High Quality Factor, Ultralow Sintering Temperature Li6B4O9 Microwave Dielectric Ceramics with Ultralow Density for Antenna Substrates

Dense Li6B4O9 microwave dielectric ceramics were synthesized at low temperature via solid-state reaction using Li2CO3 and LiBO2. Optimum permittivity ∼ 5.95, quality factor ∼ 41 800 GHz and temperature coefficient of resonant frequency ∼ – 72 ppm/°C were obtained in ceramics sintered at 640 °C with a ultrasmall bulk density ∼2.003 g/cm3 (∼95% relative density, the smallest among all the reported microwave dielectric ceramics). Li6B4O9 ceramics were shown to be chemically compatible with silver electrodes but reacted with aluminum forming Li3AlB2O6 and Li2AlBO4 secondary phases. A prototype patch antenna was fabricated by tape casting and screen printing. The antenna resonated at 4.255 GHz with a bandwidth ∼279 MHz at −10 dB transmission loss (S11) in agreement with simulated results. The Li6B4O9 microwave dielectric ceramic possesses similar microwave dielectric properties to the commercial materials but much lower density and could be a good candidate for both antenna substrate and low-temperature cofire...