Properties Of Al2O3 Thin Films Research Articles

Characteristics and electrochemical properties of Al2O3 thin films on surgical scalpel blades

Surface modification techniques play an important role in shaping the physicochemical properties of surgical tools. The article discusses the problem of the destruction of surgical scalpel blades and the methods of depositing thin films on them.

Comparison of structure and solar-selective absorbance properties of Al2O3 thin films with Al and Ni reflector interlayers

This work aims at evaluating the selective solar absorbance (SSA) of Al2O3 thin films deposited by physical vapor deposition (PVD) with two different metallic reflector interlayers. Al2O3 thin films are deposited on the same substrate stainless steel (SS) 304L, with two different interlayers between the thin film and the substrate, namely, nickel (Ni) and aluminum (Al) are used as the reflector interlayer SS304L/Al/Al2O3 and SS304L/Ni/Al2O3. A scanning electron microscope (SEM) was utilized to characterize the chemical composition by energy dispersive X-ray analysis (EDX) and surface morphology of the deposited thin films. The phases of the thin films were analyzed and identified by X-ray diffraction (XRD) to detect the present phases. The surface topography and the thickness of the deposited thin films were investigated using an atomic force microscope (AFM). The optical properties of the substrate and the deposited thin films (absorbance & emittance) in two conditions were identified by Fourier transform infrared spectroscopy (FTIR) and spectrophotometer. The obtained results demonstrate that both SS304L/Al/Al2O3 and SS304L/Ni/Al2O3 show good performance, such as high solar absorbance and low thermal emittance. However, the Al/Al2O3 thin film provides high selectivity (absorbance/emittance (α/ε)) of 0.916/0.05, compared to 0.913/0.15 for the Ni/Al2O3 coating. The effect of different properties and microstructure on the efficiency of deposited thin films showed that the SS304L/Al/Al2O3 has higher absorbance (92%) in visible and ultraviolet (UV) regions; and lower emittance (5%) than the SS304L/Ni/Al2O3. This work shows that the intermediate IR layer has a more pronounced effect on the emittance properties rather than the absorbance properties of the Al/Al2O3 layer.

Optical properties of Al2O3 thin films doped with hollow monometallic and core/shell bimetallic gold, silver nanoparticles

Optical properties of Al2O3 thin films doped with hollow monometallic and core/shell bimetallic gold, silver nanoparticles

Influence of substrate biasing on structural, chemical and electrical properties of Al2O3 thin films deposited by PEALD

High-k materials are needed to minimise the gate leakage current in high-speed and high-power switching applications. In this regard, aluminium oxide (Al2O3) deposited by plasma enhanced atomic layer deposition (PEALD) is gaining extensive attention to be used as high-k material in microelectronics. In this work, we studied the effect of substrate biasing during the oxidizing plasma step on physical, chemical and electrical properties of Al2O3 thin films grown by PEALD on silicon substrate. We show that the structural and electrical properties such as the flat band voltage, and chemical composition can be tuned with the applied substrate bias. Indeed, we highlight that the dielectric constant of the MIS capacitor decreases from 8.5 to 6.5 and the charge polarity of the film is modulated from negative to positive when the applied substrate bias is increased. Using morphological and structural characterisations, we show that the substrate bias significantly affects the chemical composition of Al2O3 thin film layer. Moreover, we highlight by cross-sectional transmission electron the presence of an interfacial layer between Si and Al2O3 which could significantly influence the electrical properties of the deposited thin film. The chemical composition of this interfacial layer can be controlled by the applied substrate bias. Using a series of energy dispersive x-ray experiments, we further confirm the formation of aluminosilicate under low substrate bias condition while silicon oxide is formed under high bias. These findings show that the substrate biasing plays a critical role in defining physical, chemical as well as electrical properties of the PEALD Al2O3 thin films.

Al2O3 Thin Films on Magnesium: Assessing the Impact of an Artificial Solid Electrolyte Interphase

Among the many emerging technologies under investigation as alternatives to the successful Lithium-ion battery, the magnesium battery is promising due to the wide availability of magnesium, its high volumetric capacity, and the possibility for safety improvements. One of the largest challenges facing rechargeable magnesium batteries is the formation of a passivation layer at the Mg metal anode interface when reactive species in the electrolyte are reduced at the electrode-electrolyte interface. To control the solid electrolyte interphase in Lithium batteries, protective layers called artificial solid electrolyte interphase (ASEI) layers have been successful in improving Li metal anode performance. The approach of protecting Mg metal anodes from electrolyte degradation has been demonstrated by fewer studies in the literature than Li systems. In this work, we discuss the properties of Al2O3 thin films deposited using atomic layer deposition as an artificial solid electrolyte interphase at the Mg anode. Our results demonstrate that Al2O3 does prevent electrolyte degradation due to the reductive nature of Mg. However, undesirable properties such as defects and layer breakdown lead to Mg growth that causes soft-shorting. The soft-shorting occurs with and without the protection layer, indicating the ALD layer does not prevent it and hinders Al2O3 from being an ideal candidate for a protection layer. Crucial effects of this layer on Mg electrochemistry at the interface were observed, including growth of Mg deposits leading to soft-shorting of the cell whose morphology showed a dependence on the Al2O3 layer. These results may provide guidelines for the future design and development of protective ASEI layers for Mg anodes.

Al2O3 Thin Films Prepared by a Combined Thermal‐Plasma Atomic Layer Deposition Process at Low Temperature for Encapsulation Applications

In this article, a combined H2O thermal atomic layer deposition of Al2O3 with in situ N2 plasma treatment process at 90 °C for encapsulation applications is reported. The effect of process parameters on the growth behavior and properties of Al2O3 thin films, such as elemental composition, residual stress, moisture permeation barrier ability, density, and roughness, is investigated. Optimization of plasma exposure time gives films with a low impurity (≈3.8 at% for hydrogen, ≈0.17 at% for carbon, and ≈0.51 at% for nitrogen), a high mass density (≈3.1 g cm−3), and a low tensile residual stress (≈160 MPa). A water vapor transmission rate of 2.9 × 10−3 g m−2 day−1 is obtained for polyethylene naphthalate substrates coated with 4‐nm‐thick Al2O3 films.

Optical Thin Films of Metal Oxides Produced by the Sol-Gel Method for Photovoltaic Applications

The use of thin films in optoelectronic and photovoltaic devices is aimed at improving the physical properties of the substrate material. The modification of the surface of the silicon substrate is thus one of the greatest challenges in research on photovoltaic materials, in order to achieve even greater efficiency or better adapt their properties depending on the application. The technologies of applying layers vary depending on the effect to be obtained and the material from which the layer is formed. In practice, the most common method is chemical vapor deposition and physical vapor deposition, and the most commonly applied optical materials are SiO2, TiO2 and Si3N4.This paper presents the results of investigations on morphology and optical properties of the prepared aluminium oxide thin films. Thin films were prepared with use of sol-gel spin coating method. Surface morphology studies were carried out using an atomic force microscope. To characterize the surface of the thin films, 3D images and histograms of the frequency of individual inequalities were made. In order to characterize the optical properties of Al2O3 thin films, the reflectance and light transmission tests were performed using a spectrophotometer. Optical constants were determined using a spectroscopic ellipsometer. Results and their analysis show that the sol-gel method allows the deposition of homogenous thin films of Al2O3 with the desired geometric characteristics and good optical properties. Uniform, continuous thin layers with a roughness not exceeding a few nanometres were deposited. Their deposition enabled to reduce the reflection of light from the polished substrate below 15% in a wide range (425-800nm) while maintaining high transparencies (over 90%). The obtained results causes that mentioned thin films are good potential material for optics, optoelectronics and photovoltaics.

Effect of bias voltage on microstructure and optical properties of Al2O3 thin films prepared by twin targets reactive high power impulse magnetron sputtering

Al2O3 thin films were deposited on silicon (100) and tin-doped indium oxide (ITO) substrates by twin targets reactive high power impulse magnetron sputtering (TTR-HiPIMS). Effects of the substrate bias voltage (Vb) on microstructure, surface morphology, chemical composition and optical transmittance of the deposited films were investigated by grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), X-ray photoelectrons spectroscopy (XPS) and Ultra violet-visible-near infrared (UV-visible-NIR) spectra, respectively. The AFM scans showed that increasing the bias voltage (Vb) from 0 to −40 V caused the weakly crystalline film to evolve into fully crystalline Al2O3 film at temperatures as low as 230 °C. However, when Vb reached −60 V, the crystallinity decreased. This result was also confirmed by GIXRD patterns, which showed that the best crystallinity of Al2O3 in γ phase was obtained for film deposited at a bias of −40 V. Besides, with the increase of Vb, the deposition rate decreased from 88 to 70 nm/h, and the O/Al ratio of the as-deposited films reduced from 1.53 to 1.44. The binary collision approximation (BCA) Monte-Carlo code SDTrimSP was also used to calculate the sputter yield of Al and Al2O3. It was found that the sputter yield of Al2O3 was about 1/8 of Al, which is supposed to be one of the main reasons for the observed low deposition rate. UV-vis-NIR transmittance spectra of Al2O3 films deposited under different bias voltages were evaluated after deposition on ITO substrates. The results revealed that all the as-deposited films had high optical transmittance (≈80%) in the wavelength range of 200–800 nm. Moreover, a marginal decrease of the transmittance was also observed with increasing Vb.

Properties of Al2O3 thin films deposited on 4H-SiC by reactive ion sputtering

In this work, the electrical properties of Al2O3 films deposited by reactive ion sputtering were investigated by means of morphological, chemical and electrical characterizations. We observe that the electron trapping affecting the insulating layer is mitigated after a rapid thermal annealing (RTA) treatment. The RTA improved also the permittivity (up to 6ε0), although the negative fixed charge remains in the order of 1012 cm−2. However, the temperature dependent electrical investigation of the metal-oxide-semiconductor (MOS) capacitors demonstrates that the room temperature Fowler-Nordheim electron barrier height of 2.37 eV lies between the values expected for SiO2/4H-SiC and Al2O3/4H-SiC systems.

Sol-gel processed high-k aluminum oxide dielectric films for fully solution-processed low-voltage thin-film transistors

High-k oxide dielectric films have attracted intense interest for thin-film transistors (TFTs). However, high-quality oxide dielectrics were traditionally prepared by vacuum routes. Here, amorphous high-k alumina (Al2O3) thin films were prepared by the simple sol-gel spin-coating and post-annealing process. The microstructure and dielectric properties of Al2O3 dielectric films were systematically investigated. All the Al2O3 thin films annealed at 300–600 °C are in amorphous state with ultrasmooth surface (RMS ~ 0.2 nm) and high transparency (above 95%) in the visible range. The leakage current of Al2O3 films gradually decreases with the increase of annealing temperature. Al2O3 thin films annealed at 600 °C showed the low leakage current density down to 3.9 × 10−7 A/cm2 at 3 MV/cm. With the increase of annealing temperature, the capacitance first decreases then increases to 101.1 nF/cm2 (at 600 °C). The obtained k values of Al2O3 films are up to 8.2. The achieved dielectric properties of Al2O3 thin films are highly comparable with that by vapor and solution methods. Moreover, the fully solution-processed InZnO TFTs with Al2O3 dielectric layer exhibit high mobility of 7.23 cm2 V−1 s−1 at the low operating voltage of 3 V, which is much superior to that on SiO2 dielectrics with mobility of 1.22 cm2/V−1 s−1 at the operating voltage of 40 V. These results demonstrate that solution-processed Al2O3 thin films are promising for low-power and high-performance oxide devices.

Main properties of Al2O3 thin films deposited by magnetron sputtering of an Al2O3 ceramic target at different radio-frequency power and argon pressure and their passivation effect on p-type c-Si wafers

In this work, 50-nm thick Al2O3 thin films were deposited at room temperature by magnetron sputtering from an Al2O3 ceramic target at different RF power and argon pressure values. The sputtering technique could be preferred to conventional atomic layer deposition for an industrial application, owing to its simplicity, availability, and higher deposition rate. The resulting thin films were characterized by UV/Vis/NIR spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The deposited Al2O3 material was always highly transparent and amorphous in nature. It was found that the O/Al ratio is higher when the Al2O3 layer is deposited at lower RF power or higher argon pressure. Also, some argon incorporation into the films was observed at low deposition pressure. On the other hand, the performance of the previously characterized Al2O3 thin films in the passivation of 2.25-Ωcm p-type float zone c-Si wafer surfaces was evaluated by the quasi-steady-state photoconductance technique. The best effective carrier lifetime value at one-sun illumination, 0.34ms (corresponding to a surface recombination velocity of 41cm/s), was obtained with the 50-nm Al2O3 deposited at the higher argon pressure studied, 0.67Pa (5.0mTorr), with the lowest RF power studied, 150W (corresponding to a power density of 3.3W/cm2), and after an annealing process, in this case at 350°C for 20min with forming gas. It was assumed that the reduction of the surface passivation quality at higher RF power or lower argon pressure is a consequence of an increased surface damage, and, probably, to a decrease of the O/Al ratio of the Al2O3 passivation material. These assumptions were confirmed with the obtainment of a lifetime of 0.73ms (a surface recombination velocity equal to 19cm/s) with a simple experiment with Al2O3 deposited with progressively varied sputtering conditions started from minimal silicon surface damage conditions: 50W (corresponding to a power density of 1.1W/cm2) and 6.67Pa (50mTorr). Finally, comments about further improvement of the effective lifetime (up to 1.25ms, corresponding to a surface recombination velocity of 11cm/s) with preliminary experiments about the incorporation of an intrinsic hydrogenated amorphous silicon interlayer are included.

Influences of annealing on structural and compositional properties of Al2O3 thin films grown on 4H–SiC by atomic layer deposition**Project supported by the National Basic Research Program of China (Grant No. 2015CB759600), the National Natural Science Foundation of China (Grant Nos. 61474113, 61574140, and 61274007), and the Beijing Nova Program, China (Grant No. xx2016071), and the CAEP Microsystem and THz Science

Annealing effects on structural and compositional performances of Al2O3 thin films on 4H–SiC substrates are studied comprehensively. The Al2O3 films are grown by atomic layer deposition through using trimethylaluminum and H2O as precursors at 300 °C, and annealed at various temperatures in ambient N2 for 1 min. The Al2O3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750 °C to 768 °C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy (XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar.

Structure and properties of Al2O3 thin films deposited by ALD process

The comprehensive investigation results of the microstructure, mechanical properties and corrosion resistance of the Al2O3 thin films deposited on hot work tool steel substrate are presented in the paper. Aluminium oxide layers were prepared using atomic layer deposition (ALD) method in temperature 150, 225 and 300 °C.The uniform structure of the investigated coatings without any visible delamination was observed as a result of measurements performed with the use of scanning electron microscope. Combined SEM, AES and ToF-SIMS studies confirmed presumed chemical composition of the layers. Despite the very low thickness (∼200 nm) the layers demonstrated an excellent adhesion to the substrate, as well as a high hardness and corrosion resistance. The best mechanical properties and corrosion resistance exhibit the layers deposited at 300 °C.The excellent properties of the ALD thin films make them suitable for various engineering and industrial applications.

Optical, morphological and mechanical properties of an Al–Al2O3 nanocomposite thin film grown by thermionic vacuum arc

An Al–Al2O3 nanocomposite thin film was deposited onto a glass substrate in high vacuum condition using Al2O3 pellets as source material by means of the thermionic vacuum arc technique in just 50s. UV–visible spectrophotometer, optical reflectometer, spectroscopic ellipsometer, XRD, FESEM and AFM were employed to investigate the optical, structural morphological and mechanical properties of the produced film. The film exhibited a high transmittance (above 80%) in the 400–1000nm region. The dispersion of the refractive index was discussed in terms of the single oscillator model. The optical band gap value derived from the Wemple–DiDomenico dispersion relationship was 5.7eV. It was observed that the results of the optical investigations agreed well with Al2O3 thin films. XRD characterization showed that the film contained Al and Al2O3 phases. The FESEM analysis revealed that the film morphology had a dense characteristic. 2D and 3D AFM micrographs indicated a smooth surface with a low value of average roughness. When compared to the mechanical properties of Al2O3 thin films, it was observed that the hardness and Young's modulus reduced due to presence of ductile Al particles.

Resistive Switching Behavior in Amorphous Aluminum Oxide Film Grown by Chemical Vapor Deposition

The repeatable bipolar resistive switching phenomenon is observed in amorphous Al2O3 prepared by metal-organic chemical vapor deposition on ITO glass, with ITO as the bottom electrode and Ag as the top electrode. The crystal structure, morphology, composition and optical properties of Al2O3 thin films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy and ultraviolet-visible-infrared spectroscopy, respectively. The electronic character of Ag/Al2O3/ITO structure is tested by an Agilent B1500A. The device shows a typical bipolar resistive switching behavior under the dc voltage sweep mode at room temperature. The variation ratio between HRS and LRS is larger than nearly three orders of magnitude, which indicates the good potential of this structure in future resistive random access memory (ReRAM) applications. Based on the conductive filament model, the high electric field is considered the main reason for the resistive switching according to our measurements.

Comparison of the physical, chemical and electrical properties of ALD Al2O3 on c‐ and m‐ plane GaN

AbstractThis study compares the physical, chemical and electrical properties of Al2O3 thin films deposited on gallium polar c‐ and nonpolar m ‐plane GaN substrates by atomic layer deposition (ALD). Correlations were sought between the film's structure, composition, and electrical properties. The thickness of the Al2O3 films was 19.2 nm as determined from a Si witness sample by spectroscopic ellipsometry. The gate dielectric was slightly aluminum‐rich (Al:O=1:1.3) as measured from X‐ray photoelectron spectroscopy (XPS) depth profile, and the oxide‐semiconductor interface carbon concentration was lower on c ‐plane GaN. The oxide's surface morphology was similar on both substrates, but was smoothest on c ‐plane GaN as determined by atomic force microscopy (AFM). Circular capacitors (50‐300 μm diameter) with Ni/Au (20/100 nm) metal contacts on top of the oxide were created by standard photolithography and e‐beam evaporation methods to form metal‐oxide‐semiconductor capacitors (MOSCAPs). The alumina deposited on c ‐plane GaN showed less hysteresis (0.15 V) than on m ‐plane GaN (0.24 V) in capacitance‐voltage (CV) characteristics, consistent with its better quality of this dielectric as evidenced by negligible carbon contamination and smooth oxide surface. These results demonstrate the promising potential of ALD Al2O3 on c ‐plane GaN, but further optimization of ALD is required to realize the best properties of Al2O3 on m ‐plane GaN. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Comparison of electrical properties of aluminum oxide thin films on silicon and gallium arsenide substrates grown by atomic layer deposition

Electrical properties of Al2O3 thin films grown by atomic layer deposition on Si and GaAs substrates were characterized and compared by current–voltage and capacitance–voltage measurements. The interfacial oxide layers thicknesses, the flat band voltages and the doping levels in the semiconductor substrates were determined. The differences in dielectric constants and breakdown fields of Al2O3 films on different substrates are attributed to different energy band alignments and the existence of different oxide interfacial layers.

Influence of the Ion Beam Current on Microstructures and Optical Properties of Al2O3 Thin Films by Oxygen Ion Beam Assisted Pulse Reactive Magnetron Sputtering

Influence of the Ion Beam Current on Microstructures and Optical Properties of Al2O3 Thin Films by Oxygen Ion Beam Assisted Pulse Reactive Magnetron Sputtering

The Etching Properties of Al2O3 Thin Films in BCl3/Cl2/Ar Plasma

In this study, the etch mechanism of ALD deposited Al2O3 thin film was investigated in BCl3/Cl2/Ar plasma. The experiments were performed by comparing etch rates and selectivity of Al2O3 over hard mask materials (such as SiO2, and Si3N4) as function of the input plasma parameters such as gas mixing ratio, DC-bias voltage and RF power under fixed process pressure. The maximum etch rate was obtained at 115.75 nm/min under 5 mTorr, RF power 600 W, Cl2 10% was added to BCl3/Ar plasma, and the highest etch selectivity was 1.17 over Si3N4 under the 10 mTorr process pressure, −50 V DC-bias voltage. We used the X-ray photoelectron spectroscopy (XPS) to investigate the chemical reactions on the etched surface.

Working Pressure Dependence of Properties of Al2O3 Thin Films Prepared by Electron Beam Evaporation

The effects of working pressure on properties of Al2O3 thin films are investigated. Transmittance of the Al2O3 thin film is measured by a Lambda 900 spectrometer. Laser-induced damage threshold (LIDT) is measured by a Nd:YAG laser at 355nm with a pulse width of 7ns. Microdefects were observed under a Nomarski microscope. The samples are characterized by optical properties and defect, as well as LIDT under the 355nm Nd:YAG laser radiation. It is found that the working pressure has fundamental effect on the LIDT. It is the absorption rather than the microdefect that plays an important role on the LIDT of Al2O3 thin film.