Radio Frequency Magnetron Sputtering Research Articles

Epitaxial growth of (Ba0.7Sr0.3)TiO3 thin films on GdScO3 substrates by magnetron sputtering

Epitaxial growth of Ba0.7Sr0.3TiO3 (BST70) thin films on GdScO3 (GSO) substrates had been realized using the radio frequency magnetron sputtering system with the epitaxial alignment [001]BST70||[110]GSO and [010]BST70||[001]GSO. Reciprocal space mapping and transmission electron microscope results confirm the epitaxial growth without an impurity phase at the interface. The Fourier-filtered image shows that the BST70 thin film grew well with few dislocations. The out-of-plane parameter of the as-deposited film was elongated due to strain, which was induced by the differences in the thermal expansion coefficients between the film and the substrate, and oxygen vacancies. The highly strained as-deposited BST70 films could be relaxed by the post-annealing procedure at 800 °C in an O2-rich atmosphere for better epitaxial quality.

IGZO thin-film transistors with tunneling contacts: towards power efficient display

We report the fabrication and characterization of indium gallium zinc oxide (IGZO) tunneling thin-film transistors. Both the IGZO channel and an Al2O3 tunneling barrier layer were deposited using the radio-frequency magnetron sputtering method. Compared with a conventional device, our device exhibited rapid saturation at a much smaller drain bias. Interestingly, we observed two different current saturation mechanisms within a single device, which can be explained as competition between the depletion envelope near the source electrode and channel depletion near the drain electrode. This work represents an industry-friendly method for implementing the tunnel-contact approach in the display industry.

Investigating the optical, electronic, magnetic properties and DFT of NiO films prepared using RF sputtering with various argon pressures

In this study, we investigated the structural, optical, magnetic, and conductive properties of nickel oxide (NiO) films on glass substrates deposited using Radio Frequency (RF) magnetron sputtering with varying Ar gas pressure and thickness. X-ray diffraction and Rietveld refinement analysis confirmed a cubic crystal structure and showed that the lattice parameters and the d(111)-space increased from 4.0559 Å to 4.2712 Å and from 2.3208 Å to 2.4582 Å, respectively, due to increased Ar pressure during deposition. Scanning electron microscopy and atomic force microscopy were used to determine the cross-sectional and surface topology of the NiO films, which exhibited uniform and homogeneous growth with an average spherical size of 54.28 ± 0.33 nm. The optical bandgap values of the films were calculated to be between 3.26 and 3.65 eV, increasing with pressure. Hall measurements confirmed the p-type semiconductor nature of the films with an average sheet carrier density of 1010 cm−2. The films exhibited soft magnetic properties, with a maximum Hc and Ms of 178.5 Oe and 5.82 emu/cm3 for 246 nm NiO film, respectively. Density functional theory (DFT) calculations confirmed the experimental results for both single to five layers NiO films and bulk NiO formations. The refined energy gap value was found to be 3.2 eV by the DFT calculation. The films produced at room temperature were found to be stable and reproducible, making them suitable as p-type materials for device construction.

Nanostructured MoS2 thin films: Effect of substrate temperature on microstructure, optical, and electrical properties

Molybdenum disulfide (MoS2), a two-dimensional transition-metal dichalcogenide, has the potential for applications in next-generation optoelectronic devices. In this work, MoS2 thin films were deposited by using radio frequency magnetron sputtering on glass and silicon substrates at different substrate temperatures. The effect of growth temperature on crystalline structure, morphology, compositional, optical, and electrical properties of MoS2 thin films was systematically evaluated. It is observed that surface morphology depended on the substrate temperature. Nanowormlike structures formed at the surface of films deposited at 100 and 200 °C. Raman analysis indicated that the mode separation distance for films deposited at room temperature was close to 25 cm−1 of the bulk value. However, mode separation was higher than 27 cm−1 when the substrate temperature was high. This can be attributed to sulfur vacancy in the MoS2 lattice and to strain formation. The bandgap of thin films was estimated to be in the range of 2.3–2.8 eV. X-ray photoelectron spectroscopy was used to investigate chemical composition as well as the effect of the substrate temperature on sulfur vacancies in films. Mo(IV)/S ratios were found to be 1.29, 1.94, and 1.87 for substrate temperatures of RT, 100 °C, and 200 °C, respectively. The conductivity of MoS2 thin films varied considerably with the substrate temperature during deposition. The highest conductivity, 10−13 S/cm, was observed at 300 K measurement temperature in films deposited at room temperature.

Morphological, compositional and phase evolutions in sulfur-rich W-S targets during magnetron sputtering

A sulfur-rich WS2.7 target was manufactured via ball milling of sulfur and tungsten-disulfide powders, followed by sintering. The target morphology, composition, and phase changes induced by sputtering processes were investigated by a number of analytical methods and compared to a stoichiometric WS2 target used as a control. Radio frequency magnetron sputtering of the WS2.7 target was conducted with progressively increasing time intervals, from a few minutes to several hours, where the target was intermittently removed for characterization. Selective sputtering of sulfur within both the control WS2 and the sulfur-rich WS2.7 targets yielded sulfur depletion over the extended sputtering time. Depressions on the target surface formed from the selective sputtering of sulfur, where at the base of these regions developed growth of metallic tungsten dendrites and additional unbonded sulfur segregation over sputtering time. A catalytically enhanced WS2 phase decomposition mechanism was proposed based on detailed analysis of phases and oxidation states from site specific spectroscopic and x-ray diffraction analysis. The observed phenomenological process exemplifies the need for monitoring and maintenance of sulfur-rich sputtered targets in their use for thin film growth.

The effect of the crystallization of indium tin oxide on indium tin oxide wet etching based on gate line with the structure of copper/indium tin oxide

AbstractIn thin film transistor‐liquid crystal display (TFT‐LCD), the copper/indium tin oxide (Cu/ITO) layer was often used to be gate line. In this event, the patterning of ITO is necessary and important. However, the high temperature generated during Cu deposition will cause ITO to crystallize, which is not conducive to ITO etching. In this paper, the ITO films prepared by radio frequency (RF) magnetron sputtering were annealed according to the monitoring results of production line to simulate and study the effect of crystallization on the etching properties of ITO film. When the annealing temperature was less than 200°C, no large size grains were detected in ITO films, and the ITO films could be easily etched by etchant. However, the ITO films transformed from amorphous structure to polycrystalline structure after being annealed more than 200°C. After wet etching experiments, the polycrystalline ITO films could be hardly removed by etchant. The X‐ray photoelectron spectroscopy (XPS) results showed that high temperature annealing induced a large amount of Sn4+ on ITO films surface. The Sn4+ was difficult to be dissolved by acid under normal conditions, which might be the most important factors that led to the greatly decreased etching rate for polycrystalline ITO films.

Study of process parameters and characteristics properties of W coatings deposited by rf plasma sputtering

Tungsten coatings were deposited on silicon substrates by radio frequency (rf) magnetron sputtering from a metallic target in Ar atmosphere. The process parameters during the sputtering process were evaluated by a Langmuir probe, particularly, the electron density and electron temperature were measured by changing the rf power and gas pressure. The morphological and structural properties of the coatings were studied as a function of the pressure. Significant correlations were found between process parameters and characteristics properties of W coatings. The influence of deposition parameters on electrical properties was investigated. The electrical resistivity of the coatings was increased from 1.3 × 10−6 to 3 × 10−5 Ω m as the pressure increased as well.

InSnO:N homojunction thin-film transistors fabricated at room temperature

Nitrogen-doped indium tin oxide (ITON) thin films of different thicknesses were deposited by radio frequency magnetron sputtering. The crystallinity, surface morphologies, and chemical compositions of the thin films were found to be influenced by film thickness, and changes in these factors eventually caused changes in the conductivity of the thin films. Therefore, we used ultrathin ITON thin films as channels and an 85-nm-thick ITON as the source/drain electrodes to fabricate thin-film transistors. The optimal device fabricated at room temperature (∼25 °C) has a threshold voltage of −2.5 V and a field-effect mobility of 10.31 cm2/(V∙s).

Influence of deposition temperature on the structure and functional properties of Mg doped hydroxyapatite coatings deposited on manufactured AZ31B alloy substrates by RF magnetron sputtering

In this paper, we study the effect of deposition temperature on the structural and nanomechanical properties on the degradation and bioactivity behaviour of Mg doped hydroxyapatite (HAP) deposited on AZ31B alloy substrates extracted by parts manufactured according to the prostheses production route. The coatings were prepared by RF (Radio Frequency) magnetron sputtering technique at room temperature (RT) and 200 °C, respectively. By adding Mg into the HAP matrix, the hardness and elastic modulus values of the coatings have significantly improved as compared to the bare HAP, the highest H3/E2 ratio of 0.022 being obtained for the HAP + Mg at 200 °C. XRD analysis showed the presence of an α-Mg hexagonal structure for the uncoated AZ31B alloy, while the GIXRD patterns revealed the presence of HAP and Mg in the coated samples. The crystallinity degree of HAP is not changed by Mg addition, while the apatite structure was preserved for all investigated coatings. All investigated samples exhibited typical IR bands of phosphate, carbonate, and hydroxyl functional groups, confirming the formation of apatite phases. By increasing the deposition temperature from room temperature up to 200 °C, the electrochemical behaviour of the coatings, in simulated body fluid and Dulbecco's Modified Eagle Medium, is improved obtaining more electropositive values for corrosion potential, smaller current densities, and higher polarization resistance. The coatings deposited at 200 °C showed the best electrochemical behaviour. Also, by increasing the deposition temperature and incorporating Mg into HAP matrix, the hardness and elastic modulus are increased by more than two-fold, as compared to pure HAP. Furthermore, all coatings deposited on AZ31B alloys are suited for further coating with a mussel-derived surface-binding peptides, but the coatings deposited at 200 °C led to the most regular peptide distribution on the surface. Overall, the results indicated that the biodegradation of HAP + Mg based coatings and the AZ31B alloys can be controlled according to the current clinical needs within implantology field.

Effect of Substrate Temperature on Variations in the Structural and Optical Properties of Cu2O Thin Films Deposited via RF Magnetron Sputtering

In the present study, Cu2O films were deposited on a glass substrate via RF (radio frequency) magnetron sputtering under substrate temperature conditions that ranged from room temperature (RT, 25 °C) to 400 °C. The structural, compositional, and optical properties of the Cu2O films were analyzed in relation to the experimental variables by applying various measurement methods. The substrate temperature was a crucial factor in shaping the structural, compositional, and optical properties of the Cu2O films that were synthesized via RF-magnetron sputtering. Our findings revealed that the Cu2O films exhibited a cubic structure, which was confirmed by XRD analysis. Specifically, the (111) and (200) planes showed different trends with respect to the substrate temperature. The intensity of the (111) peak increased at 250 °C, and above 300 °C, the preferred orientation of the (111) plane was maintained. The grain size, which was determined via FE-SEM, displayed a positive correlation with the substrate temperature. Additionally, XPS analysis revealed that the binding energy (BE) of the Cu2O film sputtered at 400 °C was similar to that which was previously reported. Notably, the as-grown Cu2O film demonstrated the highest transmittance (15.9%) in the visible region, which decreased with increasing substrate temperature. Furthermore, the energy band gap (Eg) of the Cu2O films remained constant (2.51 eV) at low substrate temperatures (25 °C to 200 °C) but exhibited a slight increase at higher temperatures, reaching 2.57 eV at 400 °C.

Tailoring the deposition of MoSe2 on TiO2 nanorods arrays via radiofrequency magnetron sputtering for enhanced photoelectrochemical water splitting

MoSe2/1 D TiO2 nanorods (NRs) heterojunction assembly was systematically fabricated, and its photoelectrocatalytic properties were investigated. The fabrication process involves the growth of 1D TiO2 NRs arrays on FTO substrates using hydrothermal synthesis followed by the deposition of MoSe2 nanosheets on the TiO2 NRs using radiofrequency magnetron sputtering (RF magnetron sputtering). The photoelectrochemical properties of the heterojunction were explored and optimized as a function of the thickness of the MoSe2 layer, which was controlled by the sputtering time. The MoSe2 grows perpendicularly on TiO2 NRs in a 2D layered structure, maximizing the exposed active edges, an essential aspect that permits maximum exploitation of deposited MoSe2.Compared to pure TiO2 NRs, the heterojunction nanostructured assembly displayed excellent spectral and photoelectrochemical properties, including more surface oxygen vacancies, enhanced visible-light absorption, higher photocurrent response, and decreased charge transfer resistance. In particular, the sample synthesized by sputtering of MoSe2 for 90 s, i.e., MoSe2@TiO2-90 s, depicted the highest current density (1.86 mA cm−2 at 0.5 V vs. Ag/AgCl) compared to other samples.The excellent photoelectrochemical activity of the heterojunction stemmed from the synergy between tailored loading of MoSe2 nanosheets and the 1D structure of TiO2 NRs, which afford a high surface/volume ratio, effective charge separation, fast electron transfer, and easy accessibility to the MoSe2 active edges. These factors boost the catalytic activity.

Radio-frequency magnetron sputtering deposition process for In2O3:H transparent conductive oxide films for application in Cu(In,Ga)Se2 solar cells

Typical Cu(In,Ga)Se2 solar cells are deposited on an opaque molybdenum back contact. However, for applications such as bifacial, semi-transparent or tandem solar cells a transparent back contact is required, for which various transparent conductive oxides have been tested, such as indium- or fluorine-doped tin oxide, and hydrogen-doped indium oxide. Here, a radio-frequency magnetron sputtering deposition process for In2O3:H (IOH) is investigated, where H is supplied from a Ar/H2 (5%) mixed gas and oxygen is pulsed during the entire deposition at room temperature. After deposition, the films are post-annealed in vacuum to optimize their optoelectronic properties. The oxygen plays an important role for the optoelectronic properties, where a high content of oxygen allows higher transparency but also increases the film sheet resistance. Optimum oxygen and Ar/H2 partial pressures of 3.2 × 10−2 Pa and 13×10−2 Pa, respectively, were found, producing IOH films with average visible transparency of 87% and sheet resistance after annealing of 19 Ohm/sq.

Structure and electrocatalytic hydrogen evolution performance of Mo2C thin films prepared by magnetron sputtering

Mo2C, which has a unique electronic structure similar to the electronic structure of Pt, is considered as the material with the greatest potential to replace Pt as a catalyst for the electrocatalytic hydrogen evolution reaction (HER). However, Mo2C thin films have not attracted enough attention in the field of electrocatalysis. This work proposes a method for preparing Mo2C thin films as a catalyst for electrocatalytic HER through radiofrequency magnetron sputtering. The HER activity of the Mo2C thin film in acidic and alkaline media is studied by changing the deposition power of the Mo2C target and doping Ni for structural modification. Results show that increasing the deposition power of Mo2C can significantly enhance the HER activity of the films in acidic and alkaline media, and metal Ni doping can further enhance the HER activity of the Mo2C films. In an alkaline environment at a current density of 10 mA cm−2, the films demonstrate an overpotential of as low as 163 mV with a Tafel slope of 107 mV·dec−1. In acidic media, the films present the corresponding overpotential of 201 mV and a Tafel slope of as low as 96 mV·dec−1. Moreover, the Ni-doped Mo2C films have excellent HER stability. The synergy between doped Ni and Mo vacancies optimizes the strength of the Mo–H bond and the adsorption and desorption equilibrium of active H, thus enhancing HER kinetics. This work guides the possible structural design of Mo2C thin films for electrocatalytic HER.

Suppression of grain boundary contributions on carrier mobility in thin Al-doped ZnO epitaxial films

Realizing very thin transparent conductive (TCO) films is a key aspect of many applications, but often the film quality tends to worsen at very small thicknesses. In this work we demonstrate that Al-doped ZnO (AZO) thin films grown epitaxially on SrTiO3 retain their optimal properties even at thicknesses as low as 30 nm. We deposit by radio frequency magnetron sputtering and investigate the film morphology, structure, crystallinity, electrical and optical properties. We prove that the Hall mobility of epitaxial films is limited mostly by ionized impurity scattering, with a negligible contribution of grain boundary scattering, leading to comparably high mobility in thin epitaxial films. On the contrary, in polycrystalline films the properties of AZO films strongly deteriorate at reduced film thickness, due to grain boundary contributions. The optical carrier density and mobility do not change significantly between epitaxial and polycrystalline films, suggesting that the different electrical properties are indeed mainly due to grain boundary scattering and not to a reduction of carriers and intrinsic mobility. In this way we obtain an epitaxial thin TCO film with the optimal properties of a bulk by a scalable technique, paving the way to applications in plasmonic devices and in thin films solar cells.

Annealing temperature effect on the temperature coefficient of resistance for vanadium oxide (VOx) thin films as bolometer materials

Vanadium oxides (VOx) are representative materials with a high temperature coefficient of resistance (TCR); however, VOx films can have complex phase structures that are dependent on their fabrication method. While past research has focused on the TCR behavior of VOx thin films, this study investigates the TCR of VOx thin films annealed at different temperatures as well as focuses on the relation between the VOx phase, surface morphology, sheet resistance, and TCR. VOx thin films were deposited via radio-frequency magnetron sputtering and annealed at 150 °C–500 °C in 20% O2. Alongside morphological changes, the deposited VOx thin films exhibited phase changes from V2O5 to VO2 with increasing annealing temperature. The VOx thin films annealed at 300 °C and 330 °C showed the lowest and highest average TCR of 1.25%/°C and 3.34%/°C, respectively. Furthermore, a bolometer fabricated using the higher-TCR film showed more than 5-fold infrared responsivity under the same infrared intensity.

Relationship Between Structural and Optical Properties in Vanadium Pentoxide

Spray pyrolysis technique (SPT) and radio-frequency magnetron sputtering (RF-MS) were used to obtain vanadium oxide (VxOy) layers. The surface morphology was visualized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Further, t

Titania nanorods array homojunction with sub-stoichiometric TiO2 for enhanced methylene blue photodegradation

TiO2 thin films are known to promote photodegradation of dyes and pollutants in water solution via heterogeneous photocatalysis. This ability is guided by the photoexcitation through photons having energies above the band gap. To improve photocatalytic activity, nanostructures with high surface area can be applied, which can ease molecular adsorption/desorption mechanisms, enhance electronic transfer properties and lower excitation energy. For this purpose, square cross-section TiO2 vertically aligned nanorod (TNR) array configuration has been chosen as a semiconductor substrate. On top of it, a thin layer of sub-stoichiometric TiO2−x has been deposited, aiming at inducing a vacancy doped homojunction between two different oxygen rich/deficient TiO2 layers, possibly leading to lower band gap and enhanced photochemical activity. In principle, promotion of electron and holes separation and suppression of charge recombination could occur. Vertically aligned TNRs have been deposited through a hydrothermal growth in acidic conditions on a pre-seeded glass conducting substrate, optimizing the seeding process through spin coating. Sub-stoichiometric TiO2−x layer (50 nm nominal thickness) has been deposited on top of TNRs via radiofrequency magnetron sputtering at three different stoichiometries, tuning the oxygen partial pressure in sputtering argon atmosphere at 10 %, 15 % and 20 %, respectively. Photocatalytic activity has been investigated in the photodegradation of an aqueous solution of methylene blue, both under UV and simulated solar light irradiation at room temperature and atmospheric pressure, resulting in the degradation of methylene blue target molecule up to 99 % under UV and 85 % under simulated solar irradiation after 6 h. These promising achievements unlock new environmental applications for enhanced dye degradation industrial processes.

Effects of processing parameters on the morphologies of complex sesquioxide thin films

Controlling and predicting the morphology of lanthanide sesquioxides in thin film form is vital to their use in current applications. In the present study, single and codeposited Sm2O3, Er2O3, and Lu2O3 thin films were grown on yttria-stabilized zirconia (8%) substrates by radio frequency magnetron sputtering at room temperature and 500 °C. The effect of two different substrate temperatures and altering the oxide cation on the structural and morphological properties of the films was analyzed. The thin films were characterized by profilometry, scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. The single-component Lu2O3 and Sm2O3 films obtained were of the cubic phase, and the Er2O3 was a mix of cubic and monoclinic phases. It was observed for both the Er2O3 and Lu2O3 films that increasing the substrate temperature to 500 °C resulted in larger grained polycrystalline films. In contrast, large grained polycrystalline films were obtained at both room temperature and 500 °C for Sm2O3 and uneven granularity increased as temperature increased. Codeposition of Lu2O3 and Sm2O3, and Lu2O3 and Er2O3 resulted in a cubic bixbyite phase (the C phase of the lanthanide sesquioxide) solid solution. It was observed that the structure and morphology of the films can be controlled by manipulating deposition parameters. Both substrate temperature and altering the oxide cation contributed to changes in crystallinity and grain structure, which can modify the chemical and physical properties of the films for their applications.

Epitaxy growth of pure phase CeFeO3 thin films with high magneto-optical performance and strong vertical magnetic anisotropy

The magneto-optical effects of rare earth ferrite can be greatly improved by doping Ce3+ ions. CeFeO3 with high Ce3+ concentration has excellent magneto-optical properties in theory. And due to its perovskite structure it is more suitable to be deposited on the substrates of optical devices compared with the commercial garnet ferrite. In this paper, the pure phase CexFe2–xO3 films were successfully obtained on the quartz glass and <100>-oriented SrTiO3 crystal substrates by radio frequency magnetron sputtering. The effects of substrate and Ce:Fe ratio on the epitaxial orientation, magnetism and magneto-optical performance of films were systematically studied. For the Ce1.0Fe1.0O3/STO film, its MCD ellipticity (ψF) intensity can reach up to 4750(°)/cm in the visible band and 14090(°)/cm in near ultraviolet band. And it also shows a strong vertical magnetic anisotropy, which makes it maintain a good thermal stability when the device size is reduced. These mean that the Ce1.0Fe1.0O3/STO film has a promising application in integrated optical communication devices.

Effects of annealing in vacuum on the microstructure of silicon-containing calcium phosphate films deposited on a ZrNb alloy by radio-frequency magnetron sputtering

Coatings were deposited on the surface of a ZrNb alloy by radio-frequency magnetron sputtering using targets consisting of either pure crystalline hydroxyapatite (HA) or silicon-containing HA (Si-HA). The coated ZrNb samples were heated in a vacuum furnace at a pressure of 5 × 10−5 Torr and temperature 700 °C for 2 h. Precursor powders of silicate-substituted HA [Ca10(PO4)6−x(SiO4)x(OH)2−x, x = 0, 0.5, or 1.72] were used to fabricate the targets for sputtering. The aim of this study was to analyze the effect of Si addition to HA on crystallization behavior and structure of the resulting films using transmission electron microscopy and electron diffraction patterns of selected sites. The average thickness of the films was in the range of 175–345 nm. The Si substitution in HA played a major role in the mechanisms of coating formation and crystallization behavior, which influenced the structure and crystallinity of the layers deposited by radio-frequency magnetron sputtering. Moreover, the results indicate that surface-induced crystallization of the deposited thin films is more pronounced than internal crystallization. A possible mechanism underlying the observed decrease in the crystallization rate with the increasing silicate content in the HA-based films is discussed.