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

Dense Li6B4O9microwave dielectric ceramics were synthesized at low temperature via solid-state reaction using Li2CO3and 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). Li6B4O9ceramics were shown to be chemically compatible with silver electrodes but reacted with aluminum forming Li3AlB2O6and Li2AlBO4secondary 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 Li6B4O9microwave 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 cofired ceramics technology.