Substrate resistance effect on the Fmax parameter of isolated BJT in BiCMOS process

High frequency test structures for bipolar devices with several guard ring configurations are described. Using these structures, the substrate effect on merit figures such as Ft and Fmax has been studied experimentally and compared to Microwave Design System (MDS) electrical simulations. A worst case for guard ring position is proposed, providing up to 15 GHz Fmax degradation.