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

This study presents a detailed experimental investigation of the combined effects of pressure and subcooling on nucleate pool boiling and critical heat flux (CHF) for degassed fluorocarbon FC-72 boiling on a plastic pin-grid-array (PPGA) chip package. In these experiments pressure was varied between 101.3 and 303.9 kPa and the subcooling ranged from 0 to 65°C. As expected, lower wall superheats resulted from increases in pressure, while subcooling had a minimal effect on fully developed pool boiling. However, the superheat reductions and CHF enhancements were found to be smaller than those predicted by existing models. The CHF for saturated liquid conditions increased by nearly 17 percent for an increase in pressure from 101.3 to 202.7 kPa. In experiments with both FC-72 and FC-87 further increases in pressure did not produce any significant increase in CHF. At a pressure of 101.3 kPa a subcooling of 30°C increased CHF on horizontal upward-facing chips by approximately 50 percent, as compared to 70 percent on vertically oriented packages. The enhancement in CHF due to subcooling decreased rapidly with increasing pressure, and the data showed that the influence of pressure and subcooling on CHF is not additive. A correlation to predict pool boiling CHF under the combined effects of pressure and subcooling is proposed.

Combined Pressure and Subcooling Effects on Pool Boiling From a PPGA Chip Package

Thermal interface materials (TIMs) have become increasingly important in reducing the interfacial thermal resistance between contacting surfaces inside electronic devices, such as at the die-heat-sink or heat-spreader-heat-sink interfaces. While the focus regarding implementing TIMs remains on reducing the thermal resistance path, the long-term performance of the TIM is important from a life-cycle standpoint. This paper presents test and analysis results examining the effect of temperature cycling and elevated temperature/humidity on the thermal performance of filled polymer TIMs using the laser flash method. A three-layer sandwich structure was used to simulate loading conditions encountered by TIMs in actual applications and to assess the change in their thermal resistances. The evaluated thermal resistance included contact and bulk resistances and was calculated using the Lee algorithm, an iterative method that uses the properties of the single layers and the three-layer sandwich structures. Test samples included three thermal putties, a gap filler, an adhesive, a gel, and two gap pads. For most materials, little change or slight improvement in the thermal performance was observed over the course of environmental exposures. Scanning acoustic microscope images revealed delamination in one group of gap pad samples and cracking in the putty samples as a result of temperature cycling. One thermal putty material showed degradation due to temperature cycling resulting from bulk material changes near the glass transition temperature, while other samples showed little change or slight improvement in the thermal performance over the course of temperature cycling.

Effects of Temperature Cycling and Elevated Temperature/Humidity on the Thermal Performance of Thermal Interface Materials

Confinement effects on nucleate boiling and critical heat flux in buoyancy-driven microchannels

The rapid emergence of nanoelectronics, with the consequent rise in transistor density and switching speed, has led to a steep increase in microprocessor chip heat flux and growing concern over the emergence of on-chip “hot spots”. The application of on-chip high heat flux cooling techniques is today a primary driver for innovation in the electronics industry. In this paper, the physical phenomena underpinning the most promising on-chip thermal management approaches for hot spot remediation, along with basic modeling equations and typical results are described. Attention is devoted to thermoelectric microcoolers — using mini-contcat enhancement and in-plane thermoelectric currents, orthotropic TIM’s/heat spreaders, and phase-change microgap coolers.Copyright © 2009 by ASME

Thermal Management of On-Chip Hot Spot

The objective of this paper is to describe the development of a computationally efficient computer-aided design (CAD) method, which uses a finite element numerical model (FEM) coupled with empirical correlations, to create an optimum heat sink design, subject to multiple constraints. A thermal optimization "challenge" problem, representative of anticipated heat sink requirements in the near future, is solved to demonstrate the proposed methodology. Particular emphasis is placed upon micro-processor central processing unit (CPU) chip cooling applications where, in addition to thermal requirements, the heat sink design specification includes constraints upon size, total mass, and air coolant pressure drop across the heat sink.

Avram Bar-Cohen

Papers

Combined Pressure and Subcooling Effects on Pool Boiling From a PPGA Chip Package

Effects of Temperature Cycling and Elevated Temperature/Humidity on the Thermal Performance of Thermal Interface Materials

Confinement effects on nucleate boiling and critical heat flux in buoyancy-driven microchannels

Thermal Management of On-Chip Hot Spot

Optimal numerical design of forced convection heat sinks