Aluminum Nitride Research Articles

DFT study of adsorption and potential detection of carbonyl fluoride on B-doped aluminum nitride nanosheets

Carbonyl fluoride (COF2) is a decomposition product that can be used to find failures in gas-insulated switchgear equipment. In this study, we applied Density Functional Theory (DFT) calculations to examine the suitability of pristine and boron-doped aluminum nitride nanosheets (AlNNS) for COF2 adsorption and sensing applications. Our investigation suggested a dissociative COF2 adsorption on pristine AlNNS, resulting in important adsorption energy (–2.19 eV), the releasing of a fluorine atom from the molecule and formation of new C–N, O–Al and F–Al bonds. Two preferential chemisorption geometries were achieved on the B-doped N-vacancy monolayer (B-vN-AlNNS), with adsorption energies of –1.04 and –3.44 eV. In the first geometry, only an O–B bond was formed, whereas in the another one similar interactions as in COF2/AlNNS took place. Furthermore, we analyzed the evolution of electronic properties in order to evaluate the performance of these nanosheets for COF2 detection purposes. Our results showed significant modifications in both energy gap and work function only after COF2 adsorption on B-vN-AlNNS. Finally, charge transfer analysis revealed electron exchange from the studied surfaces to the gas molecule. These findings suggest that B-doped AlNNS exhibits good performance for COF2 detection, and could encourage further experimental research to develop efficient sensing materials.

Cluster intercalation of aluminum tetrachloride in AlN cathode: Exploration and analysis of aluminum ion batteries.

When chloroaluminate (AlCl4-) serves as the electrolyte, aluminum nitride (AlN) has shown promise as a cathode material in aluminum ion batteries. However, there is currently a lack of research on the mechanisms of charge transfer and cluster intercalation between AlCl4 and AlN cathode materials. Herein, first-principles calculations are employed to investigate the intercalation mechanism of AlCl4 within the AlN cathode. By calculating the formation energies of stage-1-5 AlN-AlCl4 intercalation compounds with the insertion of individual AlCl4 cluster, we found that the structure of the stage-4 intercalation compounds exhibits the highest stability, suggesting that when the clusters begin to intercalate, it is important to start with the formation of the stage-4 intercalation compounds. In the subsequent phases of the charging process (stages 1 and 2), the stabilized structure with four inserted clusters demonstrates two characteristics: the coexistence of standing and lying clusters and the insertion of two standing clusters in an upside-down doubly stacked configuration, which further improve the spatial utilization while maintaining the structural stability. In addition, we infer that a phenomenon of coexisting intercalation compounds with mixed stages will occur in the course of the charging and discharging processes. More importantly, the diffusion barrier of AlCl4 in AlN-AlCl4 intercalation compounds decreases with the reduction of stage number, ensuring the rate performance of batteries. Therefore, we expect that our work will contribute to comprehend the intercalation mechanism of AlCl4 into the AlN cathode materials of aluminum ion batteries, providing guidance for related experimental work.

Bio-based eutectic composite phase change materials with enhanced thermal conductivity and excellent shape stabilization for battery thermal management

Organic phase change materials (PCMs) are commonly used for battery thermal management. Organic petroleum-based PCMs such as paraffin have an adverse effect on environment. Fatty acids as environmentally friendly bio-based PCMs, have enormous potential in sustainable development strategies. Nevertheless, the application of fatty acids in battery thermal management (BTMS) is restricted by the leakage of liquid PCM, poor thermal performance and the improper phase change temperature. We proposed a novel bio-based eutectic composite phase change materials (CPCM) with enhanced thermal conductivity and excellent shape-stabilization, composed of ethylene-vinyl acetate (EVA), Aluminum nitride (AlN), and the eutectic PCM of Lauric acid (LA) and Stearic acid (SA). Significantly, the screened eutectic PCM of LA-SA possesses a suitable phase change temperature(37.03 °C) corresponding to the battery operating temperature, and long-term thermal cycling stability of up to 100 cycles. And the cross-linked structure of EVA effectively encapsulated the eutectic PCM, whose mass only lost below 4% after being heated at 80 °C for 24 h. Simultaneously, the introduction of AlN can greatly improve their heat transfer ability and mechanical properties. LA-SA/EVA/AlN composites with 5 wt% AlN has adequate latent heat of 107.94 J.g−1 and high thermal conductivity of 0.726 W.(m·K)−1 as well as with low flexural strength of 1.72 MPa. Additionally, the proposed CPCM with 5 wt% AlN achieved the maximum temperature of battery below 45 °C during 4C discharging test. It suggested that the CPCM incorporated with AlN is capable effective cooling battery and dissipate energy inside PCM rapidly.

Deposition of highly crystalline AlScN thin films using synchronized high-power impulse magnetron sputtering: From combinatorial screening to piezoelectric devices

With the integration of 5G in day-to-day devices and the foreseeable 6G revolution, demand for advanced radio frequency (RF) microelectromechanical systems (MEMS) is growing. Aluminum scandium nitride (AlScN) has emerged as the material of choice for many of those applications due to its superior piezoelectric and electromechanical properties compared to aluminum nitride (AlN). However, synthesizing high-quality, textured AlScN thin films is challenging. Alloying of Sc in AlN induces structural frustration leading to strain, defects, disoriented grains, and disrupted crystal symmetry during growth. Higher deposition temperatures, while improving crystalline quality, risk undesirable phase precipitation and limit industrial sustainability. In addition, future MEMS technologies also demand conformal and textured coatings over diverse topographies. Addressing these challenges collectively requires new and innovative synthesis approaches. In this study, we investigate the feasibility of ionized physical vapor deposition to deposit highly oriented AlScN films with minimal defects at lower temperatures. To this end, we employ combinations of different deposition approaches, such as metal-ion synchronized (MIS) high-power impulse magnetron sputtering (HiPIMS). Leveraging the high ionization rates of HiPIMS and optimally timed substrate bias potentials, we selectively bombard the growing film with Al and/or Sc ions to enhance the adatom mobility at low temperatures while simultaneously providing the ability to tune stress and coat complex structures conformally. The nonequilibrium solubility of Sc in wurtzite AlN under different conditions is investigated using a combinatorial deposition approach. Promising candidates with ∼20% Sc composition are isolated and characterized for crystallinity and residual stress. Disoriented grains, a significant issue in growing AlScN films, are observed through atomic force microscopy and found to be completely removed by substrate rotation and application of substrate biasing. The measured piezoelectric response of the films with approximately 20% Sc concentration ranges from 6.3 to 8.8 pm/V, in line with density functional theory predictions and experimentally reported values for films deposited in a production tool with coplanar geometry. At the same time, MIS-HiPIMS-deposited films offer unique properties and flexibility to tune their stress state and structural properties, thus presenting exciting opportunities for the fabrication of advanced RF filters and next-generation MEMS devices. Published by the American Physical Society 2024

Optimization of Growth Temperature and V/III Ratio toward High-Quality Si-Doped Aluminum Nitride Thin Films on Sapphire

Optimization of Growth Temperature and V/III Ratio toward High-Quality Si-Doped Aluminum Nitride Thin Films on Sapphire

Expression of Concern “Adsorption of thiotepa anticancer by the assistance of aluminum nitride nanocage scaffolds: A computational perspective on drug delivery applications”[Colloids Surf. A Physicochem. Eng. Asp. 666 (2023) 131276]

Expression of Concern “Adsorption of thiotepa anticancer by the assistance of aluminum nitride nanocage scaffolds: A computational perspective on drug delivery applications”[Colloids Surf. A Physicochem. Eng. Asp. 666 (2023) 131276]

Nonlinear response of very high frequency contour mode resonators

We explore the source of nonlinearities in Aluminum Nitride (AlN) Contour Mode Resonators (CMRs) operating in the Very High Frequency (VHF) range. We demonstrate that the red-shift of the resonance frequency found in VHF CMRs when the input RF power increases is due to nonlinear stiffness appearing from self-heating, and variable damping due to geometric nonlinearities. Moreover, we find a linear relationship between the variable damping coefficient and the resonator quality factor (Q). Such nonlinear mechanisms are modeled using a spring-mass-damper physical system and, in the electrical domain, a modified Butterworth-Van Dyke (MBVD) circuit where the nonlinear stiffness and variable damping are captured by a charge-dependent motional capacitor and a charge-dependent motional resistor, respectively. Detailed guidelines are provided to accurately analyze nonlinear CMRs using full-wave numerical simulations based on a finite-element method. Such simulations allow us to isolate the influence of each independent nonlinear mechanism and establish a relation between variable damping and geometric nonlinearities. Circuit and full-wave numerical simulations are in good agreement with measured data from fabricated 225 MHz CMRs exhibiting different Q. Finally, we exploit nonlinearities in high-Q CMRs to generate frequency combs at the MHz range opening the door to new exciting applications in telecommunication and sensing.

Reduction mechanism of loss tangent of scandium-doped aluminum nitride thin film by post-deposition annealing

Scandium-doped aluminum nitride thin films are key materials for MEMS applications including bulk acoustic wave devices for communication. Although one drawback is the increase in the loss tangent with increasing Sc concentration, the loss tangent is reported to decrease after post-deposition annealing. However, the underlying mechanisms remain unclear. In this study, we propose the hypothesis that a low-resistivity thin layer near the surface of a substrate is one of the main reasons for the high loss tangent, and that annealing enhances the resistivity, eventually decreasing the loss tangent. The reasonability of the hypothesis was successfully confirmed by analyzing the frequency response of the loss tangent using an equivalent circuit with current–voltage characteristics, cathodoluminescence, etc. This achievement represents a significant step toward advanced methods for reducing the loss tangent and its application to other thin-film materials.

Enhancing thermal conductivity of AlN ceramics via vat photopolymerization through refractive index coupling and oxygen fixation

Despite the growing development of ceramic fabrication by vat photopolymerization (VP), major gaps remain in application. Particularly in the case of VP-printed aluminum nitride (AlN) ceramic, the thermal conductivity is still below 170 W·m−1·K−1, a critical benchmark for efficient heat dissipation. To address this challenge, here we prepared an AlN slurry with high curing thickness through RI coupling between liquid-solid phase, and took into account of the rheological property under high solid loading. Full dense AlN green bodies with solid loading up to 50 vol% were successfully printed. Aiming to to tackle the degradation of thermal conductivity issue caused by oxygen increment of AlN via VP, we systemically studied the form of oxygen in AlN preparation processes. Through the sintering optimization, the oxygen element from the hydrolysis of AlN surface was fixated in the sintering aid Y2O3. Eventually, without any special process control or additional treatment, the final sintered AlN ceramics prepared by the developed slurry present a full densification and the highest thermal conductivity (up to 187.9 W∙m−1∙K−1) of any known additive manufactured ceramics.

High Sensitivity Performance of Piezoelectric Micromachined Ultrasonic Transducer Employing Sc-Doped AlN Thin Film

Abstract Aluminum Nitride (AlN) based piezoelectric micromachined ultrasonic transducers (PMUTs) have been the prime choice in acoustic imaging, because it has advantages of high frequency and thus high resolution. However, low piezoelectric constants of AlN gives rises to limitation in transmitting sensitivity. Scandium (Sc) doping method for AlN can be used to improve its piezoelectricity. In this paper, single element PMUT based on ScAlN thin film was proposed and modeled by performing finite element method (FEM). Influence of different electrode configurations on PMUT performance were studied. The results show that, compared with other electrode configurations, PMUT has the best overall performance when the upper electrode is platinum (Pt) and the lower electrode is molybdenum (Mo). In addition, the acoustic field characteristics and its dynamic analysis of PMUT based on ScAlN in water were studied. The investigation results demonstrated that the relative pulse-echo sensitivity level M of PMUT is significantly improved with the increase of Sc doping concentration in AlN thin film. When the Sc concentration is 40%, the M reaches -44 dB, which is 20 dB higher than that without Sc (-64 dB). The PMUT based on the high Sc-doped AlN thin film has a larger effective electromechanical coupling coefficient and sensitivity, which is beneficial to the application in high sensitivity ultrasound imaging.

Preparation of coconut oil/aluminum nitride/expanded graphite composite phase change materials with high thermal conductivity and stable shape for thermal energy storage

Preparation of coconut oil/aluminum nitride/expanded graphite composite phase change materials with high thermal conductivity and stable shape for thermal energy storage

Design and Characterization of SAW-Based Wireless and Passive Temperature Sensing System

Abstract The Surface Acoustic Wave (SAW) temperature sensor has received significant attention due to its wirelessly-powered, battery-free, and chipless capabilities. This paper proposes a wireless sensing system comprising a one-port SAW resonator, antennas, and transceiver circuit. The SAW resonator utilized in this system was based on Aluminum Nitride (AlN) thin film, which exhibits high SAW velocity and excellent piezoelectric properties. To completely investigate the performance of the SAW resonator, simulation and experiments were conducted. Upon connecting the SAW sensor to the temperature sensing system via the antenna, the reflection peak of the SAW resonator was clearly observed in the spectrum of the return signal. Additionally, during the temperature tests, the response frequency displayed almost linear behavior as the temperature increased from 30°C to 150°C. The fitted temperature coefficient of frequency (TCF) was 30.68ppm/°C, indicating that the wireless temperature sensing system has high temperature sensitivity.

Design and Performance Analysis of Strip Photonic Waveguide with Coating Layer for Multimode Propagation

Introduction: Photonic devices play a pivotal role in the realm of high-speed data communication due to their inherent capability to expedite the transfer of information. Historically, research efforts in this domain have predominantly concentrated on investigating the fundamental mode propagation within photonic waveguides. Methods: This study diverges from the conventional approach by delving into the untapped potential of higher-order modes in addition to the fundamental mode of propagation. The exploration of these higher-order modes opens up new possibilities for optimizing and enhancing the performance of photonic devices in high-speed data communication scenarios. As a distinctive aspect of this study, various coating materials were scrutinized for their impact on both fundamental and higher-order mode propagation. The materials under examination included AlN (aluminum nitride), Germanium, and Silicon. These materials were chosen based on their unique optical properties and suitability for influencing different modes of light propagation. The findings from the study reveal that applying a coating of germanium demonstrates advantageous characteristics, particularly in terms of reduced signal loss, even when considering higher-order modes of propagation within photonic devices. Results: In this context, the results indicate that germanium-coated waveguides exhibit notably low propagation losses, with measurements as minimal as 0.25 dB/cm. This low level of loss is particularly noteworthy, especially when the waveguide has a width of 550 nm and is coated with a thickness of 50 nm. The dimensions and coating specifications play a crucial role in determining the efficiency of light transmission within the waveguide. Conclusion: The fact that the propagation loss is substantially low under these conditions suggests that the germanium-coated waveguide, even when considering higher-order modes of light propagation, can effectively maintain the integrity of the optical signal.

A High Q Lamb Wave Resonator with Dummy Toes Based on 20% ScAlN Film

Abstract The lamb wave resonator (LWR) based on aluminum nitride (AlN) films are preferred strategy for high-frequency filters in 5G communication due to the tunable electromechanical coupling and high Q value. However, since the low electromechanical coupling and piezoelectric coefficient of AlN films, conventional lamb filters are difficult to meet the requirements of high bandwidth and low loss. This work proposes a lamb wave resonator with dummy toes (DT-LWR) based on scandium-doped aluminum nitride (ScAlN) film to improve the quality factor(Q) meanwhile suppress the spurious modes. The processed DT-LWR was tested using a vector network analyser (VNA, Keysight N5222B), and the MBVD model was used to fit the Z parameters. The Q value of DT-LWR is 1437.23, while that of LWR is 1250.09. It is increased by 14.97%. The enhancements make the DT-IWR as an ideal for filters with minimal insertion loss.

Enhanced breakdown voltage for p-GaN gate AlGaN/GaN HEMT on AlN/Si with triple trenches: A simulation study

This study presents an analysis of an AlGaN/GaN high-electron-mobility transistor (HEMT) with a triple-trench structure (TT-HEMT) for the enhancement of breakdown voltage, which is often limited by the high electric field near the gate edge. Using COMSOL Multiphysics, simulations were run, with trenches made of gallium nitride (GaN) constructed between the GaN and aluminum nitride (AlN) nucleation layers. Each trench was positioned directly beneath the source, gate, and drain contacts. Under the metal gate, a p-type doped GaN cap is added to produce an enhancement mode device, which is more desirable in high-power applications. The results indicate that the effective dispersion of the electric field distribution enhances the breakdown voltage of the device by 70 % in comparison to a conventional HEMT. Additionally, the impact of various design parameters, such as the p-GaN doping concentration and the metal gate work function on the electrical performance, was also investigated. Overall, the proposed device structure exhibits superior electrical properties for high-power applications.

Computational Thermodynamics and Kinetics of Aluminum Nitride Precipitation in Steel—An Overview with Emphasis on Austenitic Grain Size Control

Computational Thermodynamics and Kinetics of Aluminum Nitride Precipitation in Steel—An Overview with Emphasis on Austenitic Grain Size Control

Optimisation of machining parameters in high-speed end milling of hardened AISI H13 die steel by integrating RSM and GA

ABSTRACT This study explores the potential of high-speed hard-end milling as a cost-effective alternative to the time-consuming grinding process for Chromium-molybdenum steel (AISI H13), widely used in cold and hot work tooling. The research aims to optimize machining parameters for achieving desired surface roughness, comparable to grinding and polishing. Cutting depth (0.4 - 0.8 mm), feed rate (1 - 4 μm per tooth), and cutting speed (80 - 140 m/min) were varied, and soybean oil replaced conventional lubricants. Employing Titanium Aluminum Nitride (TiAlN) coated end mills (3 mm diameter, 2 μm coating thickness) and response surface method (RSM) with Design Expert software, the study aimed at reducing tool wear and enhancing surface quality through multi-criteria optimization. Surface roughness analysis led to a streamlined surface by lowering mass flow rate and increasing cutting speed. The optimization approach predicted an optimal surface roughness value of 0.217475 μm at a cutting speed of 110 m/min, a feed rate of 1 μm/tooth, and a cut depth of 0.4 mm using genetic algorithm (GA), closely aligned with RSM’s ideal value of 0.215 μm. Both values converge around the 0.4 mm cut thickness.

Effects of sputtering pressure on microstructure and secondary electron emission properties of AlN film prepared by magnetron sputtering

In this paper, aluminum nitride (AlN) thin films were prepared by reactive radio-frequency magnetron sputtering at different sputtering pressures and the crystalline structure, surface morphology and secondary electron emission (SEE) properties of the AlN films were studied in detail. The experimental results reveal that AlN films present the preferred orientation of a-axis (100), and the grain size and surface roughness of the film decrease with the increase of sputtering pressure. Additionally, the SEE coefficient of the film reaches a maximum of 4.3 at 200 eV when the sputtering pressure is 0.55 Pa and is relatively stable under the continuous bombardment of an incident electron with the energy of 200 eV. Thus, the AlN thin film prepared under the optimized sputtering pressure has a relatively high and stable coefficient at a low incident electron energy, which promotes its potential application in the high-gain and long-life electron multipliers.

DC and RF analysis of ScAlN/GaN/β-Ga2O3 and ScAlN/InGaN/GaN/β-Ga2O3 HEMTs on SiC substrate

Scandium aluminum nitride (ScxAl1-xN) is a promising material among group III nitrides, offering outstanding polarization properties resulting in very large carrier densities. We report the comparative analysis of Sc0.18Al0.72N/GaN/β-Ga2O3 and Sc0.18Al0.72N/InGaN/GaN/β-Ga2O3 HEMTs on Silicon carbide substrate. LG = 55 nm, Sc0.18Al0.72N/GaN/β-Ga2O3 HEMT demonstrated maximum current density (IDS) of 4.38 A/mm, very large carrier density (ns) of 2.34 × 1013 cm−2, large breakdown voltage (74 V) with low on-resistance (Ron ∼ 0.2 Ω mm), and cut-off frequency (fT)/maximum oscillation frequency (fmax) of 220/242 GHz. Introduction of a very thin 5 nm In0.1Ga0.9N layer in the channel, further improves the 2DEG (two-dimensional electron density), drain current, breakdown voltage. Furthermore, Sc0.18Al0.72N/InGaN/GaN/β-Ga2O3 heterostructure shows stable transconductance (gm) over wide gate bias. A gate voltage swing (GVS) of 7.72, IDS of 6.08 A/mm, and VBR of 105 V with Ron ∼ 0.138 recorded. These findings show the merits of scandium aluminium nitride barrier material, which enables the HEMTs for next generation radar and telecommunications.

Vibration Analysis at Castello Ursino Picture Gallery (Sicily, Italy) for the Implementation of Self-Generating AlN-MEMS Sensors.

This work explores the potential of self-powered MEMS devices for application in the preventive conservation of cultural heritage. The main objective is to evaluate the effectiveness of piezoelectric aluminum nitride MEMS (AlN-MEMS) for monitoring vibrations and to investigate its potential for harvesting energy from vibrations, including those induced by visitors. A preliminary laboratory comparison was conducted between AlN-MEMS and the commercial device Tromino®. The study was then extended to the Picture Gallery of Ursino Castle, where joint measurements with the two devices were carried out. The analysis focused on identifying natural frequencies and vibrational energy levels by key metrics, including spectral peaks and the Power Spectral Density (PSD). The results indicated that the response of the AlN-MEMS aligned well with the data collected by the commercial device, especially observing high vibrational energy around 100 Hz. Such results validate the potential of AlN-MEMS for effective vibration measurement and for converting kinetic energy into electrical power, thereby eliminating the need for external power sources. Additionally, the vibrational analysis highlighted specific locations, such as the measurement point Cu4, as exhibiting the highest vibrational energy levels. These points could be used for placing MEMS sensors to ensure efficient vibration monitoring and energy harvesting.