Modulated Pulsed Power Research Articles

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.

Preparation of Alumina Thin Films by Reactive Modulated Pulsed Power Magnetron Sputtering with Millisecond Pulses

This paper aims to investigate the quality of thin alumina films deposited on glass samples using magnetron sputtering in the reactive modulated pulsed power mode (MPPMS) and evaluate the process productivity. The aluminum target was sputtered in Ar/O2 gas mixtures with different fractions of oxygen in the total gas flow, in the fixed pulsed voltage mode. The pulse-on duration was varied between 5 and 10 ms, while the pulse-off time was 100 or 200 ms. The dependences of mass deposition rate and discharge current on the oxygen flow were measured, and the specific deposition rate values were calculated. Prepared coatings had a thicknesses of 100–400 nm. Their quality was assessed by scratch testing and by measuring density, refractory index, and extinction coefficient for different power management strategies. The strong influence of pulse parameters on the coating properties was observed, resulting in a maximum density of 3.6 g/cm3 and a refractive index of 1.68 for deposition modes with higher duty cycle values. Therefore, adjusting the pulse-on and pulse-off periods in MPPMS can be used not only to optimize the deposition rate but also as a tool to tune the optical characteristics of the films. The performance of the studied deposition method was evaluated by comparing the specific growth rates of alumina coatings with the relevant data for other magnetron discharge modes. In MPPMS, a specific deposition rate of 200 nm/min/kW was obtained for highly transparent Al2O3, without using any dedicated feedback loop system for oxygen pressure stabilization, which makes MPPMS superior to short-pulse high-power impulse magnetron sputtering (HiPIMS) modes.

A fluid model of pulsed direct current planar magnetron discharge

We simulated a pulsed direct current (DC) planar magnetron discharge using fluid model, solving for species continuity, momentum, and energy transfer equations, coupled with Poisson equation and Lorentz force for electromagnetism. Based on a validated DC magnetron model, an asymmetric bipolar potential waveform is applied at the cathode at 50–200 kHz frequency and 50–80% duty cycle. Our results show that pulsing leads to increased electron density and electron temperature, but decreased deposition rate over non-pulsed DC magnetron, trends consistent with those reported by experimental studies. Increasing pulse frequency increases electron temperature but reduces the electron density and deposition rate, whereas increasing duty cycle decreases both electron temperature and density but increases deposition rate. We found that the time-averaged electron density scales inversely with the frequency, and time-averaged discharge voltage magnitude scales with the duty cycle. Our results are readily applicable to modulated pulse power magnetron sputtering and can be extended to alternating current (AC) reactive sputtering processes.

Combined Experimental and Theoretical Investigation on Formation of Size-Controlled Silver Nanoclusters under Gas Phase

Metallic nanoclusters (NCs) have been predicted to achieve the best Surface-Enhanced Raman Scattering (SERS) due to the controllable amount of atoms and structures in NCs. The Local Surface Plasmon Resonance (LSPR) effect on silver metal NCs (Ag) enables it to be a promising candidate for manipulating the LSPR peak by controlling the size of NCs, which in turn demands a full understanding of the formation mechanism of Ag. Here, we apply an extended Smoluchowski rate equation coupled with a fragmentation scheme to investigate the growth of size-selected silver NCs generated via a modulated pulsed power magnetron sputtering (MPP-MSP). A temperature-dependent fragmentation coefficient D is proposed and integrated into the rate equations. The consistency between the computational and experimental results shows that in relative low peak power ( W), the recombination of cation and anion species are the dominant mechanism for NC growth. However, in the higher region (≥800 W), the fragmentation mechanism becomes more impactful, leading to the formation of smaller NCs. The scanning electron microscopy observation shows the Ag is successfully soft-landed and immobilized on a strontium titanate crystal, which facilitates the application of the Ag/STO to the SERS research.

Deposition of Size-Selected Gold Nanoclusters onto Strontium Titanate Crystals for Water Splitting under Visible Light

Using a modulated pulse power magnetron sputtering (MPP-MSP) coupled with a quadrupole mass spectrometer (Q-MS), intensive size-selected gold nanoclusters (Aun) ranging from n = 5 to 40 in size are synthesized and soft landed onto a strontium titanate (STO) crystal surface as a co-catalyst for photocatalytic water splitting. The photocatalytic reactivity of the Aun/STO is investigated by measuring the photocurrent density of the sample under visible light radiation. It is found that the Aun co-catalysts enable the visible light response of the Aun/STO photocatalyst. The photocurrent density is sensitively dependent on the size of the Aun on the STO, and Au16 exhibits its maximum photocurrent under visible light. The underlying physics of the size-specific photocurrent are explained in terms of the size-dependent electron affinity of Aun.

Conversion of CO2 in a gliding arc discharge reactor: Discharge characteristics and the effects of different parameters

In this work, a knife-shaped gliding arc discharge (GAD) reactor driven by a modulated pulse power supply was used to convert CO2. The discharge image, voltage and current waveforms of GAD were recorded experimentally. The effects of gas flow rate, input voltage, and the duty cycle of power supply on CO2 conversion were studied. A CO2 conversion of 3.8% and energy efficiency of 39.6% could be achieved. Compared with other non-thermal plasmas, GAD has a slightly lower CO2 conversion but higher energy efficiency. In addition, the capacity of CO2 treated by GAD (6 L/min) was significantly higher than other non-thermal plasmas (e.g. 25 mL/min-125 mL/min in corona discharge and dielectric barrier discharge).

Effects of Input Power Ratio of AlCr/Ti Target on the Microstructural and Mechanical Properties of AlTiCrN Coatings Synthesized by a High-Power Impulse Magnetron Sputtering Process

In this study, five AlTiCrN nitride coatings were deposited via high-power impulse magnetron sputtering (HiPIMS). The AlTiCrN coatings were synthesized with high contents of Al or Ti and a lower fraction of Cr, using Ti and Al70Cr30 targets with five different input power ratios. Electron probe microanalyzer results revealed that the increased rate of Ti contents in the coatings can be divided into two regions due to the difference of power densities for HiPIMS (>0.5 kW/cm2) and modulated pulsed power (MPP) (<0.5 kW/cm2). The deposition rate and thickness of the coatings depended on the sputtering yield of two metal targets under HiPIMS and MPP modes. The grain size of the coatings decreased from 60 to 40 nm as the input power ratios of the AlCr/Ti targets decreased due to their lower thickness values and lower Al content. Selected area electron diffraction patterns and X-ray diffraction results revealed that the TiN and AlTiN phases can be found in the coating containing higher Ti content, whereas the AlN, CrN, and AlCrN phases were observed in the coating with a higher Al concentration. Nevertheless, decreasing the concentration of Ti had a detrimental effect on the mechanical properties of AlTiCrN coatings, due to a promotion in grain size and the formation of AlN, which is softer than TiN. It is noticed that our results differed from those in previous reports, in which a grain refinement effect was observed due to increasing Al content. In this work, the effect of processing the parameters of the HiPIMS and MPP power systems on the grain size and the mechanical property of the coating was also discussed.

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.

Properties of millisecond-scale modulated pulsed power magnetron discharge applied for reactive sputtering of zirconia

The electrical properties of a modulated pulsed power (MPP) magnetron discharge were experimentally and theoretically studied in case of reactive sputtering of metallic zirconium target in argon/oxygen mixtures. The high-power pulsing was assisted by pre-ionization provided by a low-power direct current (DC) magnetron discharge filling the pulse-off period. The ranges of stable discharge operation parameters (applied voltage and oxygen flow rate) were determined for pulse-on time of 3 ms and pulse-off time 100–1000 ms. The maximum stable peak power density was 2.1 kW cm−2. Strong dependence of the MPP discharge current waveforms on the pulse-off time was found, indicating the important role of the pre-ionizing DC discharge. In presence of oxygen, discharge peak current was observed with characteristic width up to 1.5 ms, followed by non-reactive-like plateau region. For theoretical treatment of the observed discharge current behavior, we modified the well-known Berg model of reactive sputtering by introducing the terms required for adequate description of time-dependent poisoning and sputtering processes. The reactive ion implantation term was also transformed to account for the process saturation at high ion current densities. Calculation results from the modified Berg model demonstrated good agreement between our experimental observations of discharge current evolution and target poisoning dynamics in the timescale of milliseconds.

Influence of N2 flow rate on microstructure and properties of CrNx ceramic films prepared by MPP technique at low temperature

In this study, CrNx ceramic films were prepared utilizing modulated pulsed power magnetron sputtering (MPP) technique at low deposition temperature, with varying flow rates of the reactive gas, i.e. N2. The influences of N2 flow rate on the density of the plasma surrounding the target sheath, microstructure evolution, mechanical/tribological and anti-corrosion properties of the as-deposited CrNx ceramic films were investigated systematically. Results indicated that the plasma density increased sharply with increasing N2 flow rate in the range of 75 sccm to 175 sccm. Nevertheless, with further increase of N2 flow rate to 200 sccm, the growing trend of ionization slowed down probably due to the insufficiency of the power density. With increasing N2 flow rate, the Cr elemental concentration decreased from 69.7 at.% to 57.5 at.%, and that of N increased from 23.2 at.% to 36.6 at.%. The sub-stoichiometric ratio of the CrN films could be attributed to the relative lower reactive kinetic energy at low deposition temperature. The analyses on the microstructure evolution of CrNx films revealed that with insufficient introduced nitrogen, competitive growth between Cr2N(110), Cr2N(111), Cr(110) phases (note that all crystalline planes indexed here are parallel to the coating surface) were found; and with relative sufficient nitrogen, fcc-CrN phase took over, with preferred orientation of (111). Due to the improvement of density and the fine-grain strengthening mechanism, with 100 sccm N2 flow rate, the hardness of the CrNx films obtained the maximum value of 21.4 GPa. The films deposited at 75 sccm nitrogen showed the highest friction coefficient (i.e. ~0.75), which could be partially attributed to the presence of impurity particles on the film surface. And for the remaining films, the friction coefficient maintained in the range of 0.38–0.52. As for the anti-corrosion properties, the CrNx film deposited at 100 sccm nitrogen showed the lowest corrosion current (i.e. 44.2 nA/cm2), indicating excellent anti-corrosion property.

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.

Phase composition and mechanical properties of homostructure NbN nanocomposite coatings deposited by modulated pulsed power magnetron sputtering

Homostructure NbN nanocomposite coatings with cubic δ-NbN phase and hexagonal δ’-NbN phase were deposited by modulated pulsed power magnetron sputtering (MPPMS) under varied nitrogen flow rate fN2 from 15% to 30%. Low fN2 favored the formation of δ’-NbN phase with (100) preferred orientation and δ-NbN phase with (200) preferred orientation, while high fN2 favored the formation of δ-NbN phase with (200) preferred orientation. The NbN coatings were characterized as the nanocomposite coatings with δ’-NbN nanocrystallites embedded into δ-NbN matrix. The hardness and modulus of NbN coatings went up to 36 GPa from 30 GPa and 460 GPa from 366 GPa as fN2 increased to 20% with residual compressive stress from 0.47 GPa to 1.93 GPa, then decreased to 29 GPa and 389 GPa with residual compressive stress of 1.01 GPa as fN2 further increased. Meanwhile, the toughness of coatings increased with the content of δ’-NbN phase showing an abrupt change of NbN coating toughness under the fN2 of 30%. The homostructure NbN nanocomposite coatings with both enhanced hardness and toughness were achieved by forming nanocomposite structure at low fN2. The results showed that the essential conditions of the design criterion for hard and tough coatings should be arranged in the impact of weight as follows: 1) the designed microstructure, 2) the compressive residual stress, 3) high H/E and H3/E2, 4) high We.

Stick-climb-slip induced damage mode in Cu/Si(100) thin films deposited by modulated pulsed power magnetron sputtering during scratch

Stick-climb-slip induced damage mode during a scratch test was studied in the Cu/Si(100) thin films deposited by modulated pulsed power magnetron sputtering, to characterize the adhesion of the thin films. The two typical periodical morphologies were observed on the scratch tracks after first edge chipping of the Cu/Si(100) thin films. The first type was a series of wave-like traces outside the scratch track, and another was the periodical semi-circular deformation characteristic within the scratch track. Finite element method (FEM) was used to analyze the stress-strain response in the Cu/Si(100) thin films for the moved scratch tip under the applied load. It was found that the concentrations of maximum principal stress in zones A, B and C were responsible to the formation of groove pileups accompanied by the periodical accumulation and release of the strain energy with a contact force periodically fluctuated. The scratched tip in the ductile Cu/Si(100) thin films would repeatedly experience the forward pileups along thinning and growing trace, and gradually climb up and then drop down with a sudden movement. The stick-climb-slip induced damage modes of the thin films can provide the evaluation of the critical loads in the scratch test.

Microstructure and thermal conductivity of Ti-Al-Si-N nanocomposite coatings deposited by modulated pulsed power magnetron sputtering

Hard Ti-Al-Si-N coatings are widely used in cutting tools, due to their excellent mechanical properties and superior thermal properties. In this study, Ti-Al-Si-N coatings are deposited by modulated pulsed power magnetron sputtering, with various substrate bias voltages from −35 V to −130 V. As the bias voltage goes up, the composition of coatings remained nearly unchanged, maintained as a constant of Ti0.18Al0.26Si0.05N0.51. However, the Ti-Al-Si-N coatings have a decrease in (200)-preferred orientation; dense columnar structure (Zone I) of Ti-Al-Si-N coatings gradually evolves into featureless and flat cross sections structure (Zone T). As increasing the substrate bias voltage, the hardness increases from 31.2 GPa to 37.5 GPa, the H/E* value increases from 0.079 to 0.090, while the compressive residual stress of coatings raises from -1.22 GPa to -2.15 GPa. The thermal conductivity of coatings is examined by transient thermoreflectance technique, which decreases from 5.4 W/m*K to 2.1 W/m*K with the bias voltage. The values of electric resistivity ρ for all coatings are very large, ranging from 147 kΩ⋅m to 173 kΩ⋅m. The electronic thermal conductivity has no contribution to the thermal conductivity of Ti-Al-Si-N coatings, which is mainly determined by the phonon thermal conductivity. As increasing the substrate bias voltage, the average grain size of Ti-Al-Si-N nanocomposite coatings decreases from 16 nm to 5 nm. The interfacial density per unit volume is therefore increased, and leading to more interface scattering of the phonons in the heat transport progress, which is the key parameter in determining thermal conductivity of Ti-Al-Si-N nanocomposite coatings.

Scratch behavior and FEM modelling of Cu/Si(100) thin films deposited by modulated pulsed power magnetron sputtering

A series of copper thin films on Si(100) substrate were deposited using the modulated pulsed power magnetron sputtering under a sputtering pressure from 0.11 to 0.70 Pa. The scratch behavior of Cu/Si(100) thin films was characterized by the critical loads (Lc1–4) with the aid of finite element method (FEM) simulation. Increasing the sputtering pressure, surface morphology became rougher and the cross-sectional pattern transformed from compact fine granular to coarse and crack visible columnar structure. The Cu thin films scratched were continuous and comparative intact at 0.11 Pa which occurred to be with the highest critical loads, then gradually went to vast delamination initiated at 0.30 Pa with the Lc decreasing accordingly. The maximum principal stress (σ1) calculated by FEM was employed to evaluate the transition of critical loads Lc1–Lc4 using the typical stress concentration zones A, B and C which were the zones under, around and at the sides of the scratch tip, respectively. For the Cu/Si(100) thin films with strong adhesion, the Lc1 and Lc2 were evaluated through the migration of σ1 peak from the zone B to C, while the Lc3 and Lc4 were associated with stress accumulation at the zone C and A. The scratch behavior of Cu/Si(100) thin films was quantitatively expressed with the aid of FEM simulation.

Flexible hard TiAlSiN nanocomposite coatings deposited by modulated pulsed power magnetron sputtering with controllable peak power

TiAlSiN nanocomposite coatings were deposited by modulated pulsed power magnetron sputtering (MPPMS) with the varied peak power from 24.8 to 56.8 kW. The coatings had a typical nc-TiAlN/a-Si3N4 nanocomposite structure. The microstructure of the coatings changed from a columnar structure (Zone I in Thornton's Model) at 24.8 kW and 35.2 kW to a dense glassy-like structure (Zone T) at 44.6 kW and 56.8 kW. With increasing peak power from 24.8 to 56.8 kW, the hardness increased from 23.6 to 31.3 GPa, the H/E⁎ changed from 0.079 to 0.091, elastic recovery (We) increased from 50.1% to 57.4%, and compressive macrostress (σ) changed from −0.16 to −1.59 GPa. Fracture toughness (KIC) of the coatings was measured by the indentation test with a Vickers diamond indenter at the load L of 500 mN and 1000 mN. KIC increased from 0.96 to 1.77 MPa∙m1/2 with the peak power from 24.8 to 44.6 kW, except for no fracture at the highest peak power of 56.8 kW. The highest hardness, H/E⁎ ratio and elastic recovery of 31.3 GPa, 0.091, 57.4% with the macrostress of −1.59 GPa were obtained at the peak power of 56.8 kW. The enhanced toughness of TiAlSiN nanocomposite coatings was obtained at peak power of 44.6 kW and 56.8 kW, which was attributed to dense structure in the Zone T at high peak power. Effect of the bombarding energy (Ebi) and surface mobility (D) of the incident species on Zone T structure was explained by the electron densities and temperature, and number densities of Ti and Al sputtered species simulated using a global plasma model. The critical parameter of structural transformation from a columnar structure to a dense glassy-like structure is the increase of bombarding energy E and mobility of species D. The flexible and hard TiAlSiN nanocomposite coatings were deposited by MPPMS at higher peak power.

Influence of Power Pulse Parameters on the Microstructure and Properties of the AlCrN Coatings by a Modulated Pulsed Power Magnetron Sputtering

In this study, AlCrN coatings were deposited using modulated pulsed power magnetron sputtering (MPPMS) with different power pulse parameters by varying modulated pulsed power (MPP) charge voltages (350 to 550 V). The influence of power pulse parameters on the microstructure, mechanical properties and thermal stability of the coatings was investigated. The results indicated that all the AlCrN coatings exhibited a dense columnar microstructure. Higher charge voltage could facilitate a denser coating microstructure. As the charge voltage increased up to 450 V or higher, the microvoids along the column boundaries disappeared and the coatings became fully dense. The main phase in the AlCrN coatings was the c-(Al, Cr)N solid solution phase with NaCl-type phase structure. A diffraction peak of the h-AlN phase was detected at a 2θ of around 33°, when the charge voltage was higher than 500 V. The hardness of the AlCrN coatings varied as a function of charge voltage. The maximum value of the hardness (30.8 GPa) was obtained at 450 V. All the coatings showed good thermal stability and maintained their structure and mechanical properties unchanged up to 800 °C during vacuum annealing. However, further increasing the annealing temperature to 1000 °C resulted in apparent change in the microstructure and decrease in the hardness. The charge voltages also showed a significant influence on the high-temperature tribological behavior of the coatings. The coating deposited at the charge voltage of 550 V exhibited excellent tribological properties with a low friction coefficient.

Mass spectrometric study of N2-adsorption on copper cluster cations formed by modulated pulsed power magnetron sputtering in aggregation cell

We have observed gas-phase reactions between N2 molecules and copper cluster cations, Cun+ (n=2–17), formed by a modulated pulsed power magnetron sputtering cluster ion source. By introducing N2 gas effusively between the source and an acceleration region of a time-of-flight mass spectrometer in the vacuum chamber, N2-adsorbed copper cluster cations, CunN2+, were observed in mass spectra. The N2-adsorption reactivity of Cun+ was found to be relatively lower at n≥10 than at the smaller n. The cluster-size dependence of N2-adsorption on Cun+ has a correlation with binding energies between Cun+ and N2 calculated by density functional theory.

A global plasma model for reactive deposition of compound films by modulated pulsed power magnetron sputtering discharges

A spatially averaged, time-dependent global plasma model has been developed to describe the reactive deposition of a TiAlSiN thin film by modulated pulsed power magnetron sputtering (MPPMS) discharges in Ar/N2 mixture gas, based on the particle balance and the energy balance in the ionization region, and considering the formation and erosion of the compound at the target surface. The modeling results show that, with increasing the N2 partial pressure from 0% to 40% at a constant working pressure of 0.3 Pa, the electron temperature during the strongly ionized period increases from 4 to 7 eV and the effective power transfer coefficient, which represents the power fraction that effectively heats the electrons and maintains the discharge, increases from about 4% to 7%; with increasing the working pressure from 0.1 to 0.7 Pa at a constant N2 partial pressure of 25%, the electron temperature decreases from 10 to 4 eV and the effective power transfer coefficient decreases from 8% to 5%. Using the modeled plasma parameters to evaluate the kinetic energy of arriving ions, the ion-to-neutral flux ratio of deposited species, and the substrate heating, the variations of process parameters that increase these values lead to an enhanced adatom mobility at the target surface and an increased input energy to the substrate, corresponding to the experimental observation of surface roughness reduction, the microstructure transition from the columnar structure to the dense featureless structure, and the enhancement of phase separation. At higher N2 partial pressure or lower working pressure, the modeling results demonstrate an increase in electron temperature, which shifts the discharge balance of Ti species from Ti+ to Ti2+ and results in a higher return fraction of Ti species, corresponding to the higher Al/Ti ratio of deposited films at these conditions. The modeling results are well correlated with the experimental observation of the composition variation and the microstructure transition of deposited TiAlSiN compound films, demonstrating the applicability of this approach in understanding the characteristics of reactive MPPMS discharges as well as the composition and microstructure of deposited compound films. The model for reactive MPPMS discharges has no special limitations and is applicable to high power impulse magnetron sputtering discharges as well.

Effect of N2 flow rate on the microstructure and electrochemical behavior of TaNx films deposited by modulated pulsed power magnetron sputtering

Modulated pulsed power magnetron sputtering (MPPMS) technology offers the possibility to grow high performance coatings compared to the ones developed by conventional dc magnetron sputtering. The high degree of ionization of sputtered particles developed during MPPMS can be usefully utilized to precisely tailor the properties of the growing films. One of the main advantages of such a high metal ion flux is related to the densification of the coatings due to enhance ion bombardment towards the growing film. The development of extremely dense and low-defect microstructure coatings can have a positive effect on the corrosion resistance of tantalum nitride (TaNx) films.In this study, TaNx thin films have been deposited by MPPMS in a closed field unbalanced magnetron sputtering system. Structure, surface morphology, hardness and corrosion resistance of the developed coatings have been analyzed as a function of different N2-to-Ar ratios (0, 0.25, 0.625, 1). X-ray diffraction and scanning electron microscopy analysis reveal high dependence of the grown crystal phases and the microstructure on N2-to-Ar ratio. The hardness of the TaNx coatings increases when increasing N2-to-Ar ratio up to a maximum value of 25GPa (N2-to-Ar ratio of 0.625). The corrosion behavior was investigated using electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry. EIS measurements registered at different immersion times show high impedance values (in the order of 10MΩcm2) and corrosion resistance enhancement with time, indicating the formation of a passive protective oxide layer on the top of their surfaces. TaNx film grown at 0.25N2-to-Ar ratio exhibits the highest corrosion resistance of 103.53MΩcm2 and low porosity of 1.63×10−3 and is characterized by columnar-free microstructure.