Physics, Characterization and Modeling of RF Linearity in SiGe HBT and FinFET Technologies

This paper presents transistor physics underlying distortion in RF SiGe HBTs and FinFETs, their experimental characterization and modeling, particularly the sweet spots, i.e., the V
BE
/V
GS
at which RF linearity peaks and its V
CE
/V
DS
dependence. For SiGe HBTs, collector-base junction capacitance and avalanche nonlinearities are most important besides the "intrinsic" exponential transconductance nonlinearity. For FinFETs, both the transconductance and output conductance nonlinearities are important. A sweet spot also occurs in both HBTs and FinFETs when dominant nonlinearities cancel. FinFETs have the advantage of operating with high f
T
, high f
max
and high IP3 at very high g
m
/I
DS
desired for low power RF design. Techniques for reducing or removing distortions of instruments including RF sources and receivers are discussed, including an example of using X-parameters for highly linear common-base SiGe HBTs.