Avram Bar-Cohen

Bio: Avram Bar-Cohen is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Heat transfer & Heat sink. The author has an hindex of 50, co-authored 329 publications receiving 8329 citations. Previous affiliations of Avram Bar-Cohen include Auburn University & DARPA.

Near-Junction Thermal Management for Wide Bandgap Devices

Abstract: Near-junction thermal management is critical to achieving the promise of electronic and photonic devices using wide bandgap materials. In such devices, including GaN HEMTs in PAs, the thermal resistance associated with the "near-junction" region dominates the heat removal path and is often as large as the thermal resistance of all the other elements in the resistance chain. As part of DARPA's portfolio in Thermal Management Technologies (TMT), efforts are underway to develop transformative, paradigm-changing cooling techniques. This paper will briefly review the thermal management needs of WBG devices and DARPA's Thermal Management Technologies portfolio, with emphasis on the goals and status of these efforts relative to the current State-of-the-Art. Attention will then turn to promising options in near-junction cooling and the challenges inherent in realizing their potential for WBG device thermal management.

Thermal characterization of chip packages-evolutionary development of compact models

Abstract: The expanded R/sub jc/ methodology, first proposed in 1989, makes it possible to extend the use of this common figure-of-merit to chip packages with nonisothermal cases. This proposal spurred considerable debate and contributed to renewed efforts to provide "compact" thermal models of single chip packages, for preliminary design, as well as for detailed numerical simulation of populated printed circuit boards. This presentation offers a review of the development of this modified R/sub jc/ methodology and its efficacy in replicating the chip, or junction, temperature predicted by detailed numerical simulation.

Mini-Contact Enhanced Thermoelectric Cooling of Hot Spots in High Power Devices

Abstract: Cooling hot-spots with high heat flux (e.g., >1000 W/cm2) is becoming one of the most important technical challenge in today's integrated circuit industry. More aggressive thermal solutions, than would be required for uniform heating, are highly desired. Recently, solid state thermoelectric coolers (TECs) have received more attention for hot-spot thermal management. However, present day TECs typically have cooling flux much lower than heat flux in the hot-spots. In this work, we reported an innovative technique-TE Mini-contact-to significantly increase cooling flux of TECs for the application in hot-spot cooling. A chip package featuring a TE Mini-contact cooler integrated with conventional integrated heat spreader and heat sink is designed. The cooling performance of such chip package has been investigated by using a 3-D numeric model. It is found that the cooling in the hot-spot (1250 W/cm2, 400 mum by 400 mum) can be about 19 degC better in the proposed package than that achieved in the conventional chip package without TEC. The effects of trench, die thickness, and TEC misalignment on the cooling of the hot-spot are also discussed.

Least-energy optimization of air-cooled heat sinks for sustainable development

Abstract: The development of heat sinks for microelectronic applications, which are compatible with sustainable development, involves the achievement of a subtle balance between a superior thermal design, minimum material consumption, and minimum pumping power. This presentation explores the potential for the least-energy optimization of natural and forced convection cooled rectangular plate heat sinks. The results are evaluated in terms of a heat sink coefficient of performance, relating the cooling capability to the energy invested in the fabrication and operation of the heat sink, and compared to the entropy generation minimization methodology (EGM).

Light-emitting diodes

Abstract: 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.

A review of Ga2O3 materials, processing, and devices

Abstract: 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.

Low loss dielectric materials for LTCC applications: a review

Abstract: 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...