Processing, microstructure, and electric properties of buried resistors in low-temperature co-fired ceramics

Abstract

The electrical properties of ruthenium oxide based devitrifiable resistors embedded within low-temperature co-fired ceramics were investigated from −100 °C to 100 °C. Special attention was given to the processing conditions and their effects on resistance and temperature coefficient of resistance (TCR). Results indicate that within this temperature range the conductance for these buried resistors is limited by tunneling of charge carriers through the thin glass layer between ruthenium oxide particles. A modified version of the tunneling barrier model is proposed to account for the microstructure ripening observed during thermal processing. The model parameters determined from curve fitting show that charging energy (i.e., the energy required for a charge carrier to tunnel through the glass barrier) is strongly dependent on particle size and particle–particle separation between ruthenium oxide grains. Initial coarsening of ruthenium oxide grains was found to reduce the charging energy and lower the resistance. However, when extended ripening occurs, the increase in particle–particle separation increases the charging energy, reduces the tunneling probability and gives rise to a higher resistance. The tradeoff between these two effects results in an optimum microstructure with a minimum resistance and TCR. Furthermore, the TCR of these buried resistors has been shown to be governed by the magnitude of the charging energy. Model parameters determined by our analysis appear to provide quantitative physical interpretations to the microstructural changes in the resistor, which in turn, are controlled by the processing conditions.