The hole inversion-layer mobility of strained-SiGe homo- and heterostructure-on-insulator in ultrathin-body MOSFETs is modeled by a microscopic approach. The subband structure of the quasi-2-D hole ...gas is calculated by solving the 6times6koarrldrpoarr Schrodinger equation self-consistently with the electrostatic potential. The model includes four important scattering mechanisms: optical phonon scattering, acoustic phonon scattering, alloy scattering, and surface-roughness scattering. The model parameters are calibrated by matching the measured low-field mobility of two particularly selected long-channel pMOSFET cases. The calibrated model reproduces available channel-mobility measurements for many different strained-SiGe-on-insulator structures. For the silicon-on-insulator MOS structures with unstrained-Si channels, the silicon-thickness dependence resulting from our model for the low-field channel mobility agrees with previous publications.
It is shown that the conductance in nanoscale devices near equilibrium strongly depends on the choice of the transport model. Errors larger than a factor of two can be encountered, if the ...drift-diffusion (DD) model is used instead of a model based on the full Boltzmann equation. This effect is due to a fundamental difference in carrier heating between bulk systems and devices. Although carrier heating is included in hydrodynamic models, this effect is captured only partially by these models due to the model inherent approximations. A direct consequence of the failure of the DD approximation is that the usual method for inversion layer mobility extraction from measurements in the linear regime becomes inaccurate for short gate lengths and the extracted mobilities might be too small. This error has also an impact on the modeling accuracy at strong nonequilibrium. In the case of the DD model, the overestimation of the conductivity in the linear regime can partly compensate the underestimation of the current at high bias, and the model accidentally appears to be more accurate than expected.
The hole inversion layer mobility of in-plane uniaxially stressed Si is modeled by a microscopic approach. For an arbitrary crystallographic surface orientation the two dimensional hole gas subband ...structure is calculated by solving the 6×6 k→·p→ Schrödinger equation self-consistently with the electrostatic potential. Three important scattering mechanisms are included: optical phonon scattering, acoustic phonon scattering and surface roughness scattering. The model parameters are calibrated by matching the measured low-field mobility of relaxed Si on (001) Si wafers. The calibrated model reproduces available channel mobility measurements for unstrained and uniaxially stressed Si on (001), (111) and (110) substrates.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The tunnel current models based on the Franz dispersion relation for carriers in the involved insulators are tested for several types of metal-insulator-silicon structures. The features related to ...the application of this alternative dispersion relation are analysed. Simplified approaches for tunneling current models are also examined. The positive and negative aspects of the Franz model are described. Special attention is paid to the tunneling of carriers with energies far from the insulator conduction band edge. The results of the new tunneling models are compared to those of the conventional models adopting the parabolic dispersion laws. It turns out that the physically well justified Franz relation yields typically a better agreement with experiments compared to the parabolic relation despite offering less freedom in term of adjustable parameters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The hole mobility reduction due to remote dipole scattering in p-MOSFETs with TiN/HfO2/SiO2 gate stacks is studied based on the self-consistent solution of 6×6 k·p Schrödinger equation, multi-subband ...Boltzmann transport equations and Poisson equation using a deterministic (non Monte Carlo) solver. The dipole density at the HfO2/SiO2 interface assumed in the simulations is consistent to the measured flat-band voltage shift of about 300mV which is observed after introducing the HfO2 layer. Static screening by the 2D dielectric function is considered and the polarization factor is calculated based on the full 6×6 k·p band structure. Comparing simulated and measured effective mobilities it is shown that in p-MOSFETs the mobility degradation caused by the HfO2 layer cannot be totally explained by remote dipole scattering and a dipole density which is consistent to the flat-band voltage shift. To the authors best knowledge the effect of 2D screening on Coulomb scattering and hole mobility including the influence of dipole layer position and charge separation as well as temperature dependence has not been considered before for p-MOSFETs on this detailed physical level in a semiclassical transport model.
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► Deterministic solvers for the Boltzmann equation are feasible for device simulation. ► They are superior to the stochastic Monte Carlo method in many aspects. ► They are numerically robust in the ...case of quasi 2D and 3D particle gases. ► They yield exact stationary and small-signal solutions of the Boltzmann equation. ► Electronic noise can be calculated in the whole technically relevant frequency range.
We present a review of recent advances in deterministic solvers for the Boltzmann transport equation for electrons and holes in a 3D and quasi 2D k→-space and demonstrate the capabilities of deterministic solvers by two new examples: a THz SiGe HBT and a quantum well PMOSFET. Compared to the standard approach, the Monte Carlo method, these deterministic solvers have certain advantages. They yield exact stationary solutions and they allow small-signal and noise analysis directly in the frequency range from 0 to THz. Inclusion of magnetic fields, the Pauli principle or rare events causes no problems. Thus, it is now possible to calculate certain key figures of merit for devices based on the Boltzmann transport equation, which was previously very difficult or not possible at all. On the other hand, the deterministic solvers are more memory intensive and more difficult to code than the Monte Carlo method.
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A novel technique for experimental estimation of the correlation length of insulator thickness fluctuations is proposed which is based on the statistical treatment of the results of current ...measurements for a random set of thin metal-insulator-semiconductor (MIS) capacitors. For testing purposes, the usual Al/SiO2/Si tunnel diodes with excessive thickness dispersion, as well as the less popular but potentially interesting Au/CaF2/Si structures, are taken. The verification is performed by a direct comparison of correlation lengths yielded by the new method with those obtained by diagnostics of the same dielectric films using atomic force microscopy.
The piezoresistive coefficient extraction technique for hole inversion layers based on the linear response of the mobility to uniaxial stress is generalized for material of the general diamond ...crystal type. The new derivation is applicable for arbitrary surface and channel orientations. For the simulation of piezoresistive coefficients, a mobility model for hole inversion layers based on the self-consistent solution of the
6
×
6
k
→
·
p
→
Schrödinger equation (SE), Boltzmann transport equation (BTE) and Poisson equation (PE) has been developed. Mobility variations due to uniaxial stress and biaxial strain are simulated and the simulation results reproduce available measurements. The accuracy of the piezoresistivity model, which describes the linear response and is based on the extracted piezoresistive coefficients, is examined by comparing the mobility variations resulting from the
k
→
·
p
→
simulator with the model predictions for many configurations of stress/strain and surface/channel orientation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
9.
Do hot electrons cause excess noise? Jungemann, C.; Meinerzhagen, B.
Solid-state electronics,
04/2006, Volume:
50, Issue:
4
Journal Article, Conference Proceeding
Peer reviewed
The open question whether excess noise is due to hot electrons or not is addressed for the first time by solving the full Langevin Boltzmann equation. Not only the bulk case is analyzed but also ...devices. In contrast to the well-known Monte Carlo method this new approach allows the investigation of the spatial origin of the terminal current noise. It is shown, that excess noise in devices is mainly due to cold or warm electrons. The contribution of hot electrons in a velocity saturation region is found to be negligible. This corroborates previous findings based on the less accurate impedance field method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A comprehensive investigation of the SPICE and unified compact noise models is performed by comparison with the more fundamental hierarchical hydrodynamic device model. It is shown that the rather ...simple SPICE and unified compact noise models yield good results for frequencies up to 10 GHz for state-of-the-art SiGe HBTs with a low base resistance. The base noise resistance, a key parameter of the compact noise models turns out to be independent of frequency and bias. It can be well estimated based on the sheet resistance of the intrinsic and extrinsic base or with the modified circle-fit method. The unified model, which in comparison to the SPICE model considers in addition the finite transit time of shot noise, is found to be somewhat more accurate than the SPICE model, especially at higher frequencies and collector currents. But this is achieved at the expense of a transit time parameter which cannot be determined without accurate and detailed noise measurements or physics-based numerical simulations.
