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Ga₂O₃ has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga₂O₃ power devices stimulated by early demonstrations of high-voltage Ga₂O₃ field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga₂O₃ FETs — which have predominantly been lateral devices — for power switching and radiation-hard electronics. The development of vertical Ga₂O₃ transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed.

This paper reports on the experimental method of the determination of junction temperature and thermal resistance in 840 nm InGaAlAs/AlGaAs compressive strained single quantum well (SQW) superluminescent diodes (SLDs). The linear relation between forward voltage and junction temperature clearly occurs by utilizing the forward voltage–temperature ($V$–$T$) method. The temperature coefficient $dV/dT$ has been determined. Under 100 mA continuous-wave (CW) operation condition, the thermal resistance is measured to be 81.6${}^{\circ }$C/W, which is not significantly different with the theoretical calculation result.

A distributed thermal model for analyzing the heat distribution of GaN high electron mobility transistor (HEMT) is presented in this paper. The thermal resistance calculation of multi-gate GaN HEMT with nonlinear thermal conductivity is derived. Considering the heat conduction of PCB and the nonlinear thermal conductivity, the model developed in COMSOL realizes the consistency between the simulation results and the measurement results. Based on the model, the surface and internal temperatures can be extracted for the thermal resistance calculation. The proposed method combined model simulation with numerical calculation will be helpful for designers to analyze the thermal distribution of transistors and the circuits.

This paper presents a preliminary work to evaluate the thermal resistance of a spherical medium. In the sphere, a three-dimensional pore fractal network combined with electrical double layers is constructed to represent the pore structure of medium. The construction and structural parameters of a network are illustrated in detail. The thermal resistance of a sphere is primarily associated with structural parameters of network, pore structure parameters of medium, thermal conductivities of solid phase and pore channels. In this work, the evolution of thermal resistance with the fractal network is analyzed comprehensively. Besides, the evolution mechanisms of thermal resistance with pore structure parameters of medium are revealed. The influences of types of porous materials on thermal resistance are systematically studied.

To minimize the thermal resistance of the fractal treelike heat conduction network and develop an optimization principle applicable for the network with an arbitrary cross-sectional shape, this paper first establishes a theoretical model regarding the total thermal resistance of the symmetric treelike network with arbitrary cross-sectional shapes and then studies the effects of the geometric and structural parameters of the network on its total thermal resistance. The numerical simulations are also performed to analyze the influences of the geometric and structural parameters of symmetric treelike networks with circular, rectangular and triangular cross-sectional shapes on the total thermal resistance. Both the theoretical model and the numerical simulation show that the total thermal resistance of the network with an arbitrary cross-sectional shape first decreases and then increases with increasing cross-sectional area ratio but always increases with increasing length ratio of branches at two successive branching levels when the total branch volume is constant. When the cross-sectional area ratio is equal to the reciprocal of the branching number, the treelike network has the minimum total thermal resistance. This scaling law is applicable for the treelike network with an arbitrary cross-sectional shape to achieve the minimum total thermal resistance.

The microelectronic devices are formed by a substrate that supports the functional thin film material. The thermal, electrical, and mechanical properties of the system depend strongly on the interfacial properties between a film and a substrate. The interfacial nature in a film/substrate system originates the thermal contact resistance (R_tc). We discuss the thermal and the electrical behavior in a film/substrate system (bimaterial system) making emphasis on the R_tc of the interface. Au/glass samples with different thicknesses were prepared by thermal evaporation for experimentation. The bimaterial system was heated by a DC electrical current to obtain thermal profiles. Film and substrate thermal profiles acquired with high resolution combined with a developed bimaterial model are used as an alternative method to estimate the R_tc value at atmospheric pressure, the electrical resistivity ρ, and the thermal resistive coefficient α_r in the bimaterial system. The calculated R_tc values ranged from 7.7 × 10^-4 to 1.2 × 10^-3 m² K/W for the Au/glass system, in good agreement with previously reported values. The ρ values obtained from the thermal profile data present a more reliable value due to the global character than the local values measured by the four-probe technique. Dependence on film thickness was also found in the α_r coefficient determination.

Graphitic carbon-doped silica aerogels, including graphite-doped and graphene-doped silica aerogels, were fabricated by the sol–gel method. Thermal resistance was a significant comprehensive parameter which could reflect the ability to prevent the heat transfer. In order to give a direct evaluation of the thermal insulation performance, the calculated formula of thermal resistance for graphitic carbon-doped silica aerogel thermal insulation layers had been given through theoretic analysis on the basis of the thermal conductivity and the aerogel-based heat insulation layers showed good thermal insulation performance. It was expected that theoretical evaluation and experimental research could provide a reference for the reliability and performance in the field of the aerogel-based insulation layers.

The application of Fault Detection and Diagnosis (FDD) could play a key role in operating chillers at optimum efficiency. As air-conditioning consumes a significant proportion (approximately 30% to 50%) of the total power consumption of a commercial building, an effective FDD tool is very much required for a reliable and economic chiller operation. In this paper, the renowned Simple Thermodynamic Model, STM (also known as Gordon and Ng Universal Chiller Model) was utilized to detect and diagnose some of the common faults in centrifugal chillers. Based on the readily available, nonintrusive, steady state measurements extracted from the on-site chillers, the STM model was regressed to obtain two physically meaningful coefficients, namely, Thermal Resistance and Internal Entropy Generation. These information-rich coefficients were then analyzed to evaluate the performances and the conditions of the chillers. Despite the large and yet complex on-site chiller operations, equipped with built-in heat recovery, such as economizer and intricate control mechanisms, the predictive and diagnostic capabilities of STM in detecting chiller faults has been successfully tested and evaluated based on the data collected from on-site centrifugal chillers. Faults like condenser fouling and reduction in condenser cooling water flow rate were succinctly captured by the STM model.

Thermal and hydraulic performances of various geometric shapes of a microchannel heat sink were evaluated numerically using Navier–Stokes equations. A heat sink comprised of a $1\times 1$cm² silicon wafer was investigated with water as the cooling fluid. The performances of seven microchannel shapes were compared at the same microchannel hydraulic diameter and the same average height of the bottom silicon substrate. The thermal resistance, friction coefficient, and Nusselt number were calculated for a Reynolds number range of 50 to 500. The results show that an inverse trapezoidal shape gives the lowest thermal resistance for a Reynolds number up to 300. The values of $f$Re are almost similar for all the shapes because of the constant hydraulic diameter.

Ga₂O₃ has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga₂O₃ power devices stimulated by early demonstrations of high-voltage Ga₂O₃ field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletion-and enhancement-mode Ga₂O₃ FETs — which have predominantly been lateral devices — for power switching and radiation-hard electronics. The development of vertical Ga₂O₃ transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed.