Multi-gate Mosfet For Ultra-lsi Research

Under the direction of Moore's Law, the semiconductor devices of integrated circuit are getting smaller, but the scaling of the MOSFET can not be infinite. To a certain extent in reducing the size, MOSFET will reach the physical limits, and severe short channel effects and gate leakage current will appear. This is a challenge to the validity of Moore's Law. But people actively looking for new device structures instead of scaling to improve performance. People discovered that high-k materials can replace the traditional oxide materials and new device structures can be used to reduce the SCEs, especially the latter was researched a lot. The new device structures will be the directions and trends of the next generation of semiconductor devices in the future 10 years.Primarily the proposed new structure of the devices at this stage are multi-gate MOSFETs, while of the multi-gate MOSFETs, the most promising and most studied are surrounding-gate and double-gate MOSFETs. Expanding the number and area of gate electrodes of the multi-gate MOSFETs improves the ability of controlling the inversion layer charge, so that could increase the carrier mobility, reduce the short channel effects of MOSFETs, reduce the gate leakage current, at the same time avoid decreasing the gate oxide thickness when reduce the size of the device. This study focuses on the most promising device structures--surrounding-gate and double-gate MOSFETs.We established the compact model for the multi-gate MOSFETs so that the circuit designers can achieve device electrical parameters.In the Past, the modeling of the surrounding-gate MOSFET with short-channel did not use unified carrier transport model, which is applicable in both ballistic transport region and the diffusion transport region. Our model makes up for this defect, and adds the Quantum Mechanics effects.For the surrounding-gate MOSFET, when channel length changes from 20nm to 100nm, we used superposition analysis to solve the Poisson equation analytically. On this basis we obtained the models of channel potential, sub-threshold swing and threshold voltage. And we study the dependence of channel potential on location of the channel, gate bias, channel length.For the double-gate MOSFET we also analytically solved the Poisson equation, on this basis we obtained the potential channel model and the sub-threshold swing model, and we study the dependence of sub-threshold swing on doping concentration, gate bias, as well as oxide thickness. We also study the dependence of channel potential on location of the channel, gate bias, channel length.