Modeling of floating body silicon-on-insulator n channel MOSFET

Abstract

This dissertation describes the development of a new physical model for thin film silicon-on insulator (SOI) nMOSFET, emphasizing the floating body effects that bring about the predominant parasitic BJT phenomena. Based on the charge balanced concept in floating body, a new approach is introduced to obtain the body potential. Analytical expressions for front gate threshold voltage, surface and body impact ionization rates, saturation voltage, and MOSFET and parasitic BJT current are also derived from the modulation of the body potential. The unique role of each current component is demonstrated and correlated to the current kink, the increase of the output conductance, and the degradation of breakdown voltage. To clarify this model, device simulation is necessary to characterize those abnormal effects because direct experimental measurements will disturb the body potential inside the device. Throughout the two-dimensional numerical device simulation, it is found that the body potential, due to the excess holes, triggers the lateral BJT and then major current path is moved from the front surface to the body. It is also observed that the body current plays the major role in determining the breakdown characteristics. MOSFET``s are fabricated on separation by implanted oxygen (SIMOX) film. The techniques of device parameter extraction are introduced for the practical use of the SOI MOSFET model for simulation and design. The model shows a good agreement with the measured current voltage characteristics for the various biases and geometry conditions.