Comparison of barium strontium titanate varactors on magnesium oxide and alumina substrates

A comparison of tunability and nonlinearity of planar (interdigital) barium strontium titanate varactors fabricated on magnesium oxide (MgO) and alumina substrates is presented. The results show that higher tunability is obtained on alumina than on MgO substrates. Two-tone measurements reveal that the devices fabricated on alumina exhibit more nonlinearity than those fabricated on MgO at relatively high RF power levels. The observed geometry-dependence of the non-linear performance is discussed.