Low third-order intermodulation distortion in Ba0.6Sr0.4TiO3 thin film interdigital capacitors

A new method for the theoretical analysis of the thirdorder intermodulation distortion (IM3) in barium strontium titanate (BST) thin film interdigital capacitors (IDCs) on r-plane sapphire substrates is presented. Two circuit topologies - the dual and series dual BST varactor circuit - are proposed and their theoretical models along with simulated and measured results are presented. Low IM3 is demonstrated and experimentally verified. By proper selective biasing, very low nulls are observed in both dual and series dual BST varactor circuit topologies which indicate minimum distortion. The measured first nulls are achieved at ±13V and ±20V for the dual and series dual topologies respectively. These results demonstrate the potential of incorporating these highly linear BST varactors in silicon on sapphire (SoS) applications.