Band-structure based electrostatics model for ultra-thin-body double-gate silicon-on-insulator MOS devices

The effect of quantum confinement has become significant in terms of its impact on the scalability and electrostatics of ultra-thin-body double-gate MOSFETs. In this paper, we present a simplified model to account for the effect of quantum confinement, considering the contribution of the ground-state and the first excited state of the conduction band, on the electron carrier concentration, which when incorporated into the 1-D Poisson's equation, enables the determination of the electrostatic potential. We establish the accuracy of the proposed model, over a wide range of process and electrical parameters, through aggressively benchmarking the electrostatics parameters obtained from the proposed model with results from the sp(3)d(5)s(*) tight-binding method (TBM), over a wide range of device temperatures. Furthermore, a simplified model for the integrated channel charge density is shown in the form of a diffusion layer charge where the thickness and potential of this layer, while being gate voltage dependent, enables the channel charge density obtained from the model to agree well with results from TBM. Through this physics based and accurate model for the integrated charge, a simplified understanding of the gate capacitance is shown as a series combination of the diffusion layer capacitance, strong-inversion capacitance and oxide capacitance, which includes the effects of structural confinement as well as charge confinement at low and high gate voltages, respectively.