Dielectric properties of temperature-stable Li2O–Al2O3–B2O3–CaTiO3 glass-ceramic composite for LTCC application

Abstract

In this paper, the phase composition and dielectric properties of temperature-stable (1-x)LAB + xCaTiO₃ (x = 0.225, 0.250, 0.275, 0.300) glass-ceramic composites are systematically investigated as well as their potential applications in microwave communications. The multi-phase structure of the materials, including CaTiO₃, Li₂AlBO₄, LiAlB₂O₅, and Li₂TiO₃ phases, was revealed by XRD. The enhancement of the bulk density and the relative permittivity of the materials was attributed to the high density and permittivity of CaTiO₃. Furthermore, the dielectric loss of the material is predominantly governed by its phase composition, with the Q×f value exhibiting a decline with an increase in the content of CaTiO₃, which is closely associated with the variation in the ratio between the CaTiO₃ phase and the Li₂TiO₃ phase. The temperature coefficient of resonance frequency of the 0.75LAB+0.25CaTiO₃ samples sintered at 520–560 °C was successfully regulated to within ±10 ppm/°C at 520–560 °C, which demonstrated excellent temperature stability. Moreover, 0.75LAB+0.25CaTiO₃ samples exhibited no chemical reaction with silver electrodes after co-firing at 540 °C, rendering them suitable for LTCC applications. Finally, a rectangular aperture coupled patch antenna based on this material (ε_r = 8.90, Q×f = 25609 GHz at 10.9 GHz, τ_f = 9.10 ppm/°C) was designed with a center frequency of 6.54 GHz, a bandwidth of 140 MHz, an antenna efficiency of more than 87 %, and a maximum gain of 7.858 dBi, demonstrating its great application value in microwave communications.