Processing of LTCC with embedded RuO2-based resistors

A commercial resistor was embedded in calcium boron silicate glass-ceramic and glass-ceramic+SiO2 substrates. The microstructure of the resistor/substrate interface had been investigated using scanning and transmission electron microscopy (SEM and TEM), and its correlation to the overall resistance had been discussed. Formations of second phases were examined by X-ray diffractometry (XRD) and electron diffraction. Due to interactions between resistor films and substrates, second phases and conductive particles flocculation were observed in the resistor layers. Cristobalite phase formed in the glass-ceramic substrate and at interface between the resistor and substrate. Very few second phases, such as wollastonite (CaSiO3), CaB2O4, and quartz (SiO2) crystals, were formed in the resistors under TEM observation when sintered at temperature of 850 °C. Conductive particles in the resistor film flocculated and became clusters with size of ∼200 nm. Sedimentation of clusters and glass migration to substrate layer increased the conductive cluster volume fraction. Volume fraction of conductive clusters of the embedded resistors was the major factor to determine the resistivity of the films. Resistor film with high conductive cluster volume fraction had lower resistivity comparing with a low conductive cluster volume fraction film. Due to high volume fraction of conductive cluster, the resistivities of resistor films were not affected by the second phases formed in the resistors.