Large-signal characterization and modeling of the heterojunction bipolar transistor.

Rapid improvements in Heterojunction Bipolar Transistor (HBT) device performance have made power applications in the millimeter wave regime possible. Improved large-signal modeling and characterization techniques are required for designing circuits at these frequencies. Several large-signal modeling approaches are investigated in this thesis. The most detailed model involves numerically solving moments of the Boltzmann Transport Equation. Velocity overshoot and energy relaxation effects are included in this model. After a detailed description of the numerical techniques is given, the model is used to investigate HBT operation under large-signal steady state RF conditions. Internal device carrier concentrations, electric fields, electron temperature, and electron velocity are determined at various stages during the RF cycle. While the model is a valuable tool for studying the internal device physics, its use in circuit design applications is limited due to the computer time required. The fully numerical model is then used to investigate several simpler large-signal HBT models. It is found that the commonly used Gummel-Poon model exhibits poor agreement with numerical and experimental data at millimeter wave frequencies due to neglect of transit time delays. A modified Ebers-Moll model is described which overcomes this problem by implementing the transit time delay in the frequency domain. Two large-signal measurement systems covering 8 to 35 GHz were built to compare simulated results with experimental data. A commercial tuner system was used to make measurements from 8 to 16 GHz. However, to measure beyond 26 GHz, an active loadpull system was designed and constructed to circumvent problems created by component losses. Details of this measurement system, its accuracy, and error correction techniques are given. Good agreement between measured and modeled output power, gain compression, and efficiency is obtained using the modified Ebers-Moll model over a wide range of frequency and bias. Gain compression mechanisms, optimum impedance shift, and self bias effects are investigated to demonstrate the effectiveness of the model at millimeter wave frequencies. By using both measured and modeled data in a complementary fashion, an improved understanding of large-signal HBT behavior is obtained.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103323/1/9308466.pdfDescription of 9308466.pdf : Restricted to UM users only