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

With increasing thermal fluxes, the performance of thermal interface materials (TIMs) that are used to reduce the thermal resistance between contacting surfaces in electronic devices, such as at the die-to-heat sink or heat spreader-to-heat sink interfaces, is becoming critical. However, measuring the thermal resistances of TIMs in a manner representative of actual applications is difficult. The laser flash method is a technique that may be used to determine the thermal resistance of TIMs and their degradation under environmental exposure. This paper examines three issues associated with using the laser flash method that could limit its effectiveness in calculating thermal resistance: sample holder heating, clamping, and error in the Lee algorithm outputs due to coupon-TIM thermal diffusivity differences. As a case study, the thermal performance of polymer TIMs in pad form, as well as an adhesive and a gel, were examined. Finite element simulations indicated that, without proper consideration, sample holder heating can lead to significant error in the calculated TIM thermal conductivity values.

Considerations in the Use of the Laser Flash Method for Thermal Measurements of Thermal Interface Materials

GaN has emerged as the material of choice for advanced power amplifier devices for both industrial and defense applications but near-junction thermal barriers severely limit the inherent capability of high-quality GaN materials. Recent “embedded cooling” efforts, funded by Defense Advanced Research Projects Agency Microsystems Technology Office (DARPA-MTO), have focused on reduction of this near-junction thermal resistance, through the use of diamond substrates and efficient removal of the dissipated power with convective and evaporative microfluidics. An overview of the accomplishments of the DARPA Near-Junction Thermal Transport (NJTT) program and recent results from the on-going DARPA Intra-Chip Embedded Cooling (ICECool) program are provided. It is shown that growth or bonding of diamond to GaN epitaxy has enabled a 3-5× increase in power handling capability per transistor unit area, while use of microfluidic cooling has enabled heat fluxes of 30 kW/cm2 at the transistor level and 1 kW/cm2 at the die-level, for a 3-6× improvement in the total RF output power of GaN power amplifiers. These demonstrations provide near-term validation of the large improvement in output power gained through embedded cooling and confirm the potential for well above a 6× improvement in GaN power amplifier output power to the electrical, rather than thermal, limits of GaN.

Near-Junction Microfluidic Cooling for Wide Bandgap Devices

Etude analytique et experimentale du transfert de chaleur par ebullition dans l'eau sur une paire de plaques plates, a flux thermiques egaux. Resultats experimentaux pour la temperature de la paroi en fonction de la localisation axiale du flux thermique et de l'espacement des plaques. Modele theorique du debit liquide a travers le canal et correlation de la vitesse du transfert de chaleur des parois du canal

Thermosyphon boiling in vertical channels

Thermal Management of Time-Varying High Heat Flux Electronic Devices

Delamination and/or rupture of the die-attach layer are among the primary failure mechanisms in plastic IC packages and often lower the threshold for other mechanical, as well as electrical, failure mechanisms Die-attach failure is generally caused by the thermal expansion (contraction) mismatch of dissimilar materials and the consequent development of axial and shear stresses in the adhesive and along the material interfaces To enhance the reliability of plastic packaging it is thus desirable to select the most reliable and cost-effective die-attach material Analysis of an ideal tri-material structure, using a force and momentum balance, makes it possible to derive analytical relations for the axial and shear stresses in a die-attach layer Based on these analytical relations, which are validated against FEM results, the critical material properties can be selected and used for the development of Figures-of-Merit (FOM) for material selection These FOMs are then used to evaluate the effects of moisture on the selection of the die-attach materials

Avram Bar-Cohen

Papers

Considerations in the Use of the Laser Flash Method for Thermal Measurements of Thermal Interface Materials

Near-Junction Microfluidic Cooling for Wide Bandgap Devices

Thermosyphon boiling in vertical channels

Thermal Management of Time-Varying High Heat Flux Electronic Devices

Mechanistic figures of merit for die-attach materials