Improved Compact Model for High Speed SiGe HBT Breakdown

High speed SiGe-HBTs provide only a small VCE voltage variation between the saturation region (low VCE) and the breakdown at also rather low values. For high speed circuits it is unavailable to drive the SiGe HBT near the breakdown limits. In compact models used for circuit design the breakdown is described by the week avalanche approximation which is unsufficient for modern HBTs with short collector regions. We propose a more refined approximation which is based on the deed space concept for electrons to be accelerated up to the impact ionization energy. The model is implemented in the VBIC compact model.