  This paper studies the mutual coupling in trench isolated multi emitter
bipolar transistors fabricated in a Si/SiGe:C HBT technology STMicroelectronics
featuring fT and fmax of ~300GHz and ~400GHz, respectively. Thermal coupling
parameters are extracted using three dimensional (3D) thermal TCAD simulations.
The obtained parameters are implemented in a distributed transistor model that
considers self-heating as well as thermal coupling between emitter fingers.
Very good agreement is achieved between circuit simulations and DC measurements
carried out on an in house designed test structure.
