Thick film ceramic combinatorial libraries: the substrate problem

Discrete, thick-film, combinatorial libraries of ceramics are made by computer controlled mixing of well-dispersed suspensions of commercially available powders followed by deposition of droplets on a substrate for drying and subsequent firing. The substrate influences the shape and size of the samples through spreading effects. Later, at the firing stage, interaction with the substrate can involve reactions that adulterate the composition or low adhesion that can result in sample loss during transport. We describe substrate pretreatment with a perfluorinated silane to provide control of droplet size and prevent spreading. Substrate compatibility during high temperature firing is more problematic and we discuss the limited material choices. One approach seeks a substrate that will support the library from beginning to end of the preparatory stage and during storage. An alternative method involves firing samples on low adhesion substrates followed by pneumatic transfer to a silver electroding paste and a low temperature firing. This method provides sufficiently strong adhesion to allow libraries of samples to be surface-ground a give a flat parallel configuration on a common electrode together with robust construction for storage and transport.