Ultrahigh- Q Sr _{1+ x} Y ₂O _{4+ x} ( x= 0.01–0.04) microwave dielectric ceramics for temperature-stable millimeter-wave dielectric resonator antennas

Abstract

Microwave dielectric ceramics should be improved to advance mobile communication technologies further. In this study, we prepared Sr 1+x Y 2 O 4+x (x = 0-0.04) ceramics with nonstoichiometric Sr 2+ ratios based on our previously reported SrY 2 O 4 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 SrY 2 O 4 . All Sr 1+x Y 2 O 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+x Y 2 O 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 temperaturestability requirements of 5G/6G communication systems by adding CaTiO 3 , with Sr 1.02 Y 2 O 4.02 +2wt%CaTiO 3 exhibiting ε r = 16.14, Q×f = 51,004 GHz, and τ f = 0 ppm/℃. A dielectric resonator antenna prepared using Sr 1.02 Y 2 O 4.02 +2wt%CaTiO 3 exhibited a central frequency of 26.6 GHz, with a corresponding gain and efficiency of 3.66 dBi and 83.14%, respectively. Consequently, Sr 1.02 Y 2 O 4.02 -based dielectric resonator antennas are suitable for use in 5G millimeter-wave band (24.5-27.5 GHz) applications.