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

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 Qxf 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 degrees C was successfully regulated to within +/- 10 ppm/degrees C at 520-560 degrees C, which demonstrated excellent temperature stability. Moreover, 0.75LAB+0.25CaTiO3 samples exhibited no chemical reaction with silver electrodes after co-firing at 540 degrees C, rendering them suitable for LTCC applications. Finally, a rectangular aperture coupled patch antenna based on this material (epsilon r = 8.90, Qxf = 25609 GHz at 10.9 GHz, tau f = 9.10 ppm/degrees 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.