Impact Ionization in LDMOS Transistors: Improved Compact Model and Asymmetry Under Forward and Reverse Modes of Operation

This study proposes improved compact models for impact ionization in the intrinsic and drift regions of Laterally-Diffused-Metal-Oxide-Semiconductor (LDMOS) transistors. These models are rigorously validated across a wide range of high drain and gate voltages for different channel widths, demonstrating their robustness and applicability. The model flexibility is further enhanced by incorporating a control feature that precisely regulates the progression of drain current to drift saturation current under high drain bias. Furthermore, the inherent asymmetry of the LDMOS device results in substrate current under forward $(V_{ds}\gt 0V)$ and reverse $(V_{ds} \lt 0V)$ modes differing by orders of magnitude. Therefore, we also introduce a compact model for reverse mode impact ionization current in LDMOS transistors, addressing this discrepancy. Finally, we integrate the proposed impact ionization current model into the existing Verilog-A framework of the BSIM-BULK high voltage compact model, ensuring compatibility with SPICE simulators.