Calculation time DC sweep vs. fixed voltage (DEVICE, electrical contact)


When I run two exact same simulations with a 3D electric field monitor, it takes 7 times as long to calculate results when I use a fixed voltage at 2.5V (electrical contact boundary condition) compared to sweeping the voltage from 0 to 5V with 5 interval points (thus also including the 2.5V voltage point). I seem to get exactly the same results with both.

Anybody has a clue why this could be happening?

The CHARGE solver always starts with an initial guess (the initialization stage) before it starts the iterations at each bias point. If this initial guess is a good one then the solver is able to reach a solution quickly. However, if the guess is a poor one then the solver will diverge or take a long time to reach the solution.

The solver always starts from the equilibrium case (zero bias everywhere). So when you are running a single simulation for a bias of 2.5 volt, the system is far from equilibrium and the initial guess becomes a poor guess. In the other case where you are sweeping from 0 to 5 V, the solver easily finds the solution for 0 V since it is in equilibrium. In the next step the solver uses the result from the previous bias point as the guess. Since 1 V is much closer to 0 V, the guess is a good one and the solver reaches the solution quickly. For 2V it uses the result of 1 V as the initial guess and so on. Since at all bias points the solver starts with a goo guess, the simulation in the second case is much faster even though you are sweeping through more points.

Hope this clarifies the situation.


Thank you. That clarifies things.