Small-signal intrinsic base resistance effect on InP-InGaAs, InGaP-GaAs and SiGe HBTs

In this paper, a comprehensive analysis of the effect of small-signal intrinsic base resistance (R
_bin
) on the RF performances of InP-InGaAs (Gao et al., 2004), InGaP-GaAs (Bousnina et al., 2004), and SiGe HBTs are demonstrated for the first time. It was found that for these HBTs, both the real part of the equivalent input impedance (Re(Z
_in
)) and the real part of the equivalent output impedance (Re(Z
_out
)) increase with the increase of the intrinsic base resistance R
_bin
. Therefore, an increase of R
_bin
(i.e. reducing the base doping, the base width, and the base edge length in the base contact side) makes the kink phenomena of both the scattering parameter S
₁₁
and S
₂₂
of these HBTs more obvious (Lu et al., 2001). These phenomena can be explained perfectly by our derived complete expressions of Z
_in
and Z
_out
at low and high frequencies. In addition, for relatively smaller R
_bin
, it was found that under constant collector-emitter voltage (V
_CE
), an increase of base current (which corresponds to a decrease of base-emitter resistance (r
_pi
) and an increase of trans-conductance (g
_m
)) enhances the anomalous dip. While for relatively larger R
_bin
, it was found that under constant V
_CE
, an increase of base current obscures the anomalous dip. These phenomena can also be explained by our proposed theory