A physically-based MOS transistor avalanche breakdown model

A physically based breakdown model for MOSFET's is presented to rectify the unexplained experimental breakdown behaviors. The drain avalanche breakdown in the MOS transistor can be caused by either infinite multiplication (MI) or finite multiplication with positive feedback of the substrate current (MF) due to the impact ionization in the pinch-off region. The breakdown voltages of these two modes of breakdown have different dependencies on the biasing conditions and device parameters. For MI mode of breakdown, the breakdown voltage increases slowly with the gate voltage and can be approximated by the drain saturation voltage plus a constant offset. For MF mode of breakdown, the breakdown voltage decreases as the drain saturation current becomes larger. The calculated breakdown characteristics agree well with the measured ones for devices with effective channel length in the range of 0.44~10 μm