Amitava DasGupta

Bio: Amitava DasGupta is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: High-electron-mobility transistor & MOSFET. The author has an hindex of 19, co-authored 119 publications receiving 1574 citations. Previous affiliations of Amitava DasGupta include Indian Institutes of Technology.

A micro-convection model for thermal conductivity of nanofluids

Abstract: Increase in the specific surface area as well as Brownian motion are supposed to be the most significant reasons for the anomalous enhancement in thermal conductivity of nanofluids. This work presents a semi-empirical approach for the same by emphasizing the above two effects through micro-convection. A new way of modeling thermal conductivity of nanofluids has been explored which is found to agree excellently with a wide range of experimental data obtained by the present authors as well as the data published in literature

Gate Leakage Mechanisms in AlGaN/GaN and AlInN/GaN HEMTs: Comparison and Modeling

Abstract: The gate leakage mechanisms in AlInN/GaN and AlGaN/GaN high electron mobility transistors (HEMTs) are compared using temperature-dependent gate current-voltage (IG-VG) characteristics. The reverse bias gate current of AlInN/GaN HEMTs is decomposed into three distinct components, which are thermionic emission (TE), Poole-Frenkel (PF) emission, and Fowler-Nordheim (FN) tunneling. The electric field across the barrier in AlGaN/GaN HEMTs is not sufficient to support FN tunneling. Hence, only TE and PF emission is observed in AlGaN/GaN HEMTs. In both sets of devices, however, an additional trap-assisted tunneling component of current is observed at low reverse bias. A model to describe the experimental IG-VG characteristics is proposed and the procedure to extract the associated parameters is described. The model follows the experimental gate leakage current closely over a wide range of bias and temperature for both AlGaN/GaN and AlInN/GaN HEMTs.

Subthreshold current model of FinFETs based on analytical solution of 3-D Poisson's equation

Abstract: The potential variation in the channel obtained from analytical solution of three-dimensional (3-D) Poisson's equation is used to calculate the subthreshold current and threshold voltage of fin field-effect transistors with doped and undoped channels. The accuracy of the model has been verified by the data from 3-D numerical device simulator. The variation of subthreshold slope and threshold voltage with device geometry and doping concentration in the channel has been studied.

Analytical Model of Subthreshold Current and Slope for Asymmetric 4-T and 3-T Double-Gate MOSFETs

Abstract: In this paper, analytical models of subthreshold current and slope for asymmetric four-terminal double-gate (DG) MOSFETs are presented. The models are used to study the subthreshold characteristics with asymmetry in gate oxide thickness, gate material work function, and gate voltage. A model for the subthreshold behavior of three-terminal DG MOSFETs is also presented. The results of the models show excellent match with simulations using MEDICI. The analytical models provide physical insight which is helpful for device design.

An analytical expression for sheet carrier concentration vs gate voltage for HEMT modelling

Abstract: A simple expression of the Fermi potential ( E F ) variation with the sheet carrier concentration ( n s ) in the two-dimensional electron gas at the heterojunction of a High Electron Mobility Transistor (HEMT) is presented This particular approximation is shown to lead to an analytical expression for n s in termks of the applied gate voltage ( V G ) Comparisons with the exact solutions of n s vs E F and n s vs V G as well as with several previous approximations show that our results are more accurate for a wider range of values of n s at different temperatures This single analytical expression for n s as a function of V G , valid from subthreshold to high conduction, can be used for better analytical modelling of HEMTs

Heat Transfer in Nanofluids—A Review

Abstract: Suspended nanoparticles in conventional fluids, called nanofluids, have been the subject of intensive study worldwide since pioneering researchers recently discovered the anomalous thermal behavior of these fluids. The enhanced thermal conductivity of these fluids with small-particle concentration was surprising and could not be explained by existing theories. Micrometer-sized particle-fluid suspensions exhibit no such dramatic enhancement. This difference has led to studies of other modes of heat transfer and efforts to develop a comprehensive theory. This article presents an exhaustive review of these studies and suggests a direction for future developments. The review and suggestions could be useful because the literature in this area is spread over a wide range of disciplines, including heat transfer, material science, physics, chemical engineering and synthetic chemistry.

Empirical correlating equations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids

Abstract: In this paper, two empirical correlations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids, based on a high number of experimental data available in the literature, are proposed and discussed. It is found that, given the nanoparticle material and the base fluid, the ratio between the thermal conductivities of the nanofluid and the pure base liquid increases as the nanoparticle volume fraction and the temperature are increased, and the nanoparticle diameter is decreased. Additionally, also the ratio between the dynamic viscosities of the nanofluid and the pure base liquid increases as the nanoparticle volume fraction is increased, and the nanoparticle diameter is decreased, being practically independent of temperature. The ease of application of the equations proposed, and their wide regions of validity (the ranges of the nanoparticle diameter, volume fraction and temperature are 10–150 nm, 0.002–0.09 and 294–324 K for the thermal conductivity data, and 25–200 nm, 0.0001–0.071 and 293–323 K for the dynamic viscosity data), make such equations useful by the engineering point of view, for both numerical simulation purposes and thermal design tasks.

A review of nanofluid stability properties and characterization in stationary conditions

Abstract: A new engineering medium, called nanofluid attracted a wide range of researches on many cooling processes in engineering applications, which are prepared by dispersing nanoparticles or nanotubes in a host fluid. In this paper, the stability of nanofluids is discussed as it has a major role in heat transfer enhancement for further possible applications. It also represents general stabilization methods as well as various types of instruments for stability inspection. Characterization, analytical models and measurement techniques of nanofluids after preparation by a single step or two-step method are studied.

A benchmark study on the thermal conductivity of nanofluids

Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.