High permittivity and low loss microwave dielectrics suitable for 5G resonators and low temperature co-fired ceramic architecture

Abstract

Bi₂(Li_0.5Ta_1.5)O₇ + xBi₂O₃ (x = 0, 0.01 and 0.02) ceramics were prepared using a solid state reaction method. All compositions were crystallized in a single Bi₂(Li_0.5Ta_1.5)O₇ phase without secondary peaks in X-ray diffraction patterns. Bi₂(Li_0.5Ta_1.5)O₇ ceramics were densified at 1025 °C with a permittivity (ε_r) of ∼ 65.1, Q_f ∼ 15 500 GHz (Q ∼ microwave quality factor; f ∼ resonant frequency; 16 780 GHz when annealed in O₂) and the temperature coefficient of resonant frequency (TCF) was ∼ −17.5 ppm °C⁻¹. The sintering temperature was lowered to ∼920 °C by the addition of 2 mol% excess Bi₂O₃ (ε_r ∼ 64.1, a Q_f ∼ 11 200 GHz/11 650 GHz when annealed in O₂ and at a TCF of ∼ −19 ppm °C⁻¹) with compositions chemically compatible with Ag electrodes. Bi₂(Li_0.5Ta_1.5)O₇ + xBi₂O₃ are ideal for application as dielectric resonators in 5G mobile base station technology for which ceramics with 60 < ε_r < 70, high Q_f and close to zero TCF are commercially unavailable. They may additionally prove to be useful as high ε_r and high Q_f materials in low temperature co-fired ceramic (LTCC) technology.