Modulated Pulsed Power Research Articles

Characterization of polycrystalline VO2 thin film with low phase transition temperature fabricated by high power impulse magnetron sputtering

VO2 is a unique material that undergoes a reversible phase transformation around 68[Formula: see text]C. Currently, applications of VO2 on smart windows are limited by its high transition temperature. In order to reduce the temperature, VO2 thin film was fabricated on quartz glass substrate by high power impulse magnetron sputtering with a modulated pulsed power. The phase transition temperature has been reduced to as low as 32[Formula: see text]C. In addition, the VO2 film possesses a typical metal–insulator transition. X-ray diffraction and selected area electron diffraction patterns reveal that an obvious lattice distortion has been formed in the as-deposited polycrystalline VO2 thin film. X-ray photoelectron spectroscopy proves that oxygen vacancies have been formed in the as-deposited thin film, which will induce a lattice distortion in the VO2 thin film.

Extended Smoluchowski Model for the Formation of Size-Selected Silver Nanoclusters Generated via Modulated Pulsed Power Magnetron Sputtering

Size-selected silver nanoclusters (NCs) were generated using a modulated pulsed power magnetron sputtering (MPP-MSP) system coupled with a mass spectrometer, and their formation mechanism was investigated by applying an extended Smoluchowski model. Attractive interactions between NC cations and anions were incorporated into the conventional Smoluchowski equations to explain the origin of the size tuning of Ag NCs prepared via MPP-MSP. Bunches overlapped as the repetition rate (f) and peak power (Pp) increased, resulting in the initial formation of large ionic nanoclusters, ultimately causing a reduction in the size of the NC ions due to neutralization via NC cation–anion charge recombination and the formation of aggregates.

The structure and toughness of TiN coatings prepared by modulated pulsed power magnetron sputtering

Titanium nitride (TiN) coatings were prepared on different substrates (Si wafer, M2 steel, glass) by modulated pulsed power (MPP) sputtering and continuous dc magnetron sputtering (dcMS). The structure and properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation and the Vickers indentation test. It was found that the structure was transformed from the columnar growth to the branched growth as the peak target current density (Id) increased to 0.4 A/cm2. The results of plasticity index δH and microindentation crack showed the toughness was improved. MPP TiN coating could withstand the maximum load of 4.9 N when microindentation crack was first discovered at 0.4 A/cm2 while 0.49 N at 0.02 A/cm2 in dcMS condition. This indicated that the high ion flux bombardment of the MPP plasma could be applied to change the structure and toughen TiN coatings.

Effect of microstructure on mechanical and tribological properties of TiAlSiN nanocomposite coatings deposited by modulated pulsed power magnetron sputtering

TiAlSiN nanocomposite coatings were deposited in a closed field unbalanced magnetron sputtering system by reactive sputtering from Ti0.475Al0.475Si0.05 targets using modulated pulsed power magnetron sputtering (MPPMS) under a floating substrate bias. The ratio of the nitrogen flow rate to the total gas flow rate (fN2) was varied from 0 to 40%. The application of MPPMS as sputtering sources was aimed at generating a high ionization degree of the sputtered material and a high plasma density by using a pulsed high power approach. When fN2=0%, an amorphous-like structure Ti0.479Al0.454Si0.066 coating was deposited with a hardness of 10GPa. When nitrogen was added, an optimized nanocomposite structure of nc-TiAlN/a-Si3N4 formed in the TiAlSiN coating deposited at fN2=10%, in which 5–10nm TiAlN nanocrystallites were embedded in a 2–3nm thick amorphous Si3N4 matrix. As the fN2 was increased up to 40%, the elementary composition of the coatings remained almost the same, but the grain size of nanocrystallites approached to 10–20nm and the AlN phase gradually precipitated. A maximum hardness (H) of 33.2GPa, a hardness to the elastic modulus (E) ratio of 0.081 and an H3/E*2 ratio of 0.19GPa were found in the coating deposited at fN2=10%. The friction coefficient of the TiAlSiN coatings was around 0.8–0.9 as sliding against a Si3N4 counterpart under a normal load of 0.5N. A wear rate of 2.0×10−5mm3N−1m−1 was measured in the TiAlSiN coatings deposited at fN2=20–40%. As only a low residual stress is found in the TiAlSiN coatings, we consider the complete phase separation is responsible for the enhanced mechanical and tribological properties of the nc-TiAlN/a-Si3N4 nanocomposite coatings.

Hybrid co-deposition of mixed-valent molybdenum–germanium oxides (MoxGeyOz): A route to tunable optical transmission

Mixed-valent oxides of molybdenum and germanium were deposited simultaneously using reactive magnetron co-deposition within an oxygen–argon environment. The films' stoichiometry, optical, and physical properties were varied through changes in oxygen partial pressure induced by systematic variation of the potential applied to the molybdenum cathode. The oxygen partial pressure was determined from the drop in pressure as measured by a capacitance manometer, assuming constant argon partial pressure. To facilitate deposition, a constant power of 100W DC was applied to the germanium cathode, while power was applied to the molybdenum target using a modulated pulse power supply. Modulated pulse power magnetron sputtering was used due to its ability to generate high target power densities, allowing for rapid reduction of oxygen on the surface of the “oxygen poisoned” molybdenum cathode, as well as for its highly metallic plasma resulting in increased oxygen-gettering capability. Changes in the modulated pulse power supply's capacitor bank voltage load, stepped from settings of 300 to 380V, resulted in films ranging from mixtures of transparent GeO2 (Ge4+) and MoO3 (Mo6+) to the introduction of various absorptive ionic species including Mo5+, Mo4+, Ge2+ and Ge0, as determined from X-ray photoelectron spectroscopy. The presence of each of the aforementioned ions results in characteristic changes in the films' band energies and optical absorption. As deposited MoxGeyOz thin films grown using this method have been shown to have optical gap energies that are able to be tailored between 3.57eV and 0.18eV, spanning useful ranges for devices operating in the visible and near-infrared.

Molybdenum Oxides Deposited by Modulated Pulse Power Magnetron Sputtering: Stoichiometry as a Function of Process Parameters

Molybdenum oxide films were deposited using modulated pulse power magnetron sputtering (MPPMS) from a molybdenum target in a reactive environment where the flow rate of oxygen was varied from 0 sccm to 2.00 sccm. By varying the amount of reactive oxygen available during deposition, the composition of the films ranged from metallic Mo to fully stoichiometric MoO3, when the molybdenum target became poisoned, due to the formation of a dielectric surface oxide coating. Film compositions were verified using high energy resolution x-ray photoelectron spectroscopy. Target poisoning occurred at an oxygen flow rate of 1.25 sccm and reversed when the flow rate decreased to about 1.00 sccm. MoO3 films deposited via MPPMS had densities of 3.8 g cm−3, 81% of the density of crystalline α-MoO3 as determined by x-ray reflectivity (XRR). In addition, XRR and atomic force microscopy data showed sub-nanometer surface roughness values. From spectroscopic ellipsometry, the measured refractive index of the MoO3 films at 589 nm was 1.97 with extinction coefficient values <0.02 at wavelengths above the measured absorption edge of 506 nm (2.45 eV).

On the pressure effect in energetic deposition of Cu thin films by modulated pulsed power magnetron sputtering: A global plasma model and experiments

The modulated pulsed power magnetron sputtering (MPPMS) discharge processes are numerically modeled and experimentally investigated, in order to explore the effect of the pressure on MPPMS discharges as well as on the microstructure of the deposited thin films. A global plasma model has been developed based on a volume-averaged global description of the ionization region, considering the loss of electrons by cross-B diffusion. The temporal variations of internal plasma parameters at different pressures from 0.1 to 0.7 Pa are obtained by fitting the model to duplicate the experimental discharge data, and Cu thin films are deposited by MPPMS at the corresponding pressures. The surface morphology, grain size and orientation, and microstructure of the deposited thin films are investigated by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. By increasing the pressure from 0.1 to 0.7 Pa, both the ion bombardment energy and substrate temperature which are estimated by the modeled plasma parameters decrease, corresponding to the observed transition of the deposited thin films from a void free structure with a wide distribution of grain size (zone T) into an underdense structure with a fine fiber texture (zone 1) in the extended structure zone diagram (SZD). The microstructure and texture transition of Cu thin films are well-explained by the extended SZD, suggesting that the primary plasma processes are properly incorporated in the model. The results contribute to the understanding of the characteristics of MPPMS discharges, as well as its correlation with the microstructure and texture of deposited Cu thin films.

Performance of MPPMS Cr/Cr2O3 films in protection against metal dusting

In the present work, Cr/Cr2O3 thin films were applied on 304L stainless steel substrates via modulated pulsed power magnetron sputtering to investigate their protective behaviour against metal dusting for this steel. Depositions of the films were carried out at various negative values of bias voltage. The structure of the films consisted of a very dense fine columnar structure composed of textured Cr2O3. The films showed similar, very good protective behaviour during exposition to an atmosphere of CH4+H2+residual oxygen and moisture at 1073 K for 20 h. The main protection mechanism proposed was associated to the coatings acting as barriers for outward diffusion of the alloy elements and inward diffusion of C and O into the alloy, especially early in the exposure.

Nanostructured chromium coatings with enhanced mechanical properties and corrosion resistance

Nanocrystalline chromium coatings were deposited by modulated pulsed power magnetron sputtering (MPPMS) at different peak target current densities. The substrate current density increased as the peak target current density was increased. The columnar grain structure of the Cr coatings gradually evolved to randomly oriented nanocrystallites with grain sizes less than 15nm by increasing the peak target current density to 1.2Acm−2. The nanocrystalline Cr coatings showed a 267% increase in the hardness to 16GPa and higher corrosion resistance as compared to the coating deposited by conventional dc magnetron sputtering.

모듈레이티드 펄스 스퍼터링으로 상온 증착한 Indium-Tin-Oxide (ITO) 나노 박막

High power impulse magnetron sputtering (HIPIMS), also known as the technology is called peak power density in a short period, you can get high, so high ionization sputtering rate can make. Higher ionization of sputtered species to a variety of coating materials conventional in the field of improving the characteristics and self-assisted ion thin film deposition process, which contributes to a superior being. HIPIMS at the same power, but the deposition speed is slow in comparison with DC disadvantages. Since recently as a replacement for HIPIMS modulated pulse power (MPP) has been developed. This ionization rate of the sputtered species can increase the deposition rate is lowered and at the same time to overcome the problems to be reported. The differences between the MPP and the HIPIMS is a simple single pulse with a HIPIMS whereas, MPP is 3 ms in pulse length is adjustable, with the full set of multi-pulses within the pulse period and the pulse is applied can be micro advantages. In this experiment, <TEX>$In_2O_3$</TEX> : <TEX>$SnO_2$</TEX> composition ratio of 9 : 1 wt% target was used, Ar : <TEX>$O_2$</TEX> flow rate ratio is 4.8 to 13.0% of the rate of deposition was carried out at room temperature. Ar 40 sccm and the flow rate of <TEX>$O_2$</TEX> and then fixed 2 ~ 6 sccm was compared against that. The thickness of the thin film deposition is fixed at 60 nm, when the partial pressure of oxygen at 9.1%, the specific resistance value of <TEX>$4.565{\times}10^{-4}{\Omega}cm$</TEX>, transmittance 86.6%, mobility <TEX>$32.29cm^2/Vs$</TEX> to obtain the value.

Structure and properties of CrSiN nanocomposite coatings deposited by hybrid modulated pulsed power and pulsed dc magnetron sputtering

CrSiN nanocomposite coatings were deposited at room temperature in a closed field unbalanced magnetron sputtering system by co-sputtering from Cr and Si targets using modulated pulsed power magnetron sputtering (MPPMS) and pulsed dc magnetron sputtering (PDCMS), respectively. The application of MPPMS as one of the sputtering sources was aimed at generating a high ionization degree of the sputtered material and a high plasma density by using a pulsed high power approach. When the Si content is less than 4.8at.%, Si atoms mainly go into the CrN lattice and form a solid solution. As the Si content reached 6.7at.%, a nanocomposite structure formed in the CrSiN coatings, in which 5–8nm Cr(Si)N nanocrystallites were embedded in an amorphous Si3N4 matrix. The solid solution strengthening and complete phase separation are believed to be responsible for the enhanced mechanical properties of the CrSiN coatings. A maximum hardness of 38GPa, an H/E ratio of 0.096 and an H3/E*2 ratio of 0.31GPa were identified in the coating with a Si content of 6.7at.%. The coatings with a Si content at 6.7at.% and 10.2at.% were found to be optimized for wear resistant applications. The MPPMS+PDCMS CrSiN coatings also exhibited improved corrosion resistance as compared to AISI 304 stainless steel samples tested in a 3.5wt.% NaCl aqueous solution.

The β to α phase transition of tantalum coatings deposited by modulated pulsed power magnetron sputtering

Tantalum coatings are of particular interest today as promising candidates to replace potentially hazardous electrodeposited chromium coatings for tribological and corrosion resistant applications, such as the internal lining on large-caliber gun barrels. Tantalum coatings have two crystalline phases, α-Ta (body-centered-cubic) and β-Ta (metastable tetragonal) that exhibit relatively different properties. Alpha-Ta is typically preferred for wear and corrosion resistant applications and unfortunately, is very difficult to deposit without the assistance of substrate heating or post-annealing treatments. Furthermore, there is no general consensus on the mechanism which causes α or β to form or if there is a phase transition or transformation from β→α during coating deposition. In this study, modulated pulsed power (MPP) magnetron sputtering was used to deposit tantalum coatings with thicknesses between 2 and 20μm without external substrate heating. The MPP Ta coatings showed good adhesion and low residual stress. This study shows there is an abrupt β→α phase transition when the coating is 5–7μm thick and not a total phase transformation. Thermocouple measurements reveal substrate temperature increases as a function of deposition time until reaching a saturation temperature of ~388°C. The importance of substrate temperature evolution on the β→α phase transition is also explained.

Reactive Sputter Deposition of Alumina Coatings

Highly ionized pulse plasma processes (HIPP processes) like High Power Impulse Magnetron Sputtering HIPIMS and Modulated Pulse Power MPP have matured in recent years. Current research focuses on the development for industrial processes. HIPP processes offer a tool for tailoring the film properties and to improve hardness, density, refractive index, and further properties beyond state of the art. Alumina coatings are used besides application in cutting tools as insulator for electric and sensor applications. This paper focuses on the process development of an industrial process for deposition of alumina with improved properties regarding the use as insulator. Concerning productivity a high rate deposition process is required for economic production. Therefore, the deposition rate must be increased or the film properties improved in a way that thinner films exceed reference films prepared with state of the art technology. MPP in comparison to a mid-frequency (MF-) process was investigated and the resulting rates are reported. The films were prepared without feedback control in the transition regime close to the threshold of the oxide mode. Regarding the insulating properties the films were characterized by their critical leakage field strength. MPP films with less than 1 μm thickness showed a critical leakage field strength up to 2.9 V/nm. The SEM cross sections of the prepared films showed a dense glassy structure for all the HIPP films.

Exotic Highly Ionized Pulse Plasma Processes

Highly ionized pulse plasma processes (HIPP processes), like high power impulse magnetron sputtering (HIPIMS) also known as high power pulse magnetron sputtering (HPPMS), modulated pulse power sputtering (MPP), as well as further modifications involving increased ionization in sputtering have been investigated and matured within the last decade. On European level a concerted action focusing the efforts and bringing together the leading experts was set up and is actually promoting the transition of HIPP processes to industry. Besides the well know approaches of HIPIMS/HPPMS and MPP further modifications for ionized PVD are under development. This paper focuses on HIPP processes and new technological approaches besides the well-known "big players". New approaches combining technologies like hollow cathodes in different modifications, coils for inductive coupling, arc sources for "gasless sputtering" or a modified process for constant-current HIPIMS will be presented.

Microstructure and properties of nanostructured thick CrN coatings

Thick polycrystalline CrN coatings (20μm) were deposited at a high deposition rate (10μm/h) using a highly ionized plasma generated by modulated pulsed power magnetron sputtering. The microstructure of the thick CrN coating was characterized using transmission electron microscopy. The coating exhibited a super dense microstructure with a grain size in the nanometer range of 100–150nm. The thick CrN coating showed an average high hardness of 24GPa, excellent adhesion and wear resistant.

Al doped ZnO 박막 증착을 위한 모듈레이티드 펄스 스퍼터링

Modulated Pulse Power (MPP) magnetron sputtering is a new high-power pulsed magnetron sputtering (HPPMS) technology which overcomes the low deposition rate problem by modulating the pulse voltage shape, amplitude, and the duration. Highly ionized magnetron sputtering can be performed without arcing because it can be controlled as multiple steps of micro pulses within one overall pulse period in the range of 500-3,000 <TEX>${\mu}s$</TEX>. In this study, the various waveforms of discharge voltage and current for micro pulse sets of MPP were investigated to find the possibility of controlling the strongly ionized plasma mode. Enhanced ionization of the sputtered metal atoms was obtained by OES. Large grained columnar structure can be grown by the strongly ionized plasma mode in the AZO deposition using MPP. In the most highly ionized deposition condition, the preferred orientation of (002) plane decreased, and the resistivity, therefore, increased by the plasma damage.

Pulse management in high power pulsed magnetron sputtering of niobium

High power pulsed magnetron sputtering is being intensively explored as a very promising approach for the fabrication of functional coatings with enhanced performance. However, a direct comparison of the results obtained in different systems is complicated given the variety of pulse power supplies with different pulse shape, voltage and current characteristics. In this study, we systematically investigate and compare sputtering processes above a niobium target operated in the same reactor using two commercially available power supplies: (i) a shorter (200μs) square voltage pulse generator permitting higher cathode voltage values, and (ii) a modulated pulse power generator with longer (800–300μs) custom-shaped pulses. In addition, target sputtering using a conventional DC power supply is also analyzed for comparison purposes. The pulsed discharges are characterized by time-resolved current and voltage probes and optical emission spectroscopy. The deposition rate, the microstructure, and the mechanical stress of the fabricated Nb coatings are evaluated and compared. Finally, the effect of the power delivery management is discussed in terms of discharge characteristics and coating properties.

Low Friction CrNMPP/TiNDCMS Multilayer Coatings.

Transition metal nitrides like CrN and TiN are widely used in automotive applications due to their high hardness and wear resistance. Recently, we showed that a multilayer architecture of CrN and TiN, deposited using the hybrid—high power impulse magnetron sputtering (HIPIMS) and direct current magnetron sputtering (DCMS)—HIPIMS/DCMS deposition technique, results in coatings which indicate not only increased mechanical and tribological properties but also friction coefficients in the range of diamond-like-carbon coatings when tested at RT and ambient air conditions. The modulated pulsed power (MPP) deposition technique was used to replace the HIPIMS powered cathode within this study to allow for a higher deposition rate, which is based on the complex MPP pulse configuration. Our results on MPP/DCMS deposited CrN/TiN multilayer coatings indicate excellent mechanical and tribological properties, comparable to those obtained for HIPIMS/DCMS. Hardness values are around 25 GPa with wear rates in the range of 2 × 10−16 Nm/m3 and a coefficient of friction around 0.05 when preparing a superlattice structure. The low friction values can directly be correlated to the relative humidity in the ambient air during dry sliding testing. A minimum relative humidity of 13% is necessary to guarantee such low friction values, as confirmed by repeated tests, which are even obtained after vacuum annealing to 700 °C. Our results demonstrate that the co-sputtering of high metal ion sputtering techniques and conventional DC sputtering opens a new field of applications for CrN/TiN coatings as high wear resistance and low friction coatings.

A comparison of the oxidation behavior of CrN films deposited using continuous dc, pulsed dc and modulated pulsed power magnetron sputtering

The study is aimed at comparing the oxidation behavior of the stoichiometric CrN films deposited by continuous dc magnetron sputtering (dcMS), mid-frequency pulsed dc magnetron sputtering (PMS), and modulated pulsed power (MPP) magnetron sputtering techniques in a closed field unbalanced magnetron sputtering system. These as-deposited CrN films exhibited a cubic structure and similar stoichiometric compositions, but with different microstructures and residual stresses. After annealing in the ambient air from 600 to 1000°C, the changes in the crystal phase, microstructure, and hardness of the films were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy line scan, and nanoindentation. The oxidation activation energies of the films were calculated using Arrhenius equation. It was found that the MPP CrN film exhibited superior oxidation resistance than dcMS and PMS CrN films. After annealing at 900°C, the MPP CrN film exhibited an extremely dense structure and the cubic phase was well maintained. On the other hand, the dcMS and PMS CrN films were severely oxidized into a porous structure with the development of β-Cr2N and Cr2O3 phases and a rapid degradation of the cubic phase after 700 and 800°C, respectively. The results indicate that all films showed a parabolic oxidation rate below 900°C. The oxidation activation energies for the dcMS, PMS and MPP CrN films are 116kJ/mol, 141kJ/mol, and 195kJ/mol, respectively. The better oxidation resistance of the MPP CrN film is attributed to its dense microstructure and low residual stress.

Thick CrN/AlN superlattice coatings deposited by the hybrid modulated pulsed power and pulsed dc magnetron sputtering

Thick and dense CrN/AlN superlattice coatings (up to10μm) have been deposited by a hybrid magnetron sputtering process from metallic Cr and Al targets, which were powered by modulated pulsed power (MPP) magnetron sputtering and middle frequency pulsed dc magnetron sputtering (PMS) techniques, respectively. The bilayer period (Λ) of the coatings was changed from 10 to 2.5nm by varying the ratio of the N2 flow rate to the total gas flow rate. The microstructure and properties of the CrN/AlN coatings were characterized using electron probe microanalysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, scratch test, nanoindentation, and ball-on-disk wear test. The oxidation behavior of the thick CrN/AlN coating (Λ=2.8nm) after annealing at 900 and 1000°C in an ambient air has been investigated. Thick CrN/AlN coatings showed good adhesion. Superhardness values of 40–45GPa and low wear rates in the low end of the 10−8mm3N−1m−1 range have been achieved in the coatings with Λ in a small range of 2.5 to 3.2nm. No oxides were identified in the coatings after annealing at 1000°C. The coating maintained cubic structure after annealing at 1000°C.