Review on thermal energy storage with phase change: materials, heat transfer analysis and applications

Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

The thermofluid characteristics of a chip-scale microgap cooler, including single-phase flow of water and FC-72 and flow boiling of FC-72, are explored. Heat transfer and pressure drop results for single phase water are used to validate a detailed numerical model and, together with the convective FC-72 data, establish a baseline for microgap cooler performance. Experimental results for single phase water and FC-72 flowing in 120 μm, 260 μm and 600 μm microgap coolers, 31mm wide by 34mm long, at velocities of 0.1 – 2 m/s are reported. “Pseudo-boiling” driven by dissolved gas and flow boiling of FC-72 are found to provide significant enhancement in heat transfer relative to theoretical single phase values.Copyright © 2007 by ASME

Thermofluid Characteristics of Two-Phase Microgap Coolers

As thermal management techniques for three-dimensional (3D) chip stacks and other high-power density electronic packages continue to evolve, interest in the thermal pathways across substrates containing a multitude of conductive vias has increased. To reduce the computational costs and time in the thermal analysis of through-layer via (TXV) structures, much research to date has focused on defining effective anisotropic thermal properties for a pseudohomogeneous medium using isothermal boundary conditions. While such an approach eliminates the need to model heat flow through individual vias, the resulting properties are found to depend on the specific boundary conditions applied to a unit TXV cell. More specifically, effective properties based on isothermal boundary conditions fail to capture the local “microspreading” resistance associated with more realistic heat flux distributions and local hot spots on the surface of these substrates. This work assesses how the thermal microspreading resistance present in arrays of vias in interposers, substrates, and other package components can be properly incorporated into the modeling of these arrays. We present the conditions under which spreading resistance plays a major role in determining the thermal characteristics of a via array and propose methods by which designers can both account for the effects of microspreading resistance and mitigate its contribution to the overall thermal behavior of such substrate–via systems. Finite element modeling (FEM) of TXV unit cells is performed using commercial simulation software (ansys).

Modeling Thermal Microspreading Resistance in Via Arrays

Many of the candidate fluids for immersion cooling of microelectronic components possess both low surface tension and high gas solubility. As a consequence, ebullient heat transfer with such fluids is accompanied by nucleation anomalies and a frequently observed wall temperature overshoot. The difficulty in preventing this thermal excursion and in predicting its magnitude constrains the development of immersion cooling systems. This paper begins with a brief review of the mechanisms that may be responsible for delayed nucleation and examines the limited literature on incipience superheat excursions.

Wall superheat excursions in the boiling incipience of dielectric fluids.

: High-temperature environments and device self-heating are pushing the thermal limits of power electronics. This is particularly true in automotive applications, where there is a transition from internal combustion architectures to hybrid electric and full electric vehicles. In general, two-phase cooling has emerged as an attractive solution to meeting the high-temperature, high-power cooling needs of the aforementioned electronics. However, it is important to understand the benefits and limitations of various fluids when designing a two-phase cooling system. To aid in the selection process and add to the current knowledge base, this report briefly discusses the current state of high temperature electronics, reviews platform considerations when selecting a fluid, and introduces a two-phase Figure of Merit (FOM) to analyze over 110 different fluids for cooling high-temperature electronics up to 500 deg C.

Two-phase Fluid Selection for High-temperature Automotive Platforms

The thermal performance limits of air cooled heat sinks made of a polyphenylene sulphide composite (PPS, 20W/m-K), are predicted and compared to aluminum and copper pin fin heat sinks, using a defined heat sink volume and a range of pumping powers. The thermal performance is analytically predicted across an extensive parametric space in terms of the primary thermal metrics and identifies the thermal performance limits. PPS heat sinks are seen to constitute a viable alternative material for energy efficient heat sink design and show comparable thermal performance to aluminum and copper heat sinks at low fin densities and pumping power. The analytical model used to predict the heat sink thermal performance is seen to provide good agreement with typical aluminum pin fin heat sink experimental and CFD modeling results.

Avram Bar-Cohen

Papers

Thermofluid Characteristics of Two-Phase Microgap Coolers

Modeling Thermal Microspreading Resistance in Via Arrays

Wall superheat excursions in the boiling incipience of dielectric fluids.

Two-phase Fluid Selection for High-temperature Automotive Platforms

Thermal performance limits of polymer composite pin fin heat sinks