Physical simulation of high-frequency semiconductor devices and amplifier circuits

The advancement of semiconductor technology ushered the development of some state of the art techniques for the analysis, design, and optimization of the semiconductor devices. Available device simulators are inadequate to represent the physical devices with shrinking dimensions. In order to explore the electromagnetic wave effects on the behavior of the submicron semiconductor devices and amplifier circuits, a combined electromagnetic and solid-state (CESS) simulator has been developed. The CESS simulator couples a 3D time-domain solution of Maxwell's equations to the semiconductor model. The semiconductor model is based on the moments of Boltzmann transport equations. When the semiconductor device operates in microwave and millimeter-wave range, with the device width comparable to the electromagnetic wave length and the short wave period may be comparable to the electron relaxation times, the interactions of conducting electrons with the electromagnetic waves cannot be neglected. The exchange of energy takes place between the electrons and the electromagnetic waves. The CESS model can predict the nonlinear energy build-up inside the transistor. The other advantage is its ability to show the dispersive nature of the device, especially at high frequencies. It is a very powerful and accurate simulator for high frequency devices. The electromagnetic forces on the electrons are derived from Maxwell's equations and the electron transport characteristics are obtained from the hydrodynamic model. It uses the finite-difference time-domain (FDTD) algorithm for discretization. To overcome the computational intensity of the model, parallel algorithms were developed, and the numerical simulations were performed on a Massively Parallel machine (MasPar).;To demonstrate the potential of the CESS simulator further, microwave and millimeter-wave integrated circuit amplifiers are characterized using a global modeling technique. Global modeling of millimeter-wave circuits is important to simulate the electromagnetic coupling, device-EM wave interaction, and the EM radiation effects of the closely spaced active and passive components of the MMICs. The characterization of amplifier circuits including the input and output matching networks are performed using a full-wave analysis coupled with physical modeling of the semiconductor devices. The entire amplifier is simulated with FDTD algorithm which also solves for the electromagnetic fields inside the transistor. The intensive computer memory requirement and the large simulation time are reduced by applying a hybridization approach. The small signal as well as the large signal propagation through the amplifier circuit are demonstrated. The scattering parameters are extracted for the amplifier circuit at small and large signals for different frequencies. The global technique is able to model the nonlinearity and the harmonic distortion of the amplifier circuit. The third and fifth harmonic components in the output spectrum at large signal are predicted for different frequencies. The results of this research present tremendous contribution towards device optimization and commercial MMIC system design.;Successful numerical simulations of typical microwave Metal Semiconductor Field Effect Transistor (MESFET) and Modulation Doped Field Effect Transistor (MODFET) were carried out using the CESS model. The simulation uses electromagnetic wave concept to show better performance of MODFET over MESFET. The intrinsic small signal parameters are extracted for these devices from the ac dynamic approach as well as from the quasi-static analysis. The dependence of intrinsic small signal parameters on frequency as well as on bias is reported. In ac analysis, some interesting behaviors are noticed for the two devices. Some of the results are validated with the available published works.