Effects of LiF additives, sintering method on the crystal structure, and microwave dielectric properties of Li4CaSr(SiO4)2 ceramic for low temperature co-fired ceramic application

Abstract

Two series of LiF-doped Li4CaSr(SiO4)2 (LCSS) ceramics with different LiF contents were synthesized by SSR and RS methods. The formation of single-phase LCSS + x wt% LiF (x = 0–4, SSR) (LCSSL04) and LCSS + y wt% LiF (y = 0–8, RS) (LCSSF08)ceramics with an orthorhombic structure (Pbcm space group) was confirmed by the Rietveld refinement of their XRD data. The addition of LiF improved the relative density and microwave dielectric properties of LCSS + x wt% LiF (0 <x ≤ 2, SSR) and LCSS + y wt% LiF (0 <y ≤ 3, RS). The LCSS +2 wt% LiF (SSR) ceramic exhibited good properties, presenting a dielectric permittivity (εr) of 7.03, quality factor (Q × f) of 62,195 GHz (at 11.6 GHz), and temperature coefficient of resonant frequency (τf) of −76 ppm/°C. Further, the LCSS +3 wt% LiF (RS) ceramic exhibited outstanding performances, with an εr of 6.1, Q × f of 103,086 GHz (at 15.8 GHz), and τf of −67 ppm/°C. The chemical compatibility with silver suggests that both of them are potential candidates for low temperature co-fired ceramic (LTCC) devices.