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DOE/Opt has been applied to simulator model tuning. In this case, the goal was to determine ionization coefficients in an internally enhanced version of PISCES  to match measurements of substrate current. The model is of the form . PISCES simulation decks were developed which calculate substrate current () at drain voltages , 6, and 7 volts, and gate voltage , 2, 3, and 4 volts. The input parameters to the script are the ionization model coefficients , , and exponent . A Box-Wilson experimental design varying these parameters was performed, and regression models of as a function of the ionization model coefficients were constructed. Optimization was performed using the response surface models to find ionization model coefficients that achieved the best fit to the experimental data (minimum sum of squared error). The result was approximately 15% average error across several values. A comparison between the substrate currents from measurements, simulation before calibration, and simulation after calibration is made in Fig. 8.
Two observations on the use of DOE/Opt in this problem bear special mention. First, we found that DOE/Opt is well suited to optimization and fitting to a small and mixed number of targets and constraints. In its current form, it is not ideal for ``parameter extraction'' where one desires to fit to large sets of data. Work to improve DOE/Opt's capability by interfacing to the MACH system is underway . Second, we find that the most difficult task facing a user of DOE/Opt is writing the data extraction routines used within a script body. We found it necessary to develop and make available to users utility routines that extract data (e.g. current-voltage curves) from process and device simulation output files. To support higher level tools such as DOE/Opt, it is important that the textual and binary output formats of simulation tools be well documented and available.