Closing the Loop from Materials Design to mmWave Devices: Ultrahigh-Q, Thermally Stable Mg2SiO4 Ceramics Enabled by Synergistic Ionic Engineering for 24 GHz Dielectric Resonator Antennas

Low-permittivity dielectric ceramics with ultralow loss, improved temperature stability, and reduced sintering temperature are critically required for millimeter-wave (mmWave) dielectric resonator antennas (DRAs), yet such synergistic optimization remains challenging in Mg 2 SiO 4 -based systems. Here, a coupled Ga 3+ /Li + heterovalent substitution strategy is proposed to regulate lattice energetics and chemical bonding in forsterite without disrupting its low-permittivity Si-O framework. Mg 2-x Ga 0.5x Li 0.5x SiO 4 (x = 0-0.06) ceramics exhibit enhanced densification and controlled grain growth, enabling a reduction of the optimal sintering temperature from 1500 to 1400 °C. An optimal composition at x = 0.04 achieves a low dielectric permittivity (∼6.9), an ultrahigh Qf (238 600 GHz at microwave frequencies and 295 000 GHz at 24.5 GHz), and a significantly improved temperature coefficient of resonant frequency (-42 ppm/°C). Spectroscopic analyses combined with P-V-L chemical bond theory reveal that Qf is dominated by Si-O lattice energy, whereas τ f is primarily governed by Mg-O bond characteristics. Furthermore, the introduction of SrTiO 3 enables effective τ f compensation toward near-zero values. A 24 GHz DRA further demonstrates excellent radiation efficiency, confirming the strong potential of the optimized ceramics for mmWave applications.