6.6 Grid Matters

It appeared that in contrast to MOS devices the grid in the floating body region plays a crucial role to the stability of the simulation and the quality of the result. This is due to the fact that the drain current is very sensitive to the location of the potential drop in the floating region.

For example, when using a too coarse grid in vertical direction in the body area, unphysical ripples are observed in the output characteristics (Fig. 6.17). With increasing drain-source voltage the floating body area becomes smaller and the junction moves deeper into the semiconductor. Each time the junction reaches the next grid line, a pronounced drop in the drain current can be observed. The grid in vertical direction must be refined until the interpolation of the quantities between the grid lines has no influence on the output characteristics.

Fig. 6.17 shows output characteristics of such a device using different parameter values for the modified energy transport model.

Figure 6.17: Output characteristics of an SOI similar to Device 1 but with coarser grid in vertical direction.

M. Gritsch: Numerical Modeling of Silicon-on-Insulator MOSFETs PDF