Characterization of Skin Effect in High-Speed Interconnects and Spiral Inductors

Wireless communication systems are expanding rapidly leading to the proliferation of RF applications in the UHF band (0.9-3 GHz). However stringent requirements are placed to make it essential for these applications to conform to strict technical standards and attain a high level of integration. These demands including low cost, low voltage, low power dissipation, low noise and low distortion cannot be achieved without fabricating high quality passive devices in the same substrate using the same technology. Therefore, recent advances in Bipolar, CMOS and BiCMOS processes have stimulated new approaches to circuit integration and architecture. This has included high conductivity multi-metal layers, low loss substrates and thick oxide to isolate components from lossy substrates. In parallel, with the insight gained from these investigations, simplified physical models and various numerical techniques have been developed to assess the performance of passive devices such as transmission lines and spiral inductors. Unfortunately, these approaches are not easily implemented in CAD tools and sometimes suffer from incompleteness. In fact, in many instances, circuits are successfully simulated but actual prototypes often fail to match the simulated results because of parasitic effects. This work describes the characterization of embedded transmission lines (ETL) and spiral inductors using scattering parameter measurements. A simple approximation allows for the extraction of the devices characteristics, taking into account capacitive and inductive coupling as well as losses. Thus calculations can be easily and quickly performed using these models.