Pulsed Reactive Magnetron Sputtering Research Articles

Analysis of pulsed direct current reactive magnetron sputtering on a silicon target

Reactive sputtering is a very useful technique, particularly, for producing inhomogeneous interference filters, where the refractive index changes smoothly during deposition. In such a context, precise control of deposition parameters is crucial for replicating the desired optical properties. This study employed a pulsed DC power source to investigate the influence of a duty cycle on target poisoning, sputtering plasma characteristics, electric signals, and optical and morphological properties of synthesized films. Reactive pulsed DC magnetron sputtering was characterized by analyzing the behavior of plasma emission via optical emission spectroscopy and voltage-current signals, while modulating parameters such as the oxygen content within the vacuum chamber. A set of thin films was coated on glass substrates under different system conditions. These films underwent characterization employing spectroscopic ellipsometry to ascertain their optical constants, atomic force microscopy for surface morphology analysis, and x-ray diffraction for the determination of crystalline structures. The results indicate that longer duty cycles required higher oxygen levels to poison the target. Additionally, a detailed analysis of electrical signals revealed nonsquare waveforms, whose characteristics were influenced by both the duty cycle and the oxygen content within the sputtering chamber, resulting in higher effective voltages during the on-time of the voltage pulse. Grown films via reactive pulsed DC magnetron sputtering were also compared to films grown via conventional DC magnetron sputtering at equivalent conditions of target poisoning.

Effect of solution‐processed cesium carbonate on Cu(In,Ga)Se2 thin‐film solar cells

AbstractHeavy alkali‐metal treatments have been the most recent breakthrough in improving the efficiency of Cu(In,Ga)Se2 (CIGS) solar cells. Alkali halides are generally evaporated onto the surface of the CIGS thin film by a vacuum process. Here, we report an alternative, low‐cost solution process for the surface treatment of CIGS thin films using cesium carbonate (CsCO3) as a new route to incorporate cesium (Cs) for improving solar cell performance. CIGS thin films were fabricated using pulsed hybrid reactive magnetron sputtering and the surface treatment was performed by spin‐coating CsCO3 solution on the surface of CIGS at room temperature, followed by vacuum annealing at 400°C. The surface chemistry of the CIGS thin film changed after the treatment and the efficiency of respective solar cells improved by more than 30%, mostly driven by an enhancement in open‐circuit voltage. X‐ray photoelectron spectroscopy revealed the depletion of copper and the presence of Cs on the surface of the CIGS thin film. Ultraviolet photoelectron spectroscopy showed the lowering of the valence band maximum by around 0.25 eV after the treatment, which plays a positive role in reducing interfacial recombination. High‐resolution transmission electron microscopy indicates the presence of Cs and depletion of Cu at the grain boundaries of the CIGS thin film. These findings open a low‐cost route for improving the performance of CIGS solar cells by surface modification using a solution process.

Peculiar photoelectrochemical activity of zinc oxide and tin dioxide

Zinc oxide thin films made by pulsed reactive magnetron sputtering combined with RF ECWR plasma on FTO or ITO substrates exhibit high photoelectrochemical activity for water splitting under UV light, but are unstable against photocorrosion. It can be suppressed by a protective layer of SnO2 made by atomic layer deposition. The SnO2 layer is quasi-amorphous in the as-received state, but the thermal treatment causes partial crystallization to cassiterite, without significant change of the optical band gap. Ferrocene in acetonitrile electrolyte solution is a useful redox probe for the blocking-quality tests of thin films of n-semiconductors. Both ZnO and SnO2 are sensitive to irreversible electrochemical doping at potentials negative to the flatband potential. The flipping of electrochemical work functions of the Zn-terminated (0001) and O-terminated (000–1) faces of ZnO (wurtzite) takes place in acetonitrile vs. aqueous electrolyte solutions. The potentials for photocurrent onset are near the flatband potentials in an aqueous electrolyte solution for both ZnO and SnO2.

Ultrafast UV Luminescence of ZnO Films: Sub‐30 ps Decay Time with Suppressed Visible Component

AbstractUltrafast sub‐100 picosecond luminescence is vital in many applications involving ultrafast events and time‐of‐flight systems. Materials exhibiting fast luminescence, such as barium fluoride (BaF2) and zinc oxide (ZnO), also suffer from an intrinsically slow nanosecond (ns) to microsecond (µs) luminescence. Here, 2.2 micrometer (µm)‐ to 5.7 µm‐thick undoped ZnO films on soda‐lime glass (SLG) substrates without a buffer layer by a hybrid pulsed reactive magnetron sputtering operating in the medium‐frequency range (MF magnetron) assisted by an electron cyclotron wave resonance (ECWR) plasma is deposited. The undoped ZnO films exhibited superior optical properties characterized by intense ultraviolet (UV) luminescence, unprecedented ultrafast decay times, and for the case of MF+ECWR‐deposited films, suppressed defect‐related visible luminescence. The 2.2 µm‐thick MF‐deposited film exhibited the fastest 9‐ps decay time at room temperature. The impressive properties of the films are attributed to the use of advanced deposition technology with properly tuned plasma parameters, especially a high degree of dissociation of molecular oxygen together with an increased proportion of activated zinc particles, leading to a higher deposition rate, better crystallinity, fewer defects, and a lower proportion of oxygen vacancies. These films will pave the way toward the development of time‐of‐flight detectors, high‐resolution nuclear imaging cameras, and high‐rate ultrafast timing devices.

Photocatalytic degradation of methylene blue by anatase TiO2 coating

AbstractPhotocatalytic coatings have the potential to contribute to the purification of water via an advanced oxidation process (AOP). A commonly used method for analyzing the mechanism of the photocatalytic performance of a given reactor type is to document the degradation behavior in a solution containing methylene blue. However, since methylene blue is rather unstable, the degradation results should be viewed critically. In this work, the degradation behavior of a test solution with methylene blue on quartz glass surfaces coated with photocatalytic titanium dioxide (TiO2) of the anatase modification was investigated through a variety of different light sources. The coating was deposited by physical vapor deposition (PVD) with the reactive pulsed DC magnetron sputtering ion plating (MSIP) method described in the study by Desch and Lake, while the quartz glasses were coated with a 100 nm thick TiO2 coating on the outside. The same glasses were used for all experiments with TiO2. In the determination of the degradation rate, additional experiments were performed using pure quartz glass without any coating, which made it possible to examine the influence of different light sources on the degradation rate of methylene blue in general. Three different light sources, namely UV‐A, UV‐C, and simple fluorescent lamps were used in this study. The concentration of methylene blue was recorded by photo spectrometer in 10‐min increments throughout the experiment and the experiments were performed for 24 h in all cases. Our data indicates that the methylene blue test is a poor method because the degradation rate is not clearly differentiable due to the low stability of the test substance. Without including reference testing in the absence of a catalyst, data may be subject to misinterpretation.

High-quality dense ZnO thin films: work function and photo/electrochemical properties

Compact ZnO (wurtzite) thin films are prepared on four different substrates by (i) spray pyrolysis or (ii) pulsed reactive magnetron sputtering combined with a radio frequency electron cyclotron wave resonance plasma. Films are characterized by AFM, XRD, Kelvin probe, cyclic voltammetry, electrochemical impedance spectroscopy, and UV photoelectrochemistry. Film morphologies, defect concentrations, crystallite size, and orientation provided specific fingerprints for the electronic structure of ZnO close to the conduction band minimum. Fabricated films are referenced, if relevant, to a model system based on a wurtzite single crystal with either Zn-face or O-face termination. Kelvin probe measurements of the ZnO/air interface distinguished effects of annealing and UV excitation, which are attributed to removal of oxygen vacancies close to the surface. In turn, the work function, at the electrochemical interface, specifically addressed the growth protocol of the ZnO electrodes but not the effects of crystallinity and annealing. Finally, high photocurrents of water oxidation are observed exclusively on virgin films. This effect is then discussed in terms of photocorrosion, and work function changes due to UV light.Graphical

The peculiar alterations of the optical and mechanical characteristics of the quartz glass plates with a reinforcing coating under the collision with a hyper-velocity flux of microparticles

This article experimentally investigates the collision of a high-velocity (5–8 km/s) flux of iron microparticles with quartz-glass plates and the effect of such collisions on the optical and mechanical properties of the plates protected by In–Sn–O-based coatings. Such coatings are used to protect the optical systems of spacecraft from the impacts of micrometeoroids and fragments of space debris. To ensure the safety of the optical systems of manned vehicles is crucial for the future of space exploration. This requires special protective materials that can resist external factors.In the present article, thin and thick protective coatings were formed by pulsed reactive magnetron sputtering of a tin-doped (7.5 wt%) indium target.The collision of the particles with the target's surface forms craters. The surface density of the craters ρ depends on the thickness of the coating and its physical and mechanical properties. The increased thickness up to ∼6 μm decreases the crater density 3.3 times, which is due to increased elastic modulus and crack resistance and decreased microhardness of the coated glass. For the quartz-glass specimens without the protective coating, the bombardment by the high-speed flux of iron microparticles decreases the visible-region light transmittance by ~ 6 %. The bombardment of quartz-glass specimens with thin protective In–Sn–O coating reduces the light transmittance to a lesser extent, while there is no reduction in the case of a thick coating. The transmittance linearly depends on the crater density and is inversely proportional to the total area occupied by the craters on the surface under study. This effect is due to the partial shading of the glass working area when rays of light pass through the zones occupied by the craters.

Aluminum tantalum oxide thin films deposited at low temperature by pulsed direct current reactive magnetron sputtering for dielectric applications

This research aims at studying aluminum tantalum oxide thin films (AlxTayOz) deposited at low temperature for dielectric applications. These ternary oxide layers are synthesized at 180 °C by physical vapor deposition (PVD), specifically the mid-frequency pulsed direct current reactive magnetron sputtering. The deposition process uses targets made of a mixture of aluminum and tantalum in various proportions. Four target compositions are studied containing 95 at.%, 90 at.%, 80 at.%, and 70 at.% of aluminum, corresponding to 5 at.%, 10 at.%, 20 at.%, and 30 at.% of tantalum, respectively. The ternary oxide thin films of AlxTayOz are compared to aluminum oxide (AlxOz) and tantalum oxide (TayOz) layers produced in the same experimental conditions. The AlxTayOz thin films are dense, uniform, and amorphous regardless of the experimental conditions used in this study. Their chemical composition changes as a function of the target composition. The oxygen flow used during deposition also affects the chemical composition of the oxide layers and the deposition rate. The oxide thin films with tantalum are deposited at higher deposition rates and contain more oxygen. Tantalum also promotes the amorphization of the oxide layers. The highest dielectric strength is measured for the thin film containing a low amount of tantalum combined with a high amount of oxygen.

Antimony Selenide Solar Cells Fabricated by Hybrid Reactive Magnetron Sputtering.

The fabrication of Sb2Se3 thin-film solar cells deposited by a pulsed hybrid reactive magnetron sputtering (PHRMS) was proposed and examined for different growth conditions. The influence of growth temperature and Se pulse period were studied in terms of morphology, crystal structure, and composition. The Sb2Se3 growth showed to be dependent on the growth temperature, with a larger crystal size for growth at 270 °C. By controlling the Se pulse period, the crystal structure and crystal size could be modified as a function of the supplied Se amount. The solar cell performance for Sb2Se3 absorbers deposited at various temperatures, Se pulse periods and thicknesses were assessed through current-voltage characteristics. A power conversion efficiency (PCE) of 3.7% was achieved for a Sb2Se3 solar cell with 900 nm thickness, Sb2Se3 deposited at 270 °C and Se pulses with 0.1 s duration and period of 0.5 s. Finally, annealing the complete solar cell at 100 °C led to a further improvement of the Voc, leading to a PCE of 3.8%, slightly higher than the best reported Sb2Se3 solar cell prepared by sputtering without post-selenization.

Influence of Si(111) substrate off-cut on AlN film crystallinity grown by magnetron sputter epitaxy

The increasing demand for More than Moore devices requires epitaxy technology to keep up with the discovery and deployment of new semiconductors. An emerging technology for cost-effective, device-quality growth is magnetron sputter epitaxy, though detailed studies on the process itself remain scarce. Here, we report an extensive study on the correlation between the substrate off-cut and film quality in AlN-on-Si heteroepitaxy. Controlled reactive pulsed magnetron sputtering is used to grow epitaxial AlN(0001) films on in situ Ar plasma etched off-cut Si(111) substrates with growth rates above 1.5 nm/s. Substrate off-cut angles in the range of 0.02°–0.30° are investigated and precisely determined by high-resolution x-ray diffraction. Structural examination of the AlN films is carried out by transmission electron microscopy and high-resolution x-ray diffraction. The AlN/Si interface is well-defined and two types of AlN domains with epitaxial relationships are observed. The formation of secondary rotation domains deteriorates the crystal quality substantially. Substrates with small off-cuts, ideally no off-cut substrates, appear to be crucial for suppressing the formation of secondary domains and further result in a better overall crystal quality of AlN films. We discuss this effect in relation to the AlN/Si interface, the substrate pre-treatment, and nucleation.

STRUCTURAL AND MECHANICAL PROPERTIES OF TiAlN AND TiAlN GRADIENT FILMS DEPOSITED BY REACTIVE PULSED DC MAGNETRON SPUTTERING

TiAlN and TiAlN gradient films were deposited on Si substrates by reactive pulsed DC magnetron sputtering. The crystal structure and morphology of TiAlN films were characterized via X-ray diffraction (XRD), and field emission scanning electron microscope (FE-SEM), respectively. Moreover, elemental composition, hardness, and adhesion of TiAlN films were analyzed by energy-dispersive X-ray spectroscopy (EDS), nanoindentation test, and scratch test, respectively. The TiAlN films and TiAlN gradient films showed columnar structure and cubic crystal structure with different orientation planes. The elemental mapping of TiAlN gradient films clearly demonstrated the TiAlN gradient films. TiAlN gradient films have slightly lower hardness compared to TiAlN films while adhesion of the films increases.

Formation of pure anatase TiO2 using the reactive pulsed dc magnetron sputtering method for controlling the target poisoning state

AbstractThe use of pulsed dc‐sputtering sources for reactive magnetron sputtering with oxygen offers a possibility to suppress the negative effects of target poisoning (such as arcing). This results in a wide process range for the selection of a desired operating point. The control of target poisoning plays a major role in maintaining constant coating properties and affects the stoichiometry of the reactive coating, as well as the coating rate and the economic impact of the coating process. In a hysteresis, the target poisoning during the reactive sputtering of titanium under oxygen addition proceeds nonlinearly. Without the use of a suitable target poisoning control technique, the sputtering process can abruptly change to an unstable state. As a result, variations of stoichiometry can occur during the deposition process. A proven method for maintaining a stable reactive sputtering process is the control of oxygen flow with the input variable target voltage. By determining the typical oxygen hysteresis at constant target power and constant argon flow, an operating point for the control loop is derived. The desired target voltage then serves as the input variable for the control loop of the target poisoning. The controlling technique for target poisoning is a basic requirement for the production of the photolytic active anatase phase of titanium dioxide (TiO2) using reactive magnetron sputtering. The photocatalytic equipment of surfaces with a titanium dioxide coating in the anatase phase can be realized with the reactive pulsed dc magnetron sputter ion plating process (DC‐MSIP). The pulsed DC‐MSIP process facilitates coating a variety of surfaces at temperatures below 200°C in an environmentally friendly manner.

Reactive pulsed direct current magnetron sputtering deposition of semiconducting yttrium oxide thin film in ultralow oxygen atmosphere: A spectroscopic and structural investigation of growth dynamics

An experimental investigation was conducted to explore spectroscopic and structural characterization of semiconducting yttrium oxide thin film deposited at 623 K (±5K) utilizing reactive pulsed direct current magnetron sputtering. Based on the results obtained from both x-ray diffraction and transmission electron microscope measurements, yttrium monoxide is very likely formed in the transition region between β-Y2O3 and α-Y2O3, and accompanied by the crystalline Y2O3. Resulting from either the low energy separation between 4d and 5s orbitals and/or different spin states of the corresponding orbitals’ sublevels, the stability of monoxide is most presumably self-limited by the size of the crystal in thermodynamic terms. This behavior develops a distortion in the structure of the crystal compared to the metal oxide cubic structure and it also effectuates the arrangement in nanocrystalline/amorphous phase. In addition to this, spectroscopic ellipsometry denotes that the semiconducting yttrium oxide has the dominant, mostly amorphous, formation character over crystalline Y2O3. Our purpose, by means of the current findings, is to advance the understanding of formation kinetics/conditions of yttrium with an unusual valency (2+).

Properties of CrN/TiN Multilayer Films With Nanoscale Layer Thickness

Chromium nitride (CrN)/titanium nitride (TiN) multilayer films at nanoscale layer thickness were prepared using a combination of reactive high-power impulse magnetron sputtering (HiPIMS) and pulsed magnetron sputtering. Each layer thickness was adjusted by controlling each deposition time. The hardness and Young’s modulus of the multilayer films, which were measured using nanoindentation technique, did not vary significantly with layer thickness. The film hardness ranged between 22 and 24.5 GPa, and the Young modulus was between 300 and 330 GPa. On the contrary, the compressive stress of the multilayer films gradually decreased with the increase in the TiN layer thickness. The friction coefficient of the multilayer film did not depend on the CrN layer thickness, but it reduced drastically to 0.2–0.3 with the increase in the TiN layer thickness in the range of the TiN layer thickness less than about 2 nm.

Properties of Multilayered CrN/VN Films Prepared Using a Hybrid System of High-Power Impulse Magnetron Sputtering and Pulsed Magnetron Sputtering

Nanomultilayered chromium nitride (CrN)/ vanadium nitride (VN) films with different layer thicknesses were synthesized on Si substrates using a hybrid system of reactive high-power impulse magnetron sputtering (HiPIMS) and pulsed magnetron sputtering. The microstructure and properties of the nanomultilayered CrN/VN films were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), the nanoindentation method, and the friction wear test. The XRD results showed that the multilayered films exhibited nanocrystallite structure with a (200) preferred orientation, and the estimated crystallite size was not highly dependent on the CrN and VN layer thicknesses. Inserting the VN layers decreased the compressive stress slightly compared to that of the CrN monolayer film and increased the hardness by 4-5 GPa compared to that of the CrN and VN monolayer films. The friction coefficient of the multilayered films strongly depended on the CrN layer thickness rather than on the VN layer thickness.

SiO2: A Novel Electrolyte for High-Performance All-Solid-State Electrochromic Devices

For the practical application of electrochromic devices (ECDs), the development and preparation of high-performance electrolyte materials is one of the urgent problems to be solved. In this work, an all-solid-state ECD with the integrated structure of glass/ITO/WO3/Li/SiO2/NiO/ITO has been prepared by the magnetron sputtering method. The amorphous SiO2 film prepared by pulsed direct current reactive magnetron sputtering was used as the electrolyte layer in the ECD for the first time and shows promising potential due to its ultrahigh transparency, good intrinsic electronic insulation, and loose structure for fast ion conduction. The ECD exhibits low leakage current density (8.5 μA cm–2 for bleaching and 43.4 μA cm–2 for coloring), high optical modulation (ΔT = 71.9% at 707 nm), fast response speed (1.1 s for the bleaching process and 8.5 s for the coloring process), excellent cycle stability, and high coloration efficiency (126.4 cm2 C–1). This work not only indicates that SiO2 as a dielectric material can be used as the electrolyte layer in all-solid-state ECDs but also provides new avenues in the selection of electrolyte materials for the preparation of high-performance ECDs.

Deposition of Ga2O3 thin films by liquid metal target sputtering

This paper reports on the deposition of amorphous and crystalline thin films of Ga2O3 by reactive pulsed direct current magnetron sputtering from a liquid gallium target onto fused (f-) quartz and c plane (c-) sapphire substrates, where the temperature of the substrate is varied from room temperature (RT) to 800 °C. The deposition rate (up to 37 nm/min at RT on f-quartz and 5 nm/min at 800 °C on c-sapphire) is two to five times higher than the data given in the literature for radio frequency sputtering. Deposited onto unheated substrates, the films are X-ray amorphous. Well-defined X-ray diffraction peaks of β-Ga2O3 start to appear at a substrate temperature of 500 °C. Films grown on c-sapphire at temperatures above 600 °C are epitaxial. However, the high rocking curve full width at half maximum values of ≈2.4–2.5° are indicative of the presence of defects. A dense and void-free microstructure is observed in electron microscopy images. Composition analysis show stoichiometry close to Ga2O3 and no traces of impurities. The optical properties of low absorptance (<1%) in the visible range and an optical band gap of approximately 5 eV are consistent with the data in the literature for Ga2O3 films produced by other deposition methods.

Investigation of the Microstructure, Optical, Electrical and Nanomechanical Properties of ZnOx Thin Films Deposited by Magnetron Sputtering.

The paper presents the results of an investigation of the influence of technological parameters on the microstructure, optical, electrical and nanomechanical properties of zinc oxide coatings prepared using the pulsed reactive magnetron sputtering method. Three sets of ZnOx thin films were deposited in metallic, shallow dielectric and deep dielectric sputtering modes. Structural investigations showed that thin films deposited in the metallic mode were nanocrystalline with mixed hexagonal phases of metallic zinc and zinc oxide with crystallite size of 9.1 and 6.0 nm, respectively. On the contrary, the coatings deposited in both dielectric modes had a nanocrystalline ZnO structure with an average crystallite size smaller than 10 nm. Moreover, coatings deposited in the dielectric modes had an average transmission of 84% in the visible wavelength range, while thin films deposited in the metallic mode were opaque. Measurements of electrical properties revealed that the resistivity of as-deposited thin films was in the range of 10−4 Ωcm to 108 Ωcm. Coatings deposited in the metallic mode had the lowest hardness of 2.2 GPa and the worst scratch resistance among all sputtered coatings, whereas the best mechanical properties were obtained for the film sputtered in the deep dielectric mode. The obtained hardness of 11.5 GPa is one of the highest reported to date in the literature for undoped ZnO.

Influence of structural properties on the ferroelectric behavior of hexagonal AlScN

The direct impact of structural quality on the ferroelectric properties of hexagonal Al1–xScxN with an Sc-content of x = 0.3 was investigated using dynamic hysteresis measurements, high-resolution x-ray diffraction (HRXRD), and atomic force microscopy. The films investigated were deposited on p-doped (001)-Si substrates by reactive pulsed DC magnetron sputtering under different gas mixtures to vary the structural quality and surface morphology between samples. Misoriented grains were identified as ferroelectrically inactive, as these grains resulted in an underestimation and distortion of the ferroelectric quantities. In fact, a high amount of misoriented volume was found to have a significant effect on the coercive electric field, as this is mainly determined by the crystal strain in the ferroelectric [0001]-oriented regions, independent of its origin. Furthermore, it was concluded that the crystal quality does not have a pronounced effect on the coercive field strength. Conversely, the polarization in the film is mainly determined by the crystal quality, as a difference of 1° in the HRXRD FWHM of the ω-scan resulted in a 60% loss of polarization. The amount of polarization was influenced to a lesser extent by the misoriented grains since the ferroelectric volume of the layers was only slightly overestimated. This reveals that optimizing reproducible and transferable properties, such as crystal quality and surface morphology, is more reasonable, as the film with the lowest misoriented volume and the highest degree of c-axis orientation showed the highest polarization.

Review of Cobalt Oxide (CoO) thin films prepared by various techniques

It is reviewed that for fulfilling the demands of portable devices like phones, watches, low-cost energy storage system etc, cobalt oxides and their composite play a very promising role. Recently, nanotechnology has great application toward gay to-day life. This paper reviews the various deposition techniques for cobalt thin films such as chemical spray pyrolysis, atomic layer deposition, metal organic chemical vapor deposition, plasma atomic layer deposition, facile spray pyrolysis technique, spin coating techniques and reactive pulsed magnetron sputtering. Cobalt oxides are semiconductors and this material is very useful in electronic, optical and catalytic applications. In this review paper, various methods for formation of thin films were discussed. Number of properties such as structural, electrochemical and morphological of these prepared films was studied. It was observed that annealing temperature has great intense effect on thickness of films. This paper also discussed the characterization technique carried by researcher such as UV-spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy and high-resolution scanning electron microscopy (HRSEM). It was concluded that cobalt metallic films have great contribution toward new technological applications.