Application of copper conductor and ruthenium containing oxides-glass resistor to high-frequency hybrid ICs for a portable cellular radio

An assessment of a copper-conductor and resistor system and its performance in a high-frequency hybrid application is presented. Resistance of the copper compatible resistor, containing RuO₂, increases after refiring over 600°C and drastically increases as the firing temperature is raised. Scanning-electron-microscope and energy-dispersive microprobe analyses revealed the existence of a RuO₂-poor area in the resistor adjacent to the copper terminals. The resistivity in this area is higher than that in areas removed from the terminals, and it increased with the refiring temperature. These facts indicate that the resistance change is caused by the diffusion of Ru to the copper conductor. Various approaches were taken to minimize this phenomenon. The most effective was insertion of a conductor pad between the copper conductor and resistor. Resistors with this type of Ag-Pd conductor pad meet the various requirements for practical application of hybrid ICs. Based on these results, a prototype, high-frequency hybrid IC (voltage-controlled oscillator, VCO) was fabricated