Strong Inversion Regime Research Articles

A charge-based model for short-channel MOS transistor capacitances

A model that conserves charge, is valid in the strong inversion regime, and is based on the quasi-static approximation is presented. Major second-order effects such as carrier velocity saturation, mobility degradation, and channel-length modulation are included in the derivation of current and charges. The theoretical predictions of the model are compared to both experimental and numerically simulated data and are found to be in good agreement over a wide range of gate and drain voltages and to confirm many properties that have been observed or predicted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hall effect in gratinglike potential modulated inversion layers

We present a quantitative approach to the potential fluctuation model we have previously developed in disordered semiconductors. MOSFET (metal-oxide-semiconductor field-effect transistors) were irradiated along lines parallel (L structures) or perpendicular (T structures) to the drain-source direction, using a 20-keV scanned e-beam. Thus, in the inversion regime, the surface potential ψs was periodically modulated, thereby strongly modifying the conduction processes. Hall measurements were performed as a function of temperature and gate voltage at various irradiation doses and for different periods. Conduction in L structures was influenced by lateral potential barrier scattering, whereas it was barrier controlled in T structures. The experimental results are interpreted by a simple model of energetic distribution of both carrier density n(E) and mobility μ(E), based on the existence of a conduction threshold. When barriers were wide in T structures, Hall measurements showed that part of the carriers did not participate in conductivity in the weak inversion regime, while mixed conduction processes occurred when barriers were narrow. In contrast, all the carriers conducted in the strong inversion regime, and only the mobility was perturbed. Thus the field effect in irradiated MOSFET was used to correlate the Hall carrier density with the conduction threshold energy.

A model for the intrinsic gate capacitances of short channel MOSFETs

In this paper we present a model for the gate charge and the intrinsic gate capacitances in the strong inversion regime of a short-channel MOSFET. The model accounts for various second-order effects such as carrier velocity saturation, channel-length modulation and mobility degradation. An accurate model for the d.c. characteristics is first developed which guarantees the continuity of the current and its first and second derivatives with respect to the drain voltage at the transition from the linear to the saturation region. The gate charge is then computed and the gate capacitances are derived. Finally, the theoretical predictions of the model are compared to the experimental data available from the literature.

Incoherent tunneling of electrons from three to two dimensions: Observation of conductance oscillations in a metal-insulator-semiconductor structure.

We have observed incoherent tunneling in $\frac{\mathrm{Al}}{\frac{\mathrm{ZnS}}{{\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{Te}}}$ metal-insulator-semiconductor (MIS) capacitors below $T\ensuremath{\sim}110$ K. Under thermal equilibrium, both the conductance-voltage and capacitance-voltage characteristics show strong oscillations when the MIS is biased into the strong inversion regime. On the basis of the temperature dependence of oscillation amplitudes, we explain the data by the incoherent tunneling of electrons from the three-dimensional (3D) valence band in the $p$-type bulk ${\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Cd}}_{x}\mathrm{Te}$ into 2D electronic subbands at the inversion interface, through deep traps. The observed oscillatory conductance comes from the reduced dimensionality of final tunneling states.

A charge-sheet analysis of short-channel enhancement-mode MOSFETs

A charge-sheet analysis of the short-channel MOSFET is presented. The expression achieved for the drain current, which takes into account both the drift and the diffusion components and also mobility degradation effects, holds in the strong-inversion, weak-inversion, and saturation regimes of the device operation, and results in a continuous function of all bias voltages. The model predicts an exponential dependence of the drain current on drain voltage in weak inversion and the threshold dependence on both channel length and drain voltage. Moreover, the proposed approach predicts results which satisfactorily compare with numerical simulations obtained from the two-dimensional analyzer MINIMOS and experimental data.

Transport in the inversion layer of a MOS transistor: use of Kubo-Greenwood formalism

A study of the electronic transport in MOS transistor inversion layers is presented. The use of the Kubo-Greenwood formalism allows the possibility of explaining the global behaviour of the transport coefficients (conductivity, mobility, etc.) from the weak inversion regime (non-degenerate) to the strong inversion regime (degenerate) over a wide range of temperature. In particular, it is shown that physical phenomena arising from miniaturisation and/or low-temperature operation such as quantisation of the inversion layer or carrier localisation are of primary importance for the determination of the transport coefficients of MOS transistor inversion layers. The incorporation of such phenomena into the modelling of the operation of MOS devices, is thus highly desirable, even at temperatures close to room temperature.

A small signal dc-to-high-frequency nonquasistatic model for the four-terminal MOSFET valid in all regions of operation

This paper presents a four-terminal small-signal dc-to-high-frequency model, valid in weak, moderate, and strong inversion regimes, for the intrinsic part of the long-channel MOS transistor. A charge-sheet approximation is used. Basic MOSFET equations are separated into parts corresponding to dc and ac small-signal components. The former are used to evaluate the drain current under dc conditions; the latter, describing the "transmission-line" behavior of the MOSFET, are solved to arrive at a complete set of admittance parameters. Based on different approximations of these parameters, various models are presented, each of different upper frequency limit of validity. For each model parameter, a single continuous expression is used which is valid in all regions of operation (weak inversion, moderate inversion, strong inversion; nonsaturation and saturation). The frequency range of validity of these models and the inadequacies of the quasistatic models at high frequencies are discussed. It is shown that at low frequencies the high-frequency model reduces to a quasistatic model which is widely verified by experimental results; at high frequencies the model agrees with available measurements.

Noise associated with charge injection into-a CCD by current integration through a MOS transistor

The noise charge resulting from integrating a noisy current at a CCD input (equivalent to a MOS transistor) is evaluated. The noise contributions of the signal source and of the input transistor can be separated from other components of the CCD noise. Moreover, our measurements show a very good agreement with previously reported 1/f noise results for MOS transistors working in weak or strong inversion regimes.

Interface characteristics of Ge 3N 4-( n-type) GaAs MIS devices

Passivation of GaAs surfaces was achieved by the deposition of Ge 3N 4 dielectric films at low temperatures. Electrical characteristics of MIS devices were measured to determine the interface parameters. From C- V- f and G- V- f measurements, density of interface states has been obtained as (4–6)×10 11 cm −2 eV −1 at the semiconductor mid-gap. Some inversion charge buildup was seen in the C- V plot although the strong inversion regime is absent. Thermally stimulated current measurements indicate a trap density of 5×10 18−10 19 cm −3 in the dielectric film, with their energy level at 0.59 eV.