Compact Modeling of Short Channel Common Double Gate MOSFET Adapted to Gate-Oxide Thickness Asymmetry
Compact Models are the physically based accurate mathematical description of the cir-cuit elements, which are computationally eﬃcient enough to be incorporated in circuit simulators so that the outcome becomes useful for the circuit designers. As the multi-gate MOSFETs have appeared as replacements for bulk-MOSFETs in sub-32nm technology nodes, eﬃcient compact models for these new transistors are required for their successful utilization in integrated circuits. Existing compact models for common double-gate (CDG) MOSFETs are based on the fundamental assumption of having symmetric gate oxide thickness. In this work we explore the possibility of developing models without this approximation, while preserving the computational eﬃciency at the same level. Such eﬀort aims to generalize the compact model and also to capture the oxide thickness asymmetry eﬀect, which might prevail in practical devices due to process uncertainties and thus aﬀects the device performance significantly. However solution to this modeling problem is nontrivial due to the bias-dependent asym-metric nature of the electrostatic. Using the single implicit equation based Poisson so-lution and the unique quasi-linear relationship between the surface potentials, previous researchers of our laboratory have reported the core model for such asymmetric CDG MOSFET. In this work eﬀort has been put to include Non-Quasistatic (NQS) eﬀects, diﬀerent small-geometry eﬀects, and noise model to this core, so that the model becomes suitable for practical applications. It is demonstrated that the quasi-linear relationship between the surface potentials remains preserved under NQS condition, in the presence of all small geometry eﬀects. This property of the device along with some other new techniques are used to develop the model while keeping the mathematical complexity at the same level of the models reported for the symmetric devices. Proposed model is verified against TCAD simulation for various device geometries and successfully imple-mented in professional circuit simulator. The model passes the source/drain symmetry test and good convergence is observed during standard circuit simulations.
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