A physically based predicted lateral DMOS transistor model and circuit simulator for intelligent power IC design

This dissertation describes a physically based seminumerical static and dynamic model for nonplanar-drift lateral double-diffused MOS transistor and the development of a predictive circuit simulator for power IC TCAD. With the support of PISCES simulations for device operation, the model is based on a regional approach and its implicit equations are solved numerically. A simplified quasi-two-dimensional analysis is used to characterize the nonplanar drift region which is a feature in the investigated LDMOST structure. Transient behaviors are modeled with quasi-static charge-based circuit elements, including the graded-channel charge dynamics for the first time. The complete model has an ability to account for the unique LDMOST characteristics such as the doping-graded channel, the nonplanar-drift region, the space-charge-limited current flow in the drift region, and the inherent parasitic BJT action. The validity of the models has been evaluated in the calculation of device currents, conductances, charges, and capacitances. With a set of 40 model parameters evaluated in a systematic way, the computed results are in a satisfactory agreement with experimental measurements. The developed model has been implemented directly in SPICE2G.6 source code by adding 3 new subroutines for LDMOST model and modifying 18 existing subroutines to accept the new model. Unique implementation problems, e.g., techniques necessary to ensure current/charge continuity, are described. The LDMOST is listed with ID = 15 in SPICE list contents with Y-prefix element name in the device card, and the model parameters (ID = 25) are listed with the device type NLDMT in the model card. The utility of the new model in SPICE is demonstrated through representative circuit simulations, and the theoretical predictions are in qualitative agreement with other experimental investigations. With an advantage of directly using physical/technological parameters in its device model, the modified SPICE can be effectively used in computer-aided power IC design. The developed LDMOST model is also portable to other SPICE-like circuit simulators.