Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Electrical Engineering

First Advisor

Enrico Santi

Abstract

Silicon carbide (SiC) is considered the most promising material for next-generation power semiconductor devices due to its superior physical properties in terms of switching speed, breakdown voltage, maximum operating temperature, high thermal conductivity, high current density, and extremely stable chemical characteristics. Currently, 1200V/20A SiC junction field effect transistor (JFET) is at the verge of being commercialized by various companies, including SemiSouth Laboratories, Inc. The fabrication of other devices, like high voltage SiC MOSFET, is progressing. Providing circuit simulator models for these revolutionary devices is of great importance to facilitate their adoption by circuit engineers.

Given the fact that the power JFET is a simple device and provides a good starting point for manufacturing and modeling of power devices made out of SiC, this dissertation works in two related areas of power semiconductor device modeling. One is development of physics-based models for the power JFET, currently the most mature active SiC power device. The other is definition of a hierarchy of model levels and the development of high-accuracy behavioral models and of methods to extract the parameters used by these models.

Regarding the operating conditions of SiC devices, it turns out that, in order to fully exploit the superior material characteristics of the material, SiC devices operate with high electric field in the channel region during conduction. Therefore, electric field dependant mobility plays a very important role in determining the characteristics of SiC power semiconductor devices. In the first research area, as part of this research effort, two distinct models are proposed for SiC JFETs. The first model is a piecewise model with a separate set of equations to describe operation in the linear and saturation regions. An important contribution of the proposed work is a method to determine the boundary region between linear and saturation region, which is essential for the development of a usable circuit simulator model. The second model uses a single set of equations to describe operation in both the linear and saturation region. This provides a more robust model implementation and a more physical description of the saturation phenomenon.

For the second research area, a hierarchy of model levels is defined, starting from simple behavioral models and moving on to more complex physics-based models all the way to finite-element models. The concept is that, for modeling and simulation, models with various simulation accuracy and simulation running time are needed to perform simulation studies at different levels of detail. Six model levels are defined: the first three levels are behavioral and the remaining three are physics-based. Each model level increases in complexity and provides details not available in models at lower levels. Higher level models have higher simulation accuracy, but simulation cost is higher. The JFET model described in the first research area is an example of a physics-based model. This research effort in the second research area concentrates on behavioral models, both averaged and switching, which are appropriate for system-level studies. Overall, three levels of behavioral models have been developed. They are level-0, an averaged switch model that models both conduction and switching losses, level-1A, a behavioral switch model comprising a voltage-controlled resistor V-switch and an ideal diode, level-1B, a behavioral switch model comprising a voltage-controlled resistor V-switch and a diode with reverse recovery current. These behavioral models are developed in Spice and in the Virtual Test Bed (VTB), a system simulation software developed at the University of South Carolina.

Rights

© 2010, Zhiyang Chen

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