(Ca1 − x Mx)V2O6 (M = Zn, Ba) ultra-low temperature co-firable ceramics for microwave power divider applications

Abstract

The effects of substituting Zn²⁺ and Ba²⁺ for Ca²⁺ on the crystal structure, sintering temperature, microstructure, and microwave dielectric properties of (Ca_{1 − x} M_x)VO₆ (M = Zn, Ba) [x = 0.025–0.10] have been studied. X-ray diffraction, along with refinement results, indicate that all the samples had a monoclinic crystal structure with C2/m space group, and the cationic substitutions affect the cell volume of the ceramics while retaining the crystal structure. Both Zn²⁺ and Ba²⁺ at Ca²⁺ in small percentages improved the density and dielectric properties. The (Ca_0.95 Zn_0.05)V₂O₆ ceramic sintered at 650 °C achieved ε_r = 10.6, Q × f = 42,400 GHz and τ_f =  − 60 ppm/°C, while the (Ca_0.95 Ba_0.05)V₂O₆ ceramic sintered at 600 °C showed ε_r = 10.1, Q × f = 46,100 GHz, and τ_f =  − 59 ppm/°C. All the (Ca_{1 − x} M_x) VO₆ ceramics exhibited a negative value of τ_f. The chemical compatibility with metal electrode was investigated by cofiring both ceramics with Aluminium (Al) metal at the optimised sintering temperature. XRD and EDS analysis confirmed the non-existence of reaction between ceramic and metal and formation of any other secondary phases, indicating significant potential of the ceramics for use in ULTCC applications. Furthermore, a 2-section Wilkinson power divider operating in the L band has been designed and fabricated onto the ULTCC ceramic by screen printing techniques using low temperature curable silver epoxy paste. The fabricated power divider showed a maximum insertion loss of 4.8 dB and a minimum isolation of 14 dB in 1–1.7 GHz matching with the simulation.