Al2O3 Insulation Layer Research Articles

Enhanced Magnetic Properties and Thermal Conductivity of FeSiCr Soft Magnetic Composite with Al2O3 Insulation Layer Prepared by Sol-Gel Process

FeSiCr soft magnetic composites (SMCs) were fabricated by the sol-gel method, and an Al2O3/resin composite layer was employed as the insulation coating. By the decomposition of boehmite (AlOOH) gel into Al2O3 in the temperature range of 606–707 °C, a uniform Al2O3 layer could be formed on the FeSiCr powder surface. The Al2O3 insulation coating not only effectively reduced the core loss, increased the resistivity, and improved the quality factor, but it also increased the thermal conductivity of SMCs. The best overall properties with saturation magnetization Ms = 188 emu/g, effective permeability μe = 39, resistivity ρ = 8.28 × 105 Ω·cm, quality factor Q = 94 at 1 MHz, and core loss = 1173 mW/cm3 at 200 kHz and 50 mT were obtained when the SMC was prepared with powders coated by 0.5 wt.% Al2O3 and resin. The optimized SMC exhibited the lowest core loss with 27% reduction compared to the resin only-insulated sample and 71% reduction compared to the sample without insulation treatment. Importantly, the thermal conductivity of the SMCs is 5.3 W/m·K at room temperature, which is higher than that of the samples prepared by phosphating and SiO2 coating owing to the presence of a high thermal conductive Al2O3 layer. The high thermal conductivity is beneficial to enhancing the high temperature performance, lifetime, and reliability of SMCs. This work is expected to be a valuable reference for the design and fabrication of SMCs to be applied in high-temperature and high-frequency environments.

High-Performance Atomic Layer Deposited Al2O3 Insulator Based Metal-Insulator-Metal Diode

The fabrication of metal–insulator– metal (MIM) diode using an ultrathin Al2O3 insulator layer, deposited using atomic layer deposition (ALD) is presented. The Al2O3 insulating layer was found to be highly uniform throughout the diode junction, effectively overcoming the main fabrication challenge in MIM diodes. The diodes exhibit strong non-linear current–voltage curves, have a typical zero-bias curvature coefficient of 5.4 V−1 and a zero-bias resistance of approximately 118 kΩ, a value considerably smaller than other MIM diode topologies and that allows more current to be rectified. Other results including current ratio and yield of the diode also competes favorably with the state-of-the-art MIM diodes such as the recently produced metal-octadecyltrichlorosilane (OTS)-metal structure.

Simulation of a Charged Al2O3 Film as an Assisting Passivation Layer for a-Si Passivated Contact P-Type Silicon Solar Cells

In this paper, a charged Al2O3 tunneling film as an assisting for amorphous Si (a-Si) passivated contact layer is proposed and theoretically simulated for its potential application in improving a-Si passivated contact p-type (a-PC-p) solar cell. The concept is based on an Ag/n+ c-Si/p c-Si/Al2O3/p+ a-Si/Al structure. The key feature is the introduction of a charged Al2O3 layer, which facilitates the tunneling of holes through an Al2O3 insulator layer accompanied by the reduction of interface defect density (Dit). The negative charge in the Al2O3 layer makes the energy band of p-type c-Si bend upward, realizing the accumulation of holes and repelling of electrons at the c-Si/a-Si interface simultaneously. The influence of interface negative charges (Qit) between a-Si and c-Si, Al2O3 thickness, Al2O3 bandgap, interface defect density (Dit) at the a-Si/c-Si interface are systematically investigated on the output parameters of a-PC-p cells. Inserting a charged Al2O3 film between the c-Si/a-Si interface, a + 4.2% relative efficiency gain is predicted theoretically compared with the a-PC-p cells without the Al2O3 layer. Subsequently, the device performance under various temperatures is simulated, and the insertion of a charged Al2O3 layer obviously decreases the Pmax temperature coefficient from −0.336% /°C to −0.247% /°C, which is analogous to that of Heterojunction with Intrinsic Thin layer (HIT) solar cell. The above results demonstrate a better temperature response for a-PC-p cells with a charged Al2O3 layer, paving a road for its potential application in high-efficiency and high thermal stability a-PC-p solar cells.

Vivaldi dipole nano‐rectenna for IR energy harvesting at 28.3 THz

AbstractA Vivaldi dipole rectenna system for infrared (IR) energy harvesting is investigated. First, a parametric study on the Vivaldi dipole antenna is performed to collect the maximum electric field between the Vivaldi poles. The antenna arms were optimized to achieve a high‐efficiency rectenna system. The two arms of the antenna were formed using two different metals, that is, gold and titanium. These two metals have different work functions, which facilitate the diode operation through tunneling at zero bias. The two arms of the Vivaldi dipole are overlapped, and a suitable insulator layer is injected in the overlapped area to form the metal‐insulator‐metal (MIM) diode. The MIM diode is an ideal candidate for this operation as it works without any bias, provided the two metals have different work functions. For rectenna operation, it is crucial that the rectifying diodes should work without any aid of external bias. The Al2O3 is the insulator layer of the MIM diode. We have chosen Al2O3 because it has a low dielectric constant at terahertz frequency regime, which allows us to match the operational cut‐off frequency, that is, 28.3 THz. A parametric study of the Al2O3 insulator layer is performed to increase the captured received intensity. At the end, the nano‐antenna operates at a frequency band of [26 … 30 THz] to harvest IR energy from the environment with good efficiency and demonstrate its capacity to capture incident waves and obtain high‐intensity values within its gap. It is a development that could eventually boost electricity generation.

Development of thin-film based sensors for temperature and tool wear monitoring during machining

Abstract The development of thin-film sensors for temperature and wear measurement in machining operations is presented in this work. A functional thin-film system, consisting of an Al2O3 insulation layer, a chromium sensor layer structured by photolithography and an Al2O3 wear-protection and insulation layer, is deposited by physical vapor deposition (PVD) processes onto the surface of cemented carbide cutting inserts. First specimen of the sensors are successfully fabricated and tested in laboratory experiments as well as in machining operations to demonstrate their functionality. These tool-integrated sensors can be used as an in-process monitoring device to determine the temperatures on the rake face at or close to the tool-chip contact area and to measure the progress of the flank-wear land width. The knowledge of these important process parameters opens up the possibility to develop new in-process control mechanisms in order to modify and improve the surface integrity of manufactured components. Thereby, their performance and lifetime can be enhanced.

Dynamic Absorption Enhancement and Equivalent Resonant Circuit Modeling of Tunable Graphene-Metal Hybrid Antenna.

Plasmonic antennas are attractive optical components of the optoelectronic devices, operating in the far-infrared regime for sensing and imaging applications. However, low optical absorption hinders its potential applications, and their performance is limited due to fixed resonance frequency. In this article, a novel gate tunable graphene-metal hybrid plasmonic antenna with stacking configuration is proposed and investigated to achieve tunable performance over a broad range of frequencies with enhanced absorption characteristics. The hybrid graphene-metal antenna geometry is built up with a hexagon radiator that is supported by the Al2O3 insulator layer and graphene reflector. This stacked structure is deposited in the high resistive Si wafer substrate, and the hexagon radiator itself is a sandwich structure, which is composed of gold hexagon structure and two multilayer graphene stacks. The proposed antenna characteristics i.e., tunability of frequency, the efficiency corresponding to characteristics modes, and the tuning of absorption spectra, are evaluated by full-wave numerical simulations. Besides, the unity absorption peak that was realized through the proposed geometry is sensitive to the incident angle of TM-polarized incidence waves, which can flexibly shift the maxima of the absorption peak from 30 THz to 34 THz. Finally, an equivalent resonant circuit model for the investigated antenna based on the simulations results is designed to validate the antenna performance. Parametric analysis of the proposed antenna is carried out through altering the geometric parameters and graphene parameters in the Computer Simulation Technology (CST) studio. This clearly shows that the proposed antenna has a resonance frequency at 33 THz when the graphene sheet Fermi energy is increased to 0.3 eV by applying electrostatic gate voltage. The good agreement of the simulation and equivalent circuit model results makes the graphene-metal antenna suitable for the realization of far-infrared sensing and imaging device containing graphene antenna with enhanced performance.

Microstructure, formation mechanism and magnetic properties of Fe1.82Si0.18@Al2O3 soft magnetic composites

Fe1.82Si0.18@Al2O3 soft magnetic composites (SMCs) have been fabricated by NaOH oxidation combined with subsequent spark plasma sintering (SPS). The microstructure and generation mechanism of Fe3O4 coatings on the surface of FeSiAl powders have been investigated systematically. Effects of oxidation time on the magnetic properties also have been revealed. In addition, the displacement reaction between Fe3O4 and Al during SPS process results in the formation of Al2O3 insulation layer, leading to a remarkable variation of the magnetic performances of SMCs. The increased NaOH oxidation time had positive influences on the electrical resistivity, frequency stability of permeability and core loss. The saturation magnetization first decreases then increases with the increase of oxidation time. These above results indicate that the fabrication method in this paper creates a way to form Fe3O4 nanoparticles and Al2O3 insulation layer, which enhance the magnetic performance of FeSiAl SMCs and will facilitate the design of efficient magnets in the future.

Enhanced dielectric properties and energy storage of the sandwich‐structured poly(vinylidene fluoride‐ co ‐hexafluoropropylene) composite films with functional BaTiO 3 @Al 2 O 3 nanofibres

Polymer-based composites with ceramic fillers could combine the advantages of both, which can be potentially used in electrical and electronic technology. In this work, the barium titanate (BaTiO 3 ) nanofibres and the core-shell structured BaTiO 3 @Al 2 O 3 nanofibres with Al 2 O 3 insulation layer coated on the BaTiO 3 surface were both prepared via the electrospinning method. The appropriate incorporation of the ceramic nanofibres effectively improves the dielectric properties and energy density of the polymer. Moreover, the poly(vinylidene fluoride- co -hexafluoropropylene)-based composite films with the three-layer sandwich structure were fabricated to further promote the dielectric properties. The results show that the outer two layers with a higher content of BaTiO 3 nanofibres can make more contribution to the improved permittivity of the composites. In addition, the introduction of the interlayer with low loading of BaTiO 3 @Al 2 O 3 nanofibres promotes the breakdown strength. This work gives rise to the potential in high energy storage applications.

Investigation of temperature dependent negative capacitance in the forward bias C-V characteristics of (Au/Ti)/Al2O3/n-GaAs Schottky barrier diodes (SBDs)

In this study, a metal-insulator-semiconductor (MIS) type Schottky barrier diodes (SBDs) were fabricated by growing a thin Al2O3 insulator layer between Au/Ti and n-GaAs using atomic layer deposition (ALD) method. The effect of temperature and voltage on interface states (Nss) and series resistance (Rs) of the (Au/Ti)/Al2O3/n-GaAs (MIS) type Schottky barrier diodes (SBDs) was investigated using the capacitance/conductance-voltage (C/(G/ω)-V) data measured in wide range of temperature (200–380 K) and voltage ( ± 5 V). It was found that C and G/ω are strongly dependent on temperature and voltage. The value of C in the forward bias region reaches to maximum and then becomes negative. This negative capacitance (NC) behavior of this SBD is observed for each temperature level. Also, capacitance-current (C-I) and conductance-current (G/ω-I) plots were drawn to explain the NC behavior. The negative value of C in the accumulation region corresponds to the maximum value of G/ω. Such behavior of C can be explained by the loss of interface charges located at (Al2O3)/n-GaAs interface because of impact ionization process, the existence of surface states (Nss), series resistance (Rs) and interfacial of (Al2O3) oxide layer.Therefore, the voltage dependent profiles of Rs and Nss were obtained using Nicollian-Brews and Hill-Colleman methods for enough high forward biases as a function of temperature at various positive bias voltages. The changes in Rs and Nss values were attributed to restructure and reordering of the carriers under temperature and voltage effects.

ABLATION AND DRIVE OF TYPICAL MULTI-LAYER FLYERS BY HIGH POWER LASER BEAM

Laser driving technology is an important technology in high energy physics, shock wave physics and explosive initiation application. In this paper, velocities and impact stresses of four types of laser-driven flyers (Al, Al/Al2O3/Al, CuO/Al2O3/Al, (CuO/Al)/Al2O3/Al) prepared via magnetron sputtering were obtained by photonic Doppler velocimetry (PDV) and a self-made polyvinylidene fluoride (PVDF) stress sensor at ns-class pulse width.The results showed that velocities and integrity of flyers were influenced by their diameters. Compared with Al single-layer flyer, other multi-layer flyers with Al2O3 insulation layer owned lower velocity but better integrity and initiation properties.CuO/Al as the ablation layer enhanced the velocities and shock initiation properties of multi-layer flyers. Velocity of a flyer improved with the increasing laser energy while shock initiation property did not perform in the same way. These results provide some references for the design of multi-layer flyers applied to laserdriven initiation technology.

Memory improvement in lead-free BiFeO3 ferroelectric with high-k Al2O3 buffer layer for non-volatile memory applications

We report the deposition of ferroelectric lead-free BiFeO3 perovskite film on Si (100) substrate by RF magnetron sputtering using Al2O3 as buffer layer. X-ray diffraction and multiple-angle ellipsometric analysis show the pure ferroelectric phase and maximum refractive index of the BiFeO3 film at the annealing temperature of 500 °C. For different annealing temperature of Al2O3 film, amorphous film structure and refractive index in the range 1.7–1.77 has been observed. Metal–ferroelectric–metal (MFeM), metal–ferroelectric–silicon (MFeS), metal–insulator–silicon (MIS) and metal–ferroelectric–insulator–silicon (MFIS) structure have been fabricated with BiFeO3 ferroelectric and Al2O3 insulator layer to investigate the electrical characteristics. Improvement in the memory window from 2.3 V in MFeS structure to 4.8 V in MFeIS structure has been observed with 10 nm buffer layer at the annealing temperature of 500 °C. The MFe(100 nm)I(10 nm)S structure annealed at 500 °C shows the breakdown voltage of 38 V and no degradation in the polarization charge upto the read-write cycles of 108.

ELECTRICAL PROPERTIES OF Al/p-Si STRUCTURE WITH Al2O3 THIN FILM FABRICATED BY ATOMIC LAYER DEPOSITION SYSTEM

Al2O3 insulator layer was deposited by atomic layer deposition (ALD) technique on p-type Si [Formula: see text] and the Al/Al2O3/p-Si metal/insulator/semiconductor (MIS) structures were fabricated. The current–voltage ([Formula: see text]) characteristics of these structures were investigated in two different temperatures. The main electrical parameters such as the ideality factor ([Formula: see text]), zero bias barrier height ([Formula: see text]), and series resistance ([Formula: see text]) values were found for 300 and 400[Formula: see text]K. The energy density distribution profiles of the interface state density ([Formula: see text]) were determined from the [Formula: see text] characteristics. In addition, the capacitance–voltage ([Formula: see text]) and conductance–voltage ([Formula: see text]) characteristics of devices were investigated in the frequency range 50–1000[Formula: see text]kHz at room temperature. Frequency-dependent electrical characteristics such as doping acceptor concentration ([Formula: see text]), energy difference between the valance band edge and bulk Fermi level ([Formula: see text]), diffusion potential ([Formula: see text]), barrier height ([Formula: see text]), the image force barrier lowering ([Formula: see text]), maximum electric field ([Formula: see text]), and [Formula: see text] values were determined using [Formula: see text] and [Formula: see text] plots. In addition, the [Formula: see text] values were performed using Hill–Coleman method. According to experimental results, the locations of [Formula: see text] and [Formula: see text] have an important effect on [Formula: see text], [Formula: see text] and [Formula: see text] plots of MIS structure.

Laser-driven performance of the Al/Al2O3/Al multi-layer flyer

To assess the effect of the Al2O3 layer on the performance of a laser-driven flyer, the photonic Doppler velocimetry (PDV) and the polyvinylidene fluoride (PVDF) piezoelectric film were used. The experiment results show that because of the addition of Al2O3 insulation layer the velocity of the Al/Al2O3/Al multi-layer flyer decreased 4.8% in comparison with the Al single-layer flyer, but the impact stress increased 61.4%, up to 870 MPa at 248 mJ laser energy. Moreover, the planarity and the integrity of the flyer plate were improved.

InGaN metal-insulator-semiconductor photodetector using Al2O3 as the insulator

In this paper, an InGaN metal-insulator-semiconductor (MIS) photodetector with an ultra-thin Al2O3 insulation layer deposited by atomic layer deposition (ALD) was studied. A high photoelectric responsivity of 0.25 A/W and a spectral responsivity rejection ratio of about three orders of magnitude at 1 V reverse bias were achieved for this MIS photodetector. The dominant carrier transport mechanism in the InGaN MIS photodetectors is submitted to the space charge limited current (SCLC) mechanism at high field and exhibits an Ohmic-like conduction at low electric field. The results indicate that the ultra-thin Al2O3 film deposited by the ALD technique can act as an excellent insulation dielectric for the InGaN photodetectors.

Atomic layer deposition of Pb(Zr,Ti)Ox on 4H-SiC for metal-ferroelectric-insulator-semiconductor diodes

Atomic layer deposited (ALD) Pb(Zr,Ti)Ox (PZT) ultra-thin films were synthesized on an ALD Al2O3 insulation layer on 4H-SiC substrate for metal-ferroelectric-insulator-semiconductor (MFIS) device applications. The as-deposited PZT was amorphous but crystallized into a perovskite polycrystalline structure with a preferred [002] orientation upon rapid thermal annealing (RTA) at 950 °C. The capacitance-voltage and current-voltage characteristics of the MFIS devices indicate carrier injection to the film induced by polarization and Fowler-Nordheim (FN) tunneling when electric field was high. The polarization-voltage measurements exhibited reasonable remanent and saturation polarization and a coercive electrical field comparable to that reported for bulk PZT. The piezoresponse force microscope measurements confirmed the polarization, coercive, and retention properties of ultra-thin ALD PZT films.

The leakage current mechanisms in the Schottky diode with a thin Al layer insertion between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact

This paper investigates the behaviour of the reverse-bias leakage current of the Schottky diode with a thin Al inserting layer inserted between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25–350 °C. It compares with the Schottky diode without Aluminium inserting layer. The experimental results show that in the Schottky diode with Al layer the minimum point of I–V curve drifts to the minus voltage, and with the increase of temperature increasing, the minimum point of I–V curve returns the 0 point. The temperature dependence of gate-leakage currents in the novelty diode and the traditional diode are studied. The results show that the Al inserting layer introduces interface states between metal and Al0.245Ga0.755N. Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current. The reliability of the diode at the high temperature is improved by inserting a thin Al layer.

Fabrication and characterization of MFISFET using Al2O3 insulating layer for non-volatile memory

Metal-ferroelectric-insulator-semiconductor (MFIS) structures including an Al2O3 insulator layer and a SBT ferroelectric film are fabricated with their optimum thicknesses extracted by computer simulation, and then electrical properties of MFIS structures are investigated. In Pt/Al2O3/Si structure, no hysteresis and low leakage current of 7.5 × 10−9A/cm2 have been observed. The MFIS structure, Pt/SBT/Al2O3/Si, shows a memory window width of 1.2 V at an operation voltage of 5 V and a gate leakage current density of 7 × 10−8A/cm2at 1 V. Fatigue characteristics of the MFIS structure are also studied.