Analytical Surface Potential Research Articles

Analytical ballistic theory of carbon nanotube transistors: Experimental validation, device physics, parameter extraction, and performance projection

We developed a fully analytical ballistic theory of carbon nanotube field effect transistors enabled by the development of an analytical surface potential capturing the temperature dependence and gate and quantum capacitance electrostatics. The analytical ballistic theory is compared to the experimental results of a ballistic transistor with good agreement. The validated analytical theory enables intuitive circuit design, provides techniques for parameter extraction of the bandgap and surface potential, and elucidates on the device physics of drain optical phonon scattering and its role in reducing the linear conductance and intrinsic gain of the transistor. Furthermore, a threshold voltage definition is proposed reflecting the bandgap-diameter dependence. Projections for key analog and digital performances are discussed.

Performance and analytical modelling of halo-doped surrounding gate MOSFETs

Halo structure is added to sub-100 nm surrounding-gate metal–oxide–semiconductor field-effect-transistors (MOSFETs) to suppress short channel effect. This paper develops the analytical surface potential and threshold voltage models based on the solution of Poisson's equation in fully depleted condition for symmetric halo-doped cylindrical surrounding gate MOSFETs. The performance of the halo-doped device is studied and the validity of the analytical models is verified by comparing the analytical results with the simulated data by three dimensional numerical device simulator Davinci. It shows that the halo doping profile exhibits better performance in suppressing threshold voltage roll-off and drain-induced barrier lowering, and increasing carrier transport efficiency. The derived analytical models are in good agreement with Davinci.

A physics-based analytical solution to the surface potential of polysilicon thin film transistors using the Lambert W function

A physics-based analytical solution to the surface potential of polysilicon thin film transistors (poly-Si TFTs) using the Lambert W function has been derived from poly-Si TFTs implicit surface potential equation without any empirical smoothing functions. The analytical solution eliminates the need for the complex iterative computation and is very accurate with absolute error only in nanovolt range. Its high accuracy is proved by a comparison of calculating the surface potential under various bias conditions with respective numerical results and also by the fact that the characteristics of the surface potential derivative with respect to the gate voltage show no splits and peaks. A poly-Si TFTs charge sheet model based on this precise analytical surface potential solution is developed and the results are verified using the experimental data.

A Physically Based, Scalable MOS Varactor Model and Extraction Methodology for RF Applications

A physically based scalable model for MOS varactors, including analytical surface potential based charge modeling and physical geometry and process parameter based parasitic modeling, is proposed. Key device performances of capacitance and quality factor Q are validated over a wide voltage, frequency, and geometrical space. The model, implemented in Verilog-A for simulator portability, provides for robust and accurate RF simulation of MOS varactors.

A compact-charge LDD-MOSFET model

A compact-charge LDD-MOSFET model, based on an analytical surface potential formulation at source and drain has been derived and implemented in the circuit simulator SABER for all channel length and width down to deep submicrometer. Besides well-known short- and narrow-channel effects, the model includes additional charge effects around the threshold voltage as well as a bias dependent charge description of the overlap LDD(S)-region. These additional capacitance effects are not considered in conventional submicrometer transistor models although they domain the capacitance characteristic with further downscaling. If not taken into account, simulation errors of, e.g., up to 50% in the frequency of a 0.3 /spl mu/m CMOS ring oscillator or over 100% in the 3 dB critical frequency of amplifier circuits can result.

Analytical surface potential expression for thin-film double-gate SOI MOSFETs

Using a perturbation theory, we derived an analytical surface potential expression for subthreshold and strong-inversion regions. This enabled us to derive analytical models for the subthreshold slope, threshold voltage, and induced electron concentration of a double-gate SOI MOSFET. We also clarified the dependence of the device characteristics on device parameters, and explained the ideal subthreshold factor. We do not expect volume inversion in practical devices. Our models' predictions agree well with numerical and experimental data.

The Fano-Anderson model applied to electrons in MIS-inversion layers

Subband states in n-inversion layers on narrow gap semiconductors are resonances due to the Zener coupling to the continuum of the bulk valence band. Thus excitation between subband states resembles the autoionization process of atomic physics described long ago by Fano. Starting from Kane's model for narrow gap semiconductors to describe the subband states we map the problem onto the Fano-Anderson Hamiltonian by applying a Schrieffer-Wolff transformation. This problem is solved self-consistently using an analytical surface potential. We calculate the relative transmission rate Δ T(ω) T(ω) for inversion layers on narrow-gap Hg 1− x Cd x Te and discuss our results in comparison with experimental data.

Subbands in inversion layers on NGS for Egap to 0

Subband states in n-inversion layers on HgCdTe are resonances due to the coupling to the bulk valence-band continuum. The width of the resonances increases with decreasing gap energy. Thus the existence of subband states is questionable if the gap energy is zero. The authors study the subband problem for MIS structures on narrow-gap semiconductors starting from Kane's k.p Hamiltonian. The analytical approach with no specified surface potential shows that for Egap=0 the free-electron term, which is usually neglected for narrow-gap systems, becomes crucial, because it changes the order of the subband differential equation. The authors also solve the subband probe for an analytical surface potential and calculate the density of states. The results demonstrate the existence of a subband resonance even for vanishing gap energy provided that the free-electron term is not neglected.