Ultra-Low-Temperature Cofired Ceramic Substrates with Low Residual Carbon for Next-Generation Microwave Applications

High-temperature cofired ceramics and low-temperature cofired ceramics are important technologies in the fabrication of multilayer ceramic substrates for discrete devices, electronics packages, and telecommunications. However, there is a place and need for materials with lower fabrication temperatures to decrease the associated energy consumption. The present paper studies the feasibility of two ultra-low sintering temperature cofired ceramic materials, copper molybdate and copper molybdate-Ag₂O, sinterable at 650 and 500 °C, respectively, for multilayer substrates using tape casting. The slurry composition developed uses environmentally friendly organics and a nontoxic binder and solvent. Additionally, the green cast tapes exhibit very low residual carbon (less than 5%) after sintering on analysis by X-ray photoelectron spectroscopy. The multilayer substrates show a permittivity value of about 8 with a low dielectric loss in the range of 10^-5 to 10^-4 in the frequency range of 2-10 GHz along with a low coefficient of thermal expansion in the range of 4-5 ppm/°C and good compatibility with an Al electrode. Thus, these proposed substrates have much promise, with good thermal, mechanical, and dielectric properties comparable to commercial substrates while also providing an energy and environment-friendly solution.