MICROSTRUCTURAL GLASS MODIFICATIONS IN AS-FIRED AND HIGH-VOLTAGE-SURGED RUO2-BASED THICK-FILM RESISTORS

Electrical conduction in thick film resistors has been studied, and microstructures, especially around conducting RuO2 phases in a lead-borosilicate glass matrix in as-fired and high-voltage-surged thick film resistors, have been observed in detail using transmission electron microscopy. Lattice images of as-fired thick film resistors have suggested the presence of subtle structural modifications in the very thin area across the RuO2/glass interface, whereas in the glass matrix very small dot-like contrasts on the order of 1 nm were occasionally observed and were interpreted as being small crystallites or Ru clusters. Heavy electrical loadings of thick film resistors were found to induce the local formation of plate-like crystals in glass, which were identified by electron diffraction to be a slightly modified anorthite. The significance of these observations in terms of the conduction network and the degradation due to the electrical overloading of thick film resistors are discussed.