Modeling of some electrical parameters of a MOSFET under applied uniaxial stress

Abstract

A semi analytical model describing the bulk mobility for electrons in strained-Si layers as a function of applied uniaxial strain applied at the gate has been developed in this paper. The uniaxial stress has been applied through the silicon nitride cap layer. The effects of uniaxial stress are understood on all the three components of mobility i.e. phonon, columbic and surface roughness mobility. The results show that the electron mobility is a strong rising function of applied uniaxial strain. Flatband voltage, Depletion Charge density, Inversion charge density, Energy gap and Effective surface electrical field have been analytically modeled. There is a sharp increase in the vertical electrical field and inversion charge density and decrease in the energy gap, depletion charge density and the flatband voltage when the uniaxial stress is applied. The electron mobility results have also been compared with the experimentally reported results and show good agreement.

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“…The physics behind these strained p‐channel poly‐Si TFT behavior can be explained well. There were numerous reports about the strained c‐Si MOSFET characteristics . For strained p‐channel MOSFETs, it was observed that (I) biaxial tensile, (II) longitudinal uniaxial compressive, and (III) biaxial tensile plus additional longitudinal uniaxial tensile strain increases the hole mobility.…”

“…(2) is a simplified formula and Eq. (3) is a complex one including the first and second energy band contribution . (III) Biaxial plus additive uniaxial tensile strain decreases the scattering rate more than the unique biaxial strain, resulting in the more increment of mobility …”

“…There were numerous reports about the strained c-Si MOSFET characteristics. [1][2][3][4][5][6][7] For strained p-channel MOSFETs, it was observed that (I) biaxial tensile, (II) longitudinal uniaxial compressive, and (III) biaxial tensile plus additional longitudinal uniaxial tensile strain increases the hole mobility. The carrier mobility in strained silicon is determined like the following equations.…”

“…Electrical characteristics of the strained transistors were profoundly investigated in the single crystal Si MOSFETs. It was reported that the carrier mobility increases by the decrease of the scattering rate and effective mass of carriers when strain is applied . For strained p‐MOSFETs, it was observed that (I) biaxial tensile, (II) longitudinal uniaxial compressive, and (III) biaxial tensile plus additional longitudinal uniaxial tensile strain increases the hole mobility.…”

“…It was reported that the carrier mobility increases by the decrease of the scattering rate and effective mass of carriers when strain is applied. [1][2][3][4][5][6][7] For strained p-MOSFETs, it was observed that (I) biaxial tensile, (II) longitudinal uniaxial compressive, and (III) biaxial tensile plus additional longitudinal uniaxial tensile strain increases the hole mobility. The mechanism is like that (I) the biaxial tensile strain mainly reduce the scattering rate by not only decreasing the acoustic scattering rate via altering the light and heavy hole band density of states but also decreasing the interband optical phonon scattering through light to heavy hole band splitting (ΔE) and (II) the longitudinal uniaxial compressive strain mainly reduce the conductivity effective mass by significant band warping.…”