A simple analytical model for the threshold voltage of short-channel, thin-film, fully-depleted silicon-on-insulator MOSFETs is presented. The model is based on the analytical solution for the two-dimensional potential distribution in the silicon film, which is taken as the sum of the long-channel solution to the Poisson equation and the short-channel solution to the Laplace equation. The model shows close agreement with numerical PISCES simulation results. The equivalence between the proposed model and the parabolic model of Young (1989) is also proven.

Modelling the threshold voltage of short-channel silicon-on-insulator MOSFETs

In this paper, a new structure: triple work function metal gate SOI MESFET, intended for integration into the deep-submicron CMOS technology, is proposed. The gate of the device consists of three different materials which are laterally merged into one. The difference in the work function of dissimilar gate materials introduces two step changes in the profile of channel potentials which screens the threshold-defining region of the channel from the impact of drain potential. Therefore, the effects associated with DIBL are significantly alleviated. On the basis of exact solution of the Poisson equation in the channel region, an analytical subthreshold model for the device is developed. Using the analytical data, the device has been characterized and compared with conventional device in terms of potential function, DIBL, threshold voltage roll-off, and subthreshold swing. The TCAD simulator ATLAS from Silvaco has been used to validate the analytical results. The feasibility of device fabrication is also demonstrated.

Analytical Modeling of Short-Channel Fully-Depleted Triple Work Function Metal Gate (TWFMG) SOI MESFET

This chapter focuses on analytical modeling of short-channel single-gate SOI MESFETs. In the beginning, we review the existing models presented for this device and explain the drawbacks related to each one. After that, using a new technique for solving of Poisson’s equation in the conductive channel, we develop a modified two-dimensional analytical model for the device which is free of the problems associated with the previous models. By using the presented model, the subthreshold behavior of the device is displayed and discussed. Also, the impact of device parameters and bias conditions on the device performance is investigated.

Modeling of Classical SOI MESFET

An analytical model has been proposed to simulate the threshold voltage (V/sub T/) of 3D MOSFETs in advanced VLSI/ULSI chips. The model is a quasi-3D extension of a rigorous analytical 2D model and is much faster than a numerical 3D model for computing V/sub T/. Computations have been carried out to verify the present quasi-3D model with the available experimental data and a numerical 3D model-MICROMOS. >

3D effects in VLSI/ULSI MOSFETs: a novel analytical approach to model threshold voltage

Numerical 2D and 3D models of MOSFETs, which have been developed so far, are accurate but take enormous computer time and memory for their implementation. It restricts their use only to the design and development of submicron devices. A computationally faster, analytical quasi-3D model for the threshold voltage of small geometry MOSFETs, which should be useful for VLSI circuit simulation, has been presented in this paper. The model is based on a rigorous 2D analytical model. An equivalence between the analytical 2D model and the Yau's charge sharing model has been established, and the same has been utilized to incorporate the narrow width effect. The important features of the present work are: (1) realistic channel implantation profiles for nMOSFETs have been used in developing the 2D model; (ii) the effect of birds' beaks on the lateral confinement of charges in the channels of oxide isolated MOSFETs has been considered in a simple manner; and (iii) the fringing of electric field near the edges of channels (widths) has also been considered empirically. The simulated values of the threshold voltages exhibiting 2D and 3D effects compare well with those obtained using a numerical 3D simulator (MICROMOS) and with available experimental data. The model is also capable of predicting the inverse narrow width effect observed in MOSFETs with fully recessed field oxide.

M.K. Das

Papers

A quasi-3D analytical threshold voltage model of small geometry MOSFETs