Electric Force Microscopy was used to map the electric field distribution on the surface of thick film resistors (TFRs) based on Bi-ruthenate, Pb-ruthenate and RuO{sub}2; the evolution of the microstructure with the firing conditions has been investigated in some samples. The concentration of the electric field around the conductive grains is a general feature of all the films, independently of the resistor composition. Then a meander-like path of charge carriers on a microscopic scale has been assessed. The segregated structure is enhanced at high firing temperatures. A strict correlation between the distribution of the electric field and the size of the constituents in the paste was not clearly obtained. The results are discussed in connection with the electrical and piezoresistive properties of TFRs.
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