UltrahighQ Sr_1+xY₂O_4+x (x = 0–0.04) microwave dielectric ceramics for temperature-stable millimeter-wave dielectric resonator antennas

Microwave dielectric ceramics should be improved to advance mobile communication technologies further. In this study, we prepared Sr_1+xY₂O_4+x (x = 0–0.04) ceramics with nonstoichiometric Sr²⁺ ratios based on our previously reported SrY₂O₄ microwave dielectric ceramic, which has a low dielectric constant and an ultrahigh quality factor (Q value). The ceramic exhibited a 33.6% higher Q-by-frequency (Q×f) value (Q ≈ 12,500) at x = 0.02 than SrY₂O₄. All Sr_1+xY₂O_4+x (x = 0–0.04) ceramics exhibited pure phase structures, although variations in crystal-plane spacings were observed. The ceramics are mainly composed of Sr–O, Y1–O, and Y2–O octahedra, with the temperature coefficient of the resonant frequency (τ_f) of the ceramic increasing with Y2–O octahedral distortion. The ceramic comprises uniform grains with a homogeneous elemental distribution, clear grain boundaries, and no obvious cavities at x = 0.02. The Sr_1+xY₂O_4+x (x = 0–0.04) ceramics exhibited good microwave dielectric properties, with optimal performance observed at x = 0.02 (dielectric constant (ε_r) = 15.41, Q×f = 112,375 GHz, and τ_f = −17.44 ppm/℃). The τ_f value was reduced to meet the temperature-stability requirements of 5G/6G communication systems by adding CaTiO₃, with Sr_1.02Y₂O_4.02+2wt%CaTiO₃ exhibiting ε_r = 16.14, Q×f = 51,004 GHz, and τ_f = 0 ppm/℃. A dielectric resonator antenna prepared using Sr_1.02Y₂O_4.02+2wt%CaTiO₃ exhibited a central frequency of 26.6 GHz, with a corresponding gain and efficiency of 3.66 dBi and 83.14%, respectively. Consequently, Sr_1.02Y₂O_4.02-based dielectric resonator antennas are suitable for use in 5G millimeter-wave band (24.5–27.5 GHz) applications.