Long-range Coulomb interactions in small Si devices. Part II. Effective electron mobility in thin-oxide structures

Abstract

In metal–oxide–semiconductor structures with polycrystalline Si gates, electrons in the inverted channel of the substrate scatter with electrons in the gate via long-range Coulomb interactions. For thin oxides, these interactions can cause a significant transfer of momentum from the channel to the gate, thus reducing the effective mobility of the two-dimensional electron gas in the substrate. We present calculations of the dispersion of the interface plasmons in poly-Si/SiO2/Si structures, comparing the results obtained in the long-wavelength limit to those obtained using the random-phase approximation. Employing the former model, we compute the effect of plasmon scattering on the effective electron mobility in Si inversion layers. We find a significant reduction of the mobility for oxides thinner than about 3 nm.

Role of scattering in nanotransistors

“…We consider only electron-phonon scattering, which is an important scattering mechanism in devices with undoped channels. References [6] and [7] have recently pointed out that electronelectron and plasmon scattering may play an important role in degrading nanotransistor characteristics. Electron-electron scattering in the drain side will lead to carriers having an energy larger than the source injection barrier.…”

High-performance nMOSFETs using a novel strained Si/SiGe CMOS architecture

“…By fabricating MOSFET devices on the strained Si/SiGe layers, faster CMOS devices and performance enhancements are predicted without the high costs associated with aggressive geometric scaling [4]. The enhanced mobility in strained Si/SiGe devices compensates the reduction in mobility of conventional Si transistor channels as the gate insulator thickness is reduced [7]. Furthermore, the similarity of strained Si/SiGe and conventional Si renders SiGe technology a relatively inexpensive choice for attaining high performance CMOS.…”

Effect of band warping and wafer orientation on NMOS mobility under arbitrary applied stress

“…The interplay between band warping and confinement has a direct impact on the dependence of stress gains on doping and stress levels. The strength of confinement determines the relative contributions to the total mobility gain due to the transport mass or the scattering changes with stress [11,12]. (110) wafers, due to the small inter- Fig.…”

“…The total effective mobility is calculated by summing the subband mobilities in (2) weighted by the occupation numbers. We include g-type and ftype optical and acoustic silicon phonon scattering [11][12][13], screened impurity scattering and surface roughness scattering [14] in our calculation of the momentum relaxation rate using the relaxation time approximation. 1 In these processes we include all allowed intra-and inter-subband transitions.…”