Substrate isolation in 90nm RF-CMOS technology

Substrate coupling on advanced high-speed and RF integrated circuits can have a significant impact on circuit performances. This parasitic effect is studied in the present paper in a triple-well 90nm RF-CMOS technology. Various configurations are investigated, like distance between blocks, use of P or N type guard-rings and use of triple-well junction isolation. Electrical models are proposed for these structures. At 1GHz and for a distance between blocks of 20 μm, a grounded P-ring improves the isolation by 15 dB compared to the case without guard ring. The most efficient protection to limit substrate coupling is a grounded P-ring around each block, placed at 20μm. In this case, the maximum isolation level is achieved with 60dB at 1GHz.