Mid-frequency Magnetron Sputtering Research Articles

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

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

Tribological behavior of MoS2/a-C:Si composite films in high-temperature air and vacuum environments

MoS2/a-C:Si composite films doped with different contents of carbon (C) and silicon (Si) were deposited using a hybrid deposition system consisting of a superimposed high-power impulse magnetron sputtering (HiPIMS)-direct current magnetron sputtering (DCMS) and a mid-frequency magnetron sputtering (MFMS). The content of C and Si elements in the films was controlled by changing the direct current (DC) of the graphite-silicon (C-Si) mosaic target. The effects of C and Si doping on the microstructure and mechanical properties of the films were investigated. In addition, the tribological behavior of the films in high-temperature air (up to 350 °C) and vacuum environments was evaluated in detail. The results suggested that MoS2/a-C:Si composite films exhibited excellent tribological properties in both high-temperature air and vacuum environments. MoS2/a-C:Si composite films doped with C and Si elements exhibited low coefficient of friction (COF) and wear rate (WR) at elevated temperatures due to the improved thermal stability. In particular, MoS2/a-C:Si composite film with 40.37 at% C displayed a low COF of 0.051 and a low WR of 1.47 × 10 −6 mm3/(N·m) at 350 °C in air. Moreover, MoS2/a-C:Si composite film also exhibited excellent tribological properties under vacuum conditions due to the precipitation of C on the wear track surface. The COF of MoS2/a-C:Si composite film with 40.37 at% C under vacuum conditions was as low as 0.018, and the WR of the film was as low as 1.99 × 10 −7 mm3/(N·m).

Direct Fabrication of a Copper RTD over a Ceramic-Coated Stainless-Steel Tube by Combination of Magnetron Sputtering and Sol–Gel Techniques

Reducing the economic and environmental impact of industrial process may be achieved by the smartisation of different components. In this work, tube smartisation is presented via direct fabrication of a copper (Cu)-based resistive temperature detector (RTD) on their outer surfaces. The testing was carried out between room temperature and 250 °C. For this purpose, copper depositions were studied using mid-frequency (MF) and high-power impulse magnetron sputtering (HiPIMS). Stainless steel tubes with an outside inert ceramic coating were used after giving them a shot blasting treatment. The Cu deposition was performed at around 425 °C to improve adhesion as well as the electrical properties of the sensor. To generate the pattern of the Cu RTD, a photolithography process was carried out. The RTD was then protected from external degradation by a silicon oxide film deposited over it by means of two different techniques: sol–gel dipping technique and reactive magnetron sputtering. For the electrical characterisation of the sensor, an ad hoc test bench was used, based on the internal heating and the external temperature measurement with a thermographic camera. The results confirm the linearity (R2 > 0.999) and repeatability in the electrical properties of the copper RTD (confidence interval < 0.0005).

Multilayer thin films of aluminum oxide and tantalum oxide deposited by pulsed direct current magnetron sputtering for dielectric applications

This research describes the synthesis of multilayer thin films of aluminum oxide and tantalum oxide for dielectric applications. The multilayer thin films are made of two, four, or eight oxide layers produced by physical vapor deposition (PVD), specifically mid-frequency pulsed direct current magnetron sputtering. The oxide layers are stoichiometric Al2O3 and Ta2O5 with two specific morphologies observed from cross-section images obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Al2O3 layers exhibit a columnar structure whereas the Ta2O5 layers are uniform and dense. However, the morphology of the Ta2O5 layers changes progressively in the four-layer and eight-layer systems under the influence of the morphology of the Al2O3 layer below. This behavior is induced by the morphological continuity of the interface between two oxide layers. X-ray diffraction (XRD) shows the low crystallinity of these oxide layers due to the experimental conditions used during the magnetron sputtering process, particularly the low deposition temperature. The dielectric behavior of the multilayer thin films is studied by dielectric strength measurements. The results are compared to the values obtained for single layers of Al2O3 and Ta2O5 produced under the same experimental conditions. The two-layer system shows an intermediate value compared to the single layers, higher than Al2O3 and lower than Ta2O5. The dielectric strengths of the four-layer and the eight-layer systems are higher than those measured for the single layers of Al2O3 and Ta2O5. Finally, the morphology and the crystallinity of the multilayer thin films are changed by thermal annealing of these samples at 850 °C under vacuum. The thermal annealing induces crystallization of the Ta2O5 layers and the loss of morphological continuity at the interface between the oxide layers. These modifications result however in a lower dielectric strength for all the multilayer thin films.

Deposition of tungsten oxide films by reactive magnetron sputtering on different substrates

Tungsten oxide films are deposited with the help of reactive magnetron sputtering in an argon/oxygen gas mixture. Films are deposited on different substrates, in particular, on soda lime glass, fluorine-doped tin oxide coated glass, silicon (Si), and quartz (SiO2). Thin films from three different discharge modes, in particular, high power impulse magnetron sputtering, midfrequency magnetron sputtering, and radiofrequency magnetron sputtering, are compared. Deposited films are characterized by x-ray diffraction, Raman spectroscopy, and spectroscopic ellipsometry. Composition, crystal structure, and optical properties of as-deposited and annealed films are found to depend on the deposition mode and on the substrate.

Arc energy minimization in high-power impulse magnetron sputtering

High-power impulse magnetron sputtering (HiPIMS) is rather a new and rapidly developing method for physical vapor deposition of thin films. Due to a high ionization degree of the sputtered material, the HiPIMS coatings have better properties than those produced by conventional DC magnetron sputtering (DCMS) and mid-frequency magnetron sputtering (MFMS). Along with its advantages, HiPIMS has some disadvantages, which make difficult its application. HiPIMS is characterized by the high pulsed discharge current, which provides higher arc frequency and energy than in MFMS and DCMS. This leads to larger defect size and quantity that appear in the coating obtained. This paper proposes the analytical simulation model to describe the discharge current and discharge voltage during arcing. This model helps to calculate the arc energy, lifetime, and maximum current. It also identifies what parameters of the power supply exert the highest effect on the arc parameters. The paper considers the types of the HiPIMS power supply and compares them with the view of arc quenching effectiveness. The model adequacy is verified by the experimental results of measurement the arc parameters in HiPIMS. It is shown the effect of arc energy on the size and number of defects in the carbon coatings obtained in HiPIMS.

Silicon- and tungsten-containing hydrogen-free and hydrogenated amorphous carbon films for friction-reducing applications

For tribological applications, adding Si or W to hydrogen-free a-C or hydrogenated a-C:H is highly beneficial to tailor the film properties. Hence, a direct comparison between Si- and W-containing a-C and a-C:H considerably enhances the understanding of both the interaction between Si or W and the hydrogenation state as well as its effect on the structure and tribo-mechanical properties of these films. Therefore, non-modified a-C(:H), Si-containing a-C(:H):Si, and W-containing a-C(:H):W films were systematically grown in a mid-frequency magnetron sputtering process.The formation of W-based nanocrystallites within a-C(:H):W is identified by x-ray diffraction, whereas a-C(:H):Si still possesses an amorphous character. Raman scattering spectra show higher I(D)/I(G) ratios for hydrogen-free a-C(:X) films compared to the respective a-C(:H):X, indicating a higher number and larger sizes of sp2 clusters in the carbon network. For the hydrogenated a-C:H:X films, the reduced number of sp2 clusters is related to the presence of terminating CH bonds, which were detected as stretching modes. Among the different films, a-C:W has the highest I(D)/I(G) ratio, while a-C:H and a-C:H:Si exhibit the lowest I(D)/I(G) values. While a-C:Si and a-C:H:Si are characterized by comparable hardness values of (18.7 ± 1.3) and (18.4 ± 1.1) GPa, a-C:W has a lower hardness of (13.8 ± 1.0) GPa compared to a-C:H:W with (17.5 ± 0.9) GPa. Among all modified a-C(:H):X films, a-C:Si and a-C:H:Si reveal the lowest coefficients of friction, but show highest wear rates in dry sliding against 100Cr6 steel. Contrarily, a-C:W has higher friction and wear than a-C:H:W. Consequently, the Si-containing a-C(:H):Si films demonstrate comparable tribo-mechanical properties, while the hydrogenation state leads to different tribo-mechanical properties of a-C(:H):W.

Cuprous Oxide Films Deposition by Mid-Frequency Magnetron Sputtering and Their Photocatalytic Activity under Visible Light

Cuprous oxide (Cu2O) has attracted much attention as a photocatalytic material. In this paper, the mid-frequency reactive magnetron sputtering method was used to prepare Cu2O films on glass slides, and the effects of oxygen flow and deposition time on the structures, morphologies and photocatalytic properties of the films were studied. The results show that the films prepared by this method have smooth surfaces and good absorptivity in the visible region. As the oxygen flow increases, the films transit from the mixed-phase of Cu and Cu2O to the single-phase of Cu2O. When the oxygen flow continues to increase, the films change to a mixed-phase of Cu4O3 and Cu2O. The photocatalytic decolorization of methyl orange under visible light irradiation conditions was used to assess the photocatalytic properties of the prepared films. When the oxygen flow is 6[Formula: see text]sccm and the deposition time is 15[Formula: see text]min, the film exhibits the best photocatalytic activity. Finally, the Mulliken electronegativity theory was used to explain the photocatalytic mechanism of Cu2O. This study confirmed the feasibility of preparing Cu2O photocatalytic films by magnetron sputtering, and provided the experimental basis for the subsequent study of Cu2O photocatalytic films.

Mechanical and Structural Behavior of HfN Thin Films Deposited by Direct Current and Mid-Frequency Magnetron Sputtering.

Nanocrystalline HfN thin films were deposited onto silicon substrates with direct current magnetron sputtering (dcMS) and mid-frequency magnetron sputtering (mfMS) by using hafnium metallic target with 3-inch diameter and 99.9% purity in argon/nitrogen atmosphere, under 4 different pulse frequencies and duty cycles. In order to evaluate the structural, morphological and mechanical properties, we used X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), nanoindentation tests. X-ray diffraction patterns show that films sputtered in dcMS mode have a mixed δ-HfN and HfN0.4 phases, whereas mfMS favor a single δ-HfN phase. mfMS leads to films with the higher mechanical hardness and smaller surface roughness than those of films deposited by dcMS. Hafnium nitride films with a single δ-HfN phase show the highest hardness values of 24.5 GPa while those of mixed δ-HfN and HfN0.4 phases show the lowest 18.3 GPa. In summary, the sputtering technique has a crucial role on the properties of the film and can be suitable used to adjust the structure and hardness of HfN films.

High deposition rate films prepared by reactive HiPIMS

High power impulse magnetron sputtering (HiPIMS) is characterized by a very high current density at the target during each pulse. A large fraction of sputtered target material is ionized, which allows the preparation of hard and defect-free coatings. Compared to the conventional sputtering methods, HiPIMS technology possesses a certain drawback, i.e. lower deposition rate. A promising variation, i.e. reactive HiPIMS, was described by a mathematical model (S. Kadlec, J. Čapek, JAP 121 (2017) 171910). One of the fundamental results shows that reactive HiPIMS can deliver higher deposition rates compared to the mid-frequency pulsed dc magnetron sputtering (Mf-PCDMS) due to a lower degree of target poisoning. To confirm these theoretical results, series of experiments were performed in laboratory deposition system with different target materials (Al, Cr, Ti, Zr, Hf, Ta, Nb). Two targets of the same material were employed both in dual Mf-PDCMS (pulse-on/pulse-off time ratio 45:5 μs) and in dual HiPIMS (pulse-on/pulse-off time ratio 25:725 μs) conditions at a fixed power. We confirmed that higher values of the deposition rate for Ta2O5 and Nb2O5 films can be achieved by HiPIMS when operated in the poisoned regime. Finally, we supported our experimental results by Monte-Carlo simulations performed in SRIM and SDTrimSP simulation software.

Microstructure, electrochemical and tribocorrosion behaviors of CrCN nanocomposite coating with various carbon content

The CrCN nanocomposite coatings with various carbon content were firstly synthesized via mid-frequency magnetron sputtering to seek the possibility of application in marine corrosion environment. The microstructure of the CrCN coatings were characterized systematically. In particular, the mechanical, electrochemical as well as tribocorrosion performances of the resulting coatings were evaluated in detail. The results showed that the CrCN coatings were polycrystalline structures composed of CrN phase, Cr7C3 phase and amorphous carbon. The carbon content of the CrCN coating significantly influenced its mechanical, electrochemical and tribocorrosion properties. The hardness and elastic modulus of the CrCN coating increased initially and then gradually decreased as the raising of the carbon content in the coating. And the CrCN coating with 20.3% carbon content exhibited maximum hardness of 14.7 GPa and the highest elastic modulus of 197.7 GPa among all coatings. However, the adhesion strength of the prepared coatings gradually deteriorated as the carbon element doping into CrN coating. The CrN coating with many defects exhibited poor electrochemical performances compared with the dense CrCN coatings. The CrCN coating with 20.3% carbon content presented the lowest wear rate of 3.85 × 10−7 mm3(Nm)−1 and minimum OCP value of −0.19 V, revealing its excellent tribocorrosion properties. This could ascribe to its high hardness and the obvious graphitization of the wear surface. Finally, the possible tribocorrosion mechanisms of the as-prepared coatings were proposed according to the analyzed results of their microstructure, electrochemical behaviors and wear surfaces.

Deposition of cobalt oxide films by reactive pulsed magnetron sputtering

Cobalt oxide films were deposited with the help of reactive high power impulse magnetron sputtering (HiPIMS) and mid-frequency pulsed magnetron sputtering (PMS) in argon gas at an argon gas pressure of 1 Pa and with different oxygen admixtures. The HiPIMS discharge was operated at a repetition frequency f=100 Hz with a duty cycle of 1%. Deposition rate and ion fraction were measured. The intensity of plasma ions, in particular Co+ and O+, is enhanced during HiPIMS compared to PMS and extends to larger ion energies. Films deposited on glass substrates were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. Crystal structure and electrical resistivity of as-deposited films were found to depend on the deposition conditions. Deposited films are compatible with a non-stoichiometric Co3O4 spinel type crystal structure with unoccupied cobalt sites. PMS produces films with a preferred lattice orientation. HiPIMS show a large internal stress which relaxes during annealing. Electrical resistivity is several orders of magnitude smaller for films deposited by HiPIMS compared to PMS.

Hybrid HIPIMS+MFMS power supply for dual magnetron sputtering systems

The paper presents a novel power supply device that provides a hybrid technique of dual magnetron sputtering. This power supply generates a sequence of bipolar pulses which provides both mid-frequency and high-power impulse magnetron sputtering. This allows using the advantages of both techniques, while numerous adjustable parameters considerably enhance the capabilities of the magnetron sputtering system. In the proposed power supply circuit, special attention is paid to the output pulse formers and the power switch control. The experimental results are obtained for superimposed mid-frequency and dual high-power impulse magnetron sputtering. During the aluminum film deposition, the deposition rate, the ion current density on the substrate and the ion-to-atom ratio are regulated by changing the power ratio between mid-frequency and high-power impulse magnetron sputtering.

Effect of sp3 Content on Adhesion and Tribological Properties of Non-Hydrogenated DLC Films.

Non-hydrogenated diamond-like carbon (DLC) films with various ratios of sp3/sp2 were prepared on cemented carbide YG8 with DC magnetron sputtering technology. A pure graphite target was selected as the carbon source. Before DLC deposition, a surface etching pretreatment was carried out by mid-frequency magnetron sputtering method, using Ti atoms to improve adhesion strength. The ratios of sp3/sp2 were adjusted by bias voltages. In order to investigate the effect of the ratio of sp3/sp2 on adhesion and tribological properties, Raman spectra, XPS spectra, adhesion scratch test and ball-on-disk dry friction tests were applied. The results indicated that the ratio of sp3/sp2 fluctuated with bias voltage, increasing in the range of 0.74 to 0.98. The adhesion strength decreased from 31.5 to 18.4 N with the increasing ratio of sp3/sp2, while the friction coefficient rose in DLC-Si3N4 and dropped in DLC-Ti6Al4V. For DLC-Ti6Al4V, the oxidation of Ti6Al4V had a greater influence than graphitization of DLC. The hard oxides of Ti6Al4V broke the graphite transfer layer leading to a high friction coefficient. The wear rate was approximately linearly related to bias voltage. The coefficients of the linear regression equation were influenced by different friction materials. The adhesion strength and the friction coefficient were fitted as a function of the ratio of sp3/sp2.

Power supply for mid-frequency magnetron sputtering with a wide-range control of pulses parameters

The paper presents a description of a pulsed power supply of a magnetron sputtering system with a power of 10 kW, which has a wide range of output parameters, such as the amplitude, the frequency, and duration of voltage pulses. High values of the pulse current (up to 100 A) and voltage (up to 1800 V) provide the ability to work at low duty cycle, which in turn allows to increase the value of the ion current on the substrate. It has been experimentally found, that changing the frequency and duration of the pulses can increase the ion current density to the substrate while maintaining the average discharge power.

Direct deposition of extremely low interface-contact-resistant Ti2AlC MAX-phase coating on stainless-steel by mid-frequency magnetron sputtering method

MAX-phase materials, bulk as well as film, have manifested outstanding potential applications owing to their unusual properties. Usually, MAX-phase is achieved after higher ex-situ post-annealing (≥1000 ℃) treatment. Here, we report single-step transition to Ti2AlC MAX-phase, deposited on stainless-steel(SS) by mid-frequency magnetron-sputtering system, at a lower substrate temperature of 750 ℃. The microstructure, phase and morphological characterization reveals that the compact, dense and crack-free film comprises of randomly oriented grains. Importantly, the surface of the film still remains crack-free after transition to the MAX-Phase. Moreover, a large improvement in conductivity for the film deposited at 750 ℃ (ICR = 3.27 mΩ.cm2 under 140 N. cm−2) as compared to Ti-Al-C film deposited at 500 ℃ (ICR ≥ 400 mΩ.cm2) elucidates the MAX-phase formation. The films with such low ICR values (<10 mΩ. cm2; department-of-energy(DOE) standards) are the best potential candidates for future bipolar plates coating.

Low-temperature β-SiC interlayer for diamond film on cemented carbide

ABSTRACTThe adhesion of protective diamond films to cemented carbide substrates used in fabrication of space drilling tools can be improved by the inclusion of β-SiC interlayers. Conventional CVD methods for depositing the SiC interlayers lead to interface coarsening and heat stress resulting from high temperatures of deposition. In this work, a mid-frequency magnetron sputtering technique is used to deposit the β-SiC interlayer at lower temperatures, and the effects of deposition temperature on the microstructure and properties of the interlayer and final diamond film are assessed. The results show that the β-SiC interlayers deposited at temperatures exceeding 300°C possess high compactness and crystallinity. Increasing crystal β-SiC phase has beneficial effects on the nucleation and growth of diamond film. Based on the experimental data, a six-step reaction model is proposed to show the mechanism by which the β-SiC interlayer promotes the nucleation and growth of diamond films.

Interaction effects of cathode power, bias voltage, and mid-frequency on the structural and mechanical properties of sputtered amorphous carbon films

The Design of Experiments is a promising method to investigate the cause-effect relation between the mid-frequency magnetron sputtering parameters on the structural and mechanical properties of amorphous carbon (a-C) films. Based on the Central Composite Design, the cathode power of two graphite targets, bias voltage, and mid-frequency were simultaneously varied from 1500 to 4000 W, −100 to −200 V, and 20 to 50 kHz, respectively. The chemical bonding state was characterized using UV and visible Raman spectroscopy with excitation wavelengths of 266 and 532 nm. Corresponding measurements were performed by X-ray photoelectron spectroscopy (XPS) using synchrotron radiation. Additionally, hardness and elastic modulus of the sputtered a-C films were determined in nanoindentation tests.Multi-wavelength Raman spectroscopy identified an sp3 content below 20%, with most a-C films having an sp3 value in the range of 12 to 18%. The formation of sp3 bonded atoms is negatively influenced by a high cathode power and bias voltage, whereas the highest sp3 content is obtained with a-C films sputtered with a cathode power and bias voltage of 2750 W and −150 V. However, higher values of the cathode power and bias voltage result in a film delamination and decrease of the sp3 concentration. The bonding state affects the mechanical properties, as high hardness and elastic modulus result from a high sp3 content. Therefore, a targeted adjustment of cathode power and bias voltage is necessary to obtain a-C films with a high hardness. In contrast, the mid-frequency does not have a significant impact on the mechanical properties. In conclusion, the Central Composite Design has proven to be a suitable method to investigate the cause-effects of the sputtering parameters on the properties of the a-C film.

Effect of the deposition conditions on the properties of photocatalytic WO3 thin films prepared by mid-frequency magnetron sputtering

WO3 is a widely considered photocatalytic material for water purification. In this paper, nanocrystalline WO3 films were deposited on a glass slide by the mid-frequency reactive magnetron sputtering method. The aim is to determine the photocatalytic activities of the films, which are controlled by the process parameters (oxygen flow and substrate bias). The annealed films reveal a hexagonal structure and have some absorptivity in the visible region. The field emission scanning electron microscopy pattern shows that the films exhibit a uniform, smooth surface. The photocatalytic properties of the prepared films were evaluated by the photodecolorization of methylene blue. The films exhibit the best activity at an oxygen flow rate of 30 sccm and a substrate bias of −50 V. The reason is that this film can create more electron-hole pairs as a result of the greater absorption of visible light, which enhances the photocatalytic performance. Based on the results, a possible photocatalytic mechanism has been proposed.

Structure and mechanical properties of hafnium nitride films deposited by direct current, mid-frequency, and high-power impulse magnetron sputtering

The structural properties of hafnium nitride films are mainly influenced by the deposition conditions, which are affected by the sputtering technique. A suitable use of the different sputtering modes allows to control the structural development of the films and thus to adjust the profile of the properties. NaCl-type hafnium nitride films were deposited using direct current magnetron sputtering (dcMS), mid-frequency magnetron sputtering (mfMS), and high-power impulse magnetron sputtering (HiPIMS). dcMS produces films with a columnar microstructure, whereas a fully-dense morphology is achieved by mfMS and HiPIMS. X-ray diffraction patterns show that films sputtered in dcMS mode have a (200) orientation, whereas mfMS and HiPIMS favor an orientation with the (111) plane parallel to the samples' surface. mfMS leads to films with the largest crystal sizes and lowest stresses, which is ascribed to recrystallization mechanisms during the film growth. Hafnium films with an overstoichiometric composition show the highest hardness values. In this context, the dcMS-Hf49.8N50.2, mfMS-Hf50.4N49.6, and HiPIMS-Hf49.0N51.0 have a hardness of 28.2 ± 2.1, 32.4 ± 3.4, and 30.4 ± 3.1 GPa, respectively. In summary, the sputtering technique has a crucial role on the properties of the film and can be suitable used to adjust the structure and hardness of HfN films.