FEM simulation approach to investigate electro-thermal behavior of power transistors in 3-D.

A simulation approach is presented which can be used to investigate electro-thermal behavior of power transistors in variety of operating conditions. The approach is discussed in detail and demonstrated using ANSYS simulator. The power transistor is considered as a distributed voltage controlled resistor consisting of many in parallel connected cells. Because every cell has individual gate– and drain–source voltage, 3-D effects depending on geometric configuration and used materials can be observed. This is shown on a simple power transistor model for three principal electrical operating points: below TCP (temperature compensated point), at TCP and above TCP. Additionally, a mix-mode operating point is showed. The simulation results show 3-D effect of current density distribution as a function of the operating points. The results showed very good agreement with the prediction from the theory and already published results achieved by 3-D modeling approaches.