Intermodulation Distortion in GaN HEMT

This work treats intermodulation distortion performance of GaN-HEMT high-power transistors. A detailed study on the physical parameters influencing third-order intermodulation distortions is carried out, based on the large-signal model and on physical device simulation. Devices are characterized in terms of linearity by setting up a sophisticated measurement system. Among others, an electronic fuse is used at the drain side to avoid catastrophic failure during measurement. The bias-dependent transconductance characteristic is identified as the dominating source for intermodulation distortion in GaN HEMTs, while drain-source capacitance and access resistances have only minor influence. The corresponding physical parameters governing the transconductance behavior are determined and optimized structures for high linearity are proposed. Besides characterization and analysis of conventional designs, a novel device architecture for very high linearity is presented. Finally, performance of GaN HEMTs within a hybrid amplifier configuration is shown and the combination of high power, high linearity, and low-noise characteristics is highlighted.