A new two-dimensional self-consistent Monte Carlo simulator including multi sub-band transport in 2D electron gas is described and applied to thin-film SOI double gate MOSFETs. This approach takes into account both out of equilibrium transport and quantization effects. Our method allows us to significantly improve microscopic insight into the operation of deep sub-100 nm CMOS devices. We compare and analyse the results obtained with and without quantization effects for a 15 nm long DGMOS transistor.

International audienceAlthough the number of significant modes is intuitive, this concept has never been clearly defined, and this, mainly because of the unbound number of modes involved in modal overlap. In the present paper, we show that, for a perfect stirring process, the effect of modal overlap can be modeled as an equivalent filtering formulation. By introducing the statistical-bandwidth concept we show that the electromagnetic field statistics due to an infinite number of modes can be summarized by a finite number of significant modes. The case of the electric-energy density in an mode-stirred reverberation chamber (MSRC) has been considered and a new expression of its variability has been established. The good agreement found between the new expression and experimental and simulation results support the several concepts introduced in this paper

The electron transport in the two-dimensional gas formed in tensile-strained Si 1-x Ge x /Si/Si 1-x Ge x heterostructures is investigated using Monte Carlo simulation. At first the electron mobility is studied in ungated modulation doped structures. The calculation matches very well the experimental results over a wide range of electron density. The mobility typically varies between 1100 cm 2 /Vs in highly-doped structures and 2800 cm 2 /Vs at low electron density. The mobility is shown to be significantly influenced by the thickness of the spacer layer separating the strained Si channel from the pulse-doped supply layers. Then the electron transport is investigated in a gated modulation-doped structure in which the contribution of parasitic paths is negligible. The mobility is shown to be higher than in comparable ungated structures and dependent on the gate voltage, as a result of the electron density dependence of remote impurity screening.

International audienceThe physical parameter well adapted to assess the degree of overmodedness of a reverberation chamber (RC) is the number $M_M$ of modes overlapping in a mode bandwidth. The lowest usable frequency of an RC often corresponds to a low modal overlap of one or two modes. Notwithstanding, in spite of this poor number of modes the RC still works. We show, using Monte Carlo simulation, that the number of modes must, in fact, not be restrained to $M_M$ and that the number of modes contributing to the field statistics can be, even at low modal overlap, somewhat larger than expected

Abstract-The ability of time-reversed signals in reproducing a given time-dependence of the electromagnetic field within random media is investigated. A general setup consisting of multiple sources cooperating in providing the best transmission is considered, where the constructive interference of their individual contributions is meant to improve the quality of the field generation with respect to a single-source setup. The medium response is described by means of tools from random-process theory, for the case of stationary media complex enough to ensure a large number of multi-path contributions. It is shown that even a very weak spatial coherence in the medium is sufficient to significantly hinder the improvement expected from the use of multiple-source scenarios. Experimental results obtained in a reverberation chamber support the validity of the proposed theory. Direct applications of these results can be found in recent proposals about the potential benefits of time-reversed signals used in wireless communications, imaging techniques, as well as in pulsed-field generation devices based on energy compression through dispersive media.

The ability of reverberation chambers to generate high-intensity field levels from relatively low-power input signals is reexamined for the case of time-reversed signals, proving that they lead to a higher efficiency. Moreover, the strong statistical spread typical of time-harmonic excitations can be dramatically reduced, thus improving the reliability of radiative tests, while limiting the need for a large number of independent realizations. The two excitation schemes are compared when forcing their respective input signals to display the same peak instantaneous power. Experimental results are provided, supporting the conclusions of our theoretical analysis.

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Models predicting the composite quality factor (QF) of a reverberation chamber (RC) consider, among several potential contributors, dissipation in its metallic boundaries. The related partial quality factor, Qw, is of fundamental importance, as it controls the asymptotic high-frequency behavior of an RC and, ultimately, its ability to generate high-intensity fields. Yet, the current model has been known to overestimate in certain cases the composite QF by up to several dB. This paper provides insight into the causes of these disagreements by introducing generalized models of dissipation in ferrous materials found in RCs, by first acknowledging that their magnetic permeabilities are complex quantities, which is shown to theoretically boost dissipation well beyond the GHz range. A more general dissipation model is presented, taking into account the layered nature of steel plates. Among its predictions, confirmed by experiments, are extra losses from steel surfaces in the lower frequency range and the linear increase in Qw over the GHz range, as opposed to a squareroot dependence expected for homogeneous bulk metals. Metallic coating layers, originally introduced to protect steel plates, have therefore a more fundamental role to play, controlling dissipation levels by reducing interactions with ferrous materials and should therefore be designed accordingly.