CHARACTERISTICS OF IMPACT-IONIZATION CURRENT IN THE ADVANCED SELF-ALIGNED POLYSILICON-EMITTER BIPOLAR-TRANSISTOR

With an algorithm to calculate the base current increase due to local thermal effect, we show that one can accurately measure the impact ionization current over the full range of collector current. For the first time, from the measured impact ionization ratio, we can quantitatively describe the characteristics of the space-charge modulation and base push-out effect over a wide range of collector current. Computer simulation was performed to support the measured data. We also show that one can use the measured impact ionization ratio to distinguish small collector concentration variations and thickness differences. The characterization was performed on self-aligned polysilicon-emitter transistors in an advanced BiCMOS technology.