An investigation of BST:MgTiO3 and X7R:MgTiO3 based ceramics for microwave applications

There is a growing demand for dielectrics with field tunable permittivity for use in frequency agile filters and phase shifters at microwave frequencies. The paraelectric phase composition of barium strontium titan a to (BST) is a popular choice because of its non-linear properties demonstrated by the field dependence of permittivity. However, the dielectric properties of BST compositions are temperature dependent, and thereby compromise the tunability. In this paper the dielectric properties of temperature stable X7R dielectrics (ΔC < 15% for -55°C < T < 125°C), BST and their composites with magnesium titanate (MT) have been investigated to determine their field dependent tunability. Magnesium titanate is a low permittivity material has been used to attenuate the relative permittivity and lower the dielectric loss of BST and X7R for microwave frequency applications. A series of (1-x)BST:MT and (1-x)X7R:MT composites have been synthesized (x=0.0 to 0.5), at sintering temperature ranging from 1200°C to 1400°C. Structural characterization of these composites have been carried out and their dielectric permittivity was measured as a function of temperature and DC bias field.