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Enabling superior FinFET predictability

Posted: 10 Apr 2013 ?? ?Print Version ?Bookmark and Share

Keywords:FinFET? simulation? EDA?

The quantum confinement effect in both cases shifts in the maximum of the electron distribution away from the Fin interfaces. The slight difference in the shapes of the equi-concentration contours arises from the differences in carrier velocity between the Drift Diffusion and Monte Carl simulations, and is linked to the current continuity requirements. Also, the discrete nature of the particles within Monte Carlo simulations introduces slight noise, despite time averaging. The resulting on-current variation as a function of gate length is plotted in figure 2.

As expected, the Monte Carlo simulations provide significantly greater on-current compared with Drift Diffusion simulations when the standard silicon saturation velocity is used. In both cases, an increase in on-current with reduction of gate length is observed. The variation is greater in the Monte Carlo simulation than in the Drift Diffusion simulations.

The Monte Carlo simulation results at identical leakage current are closely to the reported drive current of 1200 mA/mm for similar SOI FinFETs while the Drift Diffusion simulation underestimate the on current by more than 30% at 20 nm. Monte Carlo simulation yields a greater on-current as a result of non-equilibrium transport leading to a greater injection velocity compared to the corresponding Drift Diffusion velocity that cannot exceed the default silicon saturation velocity.

Evaluating advanced technology
The real importance of Monte Carlo simulation will grow exponentially as evaluating the scaling performance and the impact of new channel materials in the next generation transistors becomes more and more of an imperative. Ensemble Monte Carlo simulations are the only means for predictive simulations of the performance of contemporary and future CMOS transistors in the presence of non-equilibrium near-ballistic transport.

As an alternative the Monte Carlo simulations can be used to calibrate the computationally more efficient DD simulations that can be applied in comprehensive process sensitivity and statistical variability analysis and in the development of PDKs. This calibration may also be expected to hold over a useful range in the device design parameter space.

Figure 2: On-current vs. gate length results from DD simulation before and after calibration to MC simulation at LG=20nm. Excellent agreement is subsequently seen over all gate lengths.

Figure 3: Carrier velocity from source to drain from MC (solid lines) and DD (dashed lines) simulation of a series of scaled FinFETs. DD results are plotted both using default mobility model parameters, and mobility calibrated to MC simulation.

Summary
This article has clearly demonstrated that accurate 3D Monte Carlo simulations are needed in order to reliably predict the performance of contemporary deca-nanometre scale FinFETs. Drift diffusion simulation with default mobility models, operating within the limits of the local equilibrium approximation fail to accurately predict the corresponding FinFET performance. That said, it is also possible that quantum corrected Monte Carlo simulations can be used as a benchmark in the calibration of the more computationally efficient DD simulations, and this calibration may be expected to hold over a useful range in the device design parameter space.

About the author
Asen Asenov (FIEEE, FRSE) is the founder and CEO of Gold Standard Simulations (GSS) Ltd, As a James Watt Professor in Electrical Engineering and Leader of the 30 member Glasgow Device Modelling Group in the Department of Electronics and Electrical Engineering at the University of Glasgow, Dr. Asenov directs the development of 2D and 3D quantum mechanical, Monte Carlo and classical device simulators and their application in the design of advanced and novel CMOS devices. Prior to his current academic and business responsibilities, he headed the Process and Device Modelling Group in the Institute of Microelectronics, Sofia, Bulgaria and was a Visiting Professor at the Physics Department of The Technical University of Munich, Germany. He has more than 6,250 publications.

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