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5.1.5 Results

For the calculation of the response surface, 9 runs with 28 simulation steps have been executed, and the optimizer needed about 250 evaluations of this response surface.

Figure 5.4 shows the target function (on-resistance RDS on) versus the parameter space of the control variables (epi-doping concentration nepi and epi-layer thickness depi). The minimum value of the on-resistance was found on the constraint where the breakdown voltage reaches the lower limit of $105 \ {\rm V}$.

Figure 5.4: Response surface of the target function.
\resizebox{1.\linewidth}{!}{ \psfrag{epi-conc [cm^-3]}{{$n_{epi}$} [${\rm cm~{-... ...${\rm \Omega}$]} \includegraphics[width=1.\linewidth]{graphics/surface.eps} }

The optimum process parameters found are listed in Table 5.2. The on-resistance of the optimal VDMOS transistor is $R_{DS(on)}= 0.614 \ {\rm\Omega}$ . In Figure 5.5 the source region of the optimum VDMOS transistor is shown.


Table 5.2: Parameters of the optimization problem.
Parameter Minimum Maximum Optimum
depi $8.0 \ {\rm\mu m}$ $14.0 \ {\rm\mu m}$ $10.37 \ {\rm\mu m}$
nepi $7.25 \cdot 10^{14} \ {\rm cm^{-3}}$ $2.9 \cdot 10^{15} \ {\rm cm^{-3}}$ $1.9 \cdot 10^{15} \ {\rm cm^{-3}}$

Figure 5.5: Net-doping concentration (in $\ {\rm cm^{-3}}$) of the optimized VDMOS transistor.
\includegraphics[width=1.\linewidth]{graphics/colorxv.ps}

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Next: 5.2 Optimization of Analytical Up: 5.1 Optimization with a Previous: 5.1.4 Solving the Optimization

R. Plasun