ANALYSIS AND DESIGN OF NOVEL SEMICONDUCTOR DEVICES AND INTEGRATED CIRCUITS (GALLIUM-ARSENIDE MESFET, IC SIMULATION, MODFET, THIN FILM TRANSISTOR, AMORPHOUS SILICON)

The developement of new integrated circuit processing methods and semiconducting materials such as MBE grown heterostructures and hydrogenated amorphous silicon thin films have lead to many novel devices. These novel devices offer the potential for ultra-high speed digital circuits and novel applications such as very large area and three-dimensional integrated circuits. This thesis defines and follows a methodology for the analysis and design of field effect based transistors and integrated circuits. Three novel devices are studied: GaAs MESFET digital ICs, (AlGa)As/GaAS MODFET ICs and hydrogenated amorphous silicon alloy TFTs. The approach taken here is to formulate device models in a compact, analytical form based on a charge control principle and to implement CAD tools based on these models for the design and analysis of integrated circuits. A new GaAs circuit simulator, UM-SPICE, has been developed and is described here. UM-SPICE implements a simple but accurate model for low pinch-off GaAs MESFETs, an extended charge control model for MODFETs and the velocity saturation model for ungated FET load devices. From our analysis of a-Si TFT operation two new important regimes of operation were predicted: the transitional and crystalline-like regimes. Operation of a-Si TFTs in the crystalline-like regime would increase the speed of a-Si TFT based ICs by larger than an order of magnitude.