Time domain analysis of circuit- and physics-based distributed models for high-frequency FETs

The emerging demand for semiconductor devices for very high frequency applications, and the development of advanced microwave monolithic integrated circuits technology, has spurred the evolution of current state of the art global modeling techniques. Global modeling refers to the incorporation of electromagnetic (EM) wave effects into physical device simulation. Introduction of solid-state power amplifiers for high frequency operations makes the global modeling approach a prerequisite for the design and optimization of transistors before fabrication. There are many challenges in the implementation of the global modeling techniques, in particular the requirement of large computer memory, long simulation time and the overall accuracy. As a part of practical global modeling techniques, an increasing amount of research has occurred in the field of distributed circuit modeling of high frequency transistors. Complete circuit based models are especially suitable for modern computer-aided design (CAD) tools.; In this dissertation, a large signal, complete circuit based, distributed model for high frequency field effect transistors (FETs) is presented. In order to capture EM wave propagation effects along the device electrodes, the basic unit segment of the distributed circuit model is formed by embedding the intrinsic equivalent circuit with transmission line parameters. An appropriate number of unit segments is then connected together in a distributed fashion to form the complete distributed circuit model. The complete circuit based distributed model is developed both for single and multi-finger FETs, and the model is solved in the time domain. A time domain, large signal simulation technique, is developed on the basis of closed form solutions of the fully distributed circuit model. The distributed circuit model is validated by comparing the simulated results with the measured data for a test pseudomorphic high electron mobility transistor (PHEMT) device.; Finally, a hybrid model based on physical device simulation and a circuit-based transmission line model is presented. The hybrid model is developed and solved for one finger as an initial phase of research work in this direction. The results for the hybrid model are compared with different other models and its potential for large signal analysis is demonstrated.