Lead-free thick film resistors (TFRs) were prepared by mixing of ruthenium oxide (RuO_2) and CaO-B_2O_3-Si02 based-glass. The resistors were post-fired on alumina and co-fired in LTCC substrates. Different metal oxides were added into the glass phase, such as Nb_2O_5, MnO_2; MoO_3, Fe_2O_3, TiO_2. They were used as temperature coefficient of resistor (TCR) adjustment agents of the resistors. The microstructures variations and interactions at the interface between resistors and substrates were investigated. The additives made glass structure loose and conductivity of resistor decrease, the TCR values of the resistors moved toward negative direction. When 4wt% VlnCb was added into the glass, the thick-film resistors embedded in LTCC had conductivity of 2.46 (Ω-cm)~(-1), the temperature coefficient of resistor decreased to 12 ppm/°C. The conductivities of the resistors films were depended on the volume fractions of conductor-agglomeration (RuO_2), microstructures, and TCR additives of the resistor layers
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