Circuit models for quasi-3D spice simulation of turn-on transients in four-layer power bipolar devices

摘要

Improved transport models for quasi-3D circuit-based simulation (Q3DSim) of four-layer devices such as thyristors and transient over-voltage protectors (TOVPs) are presented. Q3DSim is an attractive alternative to full 3D transport equations based simulations (3D-TES), since it is much faster and requires less computer power. In Q3DSim, the thyristor is divided into four-layered square prisms, and a 1D PNP-NPN transistor pair model is associated to each of them in the anode to cathode direction. The PNP-NPN elements are interconnected through two transversal grid planes of circuit elements. The resulting equivalent circuit is simulated with Spice. Plasma-spreading velocity, used here as a benchmark, depends strongly on the current-dependent transport properties in the anode to cathode path given by the transistor gains, and on the transversal transport properties of both transistor bases. The new circuital models reported here, based on the quasi-static approximation, add drift and diffusion current components to Q3DSim transversal base planes. The circuit version of the base model was implemented with finite differences in Spice. The PNP transistor of the PNP-NPN basic model was complemented with a second PNP transistor that simulates the transport enhancement in the N-base due to the ohmic effect. All the required parameters are extracted from static TES. The power of the method was demonstrated by comparing 2D-TES plasma spreading velocity simulations with Q3DSim simulations. Both simulations were very close to each other in the 50-1200 A/cm~2 anode current density range. Moreover, the Q3DSim current wave front shapes were very close to 2D-TESs in the same current density range, showing the validity of the presented models.