The Time-dependent Research Of Nano MOS Devices

The carbon materials will be promising candidates in furthure nanoelectronic devices. In thisartical, we first introduce the Green’s functions which is a useful tool in simulating nano devices.Then we propose a hybrid material gate carbon nanotube transistor (CNTFET) structure withHALO doping. The simulation results show that when the hybrid material gate or the HALOdoping is applied, the electric field at the surface of the channel will be step-like, which canscreen the channel from the variation of drain potential, thus improving the gate control abilityand sub-thread performance. The increasing gate length will lead to larger gate capacitance andsmaller transconductance which will limit the high-frequency performance. With the increasingdifferences of work functions, the hybrid material gate can lead to greater improvement ofsub-thread performance. Combine both the HALO doping and the hybrid material gate structure,the device can get all the benfits, suppress the short channel effect (SCE), the Drain IductionBarrier Lower (DIBL) effect and hot electron effect. In addition, we also make an investigationon the influence of hybrid material gate and HALO doping on the graphene nanoribbon fieldtransistor (GNRFET). The results are quite similar to that of the CNTFET, the hybrid gate andHALO doping can still change the electric field distribution and improve the perofrmance of theGNRFET.Besides the analysis of HALO doping and hybrid material gate, a comparsion of two typicalstructures of CNTFET and GNRFET is conducted according to the different demands of digitalcircuits and analog circuits. Both the CNTFET and GNRFET can reach high cut-off frequencyand the CNTFET even reaches a few Terahertzes. The GNRFET has a quite awful on/off ratiocompared to the CNTFET and the gate control ability is worse than CNTFET either. All theseaspects indicate that the CNTFET is excellent in digital circuit and the GNRFET is suitable inanalog circuit.Finally, we discuss the time-dependent non-equilibrium Green’s functions under thetight-binding approximation. The calculation is directly conducted in the time domain,recursively solving time-dependent non-equilibrium Green’s functions and Poisson functionsuntil the process reaches self-consist state, and then obtains the current response to the ac signal.The results show that: when a voltage is applied to the electrode, the instantaneous currentsuddenly increases, similar to the overshoot effect in traditional CMOS devices. When the voltage is a single square pulse, the current shows smooth damping oscillation attenuation versustime, and reaches a steady state finally.The results in this article may be useful in evaluating the electrical properties oflow-dimensional carbon materials, and providing a preliminary theoretical basis in designing andmaking the carbon-based nanoelectronic devices which operate under ac signals in the future.