“…Advanced substrate materials for microwave integrated circuits require a low dielectric constant (ε r o10) to maximize the signal propagation speed, a high quality factor (Q Â f) to increase the frequency selectivity, and a near-zero temperature coefficient of resonance frequency (τ f ) to ensure the stability of the frequency against temperature changes [1][2][3][4]. At present, many low ε r ceramics such as Al 2 O 3 , AO-SiO 2 (A¼Ca, Mg, Zn), MTiO 3 (M¼Mg, Ca) have good microwave dielectric properties but high sintering temperatures, which is energy-consuming.…”