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

Current trends in the microelectronic industry suggest that by the mid-1990s successful thermal management will require removal of as much as 500 W and 100 W/cm2 from a single chip and in excess of 10 kW and 10 W/cm3 from a multichip module. These cooling requirements pose a serious challenge to today's cooling technology and have spurred extensive research and development of advanced thermal control techniques for microelectronics. The choice of the thermal management strategy for an electronic product has a large impact on its cost, reliability, operating environment, and performance. Thus, while thermal control is just one of several enabling packaging technologies, it deserves and often receives special attention in the development of leading-edge electronic systems. Many observers believe that direct cooling with inert, dielectric liquids may become the method of choice for electronic systems of the late 1990s. This presentation begins with a review of the trends in IC technology and the state-of-the-art in single chip packages and multichip modules. It then examines the packaging development process and defines the future requirements, options, and limits of thermal management techniques. Attention is then turned to direct liquid cooling, including implementation schemes, governing phenomena, research issues, and prospects for widespread implementation.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Thermal management of high-power microelectronic components: state of the art and future challenges

Limits of Thin Film Cooling in Microgap Channels

Pin fin two-phase micro gap coolers for concentrating photovoltaic arrays

We designed and fabricated a three-dimensional (3D) silicon microrefrigerator, which demonstrates a cooling power density over 200W/cm with only ~1degC cooling. The high cooling power density is mainly due to the high thermal conductivity and heat spreading effects. These devices have potential application in hot-spots management to reduce the chip peak temperature and realize on chip thermal management. A finite element model is developed to study and optimize these 3D devices. The simulation results showed that the optimized doping concentration to achieve the maximum cooling for these 3D silicon microrefrigerators (5e18 cm-3) is different from the conventional ID device, where S2sigma achieves the maximum at the doping of 5e19 cm-3. At its optimized doping concentration, these silicon microrefrigerators could reach a maximum cooling of 3degC. Further studies prove that this deviation is due to the nonidea factors inherent within the device, e.g. semiconductor-metal contact resistance, Joule-heating from probe contact resistance etc. Thus to optimize the real device, it is necessary to chose a full model considering all the nonideal factors

Optimization of doping concentration for three-dimensional bulk silicon microrefrigerators

The high power density of emerging electronic devices is driving the transition from remote cooling, which relies on conduction and spreading, to embedded cooling, which extracts dissipated heat on-site. Two-phase microgap coolers employ the forced flow of dielectric fluids undergoing phase change in a heated channel within or between devices. Such coolers must work reliably in all orientations for a variety of applications (e.g., vehicle-based equipment), as well as in microgravity and high-g for aerospace applications, but the lack of acceptable models and correlations for orientation- and gravity-independent operation has limited their use. Reliable criteria for achieving orientation- and gravity-independent flow boiling would enable emerging systems to exploit this thermal management technique and streamline the technology development process. As a first step toward understanding the effect of gravity in two-phase microgap flow and transport, in an earlier effort, the authors studied the effects of evaporator orientation, mass flux, and heat flux on flow boiling of HFE7100 in a 1.01 mm tall by 13.0 mm wide by 12.7 mm long microgap channel. Orientation-independence, defined as achieving similar critical heat fluxes, heat transfer coefficients, and flow regimes across orientations, was achieved for mass fluxes of 400 kg/sq.m-s and greater (corresponding to a Froude number of about 0.8). In the present effort, the authors have studied the effects of gravity, mass flux, and subcooling on flow boiling of HFE7100 in a 0.17 mm tall by 13.0 mm wide by 12.7 mm long microgap channel. The Flow Boiling in Microgap Coolers payload experienced about three minutes of weightlessness and shorter periods of high-g (up to about 5 g) during two recent flights aboard the Blue Origin New Shepard reusable launch vehicle. The results from the flight experiments will be presented and compared with published criteria for achieving gravity-independence.

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Avram Bar-Cohen

Papers

Thermal management of high-power microelectronic components: state of the art and future challenges

Limits of Thin Film Cooling in Microgap Channels

Pin fin two-phase micro gap coolers for concentrating photovoltaic arrays

Optimization of doping concentration for three-dimensional bulk silicon microrefrigerators

Gravity Effects in Two-Phase Microgap Flow