A.F. Tasch

A comprehensive model for inversion layer hole mobility for simulation of submicrometer MOSFET's

A comprehensive model of effective (average) mobility and local-field mobility for holes in MOSFET inversion layers is presented. The semiempirical equation for effective mobility, coupled with the new local-field mobility model, permits accurate two-dimensional simulation of source-to-drain current in MOSFETs. The model accounts for the dependence of mobility on transverse and longitudinal electric fields, channel doping concentration, fixed interface charge density, and temperature. It accounts not only for the scattering by fixed interface charges, and bulk and surface acoustic phonons, but it also correctly describes screened Coulomb scattering at low effective transverse fields (near threshold) and surface roughness scattering at high effective transverse fields. The model is therefore applicable over a much wider range of conditions compared to earlier reported inversion layer hole mobility models while maintaining a physically based character. >

Models for electron and hole mobilities in MOS accumulation layers

We present new physically based effective mobility models for both electrons and holes in MOS accumulation layers. These models take into account carrier-carrier scattering, in addition to surface roughness scattering, phonon and fixed interface charge scattering, and screened Coulomb scattering. The newly developed effective mobility models show excellent agreement with experimental data over the range 1/spl times/10/sup 16/-4/spl times/10/sup 17/ cm/sup -3/ for which experimental data are available. Local-field dependent mobility models have also been developed for both electrons and holes, and they have been implemented in the two-dimensional (2-D) device simulators, PISCES and MINIMOS, thus providing for more accurate prediction of the terminal characteristics in deep submicron CMOS devices. In addition, transition region mobility models have been developed to account for the transition in the mobility in going from the accumulation layer in the gate-to-source overlap region to the inversion layer region in the channel.

A universal MOSFET mobility degradation model for circuit simulation

From the physical insights provided by the universal effective mobility versus effective vertical electric field curve for electrons in MOS inversion layers, a simple general expression for the gate voltage dependence of the effective electron mobility is derived for use in SPICE circuit simulation. This expression is quite accurate over a wide range of channel doping concentrations and gate oxide thicknesses, without the need for fitting parameters, such as the theta parameter of the current SPICE level 3 mobility degradation model. It is, therefore, a much more universal model than the present SPICE level 3 mobility expression. Furthermore, the relative accuracy of this new model compared to the current SPICE model is expected to increase at the higher vertical electric fields typical of submicrometer oxide semiconductor field effect transistors (MOSFETs). >

MOSFET drain engineering analysis for deep-submicrometer dimensions: a new structural approach

A new MOS transistor structural approach (hot-carrier-induced MOSFET) capable of substantially suppressing adverse hot-carrier effects, while maintaining the other desired performance and manufacturability characteristics of deep-submicrometer MOSFETs (L/sub gate/ >

Improved universal MOSFET electron mobility degradation models for circuit simulation

Based on the physical insights provided by the universal mobility curve, an improved comprehensive universal model for effective electron mobility in inversion layers of n-channel MOSFETs is developed for circuit simulation. This model expresses the effective electron mobility at room temperature as a function of effective vertical field. It exhibits a high degree of accuracy for a wide range of different device characteristics, such as channel doping levels, gate oxide thicknesses, and channel dimensions. In addition, it predicts very well the effective mobility under the effects of substrate biases for gate voltages well above threshold, which is an improvement over earlier models. Moreover, this model has been developed with an emphasis on the functional dependence of mobility on high effective field, and is thus particularly accurate in that range of effective field. This is a significant advantage of the model since todays submicrometer MOSFETs typically operate at high effective fields. >

An experimental study of the effect of quantization on the effective electrical oxide thickness in MOS electron and hole accumulation layers in heavily doped Si

This work presents for the first time experimental results for the extraction of the increase in the effective electrical oxide thickness (/spl Delta/t/sub ox/=t/sub ox,expt/-t/sub ox,physical/) in MOS accumulation layers with heavily doped substrates due to quantum mechanical (QM) effects, using experimentally measured MOS capacitance-voltage (C-V) characteristics and experimentally verified fullband self-consistent calculations. In addition, the fullband self-consistent simulations have been extended to accumulation regions, and the experimental results for the accumulation region have been compared with simulations. It has been shown that at moderate to high doping levels, /spl Delta/t/sub ox/ is as much as 0.4 to 0.5 nm for both electrons and holes, whereas for very high doping levels (>1/spl times/10/sup 19/ cm/sup -3/) /spl Delta/t/sub ox/ approaches zero. Thus, the experimental accumulation capacitance is predicted sufficiently well by the classical analysis itself.

Room temperature electroabsorption in a Ge/sub x/Si/sub 1-x/ PIN photodiode

We present room temperature electroabsorption measurements in a Ge/sub 0.2/Si/sub 0.8/ pin photodiode. The results appear to be very similar to those reported earlier on Ge/sub x/Si/sub 1-x//Si multiple quantum wells. >

A Monte Carlo Study of Electron Transport in Silicon nMOSFET Inversion Layers

Monte Carlo simulations of uniform silicon nMOSFET inversion layers have been performed. Excellent agreement between the simulated and experimental transport characteristics has been observed in the region of strong inversion at both 300K and 77K. The contribution to the effective mobility due to individual subbands has been analyzed and qualitatively explained.

A two-dimensional model for predicting substrate current in submicrometer MOSFETs

Summary form only given. The authors present a more rigorous hydrodynamic postprocessing approach than that implemented by J.W. Slotboom et al. (1991). The proposed model is 2-D and is based on the 1-D form of energy equation described by R.K. Cook et al. (1982), implemented into the 2-D drift-diffusion simulator PISCES as a postprocessor to calculate substrate current. This new approach involves the determination of the average energy along many current contours using the 1-D energy conservation equation and the local electric fields calculated by PISCES along each current path. The impact ionization rates are calculated using an energy parameterized form of the Chynoweth law. These coefficients along with the current densities calculated by PISCES are then used to determine the 2-D distribution of generation rates, and the generation rates are integrated over the entire 2-D device structure to calculate the substrate current. The authors have demonstrated very good agreement with substrate current characteristics measured on a broad range of LDD (lightly doped drain) NMOSFET devices with varying channel lengths, gate biases, and drain biases. >