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Thermal management is one of the main challenges for the future of electronics.sup.1-5. With the ever-increasing rate of data generation and communication, as well as the constant push to reduce the size and costs of industrial converter systems, the power density of electronics has risen.sup.6. Consequently, cooling, with its enormous energy and water consumption, has an increasingly large environmental impact.sup.7,8, and new technologies are needed to extract the heat in a more sustainable way--that is, requiring less water and energy.sup.9. Embedding liquid cooling directly inside the chip is a promising approach for more efficient thermal management.sup.5,10,11. However, even in state-of-the-art approaches, the electronics and cooling are treated separately, leaving the full energy-saving potential of embedded cooling untapped. Here we show that by co-designing microfluidics and electronics within the same semiconductor substrate we can produce a monolithically integrated manifold microchannel cooling structure with efficiency beyond what is currently available. Our results show that heat fluxes exceeding 1.7 kilowatts per square centimetre can be extracted using only 0.57 watts per square centimetre of pumping power. We observed an unprecedented coefficient of performance (exceeding 10,000) for single-phase water-cooling of heat fluxes exceeding 1 kilowatt per square centimetre, corresponding to a 50-fold increase compared to straight microchannels, as well as a very high average Nusselt number of 16. The proposed cooling technology should enable further miniaturization of electronics, potentially extending Moore's law and greatly reducing the energy consumption in cooling of electronics. Furthermore, by removing the need for large external heat sinks, this approach should enable the realization of very compact power converters integrated on a single chip. Cooling efficiency is greatly increased by directly embedding liquid cooling into electronic chips, using microfluidics-based heat sinks that are designed in conjunction with the electronics within the same semiconductor substrate., Author(s): Remco van Erp [sup.1] , Reza Soleimanzadeh [sup.1] , Luca Nela [sup.1] , Georgios Kampitsis [sup.1] , Elison Matioli [sup.1] Author Affiliations: (1) Power and Wide-band-gap Electronics Research Laboratory [...]

Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spontaneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high-voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench-structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main properties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics. [ABSTRACT FROM AUTHOR]

The dissipated energy (Ediss) related to the resonant charging–discharging of a transistor output capacitance becomes a dominant loss factor for power converters operating in the MHz range. A recent letter has introduced a small-signal measurement method to quantify Ediss with a frequency-dependent small-signal resistance, Rs, and an effective small-signal output capacitance, Cosseff. This letter provides further insights on the effect of Rs and Coss upon the device losses in a broader sense. In particular, the Coss loss tangent, tan (δ), is introduced as a normalized Ediss to combine the roles of Rs and Coss together with the operating frequency into a single loss parameter. By evaluating commercial device families, it is demonstrated that tan (δ) is constant for a given family, independent of device on-state resistance, RDS(on). It is shown that a minimum Ediss is achieved by having the lowest tan (δ) for a given stored energy (Eoss) in Coss. With accompanying guidelines, this letter identifies tan (δ) as a powerful figure of merit to classify field-effect transistors (FETs) for soft-switching applications, regardless of RDS(on) variations in devices within a family. The proposed concept provides a comprehensive method to characterize and benchmark field-effect transistors for efficient operation in high and very-high-frequency (VHF) applications. [ABSTRACT FROM AUTHOR]