Title

A physics-based model for microwave heterojunction bipolar transistors

Date of Completion

January 1999

Keywords

Applied Mechanics|Engineering, Electronics and Electrical

Degree

Ph.D.

Abstract

Modeling and analysis of microwave characteristics of HBTs have been performed. The physics-based modeling of the tunneling in heterojunction provides an exact simulation of the current transport. Incorporating the Fermi-level splitting and the effective junction velocity of electron, the law of junction is revised for heterojunction and reformulated. The resulting formulation is useful to design the HBTs. The accurate model of the Early voltage in HBTs is carried out by the consideration of surface recombination and other carrier recombination mechanisms. ^ Base transit time as well as cutoff frequency in HBTs for all level injection is studied. The calculation of base transit time is obtained including the thermal effect, Kirk effect, and non-stationary transport in base region. It is found that non-stationary transport should be considered for a narrow-base HBTs. The model of base transit time in HBTs also has been applied to GaN-based HBTs by incorporating the effective velocity of electron at base-collector junction and thermal effect on junction velocity. ^ Figure of merits of microwave and millimeter-wave HBTs, unilateral gain, maximum gain, and current gain, are performed by the physics of the device, the parameters and practical small-signal equivalent circuit. The output conductance of the intrinsic HBT could not be ignored for analyzing the unilateral gain of HBTs. ^ The nonlinearity behavior of the HBTs has been studied in terms of intermodulation distortion by developing a generalized formulation of the transfer function using the Volterra series representation. A closed-form expression for output power was derived by taking into account interactions between the nonlinear parameters and generated spectral components. ^