Drive current enhancement in p-type metal–oxide–semiconductor field-effect transistors under shear uniaxial stress
ABSTRACT Recent attention has been given to metal–oxide–semiconductor field-effect transistor (MOSFET) device designs that utilize stress to achieve performance gain in both n -type MOSFETs (NMOS) and p -type MOSFETs (PMOS). The physics behind NMOS gain is better understood than that of PMOS gain, which has received less attention. In this letter, we describe the warping phenomena which is responsible for the gain seen in  uniaxially stressed PMOS devices on  orientated wafers. We also demonstrate that shear uniaxial stress in PMOS is better suited to MOSFET applications than biaxial stress as it is able to maintain gain at high vertical and lateral fields.
- SourceAvailable from: David Z. Pan
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- "The hole mobility of PMOS devices has a near linear dependence on the uniaxial stress in the channel  and . Using this, we transformed the increase in the stress values to the increase in mobility. "
ABSTRACT: Starting from the 90 nm technology node, process induced stress has played a key role in the design of high-performance devices. The emergence of source/drain silicon germanium (S/D SiGe) technique as the most important stressing mechanism for p-channel metal-oxide-semiconductor field-effect transistor devices has opened up various optimization possibilities at circuit and physical design stage. In this paper, we exploit the active area dependence of the performance improvement achievable using S/D SiGe technology for late stage engineering change order (ECO) timing optimization. An active area sizing aware cell-level delay model is derived which forms the basis of linear program based optimization of a design for achieving maximum performance or target performance under a timing budget. To control the magnitude of layout perturbation and ensure predictable timing improvement, a set of physical constraints for active area sizing is proposed. Further, an efficient minimum movement legalization algorithm is proposed to remove the overlaps caused by active area sizing of timing critical cells. Results on a wide variety of benchmarks show consistent reduction in the cycle time by up to 6.3%. Predictability of the performance improvement achievable as well as resultant minuscule layout changes make our technique very attractive for late stage ECO optimization and design closure.IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems 11/2010; DOI:10.1109/TCAD.2010.2061173 · 1.20 Impact Factor
- "This results in changes in the crystal structures and hence in the band structures. Strain effects on bulk silicon band structures have been studied using both k.p theory ,  and atomistic tight binding approach . Strain splits the six fold degeneracy of conduction band minima, reduces effective mass and inter-valley scattering, and enhances mobility , . "
Conference Paper: Effects of uniaxial strain on the bandstructures of silicon nanowires[Show abstract] [Hide abstract]
ABSTRACT: The effects of uniaxial strain on the band structures of Lt100Gt silicon nanowires of width 2.75 - 3.84 nm are studied using sp<sup>3</sup>d<sup>5</sup>s<sup>*</sup> orbital basis atomistic tight binding approach. The conduction band edge at Gamma point has almost no variation with strain and the second valley located at 0.36timespi/a of the wire Brilluoin moves down in energy with both compressive and tensile strains. The top valence band moves up in energy with both tensile and compressive strain, and therefore, the band gap reduces with both types of strain. We notice about 7% change in band gap for an application of 2% strain. The electron effective masses at Delta<sub>4</sub> and Delta<sub>2</sub> valleys show opposite dependence on strain, and the hole effective mass of top valence band has almost similar variation with both types of strain. We notice a significant change in hole effective mass with strain.Electrical and Computer Engineering, 2008. ICECE 2008. International Conference on; 01/2009
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- "enhanced PMOS have been implemented in commercial products since 2003, a comprehensive physical model describing hole transport under both uniaxial and biaxial stresses is still lacking . The first theory that explained the large mobility gain under uniaxial compressive stress along 110 directions was based on hole band structure changes calculated using empirical pseudopotential (EPM) and k · p methods , . A compact model based on simplified bands under stress has also been published . "
ABSTRACT: A comprehensive quantum anisotropic transport model for holes was used to study silicon PMOS inversion layer transport under arbitrary stress. The anisotropic band structures of bulk silicon and silicon under field confinement as a twodimensional quantum gas are computed using the pseudopotential method and a six-band stress-dependent k.p Hamiltonian. Anisotropic scattering is included in the momentum-dependent scattering rate calculation. Mobility is obtained from the Kubo-Greenwood formula at low lateral field and from the fullband Monte Carlo simulation at high lateral field. Using these methods, a comprehensive study has been performed for both uniaxial and biaxial stresses. The results are compared with device bending data and piezoresistance data for uniaxial stress, and device data from strained Si channel on relaxed SiGe substrate devices for biaxial tensile stress. All comparisons show a very good agreement with simulation. It is found that the hole band structure is dominated by 12 "wings," where mechanical stress, as well as the vertical field under certain stress conditions, can alter the energies of the few lowest hole subbands, changing the transport effective mass, density-of-states, and scattering rates, and thus affecting the mobilityIEEE Transactions on Electron Devices 09/2006; DOI:10.1109/TED.2006.877370 · 2.36 Impact Factor