Linearity of Power A1GaAs/GaAs HBTs

AlGaAs/GaAs HBTs are generating interest for their superior power performance in the 1-5 GHz frequency regime for applications such as wireless LANs and cellular telephones. Much of this interest stems from the fact that HBTs exhibit excellent linearity compared to other power devices. There has been little work done to understand and model the linearity of these devices. In this thesis the linearity properties of HBTs are addressed and an approach to developing an analytical model for predicting IMD3, the linearity figure of merit, is presented. The development is based on the two strongest sources of nonlinearity: the collector current and the base to emitter junction capacitance. The HP-Libra Harmonic Balance simulation environment based on the Gummel-Poon model was evaluated to be a good predictor of both one-tone and two-tone device performance. This simulation environment was then used to perform load and source pulls to optimize device operation. Simulations were also utilized to determine the sensitivity of IMD3 to various Gummel-Poon parameters at different biases. From the sensitivity analysis, it was found that the base to collector junction capacitance plays a significant part in the overall nonlinearity of the device at high collector current biases, whereas the base to emitter junction capacitance plays a more significant role at the low collector current biases. Thesis Supervisor: Jesis A. del Alamo Title: Professor of Electrical Engineering Acknowledgments I am indebted to my family, colleagues and friends for the successful completion of this project. I would first like to thank my family for their continuos support and love throughout my life. My parents have always created an environment where education is priority number one, providing the guidance, care and resources for such pursuits and I am indeed grateful. I would like to thank my advisor, Professor Jesis del Alamo. His knowledge, direction, help and support coupled with his mentoring have been most helpful for the completion of this project. I would like to thank Doug Teeter at Raytheon, who was very helpful in answering my questions and providing me with measurements on the devices. I would also like to thank the members of the research group who are always there to answer questions and provide insight. In addition to their cranial resources, Roxann, Mark, Alex, Chris, Jim, Taka, Sergei, Tassanee and Samuel have created an environment which is enjoyable to work in. Finally, I would like to thank my friends who have provide the necessary diversions needed to maintain sanity at MIT. I appreciate the friendship of Patrick, Q, Flash, and especially Erik Deutsch, who's advice and support I value greatly. The support for this work came partially from the Harold E. Edgerton Fund fellowship.