Radio Frequency Magnetron Co-sputtering Research Articles

Examining the Desirable Properties of ZnSnO y by Annealing Treatment with a Real-Time Observation of Resistivity.

In this report, 38 nm-thick amorphous zinc-tin oxide (a-ZTO) films were deposited by radio frequency magnetron cosputtering. a-ZTO films were annealed by in situ monitoring of the sheet resistance improvements during the annealing process. A sharp drop in the slope of the sheet resistance curve was observed. The activation energies for the sheet resistance slope were calculated. The activation energy of the reaction for a sharp drop in the slope is much higher than the activation energy for the rest of the slope. Based on the activation energy values, six annealing temperatures were selected to saturate the highest conductivity at lower annealing temperatures and to identify the effects associated with annealing time. We found a direct correlation between annealing temperatures and the duration of the annealing treatment. a-ZTO films with a high conductivity of 320 S/cm were achieved by annealing at a temperature of 220 °C. It is noteworthy that the annealing temperature of 220 °C has clearly replaced the temperature of 300 °C. An irreversible decrease in resistivity was observed for all films. The conduction mechanism of films before and after annealing was determined. We confirm that all films individually exhibit semiconducting and metallic behaviors in the conduction mechanism before and after the lowest resistivity saturation.

Crystallization of Germanium-SiO2 composite films via nanosecond laser pulse irradiation

Germanium (Ge)-SiO2 composite films fabricated by using radio frequency magnetron co-sputtering were subjected to nanosecond (ns) laser pulse irradiation. The intense laser irradiation effects on as deposited composite films lead to the modification and the formation of Ge nanocrystals (NCs) embedded in SiO2. The as-deposited and laser treated samples have been characterized with X-ray diffraction (XRD) and micro-Raman spectroscopy to understand the formation of Ge NCs due to laser irradiation. The respective Ge NCs related peaks in XRD pattern as well as the Ge-Ge related optical phonon vibrational peaks in micro-Raman spectra confirm the formation of Ge NCs. Transmission electron microscopy images indicate the formation of Ge NCs after the laser irradiation. The effects of laser pulse energy and the irradiation time play a vital role in the crystallization of the as-deposited films. The changes in the Ge NCs size related shifts in the peak position of Ge optical phonons from the Raman spectra of the respective samples are explained with Ge-Ge optical phonon vibrational model. The observed photoluminescence emission in the green and red region of the visible spectrum from the laser treated samples are explained using the phenomenon of creation of Ge NCs in the Ge+SiO2 composite films and the oxygen defects created in SiO2 during the ns laser treatment.

Optical, structural, morphological, and gas sensing properties of Mg-doped α-Fe2O3 thin films deposited by RF and DC magnetron Co-sputtering technique

In this research, Mg-doped hematite (α-Fe2O3) thin films with different Mg-doping concentrations were synthesized on glass substrates using the direct current (DC) and radio frequency (RF) magnetron co-sputtering technique, and the changes of some physical properties due to the concentration of the dopant were investigated. The optical, structural, morphological, and elemental properties of the obtained Mg-doped α-Fe2O3 thin films were determined by X-ray diffraction (XRD) analysis, UV–Vis spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), dispersive X-ray spectroscopy and atomic force microscopy (AFM). XRD analysis revealed that the investigated thin films have a rhombohedral crystal structure. The deposition of films at different DC sputtering voltages caused significant variations in stoichiometry and nanostructure. The thin films' band gap energy values were estimated based on absorption measurements, and results ranged from 2.15 eV to 2.69 eV. Raman peaks were observed between 218 cm−1 and 1305 cm−1. The thin films exhibit uniform surface morphology throughout the substrate according to the SEM images. The low RMS roughness values obtained from AFM images showed that the surfaces of Mg:Fe2O3 thin films are smooth. The Mg-doped α-Fe2O3 thin film doped by 150 W DC voltage exhibited a good gas-sensing response at 300 °C. A remarkably quick response/recovery time was achieved.

Praseodymium-Doped Ge20In5Sb10Se65 Films Based on Argon Plasma Cosputtering for Infrared-Luminescent Integrated Photonic Circuits.

In this paper, we report on the infrared luminescence of amorphous praseodymium-doped Ge20In5Sb10Se65 waveguides, which can be used as infrared sources in photonic integrated circuits on silicon substrates. Amorphous chalcogenide thin films were deposited by radiofrequency magnetron cosputtering using an argon plasma whose deposition parameters were optimized for chalcogenide materials. The micropatterning as ridge waveguides of the chalcogenide cosputtered films was performed using photolithography and plasma-coupled reactive ion etching techniques. The influence of the rare earth concentration within those thin films on their optical properties and rare earth spectroscopic properties was investigated. Using an excitation wavelength of 1.55 μm, the mid-infrared luminescence of Pr3+ ions from 2.5 to 5.5 μm was clearly demonstrated for studied chalcogenide materials. A wide range of waveguide widths and doping ratios were tested, assessing the ability of the cosputtering technique to preserve the luminescence properties of the rare earth ions initially observed in the bulk glass through the thin-film deposition and patterning process.

Comprehensive characterization of Al-doped ZnO thin films deposited in confocal radio frequency magnetron co-sputtering

Al-doped ZnO thin films with varying Aluminium (Al) content were deposited by radio frequency magnetron co-sputtering of two ZnO and Al targets in confocal configuration. A comprehensive study of the effect of Al content variation on the structural, optical and electrical properties were studied for as-deposited films and after an annealing step under controlled argon atmosphere. Chemical composition analyses, performed by both X-ray photoelectron spectroscopy and energy dispersive X-ray spectrometry, show an Al content variation in the deposited films in the 0-14 at.% range by varying the Al target power from 0 to 30 W, while the Zn target power was kept constant at 200 W. All deposited films exhibit a wurtzite crystalline structure and a decreasing crystalline quality for Al content above 5 at.% as shown by grazing incidence X-ray diffraction patterns. Atomic Force Microscopy analysis revealed films with homogeneous and dense surface morphology with roughness in the one nm range. Carrier concentration, resistivity and photoluminescence vary significantly with Al content in the ZnO films and appear optimized for an Al content window ranging from 1.5 to 5.5 at. %. Both optical and electrical properties are improved by a post-annealing at 300°C under argon. A high figure of merit of 43.6 × 10-4 sq.Ω-1 was obtained for the ZnO film with Al content of 3.6 at.% after annealing at 300°C. Optimized properties are obtained for a higher Al content than the standard value of 2 at. % widely used in published works.

Modifying crystallinity and mechanical properties of (CoCrNi)95.8Ce4.2 medium entropy alloy films by post-annealing treatment

In this work, (CoCrNi)95.8Ce4.2 medium entropy alloy films with amorphous and nanocrystalline phases were deposited on 304 steel substrates via radio frequency magnetron co-sputtering. The post-annealing treatment was conducted to investigate the effects of different annealing temperatures (250, 350, 450 and 500 °C) on the microstructures and mechanical properties of the films. The crystallinity increased with the increasing annealing temperature. When the films were annealed at 250 and 350 °C, some nanocrystals were formed in the amorphous matrix. Interestingly, plenty of stacking faults were observed in 450 and 500 °C annealed films because of the low stacking fault energy and annealing process. The hardness and Young's modulus were measured by nanoindentation. Both hardness and Young's modulus increased and then decreased with the increasing annealing temperature. The hardness and Young's modulus reached the maxima of 12.60 and 231.24 GPa, respectively, due to the increasing crystallinity and the formation of stacking faults at 450 °C annealing. However, in the annealing temperature range from 450 to 500 °C, hardness and Young's modulus decreased because of the grain growth. Therefore, the results of this work suggested that the moderate post-annealing treatment was beneficial to promote the formation of stacking faults and strengthen the mechanical properties.

CuO:Se composite films and its photovoltaic application

Cupric oxide (CuO) and selenium (Se) are old photoelectric materials, and their photovoltaic properties have always received attention. However, CuO has a high melting point (1026℃) and will decompose near its melting point, so it is difficult to prepare high crystallinity CuO films. Selenium (Se) can not efficiently absorb sunlight because of its large optical band gap (1.9 eV). Here, a CuO:Se composite film was prepared by radio frequency magnetron co-sputtering of CuO and Se and low temperature annealing (200℃). The experimental results show that this composite material film has the advantages of CuO and Se, and overcome their disadvantages. The material has strong absorption of light in the entire solar spectral range (250-2500 nm, average absorptance ~80%). A prototype solar cell based on this composite film was fabricated and its power conversion efficiency (PCE) is up to 2.05%, which is much higher than that of the pure CuO (0.007%) or pure Se (1.05%) film solar cells. This material should be promising for photovoltaic and other photo-electrical application.

Growth of High-Quality Perovskite KTa1-xNbxO3 Thin Films by RF Magnetron Co-Sputtering

In this study, we demonstrate the growth of high-quality KTa1-xNbxO3 (KTN) thin films by using multi-target radio frequency (RF) magnetron co-sputtering with KTaO3, KNbO3, and K2CO3 targets. KTaO3 and KNbO3 targets were used to control the Ta/Nb ratio while the K2CO3 target was used to supply excess potassium (K) to compensate for the K deficiency. Through careful control of the RF powers applied to each target, high-quality perovskite KTN (x = 0.53) thin films were grown on various single crystal substrates. Variable temperature Raman spectroscopy revealed that the KTN thin films exhibit a ferroelectric phase at room temperature with a Curie temperature of ~403 K. The optical constants n and k of the KTN thin film were also similar to those reported for single KTN crystals. These results present a simple route toward fabricating high-quality perovskite KTN thin films with desired structural and optical properties for various device applications utilizing the RF magnetron co-sputtering method.

Uniaxial in-plane magnetic anisotropy mechanism in Ni, Fe, and Ni-Fe alloy films deposited on single crystal Y-cut 128° LiNbO3 using magnetron sputtering

We investigated the mechanism of induced in-plane uniaxial magnetic anisotropy (Ku) in Nickel (Ni), Iron (Fe), and Ni-Fe alloy films deposited in situ on a single-crystal 128° Y-cut LiNbO3 (LNO) substrate at various substrate heating temperatures (Th) in the range 30–400 °C through radio frequency magnetron sputtering or co-sputtering. The results show that the Ku values for the Ni, Fe, and Ni-Fe alloy films are induced in the (01.2) or (21¯.0) planes of the LNO substrate. The highest value of Ku for the Ni films was observed at Th = 200 °C, which is owing to the increased orientation of the fcc Ni (311) plane. The Ni film with thickness t ∼ 20 nm deposited on the LNO substrate at Th = 200 °C possesses the highest value of Ku. Density functional theory calculations show that the magnetic anisotropic energy on the fcc Ni (311) plane differs depending on the magnetization direction in the in-plane direction in the model. Meanwhile, the value of Ku for the Fe films decreases with an increase in the value of Th because the films with higher Th are polycrystalline and have an oxide layer. The composition dependence of Ku for Ni-Fe alloy films at Th = 30 °C shows a trend similar to the crystal magnetic anisotropy for bulk Ni-Fe alloy. The induced Ku on LNO is attributed to the magnetostriction effect with the change in the crystal orientation of the ferromagnetic metal owing to a strain from the LNO substrate through the thermal expansion during sputtering. These results indicate the origin of the induced Ku in the Ni and Fe based metallic material films deposited on the LNO substrate.

Cu-Mg-O thin films by RF magnetron co-sputtering: Their band offsets with CdS in heterojunction solar cells

We report on Cu-Mg.O thin films of 100 - 300 nm in thickness produced by radio frequency (RF) reactive sputtering fromCu and Mg-metal targets in an argon-oxygen ambient. The amount of Mg in the thin films was varied through changingthe RF power applied at the Mg target. When the Mg content in the Cu-Mg-O film changed from 0 to 0.3, the opticalbandgap increased from 1.73 eV to 2.13 eV, and the electrical conductivity decreased from 9 x 10-3 Ω-1 cm-1(CuxO) to 6.7x 10-5 Ω-1 cm-1(Cuo7/Mg0.30). Solar cells of these films, FTO/ CdS/Cu0.85Mg0.15O/C-Ag, showed a short circuit current density of 2.86 mA/cm2 an open circuit voltage of 378 mV, and power conversion efficiency of 0.25%. X-ray photo-electron spectroscopy depth profile analyses of the interfaces suggest a negative conduction band offset in CdS/Cu0.85Mg0.15O( — 0.74 eV) as well as in CdS/CuxO (0.9 eV) solar cells.

Copper-Arsenic-Sulfide Thin-Films from Local Raw Materials Deposited via RF Co-Sputtering for Photovoltaics.

The inexorable increase of energy demand and the efficiency bottleneck of monocrystalline silicon solar cell technology is promoting the research and development of alternative photovoltaic materials. Copper-arsenic-sulfide (CAS) compounds are still rather unexplored in the literature, yet they have been regarded as promising candidates for use as p-type absorber in solar cells, owing to their broad raw material availability, suitable bandgap and high absorption coefficient. Here, a comprehensive study is presented on the structural and optoelectronic properties of CAS thin-films deposited via radio-frequency magnetron co-sputtering, using a commercial Cu target together with a Cu-As-S target with material obtained from local resources, specifically from mines in the Portuguese region of the Iberian Pyrite Belt. Raman and X-ray diffraction analysis confirm that the use of two targets results in films with pronounced stoichiometry gradients, suggesting a transition from amorphous CAS compounds to crystalline djurleite (Cu31S16), with the increasing proximity to the Cu target. Resistivity values from 4.7 mΩ·cm to 17.4 Ω·cm are obtained, being the lowest resistive films, those with pronounced sub-bandgap free-carrier absorption. The bandgap values range from 2.20 to 2.65 eV, indicating promising application as wide-bandgap semiconductors in third-generation (e.g., multi-junction) photovoltaic devices.

High-performance Ti-doped ZnS thin film anode for lithium-ion batteries

Thin film microbattery is urgently needed to provide a long-term stable on-chip power for various kinds of microdevices or microsystems. Anode is a core component in thin film lithium ion microbattery, however, previous researches mostly focused on metal oxide or Si-based thin film anodes, and the reports of metal sulfide thin film anodes are limited. Herein, we present a new type of Ti-doped ZnS thin film fabricated by radio frequency (RF) magnetron co-sputtering. The Ti doping is designed to enhance the overall electrical conductivity of the ZnS thin film, since the insulation of ZnS is one of the major barriers to deliver its lithium storage performance. As an anode applied in lithium ion battery, the Ti-doped ZnS thin film exhibits good cycling stability up to 500 cycles at a current density of 1.0 A·g−1, and remains a higher specific capacity of 463.1 mAh·g−1 than that of the pure ZnS thin film, showing its better electrochemical reaction reversibility. The rate capability and EIS measurements manifest the more favorable electrochemical reaction kinetics of the Ti-doped ZnS thin film, moreover, the CV tests at various scan rates indicate the improved Li+ diffusion kinetics in the electrode after Ti doping.

Mechanically Durable Organic/High-k Inorganic Hybrid Gate Dielectrics Enabled by Plasma-Polymerization of PTFE for Flexible Electronics.

To achieve both the synergistic advantages of outstanding flexibility in organic dielectrics and remarkable dielectric/insulating properties in inorganic dielectrics, a plasma-polymerized hafnium oxide (HfOx) hybrid (PPH-hybrid) dielectric is proposed. Using a radio-frequency magnetron cosputtering process, the high-k HfOx dielectric is plasma-polymerized with polytetrafluoroethylene (PTFE), which is a flexible, thermally stable, and hydrophobic fluoropolymer dielectric. The PPH-hybrid dielectric with a high dielectric constant of 14.17 exhibits excellent flexibility, maintaining a leakage current density of ∼10-8 A/cm2 even after repetitive bending stress (up to 10000 bending cycles with a radius of 2 mm), whereas the HfOx dielectric degrades to be leaky. To evaluate its practical applicability to flexible thin-film transistors (TFTs), the PPH-hybrid dielectric is applied to amorphous indium-gallium-zinc oxide (IGZO) TFTs as a gate dielectric. Consequently, the PPH-hybrid dielectric-based IGZO TFTs exhibit stable electrical performance under the same harsh bending cycles: a field-effect mobility of 16.99 cm2/(V s), an on/off current ratio of 1.15 × 108, a subthreshold swing of 0.35 V/dec, and a threshold voltage of 0.96 V (averaged in nine devices). Moreover, the PPH-hybrid dielectric-based IGZO TFTs exhibit a reduced I-V hysteresis and an enhanced positive bias stress stability, with the threshold voltage shift decreasing from 4.99 to 1.74 V, due to fluorine incorporation. These results demonstrate that PTFE improves both the mechanical durability and electrical stability, indicating that the PPH-hybrid dielectric is a promising candidate for high-performance and low-power flexible electronics.

Synthesis of Cu3SbS4, Cu3SbSe4 and CuSbTe2 thin films via chalcogenation of sputtered Cu-Sb metal precursors

Cu-Sb-X (X = S, Se, Te) based ternary chalcogenide semiconductors are potential candidates for photovoltaic and thermoelectric applications. We report the synthesis of Cu3SbS4, Cu3SbSe4 and CuSbTe2 thin films by a two-stage process. The thin films were prepared by the deposition of Cu and Sb precursors on to a sapphire substrate by radio frequency magnetron co-sputtering followed by a subsequent chalcogenation process. The crystallinity, compositional, morphological and optical properties of the synthesized samples were investigated by x-ray diffraction, elemental analyses, scanning electron microscopy, optical spectroscopy and Raman spectroscopy. The Raman spectra of the synthesized Cu3SbS4, Cu3SbSe4 and CuSbTe2 samples show dominant modes at 319 cm−1, 184 cm−1, and 114 cm−1, and the band edges estimated from the transmittance and reflectance spectra, are 1.0 eV, 0.8 eV, and 0.7 eV, respectively.

Physicochemical Properties of SnTe Thin Films Dependent on Compositional Ratios

This study introduces physicochemical properties based on the compositional ratio of the SnTe thin films (TFs) fabricated by radio frequency (RF) magnetron cosputtering. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results show that the grain sizes decrease with increasing Te content, with pure Te TFs yielding the lowest Rq value (root mean square value of roughness) of 0.76 nm. Contact angle (CA) measurements show that pure Te TFs pertain to the highest total surface free energy. X‐Ray diffraction (XRD) patterns strongly indicate that pure Te TFs exhibit a hexagonal crystal structure and pure Sn TFs exhibit a tetragonal crystal structure. The dominant oxide species on the surface is TeO2 for Te‐rich films, which is deduced by X‐Ray photoelectron spectroscopy (XPS) results. Pure Te TFs yield a work function value of 4.88 eV when measured with ultraviolet photoelectron spectroscopy (UPS) and 5.46 eV when measured with a Kelvin probe. SnTe TFs with 70% Te content exhibit the lowest electrical conductivity among the fabricated TFs.

Enhanced piezoelectric coefficient and the piezoelectric nanogenerator output performance in Y-doped ZnO thin films

We report a significant improvement of the piezoelectric coefficient of the ZnO thin film (12.4 p.m./V) by yttrium (Y)-doping (49.6 p.m./V @1.6 at % Y), demonstrating further to enhance piezoelectric nanogenerator (PENG) performance, generating output voltage (0.012 V) and output current (45 nA) more than the undoped ZnO thin film by 6 and 1.8 times, respectively. Y doping (1.6 at %) led to the formation of permanent dipoles as ferroelectric phase in ZnO evidenced by a clear, distinct hysteresis loop with remnant polarization of 0.0423 μC/cm2 and a coercive field of 0.142 V/cm. All the films were grown by radio frequency magnetron co-sputtering with the maximum Y doping concentration up to 3.5 at%. The films maintain highly oriented along the c-axis (0002) at low Y concentrations (∼1.6 at%), but become more randomly oriented with the emergence of both the (10 1‾ 1) and (112‾ 0) peaks at high Y concentrations (>1.6 at%). The morphology varies from granular microstructure with smaller grain size at low Y doping to larger elongated crystals at the Y > 1.3 at%. Concurrently, cross-sectional images revealed the conversion of columnar nanorod like microstructure into film like (thickness: 650–750 nm) with increased Y doping concentration.

Wear and corrosion behaviour of nanocrystalline TaN, ZrN, and TaZrN coatings deposited on biomedical grade CoCrMo alloy

TaZrN coatings were synthesized directly on biomedical grade CoCrMo using radio-frequency magnetron co-sputtering. The mechanical properties, adhesion, wear, and corrosion resistance of the TaZrN coatings on the Cobalt alloy were assessed to determine their potential for hip joint replacement applications. The results indicate the TaZrN coatings are highly adhesive and have a nanocrystalline structure with a Hardness and Young’s modulus of 19 GPa and 297 GPa, respectively. The TaZrN coatings showed a 3% lower wear rate of the polyethylene counterpart and an icorr value 274 times lower than the uncoated CoCrMo alloy. The excellent wear and corrosion resistance of the TaZrN coating suggest that it is a promising coating material for CoCrMo alloy to improve the lifetime of hip joint implants.

Electronic Structure and Thermoelectric Properties of Mg2Sn Films Fabricated by Using Co-Sputtering Process With Stoichiometric Modification

Colossal values of the Seebeck coefficient were first discovered in Mg-poor Mg2Sn films in the temperature range 600–700 K. Cubic and orthorhombic structures of the Mg2Sn films for solid-state thermoelectric energy conversion devices were prepared by radio frequency (RF) magnetron co-sputtering. The Mg-Sn films showed a structural phase transition between the metastable orthorhombic and the stable cubic structures as the atomic ratio Mg/Sn varied near the stoichiometric ratio. The Mg-poor orthorhombic Mg-Sn films transited from p-type to n-type conductivity at 500 K and exhibited colossal values of the Seebeck coefficient and power factor in the temperature range 600–700 K. The colossal Seebeck coefficient, which exceeded -10 mVK-1, indicates long-term stability over a wide temperature range. Furthermore, the energy band structure and density-of-state were calculated for the cubic and the orthorhombic Mg2Sn using the first-principles calculation with the Perdew-Burke-Ernzerhof (PBE0) hybrid functionals, which yielded results that were consistent with the experimental data.

Effects of Nb Addition on Microstructures and Mechanical Properties of Nbx-CoCrFeMnNi High Entropy Alloy Films

In the present work, Nbx-CoCrFeMnNi high entropy alloy films (HEAFs, 0 to 7.2 at.% Nb) were fabricated by radio frequency (RF) magnetron co-sputtering of CoCrFeMnNi alloy and Nb targets. The effects of Nb addition on the microstructures and mechanical properties of HEAFs were systematically investigated. For Nb-free film (0 at.% Nb), the face-centered cubic (FCC) peaks were identified in the X-ray diffraction (XRD) pattern. The addition of Nb resulted in a broadening of diffraction peaks, a decrease in peak intensity, and the vanishment of high-angle peaks. Transmission electron microscope (TEM) images indicated the formation of nanotwins at low Nb concentrations, and a transition from a single phase FCC solid solution to an amorphous phase was observed with the increasing Nb concentration. The films were strengthened with an increase in Nb concentration. Specifically, the hardness characterized by nanoindentation increased from 6.5 to 8.1 GPa. The compressive yield strength and fracture strength measured from micropillar compression tests were improved from 1.08 GPs and 2.56 GPa to 2.70 GPa and 5.76 GPa, respectively, whereas the fracture strain decreased from >29.4% (no fracture) to 15.8%. Additionally, shear banding was observed in the presence of amorphous phase.

Fabrication of AlGaN High Frequency Bulk Acoustic Resonator by Reactive RF Magnetron Co-sputtering System.

In this study, aluminum gallium nitride (AlGaN) thin films are used as the piezoelectric layers to fabricate solidly mounted resonators (SMR) for high frequency acoustic wave devices. AlGaN film is deposited on a Bragg reflector, composed of three pairs of Mo and SiO2 films, through a reactive radio frequency (RF) magnetron co-sputtering system at room temperature. The optimized deposition parameters of AlGaN film have a sputtering power of 175 W for Al target, sputtering power of 25 W for GaN target, N2 flow ratio (N2/Ar + N2) of 60%, and sputtering pressure of 10 mTorr. The obtained AlGaN film has a smooth surface, uniform crystal grains, and strong c-axis orientation. The contents of Al and Ga in the AlGaN film, analyzed by energy dispersive X-ray spectroscopy (EDS) are 81% and 19%, respectively. Finally, the frequency response s11 of the obtained SMR device shows that the center frequency is 3.60 GHz, the return loss is about −8.62 dB, the electromechanical coupling coefficient (kt2) is 2.33%, the quality factor (Q) value is 96.93 and the figure of merit (FoM) value is 2.26.