CASMOS-an accurate MOS model with geometry-dependent parameters: I

The overall objective of this work has been to identify an MOS model that would meet the needs of circuit designers for CAD, and for which the parameters were easily derived and could be related to process variables, and so contribute to process control. The models in SPICE and MOSAID were evaluated but found unsatisfactory. A new model, CASMOS, has been developed which accurately represents MOS devices over a wide range of geometries with a set of 17 parameters. The equations are simple and economical in CPU time. The parameters can be easily and unambiguously extracted from electrical measurements and can be related to process data. The AC model is an improved version of the Ward and Dutton model, featuring charge conservation and a more accurate representation of CGD in saturation. Continuity of charge from region to region is guaranteed so that charge pumping is suppressed. CASMOS has been incorporated into SPICE and used for circuit simulation. Results of transistor characteristics are presented to demonstrate the accuracy of the DC model and of a ring oscillator to demonstrate the AC model.