Deep Oscillation Magnetron Sputtering Research Articles

Comparative study of dry high-temperature tribological performance of hydrogen-free and hydrogenated DLC films deposited by HiPIMS in DOMS mode

Solid lubricants are crucial for industries operating at temperatures beyond 300 ºC, where liquid lubricants encounter limitations. Diamond-like carbon (DLC) films, known for exceptional solid lubrication and mechanical properties, need higher thermal stability for effective use in high-temperature applications. This study focuses on developing DLC films with the required thermal stability and solid lubricating properties. Hydrogen-free and hydrogenated DLC films were deposited utilizing deep oscillation magnetron sputtering (DOMS). Thermal characterizations revealed both films surpassed 500 ºC in thermal stability, rendering them suitable for high-temperature tribological applications. However, the hydrogenated DLC film exhibited superior solid lubricating properties, achieving an ultra-low friction coefficient below 0.05 at elevated temperatures, along with enhanced wear resistance, while effectively protecting its counterpart up to 500 ºC.

Influence of magnetic field strength on plasma, microstructure, and mechanical properties of Cr thin films deposited by MPPMS and DOMS

Magnetic field strength plays a vital role in determining the discharge behavior in magnetron sputtering. It enables the customization of discharge plasma and thin film properties. This study aims to compare the discharge behavior and investigate the potential effects on Cr thin films deposited using modulated pulsed power magnetron sputtering (MPPMS) and deep oscillation magnetron sputtering (DOMS) at different magnetic field strengths. The magnetic field strength in the target center increased from 67 to 91 mT tuning by the target thickness from 8 to 3 mm, and the average electron temperature was higher in a DOMS discharge than that in a MPPMS discharge. For both MPPMS and DOMS deposited Cr thin films, the refractive index and mechanical properties have been promoted with the increase in magnetic field strength, and almost all Cr thin films showed a Cr(110) preferred orientation. The hardness and modulus increased from 11.3 and 275.6 to 13.8 to 285.1 GPa for MPPMS deposited thin films, while the hardness and modulus for DOMS Cr thin films were much higher, increasing from 11.2 and 283.6 to 17.3 to 297.2 GPa. The possible differences between MPPMS and DOMS were analyzed based on the plasma global model and empirical equations. The analysis revealed that the high discharge current of DOMS is primarily caused by the possibility of back-attraction ion difference between MPPMS and DOMS. The voltage oscillation in a DOMS discharge provides sufficient time for ionized ions to escape from cathode attraction. Regarding the difference in deposition rate, it should at least be the cooperative results of the target back-attraction effect and ion evacuation time difference in plasma.

A hybrid plasma model for Cr thin film deposition by deep oscillation magnetron sputtering

A time-dependent hybrid plasma model composed of a zero-dimensional global model and a two-dimensional fluid model is proposed for simulation of plasma chemistry and transportation of plasma during Cr thin film deposition by deep oscillation magnetron sputtering (DOMS). The global model deals with plasma reactions in the ionization region near the target with discharge voltage and current waveforms as inputs. The temporal plasma characteristics calculated by the global model are utilized as a boundary condition for the two-dimensional fluid model to simulate high-density plasma transportation in the diffusion region through the entire macropulse period. The full momentum equation taking inertia force into consideration is applied for ion momentum conservation in the fluid model instead of using the drift-diffusion approximation, which ensures validity of the simulation for low-pressure plasmas. The deposition flux as well as the kinetic and potential energy fluxes transferred to the growing films are calculated by the hybrid model. Microstructure evolution of the DOMS deposited Cr thin films from zone I to zone T is attributed to the growing kinetic and potential energies as the charging voltage increases according to the structure zone diagram. The deposition rate loss in DOMS is explained by the back attraction effect, sputtering yield effect, and densification of the films.

Detailed pathway for a fast low-temperature synthesis of strongly thermochromic W-doped VO2 films with a low transition temperature

We report the discharge characteristics, and population of chosen atomic neutral (V, O and Ar) and ionic (V+, V2+, O+ and Ar+) species in the discharge during low-temperature (350 °C) depositions of W-doped VO x films onto a 170 nm thick Y-stabilized ZrO2 layer on a 1 mm thick conventional soda-lime glass. The depositions were performed using reactive deep oscillation magnetron sputtering with a pulsed O2 flow control and to-substrate O2 injection into a high-density plasma in front of the sputter V-W target. The pre-selected critical values of the oxygen partial pressure were in the range from 82 mPa to 92 mPa. Optical emission spectroscopy proved a relatively high density of O atoms in front of the substrate, which is important for production of the W-doped VO2 films. It was found that setting of the amount of O2 in the gas mixture determines not only the elemental and phase composition of the films and their deposition rate but also the crystallinity of the thermochromic VO2 phase in them. The crystalline W-doped VO2 films with a low transition temperature of 28 °C exhibited a high modulation of the solar energy transmittance of 8.9%. The results are important for further improvement of this new scalable sputter deposition technique for a fast (53 nm min−1 at a target-substrate distance of 100 mm in this work) low-temperature synthesis of high-performance durable thermochromic VO2-based multilayer coatings designed for smart-window applications.

Effect of hydrogen incorporation on the mechanical properties of DLC films deposited by HiPIMS in DOMS mode

The automobile industry has increased its efforts in reducing the emissions of internal combustion engines by improving their efficiency. Decreasing the energy losses by friction in the engines parts is at the core of this attempt. One of the technologies that have been applied in achieving this is the application of carbon coating in engine parts surfaces because of their low friction coefficient characteristics. In this study, DLC films, a specific type of carbon coatings, were deposited using the Deep oscillation magnetron sputtering (DOMS) method, which is a variation of the high-power impulse magnetron sputtering (HiPIMS) method. Those films were deposited with an increasingly higher hydrogen content, and then their mechanical, morphological, and tribological properties were studied. All of this was carried out to verify if the higher hydrogen content is beneficial to use as piston ring coatings in order to decrease friction losses. The variation in the hydrogen content was achieved by increasing the partial pressure of methane inside the deposition chamber during the deposition, which allowed the deposition of films with up to 30 at. % of hydrogen. The variation allowed the depositions of films with a hardness above 10 GPa, a friction coefficient lower than 0.16 (30 % lower when compared to hydrogen-free DLCs), and with specific wear rates in the order of 10−16 mm3/Nm. The hydrogen content also changed the morphology of the films' surface, as well as increasing its deposition rates by 27 %.

Optical emission spectroscopy in deep oscillation magnetron sputtering (DOMS) of titanium

Optical emission spectroscopic diagnostics are applied to determine the temporal evolution and distance dependence from the target surface for deep oscillation magnetron sputtering (DOMS) with a titanium target. In the time evolution of emission intensities for atomic lines of optically emitting species formed in DOMS plasma, the envelope of the peak emission intensity for sputtered neutrals in each pulsed discharge was observed to rise gradually with increasing distance. The increase in the distance dependence of the optical emission corresponds to plasma build-up from gas plasma to metallic plasma, which has been reported in the deposition region using a time-of-flight mass spectrometer in Sanekata et al. [J. Appl. Phys. 131, 243301 (2022)]. On the other hand, the ion confinement effect was strongly observed for sputtered ions in the region up to the edge of the magnetic trap around 40 mm downstream from the target surface for the first pulse discharge.

Growth of hard metal films by deep oscillation magnetron sputtering

ABSTRACT Pulsed vapour fluxes with proper controlled time duration were proved to be an important controlling dimension for the deposition of a desired thin film. In this work, deep oscillation magnetron sputtering was employed to tailor the ionized pulsed flux for Nb and Cr thin film grown on AISI 304 stainless steel. Through tuning the micropulse oscillating voltage-off time from 10 to 40 μs, Nb and Cr thin films showed an obvious variation on microstructure owing to the deposition flux transited from continuous to chopped ones. The deposited Nb thin films showed Nb(110) preferred orientation experienced a nanocrystallization process with compressive residual stress showing a slightly decrease. While Cr thin films showed Cr(110) preferred orientation without an obvious nancrystallization trend with its compressive stress turning to be tensile. The tailoring of the microstructure and properties relied on interval time between the two interrupted ionized deposition flux.

Global model on oscillation discharge characteristics during deep oscillation magnetron sputtering of Cr target

A time-dependent global model is developed for deep oscillation magnetron sputtering (DOMS) with a Cr target to characterize the plasma using the working Ar gas at a pressure of 0.8 Pa. An input of the global model is the target voltage and current waveforms at charging voltages from 260 to 400 V. The plasma densities vary synchronously with the oscillations of target power. During the on-time of a micropulse, the gas atoms are ionized first to ignite the plasma and subsequently the metal ions follow to sustain the discharge. During the off-time, the gas ions dominate the afterglow. The DOMS possesses a characteristic of alternating gas/metal discharge in the time domain. The peak values of plasma densities increase linearly with charging voltages, which is mainly attributed to the higher Cr+ ion density. The discharge transits from gas dominated to metal dominated at high charging voltage. The working gas rarefaction in DOMS discharge is enhanced at higher charging voltages. At charging voltages higher than 360 V, the metal self-sputtering comes into the runaway regime temporarily as indicated by the self-sputtering parameters exceeding unity, generating the dense and metal-rich plasma. The metal self-sputtering is promoted by gas rarefaction. The electrons tend to ionize the metal atoms after the gas atoms are depleted. The decreased grain size and elevated nano-hardness of the Cr thin films are explained by structure transition from zone I to zone T due to the efficient metal ion bombardment to the growing thin films as the charging voltage increases.

Time-of-flight mass spectrometry diagnostics in deep oscillation magnetron sputtering (DOMS) of titanium

Reflectron-type time-of-flight mass spectrometry was applied to the time-resolved component analysis of deep oscillation magnetron sputtering (DOMS), which has been developed as a technique of modulated pulsed magnetron sputtering. In the present study, the DOMS of a Ti target was performed under an Ar gas atmosphere by using a DOMS-specific control waveform consisting of 25 current and/or power pulses. The time evolution of the formation of ionized species (Ar+, Ar2+, Ti+, and Ti2+) after the application of the first discharge pulse was observed at the position corresponding to the deposition region. This study revealed that the plasma build-up process from non-metallic plasma to metallic plasma takes approximately two micropulses (around 100 μs from ignition) in DOMS discharge. In addition, we have found the possibility of studying sputtering processes, such as the rarefaction, and refilling processes of Ar as a function of pulse number through DOMS research.

Structure and fracture toughness of TiAlN thin films deposited by deep oscillation magnetron sputtering

TiAlN thin films were deposited on Si(100) and AISI 304 austenitic stainless steel substrates at the low deposition temperature below 250℃ by the deep oscillation magnetron sputtering (DOMS), respectively. The peak sputtering power changed from 58.7 kW to 129.9 kW by adjusting the oscillation voltage on-time (τon) / off-time (τoff) ratio with 6–12 μs to 30 μs. All TiAlN thin films have a face centered cubic structure with a composition of Ti0.22Al0.28N0.50. With increasing the peak powers, a transit of the columnar morphology in Zone I with the preferred orientation of c-TiAlN(111) to a compact morphology in Zone T with c-TiAlN(200) was characterized. The hardness, residual stress, and H/E and H3/E2 ratios of TiAlN thin films increased with the maximal values obtained at the peak power of 90.2 kW, and then slightly decreased. Correspondently, the fracture toughness (KIC) of TiAlN thin films on Si(100) and AISI 304 stainless steel increased firstly from 0.56 MPa∙m1/2 to 1.10 MPa∙m1/2 and from 0.58 MPa∙m1/2 to 1.08 MPa∙m1/2 as the structure from Zone I with c-TiAlN(111) to Zone T with c-TiAlN(200), and then decreased to 0.94 MPa∙m1/2 and 0.71 MPa∙m1/2 at the structure of Zone T with c-TiAlN(200), respectively. The higher KIC values of Ti0.22Al0.28N0.50 thin films in Zone T were achieved on Si(100) and AISI 304 stainless steel at 90.2 kW. The excellent mechanical properties of TiAlN thin films on Si(100) and AISI 304 stainless steel substrates were carried out by using DOMS at the low deposition temperature.

An inverse problem in estimating fracture toughness of TiAlN thin films by finite element method based on nanoindentation morphology

The fracture toughness of TiAlN thin films on AISI 304 austenitic stainless steel was inversely investigated by combining nanoindentation experiment with finite element method (FEM) and extended FEM (XFEM) simulation. The TiAlN thin films were deposited by deep oscillation magnetron sputtering (DOMS) with the oscillation pulse on and off times of 12 μs and 30 μs at a peak power of 136.1 kW. A completely dense TiAlN thin film with the thickness of 1500 nm has a face-centered-cubic microstructure with (200) preferred orientation. The displacements of the nanoindenter were intentionally interrupted by 1200 nm and 1800 nm, latter is thin film-crossing to induce an apparently cracking. The cross-sectional samples of TiAlN thin films with the cracks were fabricated by focused ion beam. The experimental crack number and position in the cross-sectional samples were observed by scanning electron microscopy. The maximum damage initiating stress (σmax) and corresponding crack separation distance (δc) in the Griffith–Irwin relationships were fitted using the XFEM calculation based on the crack morphology to match the crack number and position of TiAlN thin films. The fracture toughness of TiAlN thin films on AISI 304 austenitic stainless steel was calculated to be 1.09 MPa m1/2 according to the fitted parameters of 5.5 GPa for σmax and 1.5 nm for δc. Therefore, an alternative method by the nanoindentation morphology and the inversely calculation fitting was developed to estimate the fracture toughness of thin films.

On the influence of the micropulse on Nb thin films deposited by MPPMS and DOMS: A comparative study

Nb thin films deposited by modulated pulsed power magnetron sputtering (MPPMS) and deep oscillation magnetron sputtering (DOMS) were comparatively studied under a similar average power by controlling the micropulse duty cycle. It was found that DOMS discharge both showed higher discharge peak current and peak voltage, time delay between the current and voltage was much smaller compared with a MPPMS discharge. All Nb thin films were observed with Nb(110) preferred orientation and compact columnar structure. The increase of micropulse duty cycle led the gradual movement of Nb(110) to high scattering angle direction, meanwhile the DOMS Nb(100) diffraction peaks were all on the left of MPPMS Nb(110). An increase for compressive residual stress σ could be observed for both techniques, and all DOMS Nb thin films showed higher residual stress, hardness and elastic modulus. The anomalous increase in σ also led to the deterioration of DOMS Nb thin film scratch adhesion. Despite the grain sizes of DOMS Nb thin films were all smaller than MPPMS Nb thin films, σ in DOMS Nb thin films generated by the adatom diffusion and ion irradiation still overwhelmed the tensile stress generated by the volume shrinkage of the growing grains. The special afterglow of DOMS in the microsecond scale gave a new controlling dimension for thin film growth.

Dependence of Optical Emission Spectra on Argon Gas Pressure during Modulated Pulsed Power Magnetron Sputtering (MPPMS)

Modulated pulsed power magnetron sputtering (MPPMS) of titanium was investigated as a function of argon gas pressure using optical emission spectroscopy (OES). Delays in discharge and the formation of comb-like discharge current waveforms due to splitting and pulsing were observed with a decrease in pressure. This observation corresponds to the evolution from MPPMS condition to deep-oscillation-magnetron-sputtering (DOMS)-like condition by changing discharge gas pressure. The optical emission intensities of the ionic species (Ar+ and Ti+) increased as the comb-like current waveforms were formed with decreasing Ar pressure. This behavior showed a marked contrast to that of the neutral species (Ar and Ti). The Ar pressure dependence of OES was revealed to be due to the plasma build-up stage, which is the initial generation process of plasma discharge in pulsed dc magnetron sputtering, from the temporal profile for the atomic-line intensities of the optically emitting species in MPPMS and DOMS-like plasmas.

Delayed Discharge Bridging Two Sputtering Modes from Modulated Pulsed Power Magnetron Sputtering (MPPMS) to Deep Oscillation Magnetron Sputtering (DOMS)

Delayed discharges due to electrical breakdown are observed in modulated pulsed pow er magnetron sputtering (MPPMS) plasma of titanium. The delayed discharge, which is remarkable with decreasing argon gas pressure, transforms the discharge current waveform from a standard modulated pulsed discharge current waveform to a comb-like discharge current waveform consisting of several pulses with high power. In addition, the delay times, consisting of statistical times and formative times in the delayed MPPMS discharges, are experimentally measured with the help of Laue plot analysis. The pressure dependence of delay times observed indicates that the delayed discharge behavior matches the breakdown characteristics well. In the present study, the delayed discharge dynamics of the comb-like discharge current waveform, which can be the origin of deep oscillation magnetron sputtering, are investigated based on measurement of the delay times and the characteristics of discharge current waveforms.

Effect of Peak Power in Deep Oscillation Magnetron Sputtering on Film Properties

In the last decade, new magnetron sputtering deposition techniques have been developed to produce highly ionized fluxes of sputtered material and, consequently, allow greater control over the energy and direction of the sputtered species. One of such techniques is deep oscillations magnetron sputtering (DOMS). The main objective of the paper is to understand if the new deposition mechanisms that the DOMS technology brings about, in comparison to DCMS, is always an advantage for the film deposition. For this purpose, four well-known deposition systems (Cr, Ta, CrN and TiSiN) were investigated. In each case, thin films were deposited by DOMS and DCMS in order to compare their microstructural, structural and mechanical properties. Taken as examples, the four study systems are understood that, in some cases, it is possible to achieve film properties never achieved through DCMS. However, in other cases, due to their particular characteristics (high voltages), the HiPIMS advantages are diminished when compared to DCMS. Possible solutions to overcome the observed problems are proposed.

Effect of the Substrate Biasing on the Structure and Properties of Tantalum Coatings Deposited Using HiPIMS in Deep Oscillations Magnetron Sputtering Mode

The influence of energetic ion bombardment on the properties of tantalum coatings was studied. To achieve such energetic ion bombardment during the deposition process of tantalum coatings, a combination of deep oscillation magnetron sputtering (DOMS), an ionized physical vapour deposition technique, with substrate biasing was used. The substrate biasing was varied between 0 and −120 V. In this work, the structure (XRD), microstructure (SEM), surface morphology (AFM) and hardness, and Young’s modulus (nanoindentation) of the coatings were characterized. The results show with the use of such conditions it was possible to deposit a pure α-Ta (the most desired at industrial level) with improved mechanical properties (hardness equal to 22.4 GPa and Young’s modulus equal to 235 GPa). The roughness of the Ta coatings decreases up to values of about 1 nm with an increase of substrate biasing. It was possible to deposit very dense Ta coatings with 2 µm of thickness. Therefore, these results are significantly different than in previous works, offering Ta coatings with a combination of very interesting properties.

Multifunctional MoOx and MoOxNy films with 2.5 < x < 3.0 and y < 0.2 prepared using controlled reactive deep oscillation magnetron sputtering

Reactive deep oscillation magnetron sputtering with a pulsed reactive gas flow control and to-substrate reactive gas injection into the high-density plasma in front of the sputtered Mo target was used for a low-temperature (< 120 °C) preparation of MoOx and MoOxNy films with 2.5 < x < 3.0 and y < 0.2. We explain the advantages of this deposition technique, allowing us to control smoothly and reproducibly the film composition and thus the film structure and properties. Special attention is paid to the strong effect of slightly decreasing x in MoOx films and slightly increasing y in MoOxNy films on their optical and electrical properties which are directly related to varying electronic structure of the films. We discuss possible applications of these films in the field of solar cells, organic electronic devices and lithium-ion batteries.

Correlation between Substrate Ion Fluxes and the Properties of Diamond-Like Carbon Films Deposited by Deep Oscillation Magnetron Sputtering in Ar and Ar + Ne Plasmas

Recently, the use of Ne as a processing gas has been shown to increase the ionization degree of carbon in High Power Impulse Magnetron Sputtering (HiPIMS) plasmas. In this work, time-resolved measurements of the substrate’s current density were carried out in order to study the time evolution of the ionic species arriving at the growing film. The addition of Ne to the plasma resulted in a steep increase of the sp3/sp2 ratio in the films once the Ne contents in the processing atmosphere exceeded 26%. Increasing the Ne content is shown to increase both the total number of C ions generated in the plasmas and the ratio of C/gaseous ions. The time-resolved substrate ion current density was used to evaluate the possibility of substrate biasing synchronizing with the discharge pulses in the HiPIMS process. It is shown that in pure Ar plasmas, substrate biasing should be confined to the time interval between 25 and 40 µs after the pulse starts, in order to maximize the C+/Ar+ ratio bombarding the substrate and minimize the formation of film stresses. However, Ne addition to the processing gas shortens the traveling time of the carbon species towards the substrate, reducing the separation between the gaseous and carbon ion arrival times.

Low peak power deposition regime in HiPIMS: Deposition of hard and dense nanocomposite Ti-Si-N films by DOMS without the need of energetic bombardment

Nanocomposite Ti-Si-N thin films have been extensively studied for more than two decades mainly for the production of super hard materials. However, recently, several authors have shown that the use of HiPIMS in Ti-Si-N deposition bring about new opportunities for optimization of the films properties. HiPIMS allows for markedly different film growth pathways depending on the deposition conditions. In a previous work, regarding the deposition of Ti-Si-N films by DOMS (Deep Oscillation Magnetron Sputtering), authors also showed that, at low peak power, a unique optimal compromise of ionization fraction and energy of the sputtered species can be achieved. The main objective of the present work is to further investigate the low peak power regime in the deposition of Ti-Si-N films by DOMS. For this purpose, Ti-Si-N films with a Si content of 7 at.% were deposited by DOMS using a similar configuration as in our previous work but with fewer Si pellets placed on the Ti target in order to achieve a lower Si content.The Ti-Si-N films deposited in the low peak power regime have a fine compact columnar morphology with V-shaped columns with sharp and thin column boundaries (1 nm wide) with Si preferentially segregated to the column boundaries. These films have a high crystalline quality with a mosaic-like structure with sub-grains (diffraction domains) only slightly misoriented with respect to each other. Increasing the peak power (high peak power regime) results in the deposition of Ti-Si-N films with brother columns and higher compressive stresses characteristic of deposition under energetic bombardment. These results show that dense and hard Ti-Si-N films with a high degree of crystallinity can be deposited by DOMS without the need of energetic bombardments, i.e., without the need of high peak powers and/or substrate biasing.

Tunable composition and properties of Al-O-N films prepared by reactive deep oscillation magnetron sputtering

We report a low-temperature deposition of Al-O-N films in a wide range of compositions. We use and explain the advantages of reactive deep oscillation magnetron sputtering (leading to suppressed arcing on the Al target) with a pulsed reactive gas flow control and optimized reactive gas inlet position (leading to a very smooth composition control, despite the different reactivities of O2 and N2). Next, we focus on the relationships between film composition, structure and functional properties. We demonstrate a smoothly controlled refractive index at a very low extinction coefficient, and identify the Al-O-N composition leading to the highest hardness, elastic recovery and elastic strain to failure. We discuss some of the technological applications which these properties are useful for.