Interactions between ruthenia-based resistors and cordierite-glass substrates in low-temperature co-fired ceramics

Low-temperature co-fired ceramics (LTCCs) that are composed of a RuO2-based resistor and a cordierite-glass substrate have been sintered at temperatur es of 850 degrees and 900 degreesC. The microstructure of the resistor/subs trate interface has been investigated using scanning and transmission elect ron microscopy, and its correlation to the overall resistance has been disc ussed. X-ray diffractometry has revealed that lead ruthenate pyrochlore (Pb 2Ru2O6.5) in peak-fired thick-film resistors (TFRs) disappears and the co-f ired samples contain only RuO2 in the resistor film when sintered at 900 de greesC, The overall resistance of the LTCC resistors is increased by a fact or of similar to3 when temperature is increased from 850 degreesC to 900 de greesC. The cordierite- glass composition of the initial substrate reacts w ith glass in the resistor film. The greatly extended layer of the resistor/ substrate interface that contains the conductor particles is either broad o r diffuse, which contrasts the abrupt interface that often is observed in c onventional TFRs, This layer contains predominantly faceted platelike cryst als of anorthite, in addition to other phases (such as diopside, sapphirine , and cristobalite) that apparently crystallize during co-firing as vitrifi cation and chemical reactions between glass compositions of the substrate a nd the resistor occur. The increase in the resistance of the LTCC resistors is attributed to the interruption of the conducting path by platelike anor thite crystals that are produced in the resistor/substrate interface when s ubjected to co-firing.