Modeling of modern MOSFETs with strain

Abstract

We review modeling techniques used to compute strain induced performance enhancement of modern MOSFETs. While p-channel MOSFETs were intensively studied, electron transport in strained structures received surprisingly little attention. A rigorous analysis of the subband structure in thin silicon films under stress is performed. Calculated subband effective masses are shown to strongly depend on shear strain and film thickness. A decrease of the transport effective mass under tensile stress in [110] direction and an additional splitting between the unprimed subbands with the same quantum number guarantees a mobility enhancement even in ultra-thin (001) silicon films. This increase of mobility and drive current combined with the improved channel control makes multi-gate MOSFETs based on thin films or silicon fins preeminent candidates for the 22 nm technology node and beyond.Keywords MOSFETs modeling · Shear strain · Two-band k·p model for conduction band · Valley splitting · Mobility and current enhancement

Influence of the valley degeneracy on spin relaxation in thin silicon films

“…The valley splitting reductions shown in Figure 2 are also the result of the oscillating sine-like term in (9). The small increase of the shear strain leads to the decrease of the ly �-z "Y/z term.…”

“…The valley splitting oscillates with the film thickness increased. According to the theory[9], we generalize the equation for the valley splitting in an infmite potential square well including the spin-orbit coupling as with Yn, Tj, and B defined as…”

Subband Structure Engineering in Silicon-On-Insulator FinFETs Using Confinement

“…The subband structure in a confined system is computed using the k·p model proposed in (8), which has been shown to be accurate up to 0.5eV above the conduction band edge (9). Figure 3.…”

“…The lowest subband preserves six-fold degeneracy. The degeneracy can be partly lifted in a square structure with the faces along and (1)(2)(3)(4)(5)(6)(7)(8)(9)(10) directions. Yet, the lowest subband remains four-fold degenerate.…”

“…The non-zero value of the off-diagonal elements results in a non-parabolic dispersion along [001] direction for [001] valleys. For the quantization along the [001] direction a consideration similar to the one in ultra-thin body silicon films can be applied (9). If the value of the off-diagonal elements is not too large, the valley splitting is given by (9) ( )…”