This paper reports the studies of the inversion layer mobility in n- and p-channel Si MOSFET's with a wide range of substrate impurity concentrations (10/sup 15/ to 10/sup 18/ cm/sup -3/). The validity and limitations of the universal relationship between the inversion layer mobility and the effective normal field (E/sub eff/) are examined. It is found that the universality of both the electron and hole mobilities does hold up to 10/sup 18/ cm/sup -3/. The E/sub eff/ dependences of the universal curves are observed to differ between electrons and holes, particularly at lower temperatures. This result means a different influence of surface roughness scattering on the electron and hole transports. On substrates with higher impurity concentrations, the electron and hole mobilities significantly deviate from the universal curves at lower surface carrier concentrations because of Coulomb scattering by the substrate impurity. Also, the deviation caused by the charged centers at the Si/SiO/sub 2/ interface is observed in the mobility of MOSFET's degraded by Fowler-Nordheim electron injection. >

https://www-inst.eecs.berkeley.edu/~ee230/sp08/takagi%20universal%20mobility%20I%201994.pdf

On the universality of inversion layer mobility in Si MOSFET's: Part I-effects of substrate impurity concentration

The impact of statistical dopant fluctuations on the threshold voltage V/sub T/ and device performance of silicon MOSFET's is investigated by means of analytical and numerical modeling. A new analytical model describing dopant fluctuations in the active device area enables the derivation of the standard deviation, /spl sigma/V/sub T/, of the threshold voltage distribution for arbitrary channel doping profiles. Using the MINIMOS device simulator to extend the analytical approach, it is found that /spl sigma/V/sub T/, can be properly derived from two-dimensional (2-D) or three-dimensional (3-D) simulations using a relatively coarse simulation grid. Evaluating the threshold voltage shift arising from dopant fluctuations, on the other hand, calls for full 3-D simulations with a numerical grid that is sufficiently refined to represent the discrete nature of the dopant distribution. The average V/sub T/-shift is found to be positive for long, narrow devices, and negative for short, wide devices. The fast 2-D MINIMOS modeling of dopant fluctuations enables an extensive statistical analysis of the intrinsic spreading in a large set of compact model parameters for state-of-the-art CMOS technology. It is predicted that V/sub T/-variations due to dopant fluctuations become unacceptably large in CMOS generations of 0.18 /spl mu/m and beyond when the present scaling scenarios are pursued. Parameter variations can be drastically reduced by using alternative device designs with ground-plane channel profiles.

Modeling statistical dopant fluctuations in MOS transistors

A Caughey–Thomas-like mobility model with temperature and composition dependent coefficients is used in this work to describe the dependence of electron and hole mobilities on temperature, doping concentration, and alloy composition. Appropriate parameter sets are given for a large number of III–V binary and ternary compounds, including: GaAs, InP, InAs, AlAs, GaP, Al0.3Ga0.7As, In0.52Al0.48As, In0.53Ga0.47As, and In0.49Ga0.51P. Additionally, physically justifiable interpolation schemes are suggested to find the mobilities of various ternary and quaternary compounds (such as AlxGa1−xAs, In1−xGaxP, In1−xGaxAs, In1−xAlxAs, and In1−xGaxAsyP1−y) in the entire range of composition. The models are compared with numerous measured Hall data in the literature and very good agreement is observed. The limitations of the present model are also discussed. The results of this work should be extremely useful in device simulation packages, which are currently lacking a reliable mobility model for the above materials.

Empirical low-field mobility model for III-V compounds applicable in device simulation codes

The advances in the growth of pseudomorphic silicon-germanium epitaxial layers combined with the strong need for high-speed complementary circuits have led to increased interest in silicon-based heterojunction field-effect transistors. Metal-oxide-semiconductor field-effect transistors (MOSFET's) with SiGe channels are guided by different design rules than state-of-the-art silicon MOSFET's. The selection of the transistor gate material, the optimization of the silicon-germanium channel profile, the method of threshold voltage adjustment, and the silicon-cap and gate-oxide thickness sensitivities are the critical design parameters for the p-channel SiGe MOSFET. Two-dimensional numerical modeling demonstrates that n/sup +/ polysilicon-gate SiGe p-MOSFET's have acceptable short-channel behavior at 0.20 /spl mu/m channel lengths and are preferable to p/sup +/ polysilicon-gate p-MOSFET's for 2.5 V operation. Experimental results of n/sup +/-gate modulation-doped SiGe p-MOSFET's illustrate the importance of the optimization of the SiGe-channel profile. When a graded SiGe channel is used, hole mobilities as high as 220 cm/sup 2//V.s at 300 K and 980 cm/sup 2//V.s at 82 K are obtained. >

SiGe-channel heterojunction p-MOSFET's

A new, comprehensive, physically-based, semiempirical, local model for transverse-field dependent electron and hole mobility in MOS transistors is presented. In order to accurately predict the measured relationship between the effective mobility and effective electric field over a wide range of substrate doping and bias, we account for the dependence of surface roughness limited mobility on the inversion charge density, in addition to including the effect of coulomb screening of impurities by charge carriers in the bulk mobility term. The result is a single mobility model applicable throughout a generalized device structure that gives good agreement with measured mobility data and measured MOS I-V characteristics over a wide range of substrate doping, channel length, transverse electric field, substrate bias, and temperature.

An improved electron and hole mobility model for general purpose device simulation

The paper reviews the evolution of the mobility model of the MINIMOS program for the two-dimensional simulation of miniaturized MOS devices over a period of 10 years.

Marden Seavey

Papers

The evolution of the minimos mobility model

The evolution of the MINIMOS mobility model