Comparative analysis and parameter extraction automation of annular MOSFETs

Gate-enclosed MOSFETs are commonly used for extreme environments with constant radiation exposure due to its radiation tolerance. Because of its annular geometry, the standard BSIM3 models do not accurately represent what happens physically on the device. An accurate model extraction can take months to complete, thus the need for a fast extraction method. Of the several model extraction methods, the authors chose to extract the parameters through a method called conformal mapping. The mapping is performed using a Schwarz-Christoffel transformation. This allows the mapping of any arbitrary geometry into a well-known rectangular geometry. Additional parameters that change because of the geometry are recalculated for an accurate representation of short-channel effects and parasitic effects. Test chips with annular and rectangular devices were fabricated by MOSIS on AMI 0.6µm process technology. The SPICE model automation is performed with a Keithley Sourcemeter 2612 using LABVIEW. A call operation is performed to MATLAB to calculate aspect ratio using the mapping transformation toolbox. The final SPICE model should contain at least 22 parameters. This extraction can be performed in minutes on a laptop computer, allowing standard simulation without the need to create a separate device.