Robert Franz

Oxidation and diffusion processes during annealing of AlCrVN hard coatings

V-alloyed AlCrN hard coatings were deposited by reactive arc evaporation in an industrial-sized deposition system and subsequently annealed in ambient air at temperatures ranging from 550to700°C in order to study the formation mechanisms of the desired lubricious oxides. The oxidized samples were investigated by means of secondary ion mass spectrometry depth profiling, x-ray diffraction, Raman spectroscopy, and analytical transmission electron microscopy. Vanadium diffusion in the oxidized part of the coating leads to the formation of a V-rich top layer containing AlVO4 and the desired lubricious oxide V2O5 followed by a V-depleted inner oxide layer consisting of a mixed or nanocrystalline (Al,Cr,V)2O3 on top of the intact AlCrVN coating.

Investigation on structure and properties of arc-evaporated HfAlN hard coatings

HfAlN hard coatings were synthesized by cathodic arc evaporation from Hf0.75Al0.25 targets at different bias voltages and N2 pressures. Structural investigations by x-ray diffraction (XRD) revealed the formation of a face-centered cubic (fcc) structure with a change in the preferred orientation depending on the energetic growth conditions. This change in the crystal structure did not significantly influence the mechanical properties, e.g., hardness, where values ranging from 24 to 26 GPa were measured. The obtained fcc phase is stable up to 1000 °C as no significant changes in the crystal structure could be observed after annealing in vacuum. Similar experiments in ambient air and subsequent analysis of the coatings by XRD and Raman spectroscopy revealed an onset temperature for oxidation in the range of 700–800 °C and the formation of monoclinic HfO2 as the dominating oxide phase. Ball-on-disk tests at different temperatures were performed in order to evaluate the tribological properties. The coefficient...

Erosion behavior of composite Al-Cr cathodes in cathodic arc plasmas in inert and reactive atmospheres

AlxCr1−x composite cathodes with Al contents of x = 0.75, 0.5, and 0.25 were exposed to cathodic arc plasmas in Ar, N2, and O2 atmospheres and their erosion behavior was studied. Cross-sectional analysis of the elemental distribution of the near-surface zone in the cathodes by scanning electron microscopy revealed the formation of a modified layer for all cathodes and atmospheres. Due to intermixing of Al and Cr in the heat-affected zone, intermetallic Al-Cr phases formed as evidenced by x-ray diffraction analysis. Cathode poisoning effects in the reactive N2 and O2 atmospheres were nonuniform as a result of the applied magnetic field configuration. With the exception of oxide islands on Al-rich cathodes, reactive layers were absent in the circular erosion zone, while nitrides and oxides formed in the less eroded center region of the cathodes.

Functional Thin Films for Display and Microelectronics Applications

Within the last three decades, thin films grown by physical vapor deposition methods have found widespread applications. This article reports about recent research examples on molybdenum thin films, as used for thin film transistor liquid crystal displays, and on TiN diffusion barrier films, as used for microelectronics.ZusammenfassungInnerhalb der letzten drei Jahrzehnte haben dünne mit Hilfe der physikalischen Dampfphasenabscheidung hergestellte Schichten breite Anwendung gefunden. Dieser Beitrag berichtet über jüngste Forschungsbeispiele von Molybdänschichten für Dünnschichttransistor-Flüssigkristall-Bildschirme und von TiN-Barriereschichten für die Mikroelektronik.

Industrial-scale sputter deposition of molybdenum oxide thin films: Microstructure evolution and properties

The current work investigates the microstructure and property relations of molybdenum oxide thin films synthesized by reactive dc magnetron sputtering in an industrial-scale sputter deposition plant using a rotatable molybdenum target with varying oxygen/argon gas flow ratio. The evolution of microstructure and chemical bonds as a function of oxygen partial pressure was studied by x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy. With oxygen partial pressure raising from 0% to 100%, the film growth rate decreased from 350 to 50 nm/min, while the oxygen content within the films increased up to 75 at. %. The films were dominated by MoO2, polymorphs of Mo4O11 and Mo9O26, and MoO3 phases. The electrical properties changed from electrically conductive to insulating with increasing oxygen partial pressure. The optical properties are versatile, e.g., transmittance values up to 80%, absorbance values between 50% and 80% and reflectance values up to 55%, depending on the oxygen content. ...

Effect of discharge power on target poisoning and coating properties in reactive magnetron sputter deposition of TiN

Reactive magnetron sputtering is a well-established technique for the deposition of high quality functional compound coatings. However, avoiding the undesired hysteresis effect that occurs when the metal target becomes covered by a compound layer at a certain reactive gas flow or partial pressure, typically referred to as target poisoning, is still an intense field of research. In the current work, the effect of the discharge power on target poisoning and coating structure and properties was assessed by determining the hysteresis and by characterizing the sputter-deposited TiNx coatings, where x ≤ 1. With increasing discharge power, the hysteresis was shifted to higher N2 gas flow values. In metallic mode, the increase in discharge power enabled therefore the incorporation of high nitrogen fractions in the TiNx coatings at stable discharge conditions and high deposition rates. In poisoned mode, all coatings were stoichiometric, but the deposition rates were lower by a factor of 1/3. Regardless of the depo...

Deformation behavior of Re alloyed Mo thin films on flexible substrates: In situ fragmentation analysis supported by first-principles calculations

A major obstacle in the utilization of Mo thin films in flexible electronics is their brittle fracture behavior. Within this study, alloying with Re is explored as a potential strategy to improve the resistance to fracture. The sputter-deposited Mo1−xRex films (with 0 ≤ x ≤ 0.31) were characterized in terms of structural and mechanical properties, residual stresses as well as electrical resistivity. Their deformation behavior was assessed by straining 50 nm thin films on polyimide substrates in uniaxial tension, while monitoring crack initiation and propagation in situ by optical microscopy and electrical resistance measurements. A significant toughness enhancement occurs with increasing Re content for all body-centered cubic solid solution films (x ≤ 0.23). However, at higher Re concentrations (x > 0.23) the positive effect of Re is inhibited due to the formation of dual-phase films with the additional close packed A15 Mo3Re phase. The mechanisms responsible for the observed toughness behavior are discussed based on experimental observations and electronic structure calculations. Re gives rise to both increased plasticity and bond strengthening in these Mo-Re solid solutions.

A correlative experimental and ab initio approach to improve the fracture behavior of Mo thin films by alloying with Cu

The effect of Cu alloying on the deformation behavior of Mo thin films is investigated as a feasible concept to overcome their poor ductility, which severely limits performance in flexible electronics. 50 nm thick Mo1-xCux films (with 0 ≤ x ≤ 0.51) were sputter-deposited on polyimide substrates and subjected to uniaxial tensile loading while measuring their electrical resistance in situ. A significant ductility enhancement is experimentally observed with increasing Cu content. This can be rationalized by considering the associated changes in bond character as the Cu additions weaken the covalent and hence shear resistant contribution to the overall bond character.

Influence of discharge power and bias potential on microstructure and hardness of sputtered amorphous carbon coatings

This work reports on the influence of the power density and bias potential on the structure-property relations of sputter deposited amorphous carbon coatings. Coatings were deposited at power densities between 4.4 and 28 W/cm2 in both Ar and Ne atmospheres at pressures of 1 and 1.25 Pa, respectively. Measurements of the substrate temperature during deposition indicate that the coating is subjected to a substantial thermal load during deposition, which leads to growth of the graphitic clusters at higher power densities. This change of the microstructure results in a drop of the hardness of up to 40% when the power density increased to 28 W/cm2. A high hardness of up to 30 GPa, however, can be achieved when either a bias potential of −100 V is applied or when Ne instead of Ar is used as process gas. This can be attributed to the high compressive stresses present as a result of an enhanced ion bombardment.This work reports on the influence of the power density and bias potential on the structure-property relations of sputter deposited amorphous carbon coatings. Coatings were deposited at power densities between 4.4 and 28 W/cm2 in both Ar and Ne atmospheres at pressures of 1 and 1.25 Pa, respectively. Measurements of the substrate temperature during deposition indicate that the coating is subjected to a substantial thermal load during deposition, which leads to growth of the graphitic clusters at higher power densities. This change of the microstructure results in a drop of the hardness of up to 40% when the power density increased to 28 W/cm2. A high hardness of up to 30 GPa, however, can be achieved when either a bias potential of −100 V is applied or when Ne instead of Ar is used as process gas. This can be attributed to the high compressive stresses present as a result of an enhanced ion bombardment.