Multiscale Device Simulator

In this application, we have applied TiberCAD to 3D calculations of electrical characteristics of a Si-based 3-gate Finfet device.

For the last years, three-dimensional Multi-gate FET devices (double , triple or quadruple-gate) have been evolving from the silicon-on-insulator (SOI) classical, planar single gate MOSFET, in order to satisfy increasing need for higher current drive and better short channel behaviour.

The first fully depleted SOI MOSFET (early 1980's) showed superior transconductance, current drive and subthreshold swing. Its development led to the double-gate SOI MOSFET, which provided good short-channel characteristics due to the better gate control on the channel. A natural evolution of the latter was the vertical-channel double-gate FinFET. Triple-gate and gate-all-around implementations of the FinFET structure followed shortly. The phenomenon of volume inversion, leading to large transconductance, has encouraged the development of a series of these structures, ranging from quantum-wire MOSFET to circular section surrounding-gate devices with a pillar-like silicon island and vertical channel.

We consider here a three-gate FinFET structure with a 20 nm thick and 40 nm high Silicon fin. The channel length is 50 nm and the gate oxide thickness is 2 nm; we will see in the following the effects of the scaling of the device.

TiberCAD allows a multiscale simulation approach to simulation of MOSFET devices. This kind of simulation includes both macroscopic drift-diffusion current model and quantum tunneling model. The models are solved together in a self-consistent way. As an example, we study the subthreshold transfer characteristics of MOSFETs based on high-k oxides. We compare the high-k gates based on HfO₂ and ZrO₂ with a SiO₂ gate of the same equivalent thickness and show the effect of the gate oxide tunneling current on transistor performance.

In the last couple of years a huge effort has been devoted to achieve and to control the growth of III-nitride columnar-shaped nanostructures: nanorods, nanocolumns, nanopillars. Results have shown, so far, an extremely high crystal quality of the AlGaN nanocolumns, that are strain-free and have no dislocations or other extended defects, thus, yielding an outstanding emission efficiency. The achievement of nanocolumnar heterostructures including quantum disks (QDisks) and nanocavities with QDisks and Bragg mirrors have been reported.