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A Physics-based Large-signal Analytical Model for AlGaN/GaN HFETs
Hong Yin
Date: 2008-08-05
Degree: PhD - Electrical Engineering
Advisory Committee
Dr. Doug Barlage - Committee MemberDr. Griff L. Bilbro - Committee Chair
Dr. Mark Johnson - Committee Member
Dr. Robert J.Trew - Committee Co-Chair
Abstract
In this work, a complete physics-based large-signal model for AlGaN/GaN HFETs is developed. The model consists of two modules. An analytic DC model with no fitting parameters for both linear and saturated operation works as the DC module. Nonlinear analytic models for the I-V characteristics are developed in detail in this DC module. Under linear operation, the AlGaN/GaN HFET structure is divided into three zones before saturation: two zones in the two access regions; and one zone beneath the gate. In the source and drain access regions, nonlinear resistances are investigated and modeled. The nonlinear resistances affect drain current compression, which leads to a bell-shape transconductance. The Gradual Channel Approximation (GCA) is assumed in the region beneath the gate. After saturation, two additional zones appear at the gate edge close to the drain. They are denoted Space-Charge-Limited (SCL) and Charge Deficit Zone (CDZ) because of their transport physics and are proven dominant in saturated operation. For verification purpose, variant sets of examinations are designed and executed to prove the accuracy of models for each zone. The resulting equations in the various zones are linked together by voltage and current continuity at the boundaries. Good agreement between simulated and measured DC IV and transconductance is demonstrated without any adjustable fitting parameter. The RF module integrates the time-domain non-linear device model and the frequency-domain circuit model to form the complete simulator. Good agreement between simulated and measured dc and RF data is obtained for a practical device. This model is proven to be much more suitable for “what-if” device design than empirical models and much faster than physics-based numerical simulators, such as ATLAS. A large-signal equivalent circuit is suggested for future improvement and integration into commercial circuit simulators.
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