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

Heat transfer—a review of 1990 literature

Thermoelectric cooling has been well documented as a solution for hotspots in electronic devices. Hotspots arise from the heterogeneous power dissipation of most computer chips and power electronics. This paper reviews the recent progress in thermoelectric self-cooling and goes on to study the transient behavior of a germanium thermoelectric self-cooler. A 3-D thermoelectric simulation is used to explore the effects of various initial conditions, current pulse durations, current pulse magnitudes, and die thicknesses. Additionally, a new cooling metric is introduced in order to more effectively characterize the advantage of transient cooling. The results suggest that transient thermoelectric cooling has the potential to improve hotspot temperature reduction by approximately 30% relative to what is achievable in steady state operation.

Transient thermoelectric self-cooling of a germanium hotspot

Embedded cooling — an emerging thermal management paradigm for electronic devices — has motivated further research in compact, high heat flux, cooling solutions. Reliance on phase-change cooling and the associated two-phase flow of dielectric refrigerants allows small fluid flow-rates to absorb large heat loads. Our previous research as well as work of others has shown that dividing chip-scale microchannels into parallel arrays of channels with novel manifold designs can produce very high chip-scale heat transfer coefficients with low pressure drops. In such manifolded microchannel coolers, the coolant typically flows at relatively high velocities through U-shaped microgap channels, producing centripetal acceleration forces on the fluid that can be several orders of magnitude larger than gravity. The impact of such large accelerations on the two-phase flow regimes in microgap channels, and their associated transport rates, are not well understood. Moreover, because the channels are very small and optically inaccessible, the flow regimes occurring in such manifolded microchannels have yet to be imaged and documented. The present effort analyzes the effects of such high centripetal acceleration on two-phase flow characteristics, including flow morphology. Since the available literature deals almost exclusively with macroscale and miniscale channels, the differences between macroscale and microscale two-phase flows are identified and discussed. The paper also shows, using dimensionless numbers to characterize the prevailing two-phase flow regimes, that results of previous U-channel visualizations in miniscale geometries, approximately an order of magnitude larger in every geometrical dimension than the microgap channels of interest, can provide insight into the flow regimes occurring in very high-performance microgap channels.

Two-phase flow regimes in a U-shaped diabatic manifolded-microgap channel

The role of thickness and thermal effusivity in pool boiling chf in highly-wetting liquids

An advanced inverse approach, based on the transient junction temperature behavior, is proposed and implemented to quantify the resistance of the die-attach thermal interface (DTI) in high-power light-emitting diodes (LEDs). After describing the unique transient behavior of high-power LEDs associated with the forward voltage method, a hybrid analytical/numerical model is used to determine an approximate transient junction temperature behavior, which is governed predominantly by the resistance of the DTI. Then, an accurate value of the resistance of the DTI is determined inversely from the experimental data over the predetermined transient time domain using numerical modeling. The proposed inverse approach is capable of determining the DTI to an accuracy of 0.01 K/W, which is sufficiently high to evaluate the die bonding manufacturing processes.

Avram Bar-Cohen

Papers

Heat transfer—a review of 1990 literature

Transient thermoelectric self-cooling of a germanium hotspot

Two-phase flow regimes in a U-shaped diabatic manifolded-microgap channel

The role of thickness and thermal effusivity in pool boiling chf in highly-wetting liquids

Characterization of Die-Attach Thermal Interface of High-Power Light-Emitting Diodes: An Inverse Approach