Search Results (85)

The insulating rod of aramid fiber-reinforced epoxy resin composites (AFRP) is an important component of gas-insulated switchgear (GIS). Under complex working conditions, the high temperature caused by voltage, current, and external climate change becomes one of the important factors that aggravate the interface degradation between aramid fiber (AF) and epoxy resin (EP). In this paper, molecular dynamics (MD) simulation software is used to study the effect of temperature on the interfacial properties of AF/EP. At the same time, the mechanism of improving the interfacial properties of three nanoparticles with different properties (insulator Al₂O₃, semiconductor ZnO, and conductor carbon nanotube (CNT)) is explored. The results show that the increase in temperature will greatly reduce the interfacial van der Waals force, thereby reducing the interfacial binding energy between AF and EP, making the interfacial wettability worse. Furthermore, the addition of the three fillers can improve the interfacial adhesion of the composite material. Among them, Al₂O₃ and CNT maintain a large dipole moment at high temperature, making the van der Waals force more stable and the adhesion performance attenuation less. The Mulliken charge and energy gap of Al₂O₃ and ZnO decrease slightly with temperature but are still higher than AF, which is conducive to maintaining good interfacial insulation performance. Full article

The stability of thermal barrier coating (TBC) materials during service is a prerequisite for the normal operation of aircraft engines. The high-temperature corrosion of CaO–MgO–Al₂O₃–SiO₂ (CMAS) is an important factor that affects the stability of TBCs on turbine blades and causes premature engine failure. For traditional 6-8 YSZ, at temperatures of more than 1200 °C, the thermal insulation performance is significantly reduced, which makes it necessary to find new, alternative materials. La₂Zr₂O₇ has good thermal physical properties; the addition of Ce⁴⁺ improves its mechanical properties, while adding Gd₂O₃ affects its corrosion resistance. Herein, high-temperature corrosion studies of (La_1−xGd_x)₂(Zr_0.7Ce_0.3)₂O₇ (L-GZC) (x = 0, 0.3, 0.5, 0.7) ceramic TBC were conducted using CMAS glass at 1250 °C. The results indicate that CMAS rapidly dissolves L-GZC and separates the (La, Gd)₈Ca₂(SiO₄)₆O₂ apatite phase, ZrO₂, and other crystalline phases. These products form a crystalline layer at the contact boundary, which can inhibit further CMAS reactions. Among the coatings examined, the L-GZC ceramic (x = 0.7) exhibits better corrosion resistance, and the penetration depth is <200 μm after high-temperature corrosion at 1250 °C for 5, 10, and 20 h. The failure mechanism and potential risk of CMAS were also analyzed and discussed. The L-GZC ceramic material has good thermal corrosion resistance and is expected to replace the traditional YSZ to better meet the high-temperature working requirements of gas turbines and aircraft engines. 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

High-performance optical isolators are key components in photonic integrated circuits, with significant applications in nonlinear optical systems. We propose a design for a TE-mode optical isolator based on the AlGaAs-on-insulator platform. The isolator consists of non-reciprocal phase shift (NRPS) waveguides, reciprocal phase shift (RPS) waveguides, and multi-mode interference (MMI) couplers achieving low loss, high isolation, and wide bandwidth. Numerical simulations show that, at a wavelength of 1550 nm, the device provides a bandwidth of 91 nm at 30 dB isolation. The confinement factors for a magneto-optical (MO) waveguide were analyzed, and a detailed loss analysis revealed a total loss of 1.47 dB and a figure of merit (FoM) of 2.76 rad/dB. The manufacturing tolerances of the isolator are discussed referring to the requirement of stability and reliability in practical applications. This study provides an optimized design for high-performance TE-mode optical isolators in integrated photonic systems, which are well-suited for efficient and stable nonlinear optical applications. Full article

Direct wide-bandgap III-Ns and II-Os have recently gained considerable attention due to their unique electrical and chemical properties. These novel semiconductors are being explored to design short-wavelength light-emitting diodes, sensors/biosensors, photodetectors for integration into flexible transparent nanoelectronics/photonics to achieve high-power radio-frequency modules, and heat-resistant optical switches for communication networks. Knowledge of the elastic constants structural and mechanical properties has played crucial roles both in the basic understanding and assessing materials’ use in thermal management applications. In the absence of experimental structural, elastic constants, and mechanical traits, many theoretical simulations have yielded inconsistent results. This work aims to investigate the basic characteristics of tetrahedrally coordinated, partially ionic BeO, MgO, ZnO, and CdO, and partially covalent BN, AlN, GaN, and InN materials. By incorporating a bond-orbital and a valance force field model, we have reported comparative results of our systematic calculations for the bond length $\mathrm{d}$, bond polarity ${\mathsf{\alpha }}_{\mathrm{P}}$, covalency ${\mathsf{\alpha }}_{\mathrm{C}}$, bulk modulus $\mathrm{B}$, elastic stiffness $\mathrm{C}(={\displaystyle \frac{\left[{\mathrm{c}}_{11}-{\mathrm{c}}_{12}\right]}{2}})$, bond-stretching $\mathsf{\alpha }$ and bond-bending $\mathsf{\beta }$ force constants, Kleinmann’s internal displacement ζ, and Born’s transverse effective charge ${\mathrm{e}}_{\mathrm{T}}^{*}$. Correlations between $\mathrm{C}/\mathrm{B}$, $\mathsf{\beta }$/$\mathsf{\alpha }$, ${\displaystyle \frac{{\mathrm{c}}_{12}}{{\mathrm{c}}_{11}}},$ ζ, $\mathrm{a}\mathrm{n}\mathrm{d}$ ${\mathsf{\alpha }}_{\mathrm{C}}$revealed valuable trends of structural, elastic, and bonding characteristics. The study noticed AlN and GaN (MgO and ZnO) showing nearly comparable features, while BN (BeO) is much harder compared to InN (CdO) material, with drastically softer bonding. Calculations of microhardness $\mathrm{H}$, shear modulus $\mathrm{G},$ and Young’s modulus $\mathrm{Y}$ have predicted BN (BeO) satisfying a criterion of super hardness. III-Ns (II-Os) could be vital in electronics, aerospace, defense, nuclear reactors, and automotive industries, providing integrity and performance at high temperature in high-power applications, ranging from heat sinks to electronic substrates to insulators in high-power devices. Full article

With the growing demand for more efficient power conversion and silicon reaching its theoretical limit, wide bandgap semiconductor devices are emerging as a potential solution. For instance, Gallium Nitride (GaN)-based high-electron-mobility transistors (HEMTs) are getting more attention, and several structures for the normally off operation have been proposed. Adding an AlN interlayer in conventional AlGaN/GaN normally on HEMT structures is known to enhance the current density. In this work, the effect of an AlN interlayer in the normally off AlGaN/GaN MISHEMT with a buried p-region was investigated using a TCAD simulation from Silvaco. The added AlN interlayer increases the two-dimensional electron gas density, requiring a higher p-doping concentration to achieve the same threshold voltage. The simulation results show that the overall effect is a reduction in the device’s current density and peak transconductance by 21.83% and 44.4%, respectively. Further analysis of the current profile shows that because of the buried p-region and at high gate voltages, the current flows near the AlGaN/GaN interface and along the insulator/AlGaN interface. Adding an AlN interface blocks the migration of channel electrons to the insulator/AlGaN interface, resulting in a lower current density. Full article

Bow-tie diodes on the base of modulation-doped semiconductor structures are often used to detect radiation in GHz to THz frequency range. The operation of the bow-tie microwave diodes is based on carrier heating phenomena in an epitaxial semiconductor structure with broken geometrical symmetry. However, the electrical properties of bow-tie diodes are highly dependent on the purity of the grown epitaxial layer—specifically, the minimal number of defects—and the quality of the ohmic contacts. The quality of MBE-grown semiconductor structure depends on the presence of a buffer layer between a semiconductor substrate and an epitaxial layer. In this paper, we present an investigation of the electrical and optical properties of planar bow-tie microwave diodes fabricated using modulation-doped semiconductor structures grown via the MBE technique, incorporating either a GaAs buffer layer or a GaAs–AlGaAs super-lattice buffer between the semi-insulating substrate and the active epitaxial layer. These properties include voltage sensitivity, electrical resistance, I–V characteristic asymmetry, nonlinearity coefficient, and photoluminescence. The investigation revealed that the buffer layer, as well as the illumination with visible light, strongly influences the properties of the bow-tie diodes. Full article

GaN-on-Si high-electron-mobility transistors have emerged as the next generation of high-powered and cost-effective microwave devices; however, the limited thermal conductivity of the Si substrate prevents the realization of their potential. In this paper, a GaN-on-insulator (GNOI) structure is proposed to enhance the heat dissipation ability of a GaN-on-Si HEMT. Electrothermal simulation was carried out to analyze the thermal performance of the GNOI-on-Si HEMTs with different insulator dielectrics, including SiO₂, SiC, AlN, and diamond. The thermal resistance of the HEMTs was found to be able to be obviously reduced and the DC performance of the device can be obviously improved by removing the low-thermal-conductivity III-nitride transition layer and forming a GNOI-on-Si structure with SiC, AlN, or diamond as the bonding insulator dielectrics. Full article

In this work, we demonstrated the epitaxial growth of a gallium nitride (GaN) buffer structure on 200 mm SOI (silicon-on-insulator) substrates. This epitaxial layer is grown using a reversed stepped superlattice buffer (RSSL), which is composed of two superlattice (SL) layers with different Al component ratios stacked in reverse order. The upper layer, with a higher Al component ratio, introduces tensile stress instead of accumulative compressive stress and reduces the in situ curvature of the wafer, thereby achieving a well-controlled wafer bow ≤ ±50 µm for a 3.3 µm thick buffer. Thanks to the compliant SOI substrate, good crystal quality of the grown GaN layers was obtained, and a breakdown voltage of 750 V for a 3.3 µm thick GaN buffer was achieved. The breakdown field strength of the epitaxial GaN buffer layer on the SOI substrate is estimated to be ~2.27 MV/cm, which is higher than the breakdown field strength of the GaN-on-Si epitaxial buffer layer. This RSSL buffer also demonstrated a low buffer dispersion of less than 10%, which is good enough for the further processing of device and circuit fabrication. A D-mode GaN HEMT was fabricated on this RSSL buffer, which showed a good on/off ratio of ~10⁹ and a breakdown voltage of 450 V. Full article

As a promising candidate for More Moore technology, InGaAs-based n-channel metal-oxide-semiconductor field-effect transistors (nMOSFETs) have attracted growing research interest, especially with InGaAs-on-insulator (InGaAs-OI) configurations aimed at alleviating the short channel effects. Correspondingly, the fabrication of an ultrathin InGaAs body becomes necessary for the full depletion of the channel, while the deteriorated semiconductor–insulator interface-related scattering could severely limit carrier mobility. This work focuses on the exploration of carrier mobility enhancement strategies for 8 nm body-based InGaAs-OI nMOSFETs. With the introduction of a bottom gate bias on the substrate side, the conduction band structure in the channel was modified, relocating the carrier wave function from the InGaAs/Al₂O₃ interface into the body. Resultantly, the channel mobility with an inversion layer carrier concentration of 1 × 10¹³ cm⁻² was increased by 62%, which benefits InGaAs-OI device application in monolithic 3D integration. The influence of the dual-gate bias from front gate and bottom gate on gate stability was also investigated, where it has been unveiled that the introduction of the positive bottom gate bias is also beneficial for gate stability with an alleviated orthogonal electric field. Full article

Foamed concrete is increasingly utilized in engineering due to its light weight, excellent thermal insulation, fire resistance, etc. However, its low strength has always been the most crucial factor limiting its large-scale application. This study introduced an innovative method to enhance the strength of foamed concrete by using nano-Al₂O₃ (NA) as a foam stabilizer. NA was introduced into a foaming agent containing sodium dodecyl sulfate (SDS) and hydroxypropyl methylcellulose (HPMC) to prepare a highly stable foam. This approach significantly improved the foam stability and the strength of foamed concrete. Its drainage volume, settlement distance, microstructure, and stabilizing action were investigated, along with the strength, microstructure, and hydration products of foamed concrete. The presence of NA effectively reduced the drainage volume and settlement distance of the foam. NA is distributed at the gas–liquid interface and within the liquid film to play a hindering role, increasing the thickness of the liquid film, delaying the liquid discharge rate from the liquid film, and hindering bubble aggregation, thereby enhancing foam stability. Additionally, due to the stabilizing effect of NA on the foam, the precast foam forms a fine and uniform pore structure in the hardened foamed concrete. At 28 d, the compressive strength of FC0 (0% NAs in foam) is 2.18 MPa, while that of FC3 (0.18% NAs in foam) is 3.90 MPa, increased by 79%. The reason for this is that NA promotes the formation of AFt, and its secondary hydration leads to the continuous consumption of Ca(OH)₂, resulting in a more complete hydration reaction. This study presents a novel method for significantly improving the performance of foamed concrete by incorporating NA. Full article

Planar microwave bow-tie diodes on bases of selectively doped semiconductor structures are successfully used in the detection and imaging of electromagnetic radiation in millimeter and submillimeter wavelength ranges. Although the signal formation mechanism in these high-frequency diodes is said to be based on charge-carrier heating in a semiconductor in a strong electric field, the nature of the electrical signal across the bow-tie diodes is not yet properly identified. In this research paper, we present a comprehensive study of a series of various planar bow-tie diodes, starting with a simple asymmetrically shaped submicrometer-thick n-GaAs layer and finishing with bow-tie diodes based on selectively doped GaAs/AlGaAs structures of different electrical conductivity. The planar bow-tie diodes were fabricated on two different types of high-resistivity substrates: bulky semi-insulating GaAs substrate and elastic dielectric polyimide film of micrometer thickness. The microwave diodes were investigated using DC and high-frequency probe stations, which allowed us to examine a sufficient number of diodes and collect a large amount of data to perform a statistical analysis of the electrical parameters of these diodes. The use of probe stations made it possible to analyze the properties of the bow-tie diodes and clarify the nature of the detected voltage in the dark and under white-light illumination. The investigation revealed that the properties of various bow-tie diodes are largely determined by the energy states residing in semiconductor bulk, surface, and interfaces. It is most likely that these energy states are responsible for the slow relaxation processes observed in the studied bow-tie diodes. Full article

The V_th stability and gate reliability of AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with alternating O₂ plasma treatment were systematically investigated in this article. It was found that the conduction band offset at the Al₂O₃/AlGaN interface was elevated to 2.4 eV, which contributed to the suppressed gate leakage current. The time-dependent dielectric breakdown (TDDB) test results showed that the ALD-Al₂O₃ with the alternating O₂ plasma treatment had better quality and reliability. The AlGaN/GaN MIS-HEMT with the alternating O₂ plasma treatment demonstrated remarkable advantages in higher V_th stability under high-temperature and long-term gate bias stress. Full article

This article presents the utilization of the chemical–mechanical polishing (CMP) method to fabricate high-performance N-polar GaN/AlGaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) through layer transfer technology. The nucleation and buffer layers were removed via CMP to attain a pristine N-polar GaN surface with elevated smoothness, featuring a low root-mean-square (RMS) roughness of 0.216 nm. Oxygen, carbon, and chlorine impurity elements content were low after the CMP process, as detected via X-ray photoelectron spectroscopy (XPS). The electrical properties of N-polar HEMTs fabricated via CMP exhibited a sheet resistance (R_sh) of 244.7 Ω/sq, a mobility of 1230 cm²/V·s, and an n_s of 2.24 × 10¹³ cm⁻². Compared with a counter device fabricated via inductively coupled plasma (ICP) dry etching, the CMP devices showed an improved output current of 756.1 mA/mm, reduced on-resistance of 6.51 Ω·mm, and a significantly reduced subthreshold slope mainly attributed to the improved surface conditions. Meanwhile, owing to the MIS configuration, the reverse gate leakage current could be reduced to as low as 15 μA/mm. These results highlight the feasibility of the CMP-involved epitaxial layer transfer (ELT) technique to deliver superior N-polar GaN MIS-HEMTs for power electronic applications. Full article

Si₃N₄ ceramic materials have great potential in the field of insulation in SF6 gas ultra-high-voltage transmission and transformation equipment due to their excellent insulation performance and thermal stability. In this paper, Y₂O₃-Al₂O₃ was used as a sintering aid to prepare high-density (>99%) Si₃N₄ ceramics through two-step pressureless liquid-phase sintering, and the mechanism of the influence of Y₂O₃-Al₂O₃ addition on the microstructure and electrical properties of Si₃N₄ ceramics was studied. The results showed that increasing the sintering aid content could increase the grain size of Si₃N₄ ceramics, while increasing the Y₂O₃ ratio could refine the grain size. When Y₂O₃-Al₂O₃ addition was 8% and the ratio was 5:3, the room temperature volume resistivity of Si₃N₄ ceramics was the highest, 7.33 × 10¹⁴ Ω·m, and the volume resistivity was the most stable when the sintering aid content was 12%. The internal carrier migration type of Si₃N₄ ceramics was mainly ion conduction, mainly along the grain boundaries. The temperature stability of the resistivity of Si₃N₄ ceramics could be improved by doping with Y³⁺ functional ions to reduce the potential barrier conductivity level and refine the grain size to improve the conduction path. The dielectric constant and dielectric loss of Si₃N₄ ceramics were mainly affected by interface polarization. They gradually increased with the increase in sintering aid addition. Temperature had little effect on dielectric constant and dielectric loss in the range of 20–80 °C. Full article