LiMSiO4 (M = Ga, Sc and Y): Low-permittivity and high thermal conductivity microwave dielectric ceramics for millimeter-wave communications

Abstract

The advancement of millimeter-wave communication desires the ceramic substrate with low permittivity (ԑ_r) to meet the requirements of high transmission rates, low latency and wide bandwidth. However, the thermal conductivity of most low-ԑ_r ceramics is too low to deal with heat dissipation in millimeter-wave applications. In this paper, we reported novel dielectric ceramics LiMSiO₄ (M = Ga, Sc and Y) with excellent performances of low ԑ_r (< 10) and high thermal conductivity (> 6 W mK⁻¹). Their dielectric properties in both microwave and THz were investigated, where the LiGaSiO₄ ceramic achieved the lowest ԑ_r of ∼5.2, the LiScSiO₄ ceramic presented extremely low loss (Q × f ∼ 96,700 GHz, Q = 1/dielectric loss, f is resonant frequency), and the LiYSiO₄ ceramic showed a positive temperature coefficient of f (TCF ∼ +32 ppm°C⁻¹). The distinct dielectric behavior was subsequently studied by structure-performance relationship in terms of M-site cations and bond parameters using bond valence theory, Phillips–Van Vechten–Levine chemical bond theory and so on. Moreover, a 36 GHz microstrip array antenna was designed and simulated using the LiGaSiO₄ ceramic substrate, obtaining high realized gain, high radiation efficiency and low sidelobe. The result demonstrated the great potential of LiMSiO₄-type dielectric ceramics in millimeter-wave communications.