Analysis of RF Inductive Effect in S-Parameters of Body Contact PD-SOI MOSFETs

The anomalous RF inductive effect in which S
₂₁
- and S
₂₂
-parameters rotate clockwise in the lower and upper half-circles, respectively, with increasing the frequency at the high VDS region has been investigated in body contact (BCT) high-resistivity (HR) partially depleted (PD) silicon-on-insulator (SOI) nMOSFETs with a very high aspect ratio of gate finger. The negative output capacitance generated from a substrate current-induced body effect (SCBE) is physically identified for the first time as the origin of the RF inductive effect by deriving the output admittance equation of a body transconductance source in RF equivalent circuit model considering SCBE. The bias-dependent frequency effect that the drain-source conductance and negative capacitance converted from measured S-parameters are largely reduced by higher pole frequency with increasing VDS is clearly explained by admittance equations derived from the SCBE output equivalent circuit. The bias-dependencies of inductive effect parameters related to SCBE are accurately extracted using small-signal equivalent circuit modeling of BCT PD-SOI nMOSFETs. Based on this result, the bias-dependence of S
₂₁
and S
₂₂
-parameters is analyzed in detail.