Low loss, temperature stable dielectric ceramics in ZnNb₂O₆–Zn₃Nb₂O₈ system for LTCC applications

Abstract

(1 − x)ZnNb₂O₆–xZn₃Nb₂O₈ mixed phase ceramics have been prepared by conventional solid state ceramic route by both mixing ZnO with Nb₂O₅ and by ZnNb₂O₆ with Zn₃Nb₂O₈, respectively. The sintered ceramics have high relative permittivity (ε _r  = 23–25), high quality factor (Q _u xf) up to 95,500 GHz and temperature coefficient of resonant frequency (τ _f ) in the range −55 to −73 ppm/°C. The quality factors are higher for the mixtures when prepared from ZnNb₂O₆ and Zn₃Nb₂O₈. The 0.5ZnNb₂O₆–0.5Zn₃Nb₂O₈ has Q _u xf = 95,500 GHz (at 5.16 GHz), ε _r  = 22.7 and τ _f  = −65 ppm/°C when sintered at 1200 °C. The τ _f of the ceramic has been tuned close to zero by the addition of ZnTa₂O_6, which has a positive τ _f . The ceramic composition (1 − y)[0.5ZnNb₂O₆–0.5Zn₃Nb₂O₈]–yZnTa₂O₆ with y = 0.91 shows ε _r  = 34.7 and Q _u xf = 41,950 GHz (at 4.63 GHz) and zero τ _f . In order to lower the sintering temperature of 0.5ZnNb₂O₆–0.5Zn₃Nb₂O₈ ceramic for low temperature co-fired ceramic applications, low melting additives such as CuO, B₂O₃ and ACuB₂O₅ (A—Ba, Sr, Zn, Ca) have been added. 12 wt% ZnCuB₂O₅ added 0.5ZnNb₂O₆–0.5Zn₃Nb₂O₈ ceramic sintered at 875 °C has Q _u xf = 39,750 GHz (at 5.89 GHz), ε _r  = 18.3 and τ _f  = −88 ppm/°C.