Recent experimental advances have made carbon nanotubes promising material for utilizing as nano-electro-mechanical systems (NEMS). The key feature of CNT-based NEMS is the ability to drastically change electrical conductance due to a mechanical deformation. The deformation effects can be divided into two major groups: bond stretching of sp2 coordinated nanotubes and transition from sp2 to sp3 coordination. The purpose of this work is to review the change in electrical response of nanotubes to different types of mechanical deformation. The modeling consists of a combination of universal force-field molecular dynamics (UFF), density functional theory (DFT) and Green's function theory. We show that conductance of metallic carbon nanotubes can decrease by 2-3 orders of magnitude, when deformed by an AFM tip, but is insensitive to bending. These results can explain the experiment of Ref. . Such a decrease is chirality dependent, being maximum for zigzag nanotubes. In contrast, twisting and radial deformation result in bandgap openning only in armchair nanotubes. In addition, radial deformation of armchair nanotubes leads to dramatic oscillations of conductance.
Even at room temperature, sub-100 ,nm CMOS devices are strongly affected by quantum mechanical effects. In addition to commonly-known energy quantization in the channel, a charge dipole is observed to appear in the poly-gate, which shifts the threshold voltage in a different way from channel quantization. Moreover, due to the multi-dimensional nature of the structure, conventional Schrodinger/Poisson's equation solutions in 1D are no longer adequate for predicting the device characteristics. In this paper, two macroscopic, multi-dimensional quantum transport models, density gradient (DG) and non-equilibrium Green's function (NEGF), are discussed. Validity and application scope are established through comparing to measured data and benchmarking with MIT well-tempered MOSFETs (wtm25 and 90 nm, respectively). It is shown both qualitatively and quantitatively that quantum effects are now required in profile calibration and inverse modeling.