Pulsed DC 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.

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.

ScxAl1-xN piezoelectric film grown at room temperature

In order to overcome the shortcomings of AlN piezoelectric thin films such as low piezoelectric coefficient and low electromechanical coupling coefficientrealize, ScxAl1−xN thin films with CMOS process compatibility were prepared by pulsed DC reactive magnetron sputtering. High performance ScxAl1−xN piezoelectric thin films were prepared at room temperature by optimizing process parameters including power, gas flow ratio, substrate temperature, seed layers and so on. The phase separation phenomenon was investigated through XRD, TEM, and XPS. We found that the phase separation is related to the appearance of rocksalt ScN and led to the degeneration of film properties. The existence of ScN phase is a key factor affecting the performance of ScxAl1−xN. The results show that the piezoelectric constant d33 of ScAlN film achieved 27.5 pC/N and the full width at half maximum (FWHM) of the rocking curve is 1.9° in room temperature when the content of Sc reaches 35%.

Effect of copper content on the microstructure, morphology, and optical properties of ZrSiN coatings deposited using pulsed-direct current reactive magnetron sputtering

The incorporation of an element such as silicon, silver, or copper, etc. into transition metal nitrides has allowed the production of multifunctional materials. These materials exhibit distinct properties contributed by each phase, thereby enhancing the industrial application of metal nitrides. This study focuses on the deposition of ZrSiNCu coatings using pulsed-DC reactive magnetron sputtering, aiming to investigate the influence of copper on the chemical composition, morphology, microstructure, and optical behavior of the coatings. The results showed that the deposited coatings were nanostructured, with a mixture of ZrN, ZrO2, and nanocrystalline Cu, which had a profound impact on the Cu segregation on the surface and columnar boundary due to the fact that copper is relatively inert with respect to a ceramic matrix. Furthermore, an increase in the Cu content led to the presence of large aggregates on the surface and lower bandgaps.

Growth and optical properties of NiO thin films deposited by pulsed dc reactive magnetron sputtering

NiO thin films with varied oxygen contents are grown on Si(100) and c-Al2O3 at a substrate temperature of 300 °C using pulsed dc reactive magnetron sputtering. We characterize the structure and optical properties of NiO changes as functions of the oxygen content. NiO with the cubic structure, single phase, and predominant orientation along (111) is found on both substrates. X-ray diffraction and pole figure analysis further show that NiO on the Si(100) substrate exhibits fiber-textured growth, while twin domain epitaxy was achieved on c-Al2O3, with NiO(111)∥Al2O3(0001) and NiO[11¯0]∥Al2O3[101¯0] or NiO[1¯10]∥Al2O3[21¯1¯0] epitaxial relationship. The oxygen content in NiO films did not have a significant effect on the refractive index, extinction coefficient, and absorption coefficient. This suggests that the optical properties of NiO films remained unaffected by changes in the oxygen content.

Chemical Composition, Structure, and Physical Properties of AlN Films Produced via Pulsed DC Reactive Magnetron Sputtering

The chemical composition, structure, and physical properties of aluminum nitride (AlN) films obtained using pulsed DC reactive magnetron sputtering in asymmetric bipolar mode have been studied. X-ray diffraction and electron diffraction confirmed the composition of c–axis textured hexagonal AlN films required for piezoelectric applications. The surface of the films obtained is quite smooth; the arithmetic average roughness does not exceed 2 nm. Transmission electron microscopy has shown the presence of a transition layer at the film–substrate interface. Transmission electron microscopy and X-ray photoelectron spectroscopy depth profile analysis have shown that the films have an oxidized surface layer which has an influence on the optical model of the films derived from ellipsometric data. However, it does not significantly influence the films’ piezoresponse. Piezoelectric force microscopy indicated a piezoelectric effect in the films that is uniform over their surface.

Influence of Ag Doping on the Microstructural, Optical, and Electrical Properties of ZrSiN Coatings Deposited through Pulsed-DC Reactive Magnetron Sputtering

The functional properties of the transition-metal nitride coatings can be modified by adding noble metals such as silver. The incorporation of these elements has been demonstrated to be a good strategy for improving the electrical, optical, and mechanical responses of transition-metal nitride coatings. In this investigation, we report the production of Ag-ZrSiN coatings with varying silver atomic contents, deposited using pulsed-DC reactive magnetron sputtering. The effect of the incorporation of silver on the microstructure, the morphology, and the optical and electrical properties was investigated. The results revealed a nanocomposite structure of Ag-ZrSiN with nc-Ag/nc-ZrN embedded in an amorphous SiNx phase. The electrical resistivity decreased upon the incorporation of Ag from 77.99 Ω·cm to 0.71 Ω·cm for 0.0 and 12.0 at.% of Ag, respectively. A similar decreasing trend was observed in the transmittance spectra of the coatings as the silver content increased. For the Ag-ZrSiN coating, the transmittance values decreased within the wavelength range of 2500–630 nm and then remained constant down to 300 nm, at about 13.7%. Upon further increase of the silver concentration up to 12 at.%, the transmittance values continued to decrease between 2500 and 630 nm, reaching approximately zero at 630 nm, indicating that the coating becomes opaque within that spectral range.

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.

High performance inorganic all-solid-state electrochromic devices based on Si3N4 ion conducting layer

In electrochromic devices (ECDs), ion conducting layer has the vital function of conducting ions and blocking electrons. However, the limited electron blocking ability and preparation technology of conventional ion conducting materials hinder the commercial application of all-solid-state ECDs. In this work, a novel ion conducting material Si 3 N 4 film was deposited by pulsed direct current (p-DC) reactive magnetron sputtering with a Si target, and shows promising potential due to its ultrahigh transparency, anti-reflection effect and remarkable electron blocking ability. An ECD with the structure of glass/ITO/WO 3 /Li/Si 3 N 4 /NiO/ITO has been fabricated by magnetron sputtering, in which Si 3 N 4 film was used as ion conducting layer for the first time. The ECD presents much less leakage current density (<35 μA cm −2 ), large optical transmittance modulation (72.3% at 625 nm), fast response (1.3 s for bleaching and 13.1 s for coloring), high coloration efficiency (94.46 cm 2 C −1 ) and excellent cycle stability (91.4% retention of the maximum optical modulation after 10,000 cycles). This work not only demonstrates the great prospect of Si 3 N 4 film as an ion conducting layer in ECDs, but also provides a new idea in the selection of ion conducting materials for developing high-performance inorganic all-solid-state ECDs. • The Si 3 N 4 film is used as an ion conducting layer in ECDs for the first time. • Si 3 N 4 film was prepared by pulsed DC reactive magnetron sputtering. • The Si 3 N 4 film exhibits ultrahigh transparency and anti-reflection effect. • The Si 3 N 4 -based all-solid-state ECD shows large optical modulation 72.3% at 625 nm. • The ECD displays superior cycle stability over 10,000 cycles.

Widely tunable refractive index silicon nitride films deposited by ion-assisted pulsed DC reactive magnetron sputtering

Silicon nitride films were deposited by ion-assisted pulsed DC reactive magnetron sputtering, where the regulation of power on the refractive index was emphasized. The power of the ion source and target was found to affect the refractive index. Refractive indices ranged from 2.13 to 2.63 (@632 nm) at ion source powers of 150, 300, 450, and 600 W, and from 2.45 to 3.02 (@632 nm) at target powers of 800, 1000, and 1200 W. The refractive index range was further extended to 1.89–3.02 (@632 nm) by co-adjustment, and extinction coefficients remained low in the visible to near-infrared band. The composition of deposited amorphous silicon nitride films varies with power, covering nitride-rich to silicon-rich. With no obvious defects on the surface and cross-section, the roughness slightly decreased with power, and the minimum roughness recorded was only 0.12 nm. In this work, a method for depositing silicon nitride films with a widely tunable refractive index range was proposed, which is promising for the application of optical thin films and waveguides.

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.

Optical properties of oxygen-containing yttrium hydride thin films during and after the deposition

The synthesis of the photochromic YHO films is based on the oxidation of deposited yttrium hydride in ambient conditions. The actual state of the films during the deposition process, which is influenced by the deposition pressure and the oxidation caused by the residual gases, is not completely known. We report on the YHxOy thin films deposited by reactive pulsed-DC magnetron sputtering. Since the visible light transmittance is closely related to the phase and chemical composition of the films, in-situ transmittance measurements during and after deposition are performed. Ex-situ spectroscopic ellipsometry is used to determine the optical constants of YHxOy throughout the film thickness. In order to obtain metallic YH2-x films, the densest possible structure with a high deposition rate is required, otherwise the films could already be partially transparent during the deposition. The transmittance is higher if deposition pressure is increased. This is because of the oxidation promoted by more porous growth of the microstructure that is observed at the surface and cross-section images of the films. The films exhibit a refractive index gradient perpendicular to the substrate surface, which is related to the porosity and variation of the chemical composition.

Fabrication of spectrally selective tandem stack of HfZrC/HfZrCN/HfZrON/HfZrO by reactive magnetron sputtering for CSP applications

A novel HfZrC/HfZrCN/HfZrON/HfZrO based solar absorber tandem stack was successfully deposited on silicon and stainless steel (SS) substrates by pulsed DC reactive magnetron sputtering using an alloy target of HfZr. The optimized tandem stack was fabricated by varying the deposition parameters like reactive gas flow rates (C2H2, N2, and O2), sputtering power, and deposition time. X-ray diffraction and X-ray photoelectron spectroscopic methods were used to determine the structural and chemical compositions present in the optimized tandem coatings. In the tandem stack, HfZrC, HfZrCN and HfZrON/HfZrO layers act as a main absorber layer, a semi-absorber layer and double layer anti-reflection in the coating structure. The high spectral selectivity was achieved by optimizing the individual layers in the tandem stack, which exhibits 0.947 of optical absorptance in the solar region and 0.14 of low emissivity in the IR region. The optimized tandem stack is stable up to a temperature of 500 °C in a vacuum environment. The present investigation demonstrates that the developed HfZrC/HfZrCN/HfZrON/HfZrO tandem stack exhibited high solar spectral selectivity and good thermal stability, thus it can be used in high-temperature solar concentrated power applications.

Photocatalytic degradation of contaminants of emerging concern using a low-cost and efficient black bismuth titanate-based water treatment reactor

Photocatalysis is recognized as a sustainable technology for wastewater treatment, but it is limited by its scalability and efficiency. Here, we report the fabrication of a bespoke photocatalytic reactor, made from readily available consumer market components. The reactor was loaded with glass rods coated with a bismuth titanate photocatalyst deposited by reactive pulsed DC magnetron sputtering. Bismuth titanate is a remarkable material, which has shown the property of increasing its photocatalytic capabilities over repeated usage due to photoinduced oxygen vacancies, forming oxygen-vacancy rich “black” bismuth titanate. The reactor was tested with different rod configurations and photocatalytic material was cycled over 25 times, equivalent to 125 h of consecutive use, against methylene blue dye under UV light. Orange II dye degradation tests carried out in the presence of scavengers revealed that photocatalytic reactions were driven by superoxide (O2∙−) and holes (h+), when using pristine bismuth titanate and by superoxide (O2∙−), electrons (e−) and holes (h+), when using “black” bismuth titanate. Finally, the reactor was used to successfully degrade levofloxacin, a typical antibiotic, which was verified by UV–Vis (ultraviolet-visible) spectroscopy and inhibition zone tests in the presence of three different pathogens (E. coli, S. aureus and A. baumannii).

The effect of deposition parameters on microstructure and electrochemical performance of reactively sputtered iridium oxide coatings

Reactively sputtered iridium oxide (IrO2) thin films are being used as electrode coatings in neurostimulation devices due to their excellent charge exchange characteristics, low impedance and biocompatibility. This paper reports the observation of an unusual microstructure in IrO2 films and their dependence on deposition temperature, oxygen partial pressure in the sputtering gas mixture, substrate material and coating thickness. The IrO2 films were synthesized using pulsed-DC reactive magnetron sputtering at a sputtering pressure of 10 mTorr on various technologically relevant substrates. The Ar and O2 mixture ranged between 12% and 35% O2 partial pressure. The deposition temperatures were 25 °C, 200 °C and 400 °C. The IrO2 films were characterized by surface analysis methods and cyclic voltammetry in phosphate-buffered saline solution. Microstructure of the films was influenced by the deposition conditions with platelets notably forming on the surface when synthesized under some deposition conditions. The platelets were present when the (011) orientation of IrO2 was found in the x-ray diffraction spectra. Electrochemical performance measurements of the films demonstrated improved charge storage capacity up to 60 mC/cm2 using deposition conditions that resulted in the formation of the platelets.

Electrochemical enhancement of reactively sputtered rhodium, ruthenium, and iridium oxide thin films for neural modulation, sensing, and recording applications

Implantable neural interfacing devices are able to diagnose, monitor, and treat many conditions through modulating and recording electrical signals to and from neural tissue. The efficacy of treatment can be limited by a lack of specificity in targeting of neural tissue. To improve specificity and functionality, the electrodes and microelectrode arrays in these devices must be further miniaturized and must possess exceptional charge exchange characteristics. In this study, rhodium oxide (RhxOy), ruthenium oxide (RuOx), and iridium oxide (IrOx) thin films were synthesized using pulsed-DC reactive magnetron sputtering. The effect of sputtering chamber working pressure (WP) on the morphology, crystal structure, chemical composition, and electrochemical properties of the subsequent metal oxide thin films were investigated. The cathodic charge storage capacity (CSCc) and impedance of films were measured via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Results show that CSCc increases, and the overall impedance decreases with increasing WP in all oxide systems. The enhanced electrochemical performance of these films has been attributed in large part to the morphological changes that occur with increasing WP resulting in an apparent increase in the porosity. This study reviews the electrochemical properties of IrOx, and also demonstrates the viability of RhxOy and RuOx as possible electrode coatings for neural interfacing applications.

Nitrogen effects on structure, mechanical and thermal fracture properties of CrN films

In this research, reactive pulsed dc magnetron sputtering with different Ar/N2 gas flow ratios was used to deposit CrN films with three growth structures on Si substrates. The phase structure, morphology, mechanical properties, thermal fracture properties, and oxidation behavior of films were studied. The surface roughness, residual stress, preferred orientation, and hardness were affected by the gas flow ratio. The film with (200) preferred orientation and zone II structure performed the best. The surface roughness increased to 6 nm with time when the films fractured at 500 °C. The Cr interlayer oxidation caused by oxygen diffusion through grain boundaries and fracture accelerated degradation of CrN films at higher temperatures. A dense microstructure is favorable for preventing coating oxidation.

Investigation of deposition parameters on the structural properties and hardness of TiAlN films deposited via reactive pulsed DC magnetron sputteringInvestigation of deposition parameters on structural properties and hardness of TiAlN films deposited by reactive pulsed DC magnetron sputtering

In this work, titanium aluminum nitride (TiAlN) films were deposited on a silicon substrate via reactive pulsed DC magnetron sputtering. The effect of deposition parameters such as nitrogen gas flow rate, substrate temperature, and bias voltage on the structural and mechanical properties of TiAlN films was investigated. The crystal structure, morphology, and hardness of TiAlN films were characterized via X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM, and nanoindentation. An improved crystallinity of TiAlN films was obtained by varying the substrate temperature and bias voltage. The morphology of the TiAlN film exhibited a columnar structure, and the morphology gradually changed with the increase in bias voltage. The films thickness decreased upon increasing the nitrogen gas flow rate, substrate temperature, and bias voltage. In addition, the hardness of the TiAlN film was enhanced by adjusting the nitrogen gas flow rate, substrate temperature, and bias voltage, and a suitable elemental component ratio was obtained. A maximum hardness of approximately 28.9 GPa was obtained for the TiAlN film with a nitrogen gas flow rate of 4 sccm, substrate temperature of 500ºC, bias voltage of 100 V, and an elemental composition Al/(Al + Ti) of approximately 34.35%.

Reactive pulsed DC magnetron sputtering deposition of vanadium oxide thin films: Role of pulse frequency on the film growth and properties

In this study, vanadium oxide (VOx) thin films were prepared by reactive pulsed DC magnetron sputtering (PDMS). The influence of pulse frequency (Fp) on the deposition process and properties of VOx films was investigated. The obtained results indicate that with the increase of Fp, which not only can enhance the oxidation of vanadium but also can facilitate the formation of a denser microstructure and smoother surface morphology in the films. More importantly, films with composition from metal-rich to maximum stoichiometry can be accessed by tuning the Fp, without varying any other parameters, especially, the flow rate of reactive gas. And temperature dependent electrical properties of the VOx films can also be tailored via the Fp to fall in the desirable range for microbolometer applications. The impacts of Fp on the reaction between V and O, thin film growth and some dynamic processes occurring during reactive PDMS were analyzed. The corresponding underlying mechanisms were discussed in detail. Our present work may provide a practical and effective way to develop the reactive sputtering towards hysteresis-free, and also paves the way for optimizing the reactive sputtered VOx films with desirable properties via Fp.