4.3 Anomalous Output Characteristic

Calculating the drain current with the energy transport model gives a completely different and unexpected result. As can be seen in Fig. 4.5, the output characteristics differ significantly from those obtained by drift-diffusion, Fig. 4.2.

Figure 4.5: Output characteristics of the SOI (Device 1) obtained by energy transport simulations using the device simulators MINIMOS-NT and DESSIS. The influence of impact-ionization is also shown.

After reaching a maximum at about $V_{DS} = 0.2 \, \mathrm{V}$, the drain current decreases considerably. This negative differential output conductance is predicted by two different device simulators. Fig. 4.5 shows the results obtained from our device simulator MINIMOS-NT [33] and the commercially available device simulator DESSIS [34]. An implementation error of the energy transport model can therefore be ruled out as the cause for the anomalous characteristics. The results are in good qualitative agreement. The small quantitative differences are due to slightly different default values for mobility and impact-ionization parameters. Self-heating cannot cause such a large negative differential conductance and has been neglected in the simulations.

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