Aluminum Nitride Research Articles

Synthesis of pure fine AlN powder via CRN using nitridation promoter

Aluminum nitride (AlN) was synthesized using fine α-Al2O3 and carbon black through carbothermal reduction-nitridation (CRN) for heat dissipation applications in high-power electronics and electric vehicles. Pure AlN powder having a mean particle size of 0.52 μm was synthesized by CRN at 1650°C for 6h under 10L/min N2 flow. Because further reduction in particle size is needed to confer sinterability, the effects of various nitridation promoters, i.e., CaF2, AlF3, Y(NO3)3, Ca(NO3)2, and Mg(NO3)2 on decreasing the particle size were examined. The promoters containing Ca, Y, or Mg facilitate AlN conversion, while AlF3 retards it, revealing different particle morphologies. Addition of Ca(NO3)2 showed complete AlN conversion with a mean particle size of 0.38 μm after CRN at 1550°C for 10h. On the other hand, the addition of Mg(NO3)2 also revealed 100% AlN but coarser particle size of 0.45 μm along with more uniform particle size distribution. Intermediate phases generated by the reaction with promoter could be removed by optimizing the conditions for solid-state reaction to synthesize a pure fine AlN powder.

Thermophysical and Corrosion Inhibitor Evaluation of Graphene, Aluminum Nitride and Barium Titanate Nanolubricants

A newly developed kind of fluid known as nanolubricant is produced by dispersing nanometer-sized materials in base oil. The main issue with nanolubricant is particle stability, which occurs when nanoparticles aggregate due to van der Waals forces. The aim of the study is to evaluate the performance of graphene (GR), aluminium nitride (AlN), and barium titanate (BTO) nanolubricants at 0.05 and 0.1 vol. % concentrations. The stability was identified by using sedimentation photograph capturing method and zeta potential analysis, while KD2 Pro Analyzer was used to measure the thermal conductivity, and the effect of corrosion inhibitor evaluation was measured according to ASTM D130-19. The nanolubricants are prepared by two-step method and undergo ultrasonication process to ensure the nanoparticles are well dispersed in base oil. The results showed that nanolubricants containing 0.05 vol. % nanoparticles are more stable than 0.1 vol. % nanolubricants. Nanolubricants with 0.1 vol. % showed signs of instability based on low zeta potential values. This is due to the fact that the higher the concentration of nanoparticles, the closer the nanoparticles are to one another. This increased van der Waals attraction and potentially causing nanoparticle agglomeration. Improvement in thermal conductivity was obtained with high volume concentration of GR, AlN and BTO nanoparticles. All nanolubricants achieved an ASTM Standard D130 classification of 1a based on the Copper Strip Corrosion Test Standard (slight tarnish, slight colour change). As a result, it was discovered that all prepared samples are effective anticorrosion lubricating oil additives.

Phase Change Thermal Interface Materials with Interface Adaptability and Self-Healing Properties

Thermal stress resulting from excessive temperatures is a major cause of electronic device failure. In this work, with easy installation and good interface adaptability, Phase Change Thermal Interface Materials (PCTIMs) which possess high thermal conductivity were prepared. By incorporating phase change material stearic acid (SA) into the thermal interface material, the instantaneous heat absorption during the solid-liquid phase transition of SA effectively alleviates the problem of instantaneous high heat flux impacting electronic devices. Additionally, the solid-liquid transition reduces the modulus of TIMs, thereby minimizing the contact thermal resistance between the heat source and the heat sink during mechanical installation. To further enhance performance, the thermal interface material utilizes a dynamically cross-linked polyolefin elastomer (POE) with borate bonds, which effectively restricts the flow of SA even at its phase change point due to the three-dimensional cross-linked framework. By constructing a thermal conductive network using carbon fibers and aluminum nitride of different dimensions, the thermal conductivity of the thermal interface material reached 1.82 W∙m−1K−1 with a filler content of only 30 vol% . At 70°C, with a force of 50 N applied to a sample area of 400 mm², the contact thermal resistance was only 2.39×10−4K∙m2W−1. Furthermore, the PCTIMs exhibits excellent self-healing ability under thermal conditions, assuring the permanent encapsulation of small electronic devices.

Optimization of Superconducting Niobium Nitride Thin Films via High-Power Impulse Magnetron Sputtering

Abstract We report a systematic comparison of niobium nitride thin films deposited on oxidized silicon substrates by reactive DC magnetron sputtering and reactive high-power impulse magnetron sputtering (HiPIMS). After determining the nitrogen gas concentration that produces the highest superconducting critical temperature for each process, we characterize the dependence of the critical temperature on film thickness. The optimal nitrogen concentration is higher for HiPIMS than for DC sputtering, and HiPIMS produces higher critical temperatures for all thicknesses studied. We attribute this to the HiPIMS process enabling the films to get closer to optimal stoichiometry before beginning to form a hexagonal crystal phase that reduces the critical temperature, along with the extra kinetic energy in the HiPIMS process improving crystallinity. We also study the ability to increase the critical temperature of the HiPIMS films through the use of an aluminum nitride buffer layer and substrate heating.

Enhanced Electrocaloric Effect of PVDF-based Polymer Composite with Surface Modified AlN.

Poly(vinylidenefluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) relaxor ferroelectric polymer exhibits a modest electrocaloric effect (ECE) at a low electric field near room temperature and a low thermal conductivity. The low thermal conductivity causes poor heat transfer when the terpolymer is used as a cooling device, even when the ECE of the polymer is substantial. By incorporating aluminum nitride (AlN) nanoparticles, which possess high thermal conductivity and good electrical insulation properties, into polymer matrices, we can enhance both the thermal conductivity and the ECE. However, weak bonding at the AlN-polymer interface can lead to a reduced breakdown electric field. Therefore, surface modification of AlN nanoparticles is performed to strengthen the chemical bonding between AlN and the terpolymer, thereby increasing the breakdown electric field. Following the addition of surface-modified nanoparticles, the breakdown electric field of the composite films remained around 240 MV/m, which is comparable to that of the pristine polymer film. Furthermore, the ECE and thermal conductivity were improved by 44% and 55%, respectively. We found three factors influencing the ECE, including the interface effect, the change in ferroelectric-paraelectric phase transition behavior, and the Joule heating effect. To assess the interfacial effect on the ECE, composite films with AlN particles of four different sizes were prepared. It was found that as the size of the nanoparticles increased, which resulted in a decreased interface area, the ECE decreased correspondingly. This finding further confirms the significant impact of the interface area in the composites on the ECE.

Fabrication of uniform, periodic arrays of exotic AlN nanoholes by combining dry etching and hot selective wet etching, accessing geometries unrealisable from wet etching of planar AlN

Aluminium nitride (AlN) is a wide bandgap semiconductor with far reaching realised and potential applications in electronics and optoelectronic technology. For example, gallium nitride (GaN) quantum dots (QDs) housed within an AlN matrix are attractive due to the large bandgap offsets. However, making suitable AlN sites to house GaN QDs is challenging due to the difficulty in fashioning 3D AlN structures. This results from AlN's strong bonds that are difficult to chemically etch.Whilst dry etching of AlN nanostructures has been explored, wet etching at the nanoscale has been limited by the common exposed facet of AlN being etch-resistant. Hence, wet etching of AlN to create uniform arrays of periodic nanohole nanostructures has, thus far, not been heavily explored.In this paper, an initial dry etching of a 2D AlN planar template is used to expose alternative wet-etchable facets so that periodic arrays of nanohole structures are revealed by wet-etching. Both a study of different initial dry etched structures, including tapered nanoholes, and wet etching time were performed. A model to describe the dynamics of wet etching on the different dry etched nanohole structures is proposed. Periodic arrays of uniform nanohole features are realised that hold promise for applications such as the housing of site-controlled quantum dots.

Formation of aluminum nitride in dross by contact-diffusion reaction during aluminum recycling

Secondary aluminum dross is a solid waste after aluminum extraction from the slag produced during aluminum recycling. It is classified as a hazardous waste due to the high content of active aluminum nitride (AlN). This work studied the thermodynamics and kinetics of AlN formation in aluminum dross. Aluminum tends to react with N2 to form AlN, when the partial pressure of nitrogen (N2) is much greater than that of oxygen (O2) (PN2≫PO2) in thermodynamics. Additionally, the reaction between aluminum and N2 is accelerated with the increasing temperature. Approximately 36.37 wt% of aluminum was transformed into AlN at 700°C according to kinetic analysis. Aluminum recycling involves smelting, refining, and dross processing. The dross produced from these different processes has various compositions and hazardous properties. The formation mechanism of AlN from the three processes was revealed based on the thermodynamic and kinetic analyses. The reaction mechanisms in these processes were identified as surface contact reaction, internal and surface contact reaction, and rotational surface contact reaction between the aluminum melt and N2, respectively. X-ray diffraction (XRD) and electron probe microanalysis (EPMA) analyses were used to determine the phase and composition of the aluminum dross. The nitrogen content in the aluminum dross from smelting, refining, and dross processing was found to be 3.3 wt%, 5.2 wt%, and 9.6 wt%, respectively. The monthly dross production were 276.3 tons, 22.7 tons, and 318.2 tons, respectively, according to statistics. It was calculated that the nitrogen generated in the three process was 9.12 tons, 1.18 tons, and 20.25 tons, respectively. Therefore, dross processing is the primary source of AlN. A rapid dross processing method with small-scale vertical stirring was proposed to shorten the reaction between the aluminum melt and N2, thereby reducing AlN formation. This work could provide guidance for reducing hazardous AlN in aluminum dross and optimizing the aluminum recycling process.

Study on the uniaxial tensile mechanical behavior of two-dimensional single-crystal aluminum nitride

Abstract To investigate the tensile behavior and mechanical properties of single-crystal aluminum nitride (AlN) at the microscopic level, molecular dynamics simulations were used to study the effects of crystal orientation, strain rate, environmental temperature, and hole defect size on fracture strength, fracture mechanism, and potential energy during uniaxial tensile. The results show that the tensile strength of AlN in the [100] crystal direction is stronger. The anisotropic behavior characteristics of Al-N bonds fracture mechanism, crack growth rate, and cracking degree are significant when stretched along the [100], [010], and [110] crystal directions. Under high temperature condition, the lattice structure undergoes changes, causing grain boundaries to move and slip. This facilitates the breaking of bonds, leading to a decrease in tensile strength and a reduction in stored potential energy. Hole defects cause more lattice damage, reducing the energy required for Al-N bonds breakage and facilitating the propagation of microcracks. Additionally, it was found that the strain rate affects the stress–strain behavior of the model. An increase in strain rate leads to an increase in breaking stress, and the rapid deformation of AlN results in more energy being stored in the lattice in the form of potential energy. Therefore, the tensile strength and potential energy are improved.

Evaluating the efficacy of lead-free piezoelectric materials in microcantilever based vibration energy harvesters

Abstract The piezoelectric materials have been extensively utilized in various applications, such as sensors, actuators, and energy harvesters. This study evaluates the performance of six lead-free piezoelectric materials- aluminium nitride (AlN), barium titanate (BaTiO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), polyvinylidene fluoride (PVDF), and zinc oxide (ZnO) in MEMS-based piezoelectric vibration energy harvesters (PVEHs) using cantilever configurations. Finite element analysis via COMSOL Multiphysics was employed to assess the deflection, voltage, and power outputs of these materials at their resonance frequencies, both with and without proof masses. The results indicate that BaTiO3 and PVDF cantilevers exhibited the highest voltage outputs, reaching 207.14 mV and 202.07 mV, respectively, with AlN also showing comparable performance at 184.72 mV. ZnO-based cantilevers demonstrated the highest power output of 1.35 nW without proof masses and 190.5 nW with proof masses, indicating its potential for high-power applications. The addition of proof masses generally reduced resonant frequencies but enhanced power outputs, like for ZnO. This comprehensive analysis underscores the critical impact of material selection and structural modifications on the efficiency of PVEHs, with BaTiO3, PVDF, and ZnO emerging as the most promising candidates for optimizing energy harvesting devices. This research lays a foundation for further advancements in piezoelectric MEMS technology, aiming for more efficient energy harvesting solutions.

Device structural engineering and modelling of emerging III-nitride/β-Ga2O3 nano-HEMT for high-power and THz electronics

Abstract III-nitrides, such as gallium nitride (GaN) and aluminium nitride (AlN), possess a wide bandgap, a high breakdown voltage, and a high thermal conductivity, making them an attractive choice for high frequency and high-power applications. A further benefit of III-nitride-based HEMTs is their high current density, low noise figure, and higher electron mobility, which enable efficient radio-frequency signal amplification. In this research work, the polarization induced graded buffer technique and improved lattice matched β-Ga2O3 substrate is employed to minimize the buffer-related issues in III-Nitride Nano-HEMTs (high electron mobility transistors), such as reduction in the buffer leakage current losses. The polarization-induced doping in buffer region can considerably reduce the buffer leakage current, enhance breakdown voltage and RF characteristics, and bend the conduction band upwardly convex, improving two-dimensional electron gas (2DEG) confinement. A detailed comparison between the graded buffer technique of the HEMT and the HEMT having normal buffer has been conducted. The results demonstrated that the suggested HEMT demonstrated better DC and RF characteristics up to the Tera (1012) hertz range of frequencies. The improved characteristics of the proposed HEMT allow it to be a feasible solution for emerging technologies and cutting-edge communication systems that require efficient signal processing at very high frequencies.

Theoretical Investigation of Transition Metal (Cr, Fe)-Doped AlN in a rocksalt structure: A DFT Study on Physical Properties

This study presents first-principles computations to explore the structural, electronic, optical, elastic, vibrational, and thermodynamic properties of Aluminum Nitride (AlN) doped with the transition metals Chromium (Cr) and Iron (Fe) in the rocksalt structure. Using spin-polarized density functional theory (DFT) within the CASTEP code, we applied GGA-PBE, GGA+U, and HSE06 approximations for exchange-correlation functions. Our results reveal that Cr doping transforms AlN into a dilute magnetic semiconductor (DMS), while Fe doping induces a transition to a metallic state. Both Al0.₇₅Cr₀.₂₅N and Al₀.₇₅Fe₀.₂₅N exhibit strong covalent bonding, contributing to enhanced hardness. The substantial increase in static dielectric constant and refractive index suggests strong optical responses. Furthermore, our analysis confirms the mechanical and dynamic stability of these compounds. Al₀.₇₅Cr₀.₂₅N is a promising candidate for electronic and spintronic applications, whereas Al₀.₇₅Fe₀.₂₅N, with its high conductivity, is well-suited for magnetic storage devices and electrical contacts. Our findings for AlN are consistent with prior theoretical and experimental data, while the results for Al₀.₇₅Cr₀.₂₅N and Al₀.₇₅Fe₀.₂₅N offer novel insights for future research.

Cu/AlN composite and functionally graded materials with high strength and high electrical- and thermal-conductivity fabricated by spark plasma sintering

In this study, Cu/AlN composites and functionally graded materials (FGMs) were fabricated with the spark plasma sintering method. It was observed that a two-step sintering process, involving sintering under low pressure as the initial stage to remove adsorbed chemicals on the powder, was an effective method for producing sintering objects with high relative density. The hardness of the composites significantly increased with higher volume fraction of aluminum nitride (AlN) particles, while electrical- and thermal-conductivity decreased. Nevertheless, the advanse impact of AlN on thermal-conductivity was found to be minimal. Additionally during compression test, a crack was noted at the interface between Cu and Cu-5 vol%AlN region in two-layered FGMs after, whereas no such crack was observed in the three-layered FGMs. Therefore, it is confirmed that the concept of FGMs is useful in overcoming the shortcomings of mutually exclusiveness among high strength, high electrical- and high thermal-conductively.

Effect of classified aluminum nitride whisker addition on densification and mechanical strength of low-temperature-sintered aluminum nitride ceramics

Effect of classified aluminum nitride whisker addition on densification and mechanical strength of low-temperature-sintered aluminum nitride ceramics

Shear properties of low-temperature soldered joints of aluminum nitride metallized with Sn-1.0Ag-0.5Cu-Ti alloys

Shear properties of low-temperature soldered joints of aluminum nitride metallized with Sn-1.0Ag-0.5Cu-Ti alloys

Polarity controlled ScAlN multi-layer transduction structures grown by molecular beam epitaxy

We report on the molecular beam epitaxial growth and characterization of polarity-controlled single and multi-layer Scandium Aluminum Nitride (ScAlN) transduction structures grown directly on ScAlN templates deposited by physical vapor deposition (PVD) on Si(001) substrates. It is observed that direct epitaxial growth on PVD N-polar ScAlN leads to the flipping of polarity, resulting in metal (M)-polar ScAlN. By effectively removing the surface impurities, e.g., oxides, utilizing an in situ gallium (Ga)-assisted flushing technique, we show that high quality N-polar ScAlN epilayers can be achieved on PVD N-polar ScAlN templates. The polarity of ScAlN is confirmed by utilizing polarity-sensitive wet chemical etching and atomic-resolution scanning transmission electron microscopy. Through interface engineering, i.e., the controlled formation or removal of surface oxides, we have further demonstrated the ability to epitaxially grow an alternating tri-layer piezoelectric structure, consisting of N-polar, M-polar, and N-polar ScAlN layers. Such multi-layer, polarity-controlled ScAlN structures promise a manufacturable platform for the design and development of a broad range of acoustic and photonic devices.

Porous mesh manifold for enhanced boiling performance

High-performance electronics are continuously demanding cooling of higher heat fluxes. Phase-change cooling, including pool boiling, is a useful approach to address this challenge; however, competition between liquid and vapor flows generally limit the heat fluxes that can be dissipated. A range of strategies to control these flows have been investigated previously, including capillary guides. Here a manifold structure formed from a metallic mesh is investigated to control the disposition of liquid and vapor phases above a pool fed boiling surface enhanced with porous structures. Copper mesh forms defined liquid flow paths, using capillary action to guide and distribute liquid evenly over the heated surface, along with open channels to facilitate vapor escape. The mesh provides a novel structure for liquid guidance that imposes low resistance to liquid flow while occluding a minimal area of heated surface underneath. The manifold performance is characterized in boiling fed by a pool of water above a laser-textured aluminum nitride heat dissipation surface with pin–fin structures having heights of 110 µm and spacing of 30 µm with a heated area of 5mm x 5mm. A maximum heat flux of 490 W/cm2 is reached with the manifold in the pool fed configuration, representing an increase of more than 65% over the porous pin fin surface alone. The maximum stable superheat observed for the manifold of 36K is 14K higher than that for the porous surface without the manifold. The factors limiting performance of the manifold are analyzed. High superheat is attributed to partial flooding of the boiling surface as suggested by the reduction in superheat using external suction. Similar systems and structures for enhanced two-phase cooling are compared.

Ti1-xAlxN or TiN + AlN: an investigation about Al influence on titanium aluminum nitride thin films structural organization

Ti1-xAlxN or TiN + AlN: an investigation about Al influence on titanium aluminum nitride thin films structural organization

Advances in Room Temperature of Indium Aluminum Nitride InAlN Deposition via Direct Current (DC) Co-Sputtering for Solar Energy Applications

This study presents an innovative method for the synthesis of indium aluminum nitride (InAlN) layers by direct current (DC) co-sputtering at room temperature, with the aim of reducing production costs of optoelectronic devices. Indium and aluminum targets are used, varying the power applied to the aluminum target. The results show that increasing the target power favors the formation of aluminum nitride (AlN), which modifies the chemical composition of the material. The layers obtained present smooth surfaces with a roughness of less than 3 nm, which is beneficial for applications requiring interfaces with low defect density. Regarding the optical properties, it is observed that the optical bandgap varies between 1.8 eV and 2.0 eV, increasing with the target power. Hall effect measurements indicate a decrease in the free carrier concentration and an increase in the resistivity with increasing power. This approach allows for the synthesis of InAlN with properties suitable for optoelectronic applications, solar cells, photocatalysis, and photoelectrocatalysis at low cost.

General Approach to Hydrolysis Resistive Aluminum Nitride and Its High-Performance Thermal Interface Materials.

Aluminum nitride (AlN), noted for its excellent thermal conductivity and exceptional electrical insulation, presents a promising alternative to traditional ceramic particles in thermal interface materials (TIMs). However, its broader adoption in practical applications is limited by performance degradation due to the vulnerability of its crystal structure to ubiquitous moisture. This study introduces a dual solution, utilizing a mechanochemical method to design a dense outer layer of Galinstan liquid metal (LM) that simultaneously enhances AlN's resistance to hydrolysis and improves its thermal performance in TIM applications. The high surface free energy of the LM layer imparts hydrophobic properties to the AlN surface and, combined with outer metal oxides, forms a dual-layer protective barrier that prevents water penetration, significantly enhancing the TIM's long-term stability in high-humidity conditions. Additionally, the LM layer at the interface improves the thixotropic properties of the TIM and enhances interfacial heat transport through the bridging effect of the LM, resulting in improved rheological mobility and thermal conductivity of the composite material. This win-win surface modification strategy opens opportunities for the practical and durable application of AlN in widespread electronic thermal management.

Strain induced phase transitions and hysteresis in aluminium nitride: a density functional theory study

Computer atomistic simulations based on density functional theory were carried out to investigate strain induced phase transitions in aluminium nitride (AlN). The wurtzite to graphitic and graphitic to wurtzite transformations were investigated at the atomic level and their physical origins were identified. Both phase transitions were found to be of the first order. The wurtzite to graphitic phase transition takes place in the tensile regime at a strain value of +7%. The driving force for this transformation was identified to be an elastic instability induced by tensile strain. A hysteresis was demonstrated where the graphitic structure is separated from the wurtzite by a kinetic energy barrier. The origin of the observed hysteresis is due to the asymmetry of bond formation and bond breaking associated with the wurtzite to graphitic and graphitic to wurtzite transitions, respectively. A dynamic instability taking place at +3%, along the graphitic path, prevents the hysteresis to fully occur. The possible occurrence of the hysteresis has then to be taken into account when growing the graphitic phase by heteroepitaxy. Otherwise, maintaining the graphitic structure at low strain, through the hysteresis, offers new possibilities in the development of novel future applications.