2.4.2 Silicon and Silicon Germanium Heterojunction Bipolar Transistors

Figure 2.12: $f_T$ as a function of $BC_{EO}$ for Si bipolar technologies.

Figure 2.13: $f_T$ as a function of $BC_{EO}$ for several published SiGe HBT technologies.

For medium digital integration densities at high-speed of operation Si bipolar and SiGe heterojunction bipolar transistors are available. Pseudomorphic AlGaAs/InGaAs HEMTs and GaAs HBTs are in strong competition with those devices for the 40 Gbit/s high data rate communication. Despite of the Johnson limit constraints also for the next generation of 80 Gbit/s, SiGe HBTs will try to address as many chip functions as possible. Fig. 2.12 and Fig. 2.13 show the comparison of several Si and SiGe (H)BT technologies, taken from recent publications [45,69,117,141,197,308]. A behaviour is visible consistent with the product of ${\it f}_\mathrm{T}$  and ${\it BV}_{\mathrm{CE0}}$ (collector emitter breakdown voltage) obeying the Johnson limit, which confirms the trade off between RF-power and speed for this technology. A large optimization potential was suggested in [68] (e.g. ${\it BV}_{\mathrm{CE0}}$= 2 V, ${\it f}_\mathrm{T}$= 113 GHz also shown in Fig. 2.13). Recently published data for ${\it f}_\mathrm{T}$ and ${\it BV}_{\mathrm{CE0}}$ can be fitted by a value of 210 GHz V. ${\it f}_\mathrm{T}$ values as high as 130 GHz have been reported in [199], unfortunately without reporting the ${\it BV}_{\mathrm{CE0}}$ value.