With downscaling of MOSFET to nanometers, gate induced drain leakage (GIDL), short channel effect (SCE), etc. greatly affect its characteristics.
Adaptation of a double-gate (DG) in MOSFETs can improve the SCE and GIDL can be alleviated by a structure of dual materials. DMDG-MOSFETs have been proposed and studied in some aspects.
Ri Hui Chol, a section head at the Semiconductor Institute, has proposed a model for potential distribution and subthreshold swing through the entire channel. In the DMDG-MOSFET structure, he adopted the structure of two gate materials that have different work functions. This structure enables potential to increase through two steps so that the potential change rate may be decreased. Thus, the intensity of the electric field on the position close to the drain can get lower. This feature is useful for improving electron mobility and for hot electron generation.
When VGS was relatively small, the simulation on the model and the previous results agreed well. But as the applied bias increased, so did the deviation.
It is because he employed depletion approximation that only accounts for ion concentration. When VGS is relatively small, carrier concentration is low, so the influence of neglecting this term is not so significant. But VGS reaches a certain extent, the influence of the gate voltage on channel potential is eliminated by inversed charge so that it may result in deviation.
Especially, under the double-material gate configuration the band voltage of part M2 is relatively small and the effective gate voltage is big, so the inversed charge can be generated more easily. Thus, though both models (double-material gate model and single-material gate model) are obtained in the same method, the accuracy is different, that is, the accuracy of the DMDG-MOSFET model may be lower than SMDG-MOSFET’s.
The simulation results indicate that the subthreshold swing increases with the decrease in the channel length like general DG MOSFETs, and that the subthreshold feature is deteriorated with the increase in the thickness of the gate oxide and the channel.
If further information is needed, please refer to his paper “Simulation for characteristics of the Dual-Material Double-Gate MOSFET” in “Journal of Analog and Digital Devices” (EI).
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