Direct Parameter Extraction for Dispersive Large-Signal GaN-HEMT Models from Nonlinear Measurement

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Accurate transistor models are required in order to simulate monolithically integrated microwave circuits. These models are commonly determined from numerous measurements, e.g. to determine sequenceally the extrinsic elements, the DC behavior and the capacitances. Although a lot of these measurements are carried out in conditions that are very different from the regular transistor operation, it is assumed that the transistor performance is consistent in the way that the underlying assumptions concerning the transistor physics are correct. Combining the results of the different parameter extraction steps needs to yield a model for the transistor in total. This assumption can't be taken for granted. The most interesting transistor type that is difficult in this respect is the GaN HEMT. Traps are still dominant in this type of transistor and lead to dispersive behavior, or memory effects. The GaN HEMT usually behaves differently, if e.g. output IV curves, S-parameters, or load-pull measurements are performed. The GaN HEMT and its traps is a matter of ongoing research, which is closely linked to the question of how to characterize its performance. This project therefore attempts to determine the transistor model parameters directly from large-signal voltage and current waveforms though analytical algorithms. The question is how this measurement data can be interpreted and arranged in a way that allows a direct parameter extraction without relying on global optimization. The advantage of such an approach would be on one hand, that the measurement from which the parameters are determined resembles the real operation conditions. On the other hand, one would still keep the possibility to get some insight into the transistor physics. The project is divided in three parts.In a first step, a simple measurement setup will be implemented, that allows for the measurement of voltage and current wave forms in the lower MHz range. In contrast to the GHz measurement system that is already available, it will be possible to neglect the impact of capacitances in the lower MHz range. An investigation of how to determine the transistor's current source will be carried out based on these measurements. Finally, the extraction of the transistor capacitances will be addressed. As the outcome of this project, the theoretical and practical requirements for the direct extraction of transistor model parameters from large-signal current and voltage waveforms will be known. The requirements in terms of measurement and transistor behavior enabling a successful extraction will be given, and limitations will be theoretically described and verified by measurement.