Candidate:Â Yuan Fang
Date: May 2, 2025
Time: 1:00 pm
Location: Zoom (online)
Supervisors: Drs. Lan Wei and Ujwal Radhakrishna
All are welcome!
Abstract:
Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) are rapidly being featured as core components in modern high voltage and high frequency systems due to their wide bandgap, high breakdown voltage, and superior electron mobility. They are rapidly finding new topologies and technologies to address industrial challenges. The MIT Virtual Source GaN (MVSG) model is a physics-based compact model that accurately predicts device behaviour of a wide variety of effects seen in GaN HEMTs.
A central contribution of this work is the development of a systematic extraction flow that is easy to understand, but thoroughly calibrates a model to the highest potential. It features extraction of contact resistances using transmission line model (TLM) structures, capacitances with various small signal analyses, and a thorough channel transport extraction, all with temperature coefficients and guidelines on measurement techniques. Calibration of the thermal module is considered throughout the extraction flow, allowing better isolation between different parameters. A robust way to obtain the thermal capacitance is also present, further enhancing the utility of the model. For the first time ever, an extraction flow has been added to a charge trapping model, only requiring transient measurements to be obtained, but allowing all parameters to be obtained accurately.
To support further development of the GaN HEMT industry, the MVSG model has been augmented with a more robust high injection model and p-GaN module — both of these a first in compact modeling. The high injection model is robust and computationally simple, producing textbook quality curves. The p-GaN module, based in physical principles, allows modeling of Schottky gated devices, as well as hybrid devices, offering a wide spectrum of applicable use cases. It accurately predicts behaviours seen all across industry, including the Dynamic Vt0V_{\textrm{t0}} shift, charge storage, and voltage division effects. With the rapid commercialization of enhancement mode devices, this model is essential to circuit design simulations.
The MVSG model has been used extensively to characterize GaAs devices, using the same extraction methodology for GaN devices. The predictive capabilities of the model were put to the test with the availability of different geometries, where excellent agreement with measurements was achieved.
Future work from this thesis includes further refinement of the p-GaN module and extracting parameters. Geometry dependent thermal module parameters are also an area of interest. Bi-Directional GaN HEMTs, with symmetrical IV capabilities, are also starting to be developed. These devices use the p-GaN technology that is modeled in this thesis.
In summary, the parameter extraction flow and model enhancements significantly improve the utility of the MVSG compact model. These contributions form a foundation for further development, fueling the next generation of computer aided design in the GaN industry.