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

(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 (e 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), e 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 ZnTa2O6, which has a positive τ f . The ceramic composition (1 − y)[0.5ZnNb2O6–0.5Zn3Nb2O8]–yZnTa2O6 with y = 0.91 shows e 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), e r = 18.3 and τ f = −88 ppm/°C.