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 paper investigates the potential application of an R134a-cooled two-phase micro/mini-cooler for thermal management of a triple junction solar cell under 2000 suns concentration An analytical model for the triple-junction solar cell temperature based on prediction of two-phase flow boiling in mini/microchannel coolers is developed and exercised with empirical correlations from the open literature for the heat transfer coefficient, pressure drop, and critical heat flux The thermofluid analysis is augmented by detailed energy modeling, using two uniquely defined coefficient of performance metrics — COP relating the solar energy harvest to pumping power consumption and COPT relating the solar energy harvest to the “parasitic” work expended to provide the requisite cooling, including pumping power and the energy consumed in the formation and fabrication of the microcooler itself Three constant fin thicknesses of 100μm, 300μm and 500μm are examined for a range of R134a flow rates and geometries to determine the energy efficient design for a 10mm×10mm triple junction CPV cell The results reveal that two-phase cooling of CPV’s can achieve very high COPT values, substantially exceeding 104 for much of the design space of interest, though the energy efficiency is dependent on microcooler geometry and the number or pitch of the microcooler channelsCopyright © 2012 by ASME

Energy Efficient Two-Phase Micro-Cooler Design for a Concentrated Photovoltaic Triple Junction Cell

MEMS micropumps, based on PZT membranes have been designed and fabricated at the Microtechnology Laboratory of the University of Minnesota for use in fluid flow control, and as chemical and pressure sensors. Design, fabrication and numerical analyses of the PZT cantilever beams were presented at the MSM99, and are now extended to new MEMS devices; specifically reactive ion etched (RIE) bulk micromachined PZT membranes. Four major geometries including square, rectangular, circular and elliptic devices with different sizes have been successfully fabricated. The main advantage of the new devices is in providing more resonant points than the microcantilever beam, thus creating a larger working interval. Numerical studies have been carried out by using ANSYS Finite Element software. Numerical results compared well with the experimental findings.

https://briefs.techconnect.org/wp-content/volumes/MSM2000/pdf/T42.04.pdf

Design, Fabrication and Experimental-Numerical Study of PZT Sensors

Proposed uses of solid-state thermoelectric micro- coolers for hot spot remediation have included the formation of a superlattice layer on the back of the microprocessor chip, but there have been few studies on the cooling perfor- mance of such devices. This paper provides the results of 3-D, electrothermal, finite element modeling of a superlattice micro- cooler, focusing on the hot spot temperature and superlattice surface temperature reductions, respectively. Simulated temper- ature distributions and heat flow patterns in the silicon, associated with variations in microcooler geometry, chip thickness, hot spot size, hot spot heat flux, and superlattice thickness are provided. Comparison is made to hot spot cooling achieved by the Peltier effect in the silicon microprocessor chip itself. The numerical results suggest that, for a variety of operating conditions and geometries, while increasing the superlattice thickness serves to decrease the exposed superlattice surface temperature, it is ineffective in reducing the hot spot temperature below that due to the silicon Peltier effect.

Superlattice µTEC Hot Spot Cooling

Shrinking feature size and increasing transistor density, combined with the high performance demanded from next-generation microprocessors and other electronic components, have lead to the emergence of severe on-chip “hot spots,” with heat fluxes approaching — and at times exceeding — 1 kW/cm2 . The cost-effective thermal management of such chips requires the introduction and refinement of novel cooling techniques. Mini-contact enhanced, miniaturized thermoelectric coolers (TECs) have been shown to be a viable approach for the remediation of on-chip hot spots, but their performance is constrained by the thermal resistance introduced by the attachment of this thermal management device. This paper uses a detailed finite-element package-level model to examine the parasitic effects of the thermal contact resistance (at the interfaces of the mini-contact and TEC) on the cooling efficacy of this thermal solution. Particular attention is devoted to the deleterious effect of contact resistance on the thermoelectric leg height and the mini-contact size required to achieve the greatest hot spot temperature reduction on the chip. Data from experiments with TECs (with a leg height of 130 μm) combined with several sizes of mini-contact pads, are used to validate the modeling approach and the overall conclusions.Copyright © 2009 by ASME

Avram Bar-Cohen

Papers

Energy Efficient Two-Phase Micro-Cooler Design for a Concentrated Photovoltaic Triple Junction Cell

Design, Fabrication and Experimental-Numerical Study of PZT Sensors

Superlattice µTEC Hot Spot Cooling

Effect of Thermal Contact Resistance on Optimum Mini-Contact TEC Cooling of On-Chip Hot Spots

Development and validation of boundaries for circumferential isothermality in horizontal boiler tubes