Accurate modeling and numerical techniques in simulation of impact-ionization effects on BJT characteristics

The inclusion of impact ionization in device simulation often suffers from numerical instability. In the present work, a general technique is demonstrated for applying circuit boundary conditions to achieve numerical stability. This technique has been used in the simulation of BV/sub CEO/ of an advanced silicon bipolar device. An I-V curve was obtained showing a new, previously unreported feature, namely, two distinct regions where snap-back occurs. Measurements on fabricated devices confirmed this phenomenon. A detailed physical explanation for the shape of the I-V curves is provided. The dependence on the width and doping of the epi-layer part of the collector is also analyzed.<>