Reducing silicon-substrate parasitics of on-chip transformers

Three-terminal transformers have been fabricated on 20-/spl mu/m-deep silicon-oxide blocks formed in the silicon substrate. The thick isolation blocks drastically reduced the parasitics between the devices and the silicon substrate underneath. The quality factors and the self-resonant frequencies were thus increased by more than 100% and 70%, respectively. Such oxide blocks also greatly reduce the cross talk between adjacent devices by as much as 15 dB.