Current investigation is surveyed the role of altering Lorentz force on nanomaterial flowing within two discs and its thermal behavior. The basis governing formula convert to ODEs based on applying two phase model. Based on acquired outcomes, there is direct correlation between Nu and Nt. Invoking the impact of S, it is concluded that growth of S guides to reduce in Nu and similar tendency can be seen for A because of reduction of temperature gradient with rise of amount of inlet velocity. Impermeable wall leads to stronger influence of Nt and outcomes reveal that Nu has direct relationship with Nt. Reducing impact of A declines with rise of Nt which means that thermophoresis act against permeability.

Nanomaterial between two plates which are squeezed with impose magnetic force

We investigate the hybrid nanofluid convection transportation within a permeable medium in appearance of an externally applied magnetic force by modeling it through control volume-based finite element method. To employ the permeability effect terms, one term was added in momentum and radiation was involved to show the diverse states of nanoparticles. The impact of Darcy and Rayleigh as well as magnetic and radiation parameters on the nanofluid performance is investigated and presented. We observe that the conduction mode enhances with higher values of Ha. Nusselt number Nu augments with the consideration of radiation source term. The addition of Lorentz force makes the conduction mode more sensible. The agreement with the published results makes us more confident about the validity of our numerical computations.

Analysis of hybrid nanofluid behavior within a porous cavity including Lorentz forces and radiation impacts

Innovative approach for simulation of nanoliquid natural convection through a permeable wavy space was scrutinized. Analysis has been conducted within inclined porous rectangular cavity having cold side borders under the impacts of heated internal wavy horizontal cylinder and uniform tilted magnetic field. The considered boundary-value problem devised on the basis of the Darcy linear law, Boussinesq relation, Rosseland approach and Lorentz force has been resolved by the finite volume technique. The impacts of nanomaterials’ shape, buoyancy force, radiation term and Hartmann number on nanoliquid hydrodynamic treatment have been investigated. Outcomes have proved that greater quantities of shape factor result in the greater convection. By enhancing magnetic forces, convection becomes weaker.

Simulation of nanoliquid thermogravitational convection within a porous chamber imposing magnetic and radiation impacts

The constructal design-based model is reported to analyze the thermal control and heat augmentation inside a split lid-driven square cavity. A Y-shaped obstacle is placed within the cavity, which is filled with Al2O3–Cu–water hybrid nanofluids. The concept of the split-lid-driven cavity is utilized for the first time. The governing flow mathematical structure is obtained in terms of a system of partial differential equations and converted to a non-dimensional form through dimensionless variables. The numerical experiments are performed by employing a Galerkin finite element scheme for different values of involved physical parameters. The effects of pertinent parameters on the streamlines, isotherms, dimensionless temperature, and Nusselt numbers are investigated for different values of the Richardson number. Due to the simultaneous motion of the split-lids, the streamlines and isotherms show symmetrical distribution. The local Nusselt number increases with the moving split-lids and attains the maximum value when both lids meet. The average Nusselt number decreases with an increase in the Richardson number. It is important to note that the Y-shaped obstacle enhances the heat transfer rate in the cavity.

Finite element analysis of hybrid nanofluid flow and heat transfer in a split lid-driven square cavity with Y-shaped obstacle

A unique thermal conductivity model (ANN) for nanofluid based on experimental study

Numerical analysis of magneto-hydrodynamic flow has been a matter of concern for research engineers and scientists. In this paper, magneto-hydrodynamic convection in square tank occupied with Cu-H 2 O nanomaterial is investigated for different configurations of heater-sink, in which Artificial Neural Network (ANN) model was used as an advanced predictive tool. The active semi-circular thermal location (heater and sink) at the left- right vertical sides are kept constantly at high and low temperatures respectively, whereas other walls are kept adiabatic. To reach the solution, Galerkin residual finite element analysis has been implemented. The investigation has been done for Hartmann number (Ha = 0 – 100), Rayleigh number (Ra = 103-107) and nanomaterial concentration ( φ = 0 – 0.05) and finally, streamlines, isotherm contours and entropy generation contours are discussed thoroughly. The overall heat transfer and generation entropy are quantitatively investigated by overall Nusselt number (Nu) and Bejan number (Be), respectively. Existence of external Lorentz forces affects on both non-dimensional performance parameters, Nu and Be. Finally, the higher heat transfer is found for middle–middle configuration of heater-sink walls. The impact of Ha and φ on Nu and Be found from the numerical heat transfer analysis has been predicted and compared with ANN prediction model. To be noted, ANN is widely used technique to compare and predict different experimental and numerical data accurately in many engineering applications.

Prediction of MHD flow and entropy generation by Artificial Neural Network in square cavity with heater-sink for nanomaterial

Featuring broadband operation and high efficiency, gallium nitride (GaN)-based radio frequency (RF) power amplifiers are key components to realize the next generation mobile network. However, to fully implement GaN high electron mobility transistors (HEMT) for such applications, it is necessary to overcome thermal reliability concerns stemming from localized extreme temperature gradients that form under high voltage and power operation. In this work, we developed a deep-ultraviolet thermoreflectance thermal imaging capability, which can potentially offer the highest spatial resolution among diffraction-limited far-field optical thermography techniques. Experiments were performed to compare device channel temperatures obtained from near-ultraviolet and deep-ultraviolet wavelength illumination sources for the proof of concept of the new characterization method. Deep-ultraviolet thermoreflectance imaging will facilitate the study of device self-heating within transistors based on GaN and emerging ultra-wide bandgap semiconductors (e.g., β-Ga2O3, AlxGa1-xN, and diamond) subjected to simultaneous extreme electric field and heat flux conditions.

Deep-Ultraviolet Thermoreflectance Thermal Imaging of GaN High Electron Mobility Transistors

Ulta-wide bandgap semiconductors based on $\beta$-Ga$_2$O$_3$ offer the potential to achieve higher power switching performance, efficiency, and lower manufacturing cost than today's wide bandgap power semiconductors. However, the most critical challenge to the commercialization of Ga$_2$O$_3$ electronics is overheating, which impacts the device's performance and reliability. We fabricated a Ga$_2$O$_3$/4H-SiC composite wafer using a fusion-bonding method. A low temperature ($\le$ 600 $^{\circ}$C) epitaxy and device processing approach based on low-temperature (LT) metalorganic vapor phase epitaxy is developed to grow a Ga$_2$O$_3$ epitaxial channel layer on the composite wafer and subsequently fabricate into Ga$_2$O$_3$ power MOSFETs. This LT approach is essential to preserve the structural integrity of the composite wafer. These LT-grown epitaxial Ga$_2$O$_3$ MOSFETs deliver high thermal performance (56% reduction in channel temperature), high voltage blocking capabilities up to 2.45 kV, and power figures of merit of $\sim$ 300 MW/cm$^2$, which is a record high for any heterogeneously integrated Ga$_2$O$_3$ devices reported to date. This work is the first realization of multi-kilovolt homoepitaxial Ga$_2$O$_3$ power MOSFETs fabricated on a composite substrate with high heat transfer performance which delivers state-of-the-art power density values while running much cooler than those on native substrates. Thermal characterization and modeling results reveal that a Ga$_2$O$_3$/diamond composite wafer with a reduced Ga$_2$O$_3$ thickness ($\sim$ 1 $\mu$m) and thinner bonding interlayer ($<$ 10 nm) can reduce the device thermal impedance to a level lower than today's GaN-on-SiC power switches.

Ultra-Wide Bandgap Ga$_2$O$_3$-on-SiC MOSFETs

Ultra-wide bandgap semiconductor devices based on β-phase gallium oxide (Ga2O3) offer the potential to achieve higher switching performance, efficiency, and lower manufacturing cost than today’s wide bandgap power electronics. However, the most critical challenge to the commercialization of Ga2O3 electronics is overheating, which impacts the device performance and reliability. We fabricated a Ga2O3/4H-SiC composite wafer using a fusion-bonding method. A low temperature (≤ 600°C) epitaxy and device processing scheme was developed to fabricate MOSFETs on the composite wafer. The low-temperature grown epitaxial Ga2O3 devices deliver high thermal performance (56% reduction in channel temperature) and a power figure of merit of (~300 MW/cm, which is highest among heterogeneously integrated Ga2O3 devices reported to date. Simulations calibrated based on thermal characterization results of the Ga2O3-on-SiC MOSFET reveal that a Ga2O3/diamond composite wafer with a reduced Ga2O3 thickness (~1 μm) and thinner bonding interlayer (<10 nm) can reduce the device thermal impedance to a level lower than today’s GaN-on-SiC power switches.

Table of Contents Graphic Ultra-Wide Bandgap Ga2O3-on-SiC MOSFETs


 The demand for high power and high-frequency radio frequency (RF) power amplifiers makes AlGaN/GaN high electron mobility transistors (HEMTs) an attractive option due to their large critical field, high saturation velocity, and reduced device footprint as compared to Si-based counterparts. However, due to the high operating power densities, intense device self-heating occurs, which degrades the electrical performance and compromises the device’s reliability. The self-heating behavior of AlGaN/GaN HEMTs is known to be not solely a function of the dissipated power but is highly bias-dependent. As the operation of RF power amplifiers involves alteration of the device operation from fully-open to pinched-off channel conditions, it is critical to experimentally map the full channel temperature profile as a function of bias conditions. However, such measurement is difficult using optical thermography techniques due to the lack of optical access underneath the gate electrode, where the peak temperature is expected to occur.
 To address this challenge, an AlGaN/GaN HEMT employing a transparent gate made of indium tin oxide (ITO) was fabricated, which enables full channel temperature mapping using Raman spectroscopy. It was found that the maximum channel temperature rise under a partially pinched-off condition is more than ∼93% higher than that for an open channel condition, although both conditions would lead to an identical power dissipation level. The channel peak temperature probed in an ITO-gated device (underneath the gate) is ∼33% higher than the highest channel temperature that can be measured for a standard metal-gated AlGaN/GaN HEMT (i.e., next to the metal gate structure) operating under an identical bias condition. This indicates that one may significantly underestimate the device’s thermal resistance when solely relying on performing thermal characterization on the optically accessible region of a standard AlGaN/GaN HEMT. The outcomes of this study are important in terms of conducting a more accurate lifetime prediction of the device lifetime and designing thermal management solutions.

Anwarul Karim

Papers

Prediction of MHD flow and entropy generation by Artificial Neural Network in square cavity with heater-sink for nanomaterial

Deep-Ultraviolet Thermoreflectance Thermal Imaging of GaN High Electron Mobility Transistors

Ultra-Wide Bandgap Ga$_2$O$_3$-on-SiC MOSFETs

Table of Contents Graphic Ultra-Wide Bandgap Ga2O3-on-SiC MOSFETs

Experimental Probing of the Bias Dependent Self-Heating in AlGaN/GaN HEMTs With a Transparent Indium Tin Oxide Gate