Room-temperature-densified H3BO3 microwave dielectric ceramics with ultra-low permittivity and ultra-high Qf value

With the rapid development of mobile communication technology towards 5G and 6G, the microwave dielectric materials with ultra-low permittivity and ultra-high Qf value are urgently demanded. Here, the excellent microwave dielectric properties are reported in H3BO3 ceramics with the molecular crystal structure, whose permittivity (2.84) and density (1.46 g/cm3) are record-low among the low-loss ceramics. The ultra-high Qf value of 146,000 GHz (or the ultra-low dielectric loss of 1.03 × 10−4 at 15 GHz) is also distinguished. Besides, the H3BO3 ceramics can be densified at room temperature by a simple cold sintering process in a short time of 10 min, and this brings many advantages for the integration with microwave circuits. The large molecule volume originating from the molecular crystal structure and the low dielectric polarizabilities of H+ and B3+ are responsible for the ultra-low permittivity of H3BO3 ceramics, and more microwave dielectric materials with ultra-low permittivity and ultra-high Qf value are expected to be explored in the molecular crystals. [Display omitted] •Dense H3BO3 ceramics were prepared at room temperature by a simple cold sintering process.•H3BO3 ceramics with record-low εr (2.84) and ultra-high Qf value (146,000 GHz) are distinguished among low-loss ceramics.•The ultra-low εr is attributed to the large molecule volume of H3BO3 and low polarizabilities of H+ and B3+.•More microwave materials with ultra-low εr and ultra-high Qf value are expected to be explored in molecular crystals.