In recent years, carbon nanotubes have received widespread attention as promising carbon-based nanoelectronic devices. Due to their exceptional physical, chemical, and electrical properties, namely a high surface-to-volume ratio, their enhanced electron transfer properties, and their high thermal conductivity, carbon nanotubes can be used effectively as electrochemical sensors. The integration of carbon nanotubes with a functional group provides a good and solid support for the immobilization of enzymes. The determination of glucose levels using biosensors, particularly in the medical diagnostics and food industries, is gaining mass appeal. Glucose biosensors detect the glucose molecule by catalyzing glucose to gluconic acid and hydrogen peroxide in the presence of oxygen. This action provides high accuracy and a quick detection rate. In this paper, a single-wall carbon nanotube field-effect transistor biosensor for glucose detection is analytically modeled. In the proposed model, the glucose concentration is presented as a function of gate voltage. Subsequently, the proposed model is compared with existing experimental data. A good consensus between the model and the experimental data is reported. The simulated data demonstrate that the analytical model can be employed with an electrochemical glucose sensor to predict the behavior of the sensing mechanism in biosensors.
High-field electron transport properties in a two-dimensional nanolayer are studied by an application of the anisotropic nonequilibrium distribution function, a natural extension of the Fermi-Dirac distribution by inclusion of energy gained/absorbed in a mean free path (mfp). The drift velocity for conical band structure of graphene is shown to rise linearly with the electric field in a low electric field that is below the critical electric field. The critical electric field, equal to thermal voltage divided by the mfp, marks the transition from ohmic linear transport to saturated behavior in a high electric field. As field rises beyond its critical value, the drift velocity is sublinear resulting in ultimate saturation; the ultimate saturation velocity is comparable to the Fermi velocity in graphene. The quantum emission is found not to affect the mobility, but is efficient in lowering the saturation velocity. Excellent agreement is obtained with the experimental data for graphene on silicon dioxide substrate.
An explicit charge-based solution for the drain current, terminal charges and intrinsic capacitance of a long-channel junctionless nanowire transistor (JNT) incorporating the importance of an interface trap density that affect the threshold voltage and the subthreshold slope is presented in this study. Initially, a continuous implicit solution of the unified charge-based control model (UCCM) is derived from the 1D Poisson equation by invoking the parabolic potential approximation. The the continuous solution of the mobile charge density at the source/drain is obtained by adding the decoupled UCCM expression for the depletion and complementary parts, where each part is explicitly solved using the Lambert function without having an additional smoothing function to unify the two limits. The omission of an additional smoothing function could lead to a shorter computation time. Secondly, by solving Pao-Sah’s dual integral, a continuous charge-based expression for the drain current is derived. The expressions for the terminal charge are then derived based on the decoupled drain current model that also becomes an input for computing all four independent capacitances of the JNT. The explicit continuous models show a good agreement with numerical simulation over practical terminal voltages, doping levels, and geometry effects. For a given maximum surface potential error of 5%, the model is accurate for a dopant-geometry ratio of 0.001 < qNDR2/4ϵSi < 0.3 and it is also independent of fitting parameters that may vary for different terminal biases or dopant geometries. The nonpiecewise models for drain current, terminal charges and intrinsic capacitance are significantly resolved by decoupling the mobile charge into depletion and complementary parts with no additional smoothing function to unify between operating regions, and omitting fitting parameters that have no physical meaning.
The ballistic saturation velocity in a nanoscale metal-oxide-semiconductor field effect transistor (MOSFET) is revealed to be limited to the Fermi velocity in a degenerately induced channel appropriate for the quasi-two-dimensional nature of the inverted channel. The saturation point drain velocity is shown to rise with the increasing drain voltage approaching the intrinsic Fermi velocity, giving the equivalent of channel-length modulation. Quantum confinement effect degrades the channel mobility to the confining gate electric field as well as increases the effective thickness of the gate oxide. When the theory developed is applied to an 80nm MOSFET, excellent agreement to the experimental data is obtained.
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