Electrostatic capacitances of high-speed SiGe HBT

The extrinsic electrostatic capacitances of high-speed SiGe HBTs are evaluated both with measurement and modeling. Shrinking dimensions of the core of the HBT increases the influence of the extrinsic capacitance in the performances. The extrinsic capacitances are of half values compare to the intrinsic ones, limiting the cut-off frequencies f
T
and f
MAX
by 10∓12%, but care must be taken to avoid higher limitations associated with large electrostatic coupling in next device generation.