ULTCC Glass Composites Based on Rutile and Anatase with Cofiring at 400 °C for High Frequency Applications

The article presents the very first materials to the ultralow temperature cofired ceramic (ULTCC) technology with the sintering temperature of 400 °C. The dielectric composites are based on a rutile and anatase with commercial GO17 sealing glass. In addition to the bulk samples, the tape casting procedure is also introduced to show its feasibility to cofiring with commercial Ag electrodes at 400 °C. The structural, microstructural, thermal, and microwave dielectric properties in the green and sintered samples were investigated. The optimum amount of glass to fabricate substrates was found to be 30 vol %. The ULTCC substrates with the anatase TiO₂A-30GO17 and rutile TiO₂R-30GO17 that were sintered at 400 °C showed a relative permittivity of 9.9 and 15 and a dielectric loss of 0.006 and 0.003, respectively, at the measurement frequency of 9.9 GHz. The temperature dependences of the relative permittivity were +70 and -400 ppm/°C, respectively. Moreover, the coefficients of the thermal expansion of the substrates were 7.4 and 8.3 ppm/°C in the measured temperature range of 50-300 °C. A preliminary test to study the feasibility of the anatase TiO₂A-30GO17 for a dual band antenna was performed due its relatively stable temperature behavior.