase, Pb2 Al2 O5 ; and (ii) an interdiffusion process involving Pb and the intergranular amorphous phase in the ceramic substrate. This latter process results in a compositional change of the intergranular phase at considerable depths inside the ceramic substrate, as well as in the formation of a high lead glass layer on the substrate surface. Since PbO is not completely reacted, the Pb 1/2 penetration in the ceramic is diffusion limited (penetration depth w ΓΈ td , where td is the reaction time) with an activation energy of 1.20 6 0.05 eV. The ceramic microstructure significantly affects the interaction processes.
I. INTRODUCTION
A myriad of different thick film materials are currently prepared by screen printing and firing processes on ceramic substrates for either hybrid thick film circuits or thick film sensors.1,2 A vital requirement is that the ink contains a constituent which interacts with the ceramic and/or acts as a promoter of adhesion between the functional phase and the substrate. In many thick films the role of adhesion promoter is played by a glassy phase obtained through the dispersion of a glass frit with the primary functional phase in the ink. The evolution of the glass component during the film formation and the interactions of high lead glasses for hybrid microelectronics have been clarified in some relevant materials.3,4 However, this approach cannot be generally resorted to, since in several materials (e.g., CdS and CdTe photoconductors, ZnO layers for gas sensors, ZrO2 solid electrolytes, PZT ferroelectrics) the presence of a glassy phase can be detrimental for the properties of the layer, and even be responsible for vanishing the desired functional behavior.2 In these cases a metal oxide may be an efficient alternative approach; this is the case in unfritted thick film conductors where CuO is often the adhesion promoter.5,6 Proper selection of the metal oxide is required, according to the functional material to be prepared and the firing conditions. Unfortunately, scarce information a)
Now with CMBM (Centre of Medical Biophysics and Materials), Povo, Trento, Italy. J. Mater. Res., Vol. 12, No. 2, Feb 1997
is available on interaction mechanisms between metal oxides and ceramic substrates for thick film technology, in comparison to the extensive inv
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