Search Results (147)

The rapid advancement of high-performance electronics has intensified the demand for wide-bandgap semiconductor materials capable of operating under high-power and high-temperature conditions. Among these, silicon carbide (SiC) has emerged as a leading candidate due to its superior thermal conductivity, chemical stability, and mechanical strength. However, the high cost and complexity of SiC wafer fabrication, particularly in slicing and exfoliation, remain significant barriers to its widespread adoption. Conventional methods such as wire sawing suffer from considerable kerf loss, surface damage, and residual stress, reducing material yield and compromising wafer quality. Additionally, techniques like smart-cut ion implantation, though capable of enabling thin-layer transfer, are limited by long thermal annealing durations and implantation-induced defects. To overcome these limitations, ultrafast laser-based processing methods, including laser slicing and stealth dicing (SD), have gained prominence as non-contact, high-precision alternatives for SiC wafer exfoliation. This review presents the current state of the art and recent advances in laser-based precision SiC wafer exfoliation processes. Laser slicing involves focusing femtosecond or picosecond pulses at a controlled depth parallel to the beam path, creating internal damage layers that facilitate kerf-free wafer separation. In contrast, stealth dicing employs laser-induced damage tracks perpendicular to the laser propagation direction for chip separation. These techniques significantly reduce material waste and enable precise control over wafer thickness. The review also reports that recent studies have further elucidated the mechanisms of laser–SiC interaction, revealing that femtosecond pulses offer high machining accuracy due to localized energy deposition, while picosecond lasers provide greater processing efficiency through multipoint refocusing but at the cost of increased amorphous defect formation. The review identifies multiphoton ionization, internal phase explosion, and thermal diffusion key phenomena that play critical roles in microcrack formation and structural modification during precision SiC wafer laser processing. Typical ultrafast-laser operating ranges include pulse durations from 120–450 fs (and up to 10 ps), pulse energies spanning 5–50 µJ, focal depths of 100–350 µm below the surface, scan speeds ranging from 0.05–10 mm/s, and track pitches commonly between 5–20 µm. In addition, the review provides quantitative anchors including representative wafer thicknesses (250–350 µm), typical laser-induced crack or modified-layer depths (10–40 µm and extending up to 400–488 µm for deep subsurface focusing), and slicing efficiencies derived from multi-layer scanning. The review concludes that these advancements, combined with ongoing progress in ultrafast laser technology, represent research opportunities and challenges in transformative shifts in SiC wafer fabrication, offering pathways to high-throughput, low-damage, and cost-effective production. This review highlights the comparative advantages of laser-based methods, identifies the research gaps, and outlines the challenges and opportunities for future research in laser processing for semiconductor applications. Full article

The objective of this study is to evaluate the impact of thermal and thermochemical treatment, specifically gas nitriding, on the wear properties of AISI D2 cold work tool steel. The steel was austenitized at 1050 °C, then subjected to two annealing cycles at 560 °C for two hours each. It was then gas-nitrided for 16 and 36 h. The Vickers microhardness measurements of AISI D2 steel for the three distinct conditions, non-nitrided (NN), nitride at 16 h (N16) and nitride at 36 h (N36), are 560 HV0.1, 1050 HV0.1 and 1350 HV0.1, respectively. Wear tests were conducted utilizing a ball device, under dry friction conditions at ambient temperature, with loads of 5, 10 and 15 N, over 5000, 10,000 and 15,000 cycles at a constant sliding velocity of 30 mm/s and a sliding distance of 10 mm. Furthermore, the utilization of ANFIS modeling of experimental data facilitated the prediction of the variation in the coefficient of friction as a function of nitriding conditions and specific test parameters. The results show a significant effect of nitriding, leading to a marked reduction in the coefficient of friction. In the non-nitrided condition, the average value reaches 0.80, while extended nitriding to 36 h reduces this value to around 0.49, confirming a substantial tribological improvement. This enhancement is ascribed to the formation of hard, resilient nitride layers on the steel surface, thereby increasing wear resistance and cur-tailing in industrial applications. Full article

Crystal grain size control in steel is critical for achieving mechanical properties. This study investigates the effectiveness of microalloying with titanium, niobium, zirconium, and yttrium to inhibit grain growth with the pinning effect. The comparison of selected microalloying elements in the exact same conditions is crucial for understanding their effect and is novel. Hot-rolled samples were annealed across a wide range of temperatures (1050 to 1200 °C) for up to eight hours. Microstructural analysis confirmed the presence of stable precipitates and non-metallic inclusions such as Nb(C,N), Ti(C,N), ZrO₂, and Y₂O₃ acting as obstacles to grain boundary migration. All microalloying elements significantly outperformed the reference steel, but their effectiveness was highly dependent on the annealing temperature. Titanium was the most effective inhibitor at lower temperatures (1050 °C), while zirconium maintained control up to 1150 °C. Critically, at the highest temperature of 1200 °C, only the yttrium-alloyed steel retained a fine-grain structure, demonstrating superior thermal stability. Niobium, conversely, only showed a minimal effect at 1050 °C, though this grade also exhibited the highest hardness (up to 165 HB) due to precipitation hardening. The kinetics of grain growth were successfully modeled using the Arrhenius-type Sellars–Whiteman equation, accurately describing the behavior for up to four hours of annealing. The findings provide critical insight for selecting optimal microalloying strategies based on maximum operating temperature. Full article

Ultrashort pulsed laser annealing is an efficient technique for crystallizing amorphous semiconductors with the possibility to obtain polycrystalline films at low temperatures, below the melting point, through non-thermal processes. Here, a multilayer structure consisting of alternating amorphous silicon and germanium films was annealed by mid-infrared (1500 nm) ultrashort (70 fs) laser pulses under single-shot and multi-shot irradiation conditions. We investigate selective crystallization of ultrathin (3.5 nm) a-Ge non-hydrogenated films, which are promising for the generation of highly photostable nanodots. Based on Raman spectroscopy analysis, we demonstrate that, in contrast to thicker (above 10 nm) Ge films, explosive stress-induced crystallization is suppressed in such ultrathin systems and proceeds via thermal melting. This is likely due to the islet structure of ultrathin films, which results in the formation of nanopores at the Si-Ge interface and reduces stress confinement during ultrashort laser heating. Full article

Chitosan films obtained by solution casting were investigated by broadband dielectric spectroscopy (BDS) to explore both their glass transition and the effects of thermal annealing on molecular dynamics, deriving from residual water content as well as from cold crystallization. Glass transition at low temperatures could be evidenced in as-produced as well as thermally annealed films, where non-Arrhenian dielectric relaxation processes, consistent with a structural (α) relaxation, could be detected. The process detected at low temperatures could reflect the dynamics of residual water slaved by the polymer matrix. Secondary (β) relaxations, along with a slow process ascribed to interfacial polarization at the amorphous/crystalline interfaces, were concurrently detected. In most cases, a further Arrhenian process at intermediate temperatures (α_c) was present, also indicative of crystallization. Notably, the α processes, due to the primary relaxation of the polymer matrix plasticized by water, could be discriminated from other processes, present in the same frequency range, thanks to improvements in the dielectric fitting strategy. All relaxation processes showed the expected dependence on T_a. The more accurate exploration of the glass transition for chitosan helps to better rationalize its crystallization behavior, in view of an optimized application of this biopolymer. Full article

This study investigates the subsequent stages of recrystallisation in Interstitial-Free (IF) steel subjected to an unconventional continuous annealing process with a controlled thermal gradient. A cold-rolled steel strip was exposed to varying annealing temperatures along its length, enabling the analysis of microstructural evolution during the course of recrystallisation. The microstructure and stored energy were assessed at various positions along the strip using Electron Backscatter Diffraction (EBSD). The results underscore the significant influence of local misorientation and structural inhomogeneity on orientation selection during recrystallisation. The remaining non-recrystallised volume fraction (NRF) strongly correlates with the average misorientation gradient, obeying a phenomenological power-law correspondence with an exponent of ~3.7. This indicates that the recrystallisation process is highly sensitive to small changes in local orientation gradients. These findings highlight the crucial role of stored energy distribution for texture evolution, particularly during the early stages of recrystallisation in continuous annealing. It is observed that g-fiber grains, in comparison to a-fiber grains, are much more susceptible to grain fragmentation and therefore develop more robust intra-granular misorientation gradients, allowing for successful nucleation events to occur. In the present study, these phenomena are documented in a statistically representative manner. These insights are valuable for optimising thermal processing in interstitial-free (IF) steels. Full article

The continuous annealing process is widely used in the production of advanced high-strength steels. However, to tightly regulate the mechanical properties of the steel, precise control of processing parameters is needed. Although some techniques are available to monitor the mechanical properties of the steel on entry and exit to the furnace, monitoring the evolving microstructure of the steel through installation of sensors in the annealing line is extremely challenging due to the high temperature, high speed of the steel strip and limited space in the furnace. This study presents the development and validation of a multifrequency electromagnetic sensor system for real-time monitoring of microstructural transformations in steel during thermal cycling, intended for deployment in a continuous annealing line. Experiments were conducted on austenitic stainless steel to study the signal response to an increase in resistivity without a change in magnetic permeability. Pure nickel was tested to investigate the response to a change in magnetic permeability and the ferromagnetic-to-paramagnetic transition at its Curie temperature. A ferritic stainless steel was also tested to assess the performance of the system for high-temperature ferromagnetic materials and a higher-temperature ferromagnetic-to-paramagnetic transition. The tests indicate a strong response to material resistivity and permeability changes, with complementary information from different frequencies. Test results are supplemented by a finite element modelling study into the effect of a change in frequency and permeability on sensor response, with a discussion on the implications of experimental and modelling results for future applications. The results show that the developed system has the potential to characterise thermally induced changes in steels, establishing proof of concept for non-destructive, high-temperature electromagnetic sensing in steel processing and setting the foundation for further industrial deployment in phase and recrystallisation monitoring. Full article

In this work, we present an innovative, crosslinker-free method for preparing chitosan-based hydrogel precursors, fully aligned with green chemistry principles and composed of only five non-toxic, readily available reagents. The key novelty lies in the use of glycerin, which, during thermal annealing, evaporates and triggers a surface or bulk chemical transformation of chitosan, depending on its concentration. This process significantly enhances the material’s mechanical properties after swelling—with up to a 35% increase in tensile strength and a notable reduction in water uptake compared to systems containing AMPS-based crosslinkers. FTIR analysis indicates a partial re-acetylation of chitosan, shifting its structure toward that of chitin, which correlates with improved hydrophobicity (as shown by increased contact angles up to 92°) and greater structural integrity. These improvements are particularly pronounced at glycerin concentrations of 10–20%, whereas higher concentrations (50%) result in brittle, non-moldable films. Importantly, preliminary biological tests confirm that the resulting hydrogels are effectively colonized by mammalian cells, making them promising candidates for bioimplant or tissue engineering applications. Surface morphology and compatibility were further assessed via SEM, AFM, and contact angle measurements. Full article

There is growing interest in measuring the temperature-dependent dielectric properties of bio-tissues using dual-mode techniques (scattering measurements and thermal treatment). Uncooled coaxial antennas are preferred for their direct contact with the measured medium and reduced complexity; however, they exhibit structural changes during ablation due to the thermal expansion of polytetrafluoroethylene (PTFE). This paper presents an experimental study on PTFE expansion in an uncooled coaxial insulated monopole antenna in response to changes in the tissue’s thermal environment. Furthermore, it presents a methodology to mitigate these effects through coaxial annealing. The investigation consists of two distinct experiments: characterising PTFE expansion and assessing the effects of annealing through microwave ablation. This was achieved by simulating the thermal effects experienced during ablation by immersing the test antenna in heated peanut oil. PTFE expansion was measured through camera monitoring and using a toolmaker’s microscope, revealing two expansion modalities: linear PTFE expansion and non-linear plastic deformation from manufacturing processes. The return loss during ablation and consequential changes in the ablated lesion were also assessed. Antenna pre-annealing increased resilience against structural changes in the antenna, improving lesion ellipticity. Therefore, this study establishes a fabrication method for achieving an uncooled thermally stable antenna, leading to an optimised dual-mode ablation procedure, enabling quasi-real-time permittivity measurement of the surrounding tissue. Full article

This review article provides a comprehensive analysis of the photonic sintering conditions necessary to process non-oxide ceramics, to obtain similar material properties when compared with those of thermally annealed ones, for various applications in printed electronics. This article presents a thorough examination of the scientific literature on this topic, discussing the principles of photonic sintering applied to non-oxide ceramics, its advantages over traditional post-processing methods, and a quantitative overview of the performance of devices fabricated with the crystalline materials obtained. Full article

Pulsed detonation–plasma technology (PDT) is a surface-modification technology used in an atmospheric environment, where plasma, a detonation impact and thermal conditions are combined and have an effect on the material’s surface. In this study, annealed 65Mn steel was selected to further study the principle of PDT modification. The results show that the modified layer with fine grains was divided into an infiltration layer with a large amount of non-uniformly distributed granular CW₃ carbides and a heat-affected layer below the infiltration layer after PDT treatment. However, a higher amount of acicular martensite and a lower amount of austenite was achieved in the modified layer, containing a large number of small-angle grain boundaries, dislocations, and twin grains. After the PDT treatment, the hardness of the modified layer, heat-affected layer, and substrate was 980 HV, 856.2 HV, and 250 HV, respectively. The mass loss of the sample before and after PDT treatment was 21.1 mg and 12.4 mg, respectively. The hardness and wear resistance of the modified layer were greatly improved compared with the substrate because of the combined effect of the solid-phase transformation, element infiltration, and distortion. Full article

This study introduces an enhancement-mode AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) featuring a self-aligned p-GaN gate structure, fabricated using a gate-first process. The key innovation of this work lies in simplifying the fabrication process by utilizing gate metallization for both electrical contact and etching mask functions, enabling precise self-alignment. A highly selective Cl₂/N₂/O₂ inductively coupled plasma (ICP) etching process was optimized to etch the p-GaN layer in the access regions, with a selectivity ratio of 33:1 and minimal damage to the AlGaN barrier. Additionally, a novel, non-annealed ohmic contact formation technique was developed, leveraging ICP etching to create nitrogen vacancies that facilitate contact formation without requiring thermal annealing. This technique streamlines the process by combining ohmic contact formation and mesa isolation into a single lithographic step. Incorporating a SiNx gate dielectric layer led to a 4.5 V threshold voltage shift in the fabricated devices. The resulting devices exhibited improved electrical performance, including a wide gate voltage swing (>10 V), a high on/off current ratio (~10⁷), and clear pinch-off characteristics. These results demonstrate the effectiveness of the proposed fabrication approach, offering significant improvements in process efficiency and manufacturability. Full article

In this manuscript, strontium barium titanate (BST) ferroelectric memory film materials for applications in the feasibility of applying to non-volatile RAM devices were obtained and compared. Solutions were synthesized with a proportional ratio and through the deposition of BST films on titanium nitride/silicon substrates using the sol–gel method, using rapid thermal annealing for defect repair and re-crystallization processing. The crystallization structure and surface morphology of annealed and as-deposited BST films were obtained by XPS, XRD, and SEM measurements. Additionally, the ferroelectric and resistive switching properties for the memory window, the maximum capacitance, and the leakage current were examined for Al/BST/TiN and Cu/BST/TiN structure memory devices. In addition, the first-order reaction equation of the decay reaction behavior for the BST film RRAM devices in the reset state revealed that $r=0.19{[O^{2-}]}^1$. Finally, the Cu/BST/TiN and Al/BST/TiN structures of the ferroelectric BST films RRAM devices exhibited good memory window properties, bipolar switching properties, and non-volatile properties for applications in non-volatile memory devices. Full article

Micro-size light-emitting diodes (μLEDs) are high-brightness, low-power optoelectronic devices with significant potential in display technology, lighting, and biomedical applications. AlGaInP-based red LEDs experience severe size-dependent effects when scaled to the micron level, and addressing the fabrication challenges of GaN-based red μLED arrays is crucial for achieving homogeneous integration. This study investigates the employment of KOH wet treatments to alleviate efficiency degradation caused by sidewall leakage currents. GaN-based red μLED arrays with pixel sizes ranging from 5 × 5 µm² to 20 × 20 µm² were grown using metal-organic chemical vapor deposition (MOCVD), and then fabricated via rapid thermal annealing, mesa etching, sidewall wet treatment, electrode deposition, sidewall passivation, chemical-mechanical polishing, and via processes. The arrays, with pixel densities ranging from 668 PPI (Pixel Per Inch) to 1336 PPI, consist of 10,000 to 40,000 emitting pixels, and their optoelectronic properties were systematically evaluated. The arrays with varying pixel sizes fabricated in this study were subjected to three distinct processing conditions: without KOH treatment, 3 min of KOH treatment, and 5 min of KOH treatment. Electrical characterization reveals that the 5-min KOH treatment significantly reduces leakage current, enhancing the electrical performance, as compared to the samples without KOH treatment or 3-min treatment. In terms of optical properties, while the arrays without any KOH treatment failed to emit light, the ones with 3- and 5-min KOH treatment exhibit excellent optical uniformity and negligible blue shift. Most arrays treated for 5 min demonstrate superior light output power (LOP) and optoelectronic efficiency, with the 5 µm pixel arrays exhibiting unexpectedly high performance. The results suggest that extending the KOH wet treatment time effectively mitigates sidewall defects, reduces non-radiative recombination, and enhances surface roughness, thereby minimizing optical losses. These findings provide valuable insights for optimizing the fabrication of high-performance GaN-based red μLEDs and contribute to the development of stable, high-quality small-pixel μLEDs for advanced display and lighting applications. Full article

The heterogeneous integration of ferroelectric thin films on silicon- or silicon nitride-based platforms for photonic integrated circuits plays a crucial role in the development of nanophotonic thin film modulators. For this purpose, an ultrathin seed film was recently introduced as an integration method for ferroelectric thin films such as BaTiO₃ and Pb(Zr,Ti)O₃. One issue with this self-orienting seed film is that for non-planarized circuits, it fails to act as a template film for the thin films. To circumvent this problem, we propose a method of planarization without the need for wafer-scale chemical mechanical polishing by using hydrogen silsesquioxane as a precursor to forming amorphous silica, in order to create an oxide cladding similar to the thermal oxide often present on silicon-based platforms. Additionally, this oxide cladding is compatible with the high annealing temperatures usually required for the deposition of these novel ferroelectric thin films (600–800 °C). The thickness of this silica film can be controlled through a dry etch process, giving rise to a versatile platform for integrating nanophotonic thin film modulators on a wider variety of substrates. Using this method, we successfully demonstrate a hybrid BaTiO₃-Si ring modulator with a high Pockels coefficient of $r_{wg}=155.57\pm 10.91$ pm V⁻¹ and a half-wave voltage-length product of $V_{\pi }L=2.638\pm 0.084$ V cm, confirming the integration of ferroelectric thin films on an initially non-planar substrate. Full article