3D integration has well-developed for traditional CMOS technology operating at room temperature, but few studies have been performed for cryogenic applications such as quantum computers. In this paper, a wafer-to-wafer bonding of superconductive joints based on niobium nitride (NbN) is performed to demonstrate the possibility of 3D integration of superconducting chips. The NbN thin films are deposited by magnetron sputtering. Its high critical temperature (15.2 K) is achieved by optimizing the sputtering recipe in terms of N₂ flow rate and discharge voltage. Wafer-level bumping is bonded by the thermo-compression method. The sheet resistance of the thin film and the contact resistance of the joints are measured by the Greek-cross (4-point Kelvin method) and daisy chain structures at cryogenic temperature, respectively. Direct-bonding wafers with NbN superconductive joints avoid using adhesive layers and the bonding interface could still present superconducting electrical connections in a cryogenic environment above 4 K, which will allow us to use a smaller and high-cooling power cryostat. The contribution of this work could lead to the fabrication of multi-layered superconducting chip that operates beneficially in cryogenic temperature, which is essential in building scalable quantum processors.

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In this paper, the compressive stress of pristine and coated vertically-aligned (VA) multi-walled (MW) carbon nanotube (CNT) pillars were investigated using flat-punch nano-indentation. VA-MWCNT pillars of various diameters (30–150 µm) grown by low-pressure chemical vapor deposition on silicon wafer. A conformal brittle coating of niobium-titanium-nitride with high superconductivity temperature was deposited on the VA-MWCNT pillars using atomic layer deposition. The coating together with the pillars could form a superconductive vertical interconnect. The indentation tests showed foam-like behavior of pristine CNTs and ceramic-like fracture of conformal coated CNTs. The compressive strength and the elastic modulus for pristine CNTs could be divided into three regimes of linear elastic, oscillatory plateau, and exponential densification. The elastic modulus of pristine CNTs increased for a smaller pillar diameter. The response of the coated VA-MWCNTs depended on the diffusion depth of the coating in the pillar and their elastic modulus increased with pillar diameter due to the higher sidewall area. Tuning the material properties by conformal coating on various diameter pillars enhanced the mechanical performance and the vertical interconnect access (via) reliability. The results could be useful for quantum computing applications that require high-density superconducting vertical interconnects and reliable operation at reduced temperatures.@en

In this paper, the growth of optimized vertically aligned multi-walled carbon nanotube (VA-MWCNT) forests by LPCVD method for use in a large-area absorber in infrared detectors is presented. The effect of synthesis temperature (500−700 °C) and time (1−10 min) on the optical absorption coefficient in the infrared (2−20 μm) is investigated by FT-IR measurement at various incident angles (15-80°). The structural properties of VA-MWCNT are characterized by SEM, TEM and Raman spectroscopy. Spectral measurements show an increasing absorption with the height of the forest that results at increased synthesis time and temperature. However, the absorption coefficient decreases with increasing synthesize time and temperature, while it is also affected by other properties, such as diameter, density, alignment, and uniformity. Moreover, the reduction in absorption at oblique incident angles demonstrates the relevance of surface properties. Finally, a circular graphite waveguide system is used to model the absorption characteristics of an MWCNT forest.@en

Corrugating channel wall is considered to be an efficient procedure for achieving improved heat transfer. Further enhancement can be obtained through the utilization of nanofluids and porous media with high thermal conductivity. This paper presents the effect of geometrical parameters for the determination of an appropriate configuration. Furthermore, the optimization of forced convective heat transfer and fluid/nanofluid flow through a sinusoidal wavy-channel inside a porous medium is performed through the optimization of entropy generation. The fluid flow in porous media is considered to be laminar and Darcy-Brinkman-Forchheimer model has been utilized. The obtained results were compared with the corresponding numerical data in order to ensure the accuracy and reliability of the numerical procedure. As a result, increasing the Darcy number leads to the increased portion of thermal entropy generation as well as the decreased portion of frictional entropy generation in all configurations. Moreover, configuration with wavelength of 10 mm, amplitude of 0.5 mm and phase shift of 60° was selected as an optimum geometry for further investigations on the addition of nanoparticles. Additionally, increasing trend of average Nusselt number and friction factor, besides the decreasing trend of performance evaluation criteria (PEC) index, were inferred by increasing the volume fraction of the nanofluid (Al₂O₃ and CuO).

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Pool boiling is an effective heat transfer process in a wide range of applications related to energy conversion, including power generation, solar collectors, cooling systems, refrigeration and air conditioning. By considering the broad range of applications, any improvement in higher heat-removal yield can ameliorate the ultimate heat usage and delay or even avoid the occurrence of system failures, thus leading to remarkable economic, environmental and energy efficiency outcomes. A century of research on ameliorating critical heat flux (CHF) has focused on altering the boiling surface characteristics, such as its nucleation site density, wettability, wickability and heat transfer area, by many innovative techniques. Due to the remarkable interest of using nanoparticle deposition on boiling surfaces, this review is targeted towards investigating whether or not metal oxide nanoparticles can modify surface characteristics to enhance the CHF. The influence of nanoparticle material, thermo-physical properties, concentration, shape, and size are categorized, and the inconsistency or contradictions of the existing research results are recognized. In the following, nanoparticle deposition methods are presented to provide a worthwhile alternative to deposition rather than nanofluid boiling. Furthermore, possible mechanisms and models are identified to explain the amelioration results. Finally, the present status of nanoparticle deposition for CHF amelioration, along with their future challenges, amelioration potentials, limitations, and their possible industrial implementation, is discussed.@en

As an increasing attention towards sustainable development of energy and environment, the power electronics (PEs) are gaining more and more attraction on various energy systems. The insulated gate bipolar transistor (IGBT), as one of the PEs with numerous advantages and potentials for development of higher voltage and current ratings, has been used in a board range of applications. However, the continuing miniaturization and rapid increasing power ratings of IGBTs have remarkable high heat flux, which requires complex thermal management. In this paper, studies of the thermal management on IGBTs are generally reviewed including analyzing, comparing, and classifying the results originating from these researches. The thermal models to accurately calculate the dynamic heat dissipation are divided into analytical models, numerical models, and thermal network models, respectively. The thermal resistances of current IGBT modules are also studied. According to the current products on a number of IGBTs, we observe that the junction-to-case thermal resistance generally decreases inversely in terms of the total thermal power. In addition, the cooling solutions of IGBTs are reviewed and the performance of the various solutions are studied and compared. At last, we have proposed a quick and efficient evaluation judgment for the thermal management of the IGBTs depended on the requirements on the junction-to-case thermal resistance and equivalent heat transfer coefficient of the test samples.@en

Thermal analysis plays a crucial role in designing and reliability of contemporary semiconductor devices. In this paper, the analogy between the electrical and thermal systems is extended for analysis of nonlinear two dimensional hyperbolic heat conduction (HHC) in Silicon-On-Insulator (SOI) transistor. The equivalent Resistance-Inductance-Capacitance(RLC) transmission line network is solved fast and easily by an electric solver tool such as HSPICE. The influence of a temperature dependent thermal conductivity and relaxation time in temperature distribution is discussed. The results demonstrate the wave character phenomena of the heat propagation that is occurring in nano-scaled high frequency electronic devices.@en

Nanostructured microporous surfaces were electrodeposited at various electrolyte temperatures on copper substrate to investigate the saturated pool boiling enhancement of distilled water at atmospheric pressure. Surface structure topography and wickability were analyzed to investigate their relation to critical heat flux. Scanning electron microscope showed that the micro-clusters have nanostructures from cubic at 5°C to dendritic at 60°C electrolyte temperature. Rate-of-rise experiments demonstrated that dendritic copper structure has the best capillary performance. The experimental results of pool boiling heat transfer indicate that the critical heat flux increased with surface wickability. Electrodeposited porous surface in hot electrolyte showed the highest critical heat flux and heat transfer coefficient of the 124 W/cm² and 17 W/cm²K, respectively, which is 50% and 270% higher than that of plain surface. However, the two-step electrodeposition and annealing were used in fabrication of surfaces, but the mechanical strength of layer needs more improvement by changing the electrochemical process parameters.

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Copper nanowires (NWs) were constructed on a dendritic copper powder precursor by a facile thermal oxidation-reduction method. First, copper oxide NWs were grown from high purity dendritic copper powder by thermal oxidation at 500°C. Next, these oxide NWs were reduced to copper NWs under a hydrogen flow at two different temperatures of 220 and 500°C. Oxide NW diameters distribution was in the range of 50-105 nm with length ranging from 1 to 5 μm while copper NWs were shorter and wider. A time-dependent study of oxide NWs growth was carried out. The morphology, composition and crystal structure of the resulting products were characterised by X-ray diffraction and scanning electron microscope. The results indicated that the final product of oxidation process was dispersed cupric oxide (CuO) NW whose density and length increased with time. Furthermore, it was observed that as the reduction temperature increased, the copper NW melted and adhered to the powder surface.@en