Combined Device-Circuit Simulation for Advanced Semiconductor Devices

To develop and optimize semiconductor devices it is common practice to advocate numerical device modeling by using simulation programs. Typically the simulation of a unit is split into levels, starting with process simulation (to study the effect of wafer-processing steps) and device simulation (to study the electrical behavior), to circuit simulation (to study the electrical features of an ensemble of devices), leading possibly to the logic simulation of a whole unit. Unfortunately, this approach makes it very hard to model the interaction of the device and the circuit in the transient case: therefore, in order to optimize the transient behavior of a particular device it is necessary to include the effects of both the drive circuit (i.e., control part), as well as the load circuit. During the last year, we have developed a software environment for combined device-circuit simulation studies dedicated to semiconductor power devices, magnetic field sensors, and Bicmos structures augmented with simple circuits. In our work we discuss some critical points in detail. These include the grid generation and adaptation, the scaling of the unknowns (i.e., how to deal with high voltages), the numerical procedures used to solve the transient problem (with special attention to supercomputer architectures), the assembly of the device (element assembly versus edge assembly) and circuit equations as well as the physical models used. We show that it is essential to properly chose the numerical techniques to obtain accurate and reliable results. Studies of the turn-off of power devices, the switching of BiCMOS structures, and of magnetic field sensors indicate the success of the current approach.