Novel in-situ constructing approach for vertically aligned AlN skeleton and its thermal conductivity enhancement effect on epoxy

As one of the key components of electronic devices, thermal management materials (TMMs) with high thermal conductivity are essential to ensure their safety and long service life. For polymer-based TMMs, AlN is one of the preferred fillers, but it has some drawbacks such as high cost and easy hydrolysis. Herein, a controllable and continuously oriented three-dimensional AlN skeleton (3D-AlNNS) was in-situ transformed from a low-cost 3D Al-containing skeleton (3D-AlNS) by combining the ice-templating and nitriding reaction sintering. Subsequently, AlN/epoxy composites were obtained by a vacuum infiltration. The composite containing 39.69 vol% AlN had the highest thermal conductivity of 4.29 W m^?1·K^?1, which was 21.45 times higher than that of pure epoxy. The composite substrates showed excellent heat dissipation performance in practical applications due to their high thermal conductivity. The continuous directional alignment of AlN powders in the 3D skeleton and intersection of AlN whiskers between the skeleton walls produced in-situ contributed to the formation of effective multichannel heat transferring paths and improvement in thermal conductivity. This novel approach has the advantages of low-cost, short processing time, simple operation and repeatability, and provides a new idea for developing heat-conducting polymer composites, which can also be extended to the preparation of similar TMMs.     

Hybrid laser processes for thick silver coating fabrication on AlN substrate

Aluminum nitride (AlN) are particularly suitable as integrated circuits (ICs) substrates due to its high thermal conductivity and excellent electricity insulation. However, its poor weldability with metals limits its usage. Recent research on surface metallization of AlN provides possible solutions to tackle this defect. Nevertheless, these solutions show some shortages such as complicated processes or insufficient electrical conductivity. In this paper, we report a method that consists of laser induced surface metallization and laser sintering of silver (Ag) coatings. A nanosecond laser was applied to induce a 10 μm thick aluminum (Al) layer from the AlN substrate. Afterwards, laser sintering of Ag layers was implemented, which could enhance the conductivity and the bonding performance between layers. With optimized laser parameters applied, both the electrical conductivity and the bonding tests demonstrated excellent physical properties. Finally, simulation and EDS analysis illustrated the melting evolution and confirmed a metallurgical combination of Al and Ag, thus enhancing bonding strength. Thanks to the small size of focused laser spot, electrical circuits width could be greatly narrowed if these findings were applied; hence highly dense ICs on AlN substrate become potentially available.     

Stress and defects cooperatively regulate the photocatalytic performance of AlN bulk phase materials

Due to the wide bandgap width, the lack of oxidation capacity, high carrier recombination rate and limited solar absorption seriously inhibit the photocatalytic activity of pure AlN. Using first principles, we report an efficient method, nonmetal-nonmetal (C–F and B–O) passivation co-doping and H interstitial synergistic biaxial stress action, to solve all the above problems in AlN. We found that by applying appropriate tensile strain, Al₃₆N₃₄C_N1F_N3H and Al₃₆N₃₄B_N1O_N3H doped structures can reduce the band gap and make the UV absorption edge redshift. The electron and hole can be separated quickly, and Al₃₆N₃₄C_N1F_N3H has better photocatalytic activity. It can also raise the potential of CBM and VBM to generate hydrogen and oxygen spontaneously and is beneficial to broadening the absorption range of sunlight. Through the theoretical evaluation of HER and OER activities of Al₃₆N₃₄C_N1F_N3H, we found that Al₃₆N₃₄C_N1F_N3H is suitable to be a good catalyst for the photocatalytic reaction. Our results are helpful for the design of high-efficiency sunlight responsive AlN photocatalysts for solar water splitting.     

Improving the energy storage performance of 0.88(Bi0.4Ba0.2Na0.2K0.2)TiO3–0.12Sr(Mg1/3Nb2/3)O3 high-entropy relaxor ceramics by AlN doping

In this study, we report the effects of AlN additives on the microstructure and energy performance of 0.88(Bi_0.4Ba_0.2Na_0.2K_0.2)TiO₃-0.12Sr(Mg_1/3Nb_2/3)O₃ high-entropy relaxor ceramics. We show that AlN partially reacts with/dissolves into the matrix and only forms a secondary phase when its concentration is above a threshold. AlN doping can only affect the shape of the P-E loop and improve the breakdown strength when it formed the secondary phase. The breakdown strength first increased and then decreased with increasing AlN concentration. When the AlN concentration is 6 mol%, the ceramic has the optimal energy storage performance with a breakdown electric field of 340 kV/cm, a recoverable energy density of 3.85 J/cm³, and an efficiency of 85.8%. The study suggests that the addition of AlN is an effective way to improve the energy storage performance of high-entropy ceramics.     

High temperature lattice structure evolution of C-axis preferred orientation AlN thin films and its application in temperature measurement

In order to measure the surface temperature of aerospace hot-end components accurately, AlN thin film temperature measurement technology was explored. In this research, C-axis preferred orientation AlN thin film was deposited on Ni-based superalloy substrates by medium frequency (MF) reaction magnetron sputtering. Effect of temperature on the lattice structure of AlN thin film was studied. X-ray diffraction results show that the diffraction angles (2θ) of AlN thin films shift to the left side monotonously with the increase of annealing temperature and annealing time. Based on this phenomenon, the maximum temperature experienced by the film can be deduced according to 2θ values. A temperature interpretation algorithm equation was established with MATLAB. The algorithm is a binary linear equation, whose dependent variable is 2θ and the independent variables are annealing temperature and annealing time. Then, temperature interpretation software was developed with Visual Studio 2019. The temperature interpretation range is 700–1200 °C and the relative interpretation error is less than 4.26%.     

Mechanical and heat transfer properties of AlN/Cu joints based on nanosecond laser-induced metallization

In this paper, AlN ceramic was directly joined to copper without active brazing filler metal. By exerting the nanosecond laser irradiation on the AlN surface, the AlN ceramic was thermally decomposed to aluminum and the surface was metalized. The as-metalized AlN ceramic was successfully joined to copper through the eutectic reaction between aluminum and copper. The effect of the groove interface structure fabricated with various laser scanning speeds on the mechanical and heat transfer properties of AlN/Cu joints was investigated. The joints obtained optimal shear strength and thermal diffusivity of 10.64 MPa and 51.75 mm²/s at the scanning speed of 250 mm/s. The micro groove structures of the interface contributed to the enhancement of mechanical and heat transfer properties of joints. The approach of laser-irradiation assisted joining proposed in this paper provided a novel thought for the fabrication of metal/ceramic composite structures.     

AlN基板材料研究进展

氮化铝基板因具有高热导率、低介电常数、与硅相匹配的热膨胀系数等优良的物理性能，被誉为新一代理想基板材料。详细综述了AlN板的国内外研究现状及其导热机理；介绍并分析了基片制备的工艺流程和影响因素；概括总结了AlN基板的金属化和烧结工艺方面的研究进展；展望了AlN基板的发展趋势和前景。     

球型Al2O3-AlN颗粒复配填充型硅橡胶的制备及导热性能研究

以 Al2O3 和 AlN 的球形粉体颗粒作为导热填料、以硅橡胶为基体,通过特定的工艺手段得到具有高导热特征的 Al2O3-AlN/硅橡胶复合材料。结果表明：根据颗粒级配理论模型的计算可得最密堆积配方,该配方的复合材料在 9.6 wt% 填料填量下的热导率可高达 9.6 W/(m·K),其热导率相比只填充 Al2O3颗粒的样品提高了 60%。复合材料热导率的显著提高和样品内部导热路径的增多密切相关。通过极端的冷热循环应用条件模拟测试,该复合材料的热导率保持良好,表现出了良好的可靠性。