Maximum Operating Voltage Limitations Due to Parasitic Bipolar Action in VLSI CMOS

The influence of the PBTA (Parasitic Bipolar Transistor Action) induced by impact ionization on the maximum operating voltages as well as on the isolation performance in VLSI CMOS structures was investigated using the sensitivity of the nMOS- and bipolar-parameters to the operating voltages. Strong coupling between the MOS-and bipolar-currents exists due to the potential drop caused by the impact ionization currents of the nMOSFET. The base currents of the bipolar transistors reduce the measurable substrate current. The maximum operating voltage in CMOS is limited by the impact ionization induced PBTA. The isolation performance is reduced by the collector current of the vertical transistor.