Extrinsic loss mechanisms in BST for tunable RF/Microwave passive components

Dielectric properties of (Ba/sub 1-x/Sr/sub x/)TiO/sub 3/ of x=0.35-0.55 were studied in the frequency range 1-3 GHz. Samples sintered at 1350/spl deg/C for 3 hours in oxygen exhibited permittivity values > 400 along with /spl sim/3% loss at >1GHz. Air sintered samples had higher loss (/spl sim/5%) and lower permittivity. This peculiar behavior of paraelectric BST is discussed within the framework of the model proposed by Vendik et al.[1969]. Extended sintering times (/spl sim/6 hours) were found to promote lower losses (/spl sim/0.4%) and it can be attributed to higher chemical homogeneity and larger grain size.