Radio Frequency Magnetron Co-sputtering Research Articles

Effects of cerium addition on microstructures and mechanical properties of CoCrNi medium entropy alloy films

In this work, the effects of rare-earth element Ce addition on the microstructures and mechanical properties of (CoCrNi)100-xCex (x = 0, 1.05, 2.61, 4.2, 5.96) medium entropy alloy films (MEAFs) were investigated. A series of (CoCrNi)100-xCex MEAFs was fabricated by radio frequency magnetron co-sputtering. The XRD and TEM results showed that the structure transformed from FCC to FCC + HCP at x = 2.61. Also, as Ni precipitated with Ce to form CeNi5 HCP phase, the localized depletion of Ni would encourage CoCrNi to transform from FCC to HCP phase. With the further increase in Ce content, Ce4.2 film became mixed nanocrystalline and amorphous structures and Ce5.96 film was fully amorphous. The nanoindentation and micro-pillar compression tests were conducted to study the mechanical properties of films. Both the hardness and Young's modulus showed an initial increase, reached the maxima of ~10 GPa and ~200 GPa, respectively, at x = 1.05, and then decreased with the increasing Ce content. The trends of yield strength and ultimate strength versus Ce content were similar to hardness. These results demonstrated that small amounts of Ce addition could strengthen CoCrNi MEAFs due to solid solution strengthening. However, excessive Ce addition would reduce the grain size to below ~10 nm and weaken the CoCrNiCe system due to the inverse Hall-Petch effect.

Super-Nernstian pH sensitivity of TbTaO4 sensing film for a solid-state pH sensor

In this work, a super-Nernstian pH sensitivity of TbTaO4 sensing film was developed for an electrolyte-insulator-semiconductor (EIS) solid-state pH sensor. The TbTaO4 sensitive films deposited on the Si substrates through radio-frequency magnetron co-sputtering were prepared under three various Ta plasma powers (80, 120, and 160 W) and then annealed at 800 °C. To investigate the impact of tantalum plasma power, multiple material analyses including X-ray diffraction, secondary ion mass spectrometry, atomic force microscopy, and X-ray photoelectron spectroscopy were performed. Results indicate that the film processed with the 120 W condition might form a stoichiometric TbTaO4 structure and possess a rough surface. Therefore, the best sensing performance was observed for the TbTaO4-based EIS sensor fabricated at the 120 W. In addition, the TbTaO4-based EIS also showed good selectivity for H+ ion over other ions (Na+, K+, Mg2+, and Ca2+). The proposed film fabrication process and analysis may represent a promising approach for the exploration of a novel pH-sensitive TbTaO4 film.

Tailoring the Surface Characteristics of CuSe Thin Films by Adjusting the Compositional Ratio

CuSe Thin Films In article number 2100148 by Yong-Cheol Kang and co-workers, copper selenide thin films (TFs) with various ratios of Se are fabricated by using radio frequency (RF) magnetron co-sputtering. The cover describes that the surface characteristics are dependent on whether the thin film is Cu-rich or Se-rich. To elaborate, the surface is hydrophobic and rough for Cu-rich thin films, while the surface is hydrophilic and smooth for Se-rich thin films.

Tailoring the Surface Characteristics of CuSe Thin Films by Adjusting the Compositional Ratio

Using radio frequency (RF) magnetron cosputtering, copper selenide thin films (TFs) with various ratios of Se are fabricated herein. To observe how the chemical and physical properties change based on morphology, the ratio of metallic Cu to nonmetallic Se is tuned to form multiple different compositions. The compositional percentage of the surface is determined by X‐ray photoelectron spectroscopy (XPS). Noticeable transitions of the characteristics of TFs are affected by Cu to a higher degree than Se. Larger grain sizes are observed when the Se ratio is high in Cu‐rich TFs. Most copper selenide TFs are hydrophobic and portray these characteristics the strongest when the surface Se ratio of TF is 16.62% as the contact angle with distilled water is 129°. In addition, the electrical conductivity is the highest at 2.04 (±0.13) × 107 S m−1 when the surface Se ratio is 10.95%.

Multifunctional Oxygen Scavenger Layer for High-Performance Oxide Thin-Film Transistors with Low-Temperature Processing.

In this study, the oxygen scavenger layer (OSL) is proposed as a back channel in the bilayer channel to enhance both the electrical characteristics and stability of an amorphous indium-gallium-zinc oxide thin-film transistor (a-IGZO TFT) and also to enable its fabrication at low temperature. The OSL is a hafnium (Hf)-doped a-IGZO channel layer deposited by radio-frequency magnetron cosputtering. Amorphous IGZO TFTs with the OSL, even if annealed at a low temperature (200 °C), exhibited improved electrical characteristics and stability under positive bias temperature stress (PBTS) compared to those without the OSL, specifically in terms of field-effect mobility (31.08 vs 9.25 cm2/V s), on/off current ratio (1.73 × 1010 vs 8.68 × 108), and subthreshold swing (0.32 vs 0.43 V/decade). The threshold voltage shift under PBTS at 50 °C for 10,000 s decreased from 9.22 to 2.31 V. These enhancements are attributed to Hf in the OSL, which absorbs oxygen ions from the a-IGZO front channel near the interface between a-IGZO and the OSL.

Radio-frequency magnetron co-sputtered Ge-Sb-Te phase change thin films

Radio-frequency magnetron co-sputtering technique with GeTe and Sb2Te3 targets has been used for the deposition of Ge-Sb-Te amorphous thin films. Fabricated layers cover broad region of chemical composition (~17.4-35.0 at. % of Ge, ~14.2-29.0 at. % of Sb) with slight variation in Te content (50.8-53.6 at. % of Te). Upon annealing-induced crystallization, large variations in electrical contrast up to eight orders of magnitude were found. Phase change from amorphous to crystalline state leads also to drastic changes of optical functions demonstrated by optical contrast values up to |Δn|+|Δk| = 2.96 for GeTe layers at Blu-ray wavelength. Reflectivity contrast at Blu-ray wavelength reaches up to ~43% with increasing content of GeTe in Ge-Sb-Te thin films, confirming importance of GeTe content in Ge-Sb-Te thin films.

Trace amount of niobium doped [formula omitted]-Ga[formula omitted]O[formula omitted] deep ultraviolet photodetector with enhanced photo-response

The growth of trace amount of niobium (Nb) doped β-Ga2O3 thin films have been demonstrated on (0001) sapphire substrates by radio frequency magnetron co-sputtering method. The crystallization, morphology and optical properties of Nb doped β-Ga2O3 films have been investigated. The deep ultraviolet (DUV) photodetector with a metal–semiconductor–metal structure based on trace amount of Nb doped β-Ga2O3 thin film was fabricated. The DUV photodetector exhibits high photo-to-dark-current ratio and fast photo-response speed, suggesting the performance of β-Ga2O3 photodetector can be improved by doping trace amount of Nb in β-Ga2O3 thin film.

Impurity Phases and Optoelectronic Properties of CuSbSe2 Thin Films Prepared by Cosputtering Process for Absorber Layer in Solar Cells

When there is a choice of materials for an application, particular emphasis should be given to the development of those that are low-cost, nontoxic, and Earth-abundant. Chalcostibite CuSbSe2 has gained attention as a potential absorber material for thin-film solar cells, since it exhibits a high absorption coefficient. In this study, CuSbSe2 thin films were deposited by radio frequency magnetron cosputtering with CuSe2 and Sb targets. A series of CuSbxSe2 thin films were prepared with different Sb contents adjusted by sputtering power, followed by rapid thermal annealing. Impurity phases and surface morphology of Cu–Sb–Se systems were directly affected by the Sb sputtering power, with the formation of volatile components. The crystallinity of the CuSbSe2 thin films was also enhanced in the near-stoichiometric system at an Sb sputtering power of 15 W, and considerable degradation in crystallinity occurred with a slight increase over 19 W. Resistivity, carrier mobility, and carrier concentration of the near-stoichiometric thin film were 14.4 Ω-cm, 3.27 cm2/V∙s, and 1.33 × 1017 cm−3, respectively. The optical band gap and absorption coefficient under the same conditions were 1.7 eV and 1.75 × 105 cm−1, which are acceptable for highly efficient thin-film solar cells.

Electrical and Optical Properties of Al-Doped ZnO Transparent Conductive Oxide Films Prepared via Radio Frequency Magnetron Co-Sputtering System.

In this study, the optical and electrical properties of a transparent conductive oxide (TCO) film synthesized via the radio frequency (RF) magnetron co-sputtering of Al-doped ZnO (AZO) and ZnO targets on a glass substrate were investigated. In the visible region, the resistivity, transmittance, and carrier concentration of the TCO film are influenced by the ratio of Al doping. The samples were prepared using two targets with the same deposition condition, except several different power levels on an AZO target to obtain different Al compositions in the film. The power range was 100-160 W in 20 W steps on the AZO target with a constant 50 W power level on the ZnO target. The electrical and optical characteristics of the film were measured using several apparatuses. The cross-section of the films was measured with via field emission scanning electron microscopy (FESEM) to determine the thickness of the film. The electrical and optical properties of the AZO films were measured via Hall measurement and UV-visible spectroscopy. The structural characteristics of the AZO films were confirmed by Raman spectroscopy.

Fabrication of Cr-Si-N coatings using a hybrid high-power impulse and radio-frequency magnetron co-sputtering: The role of Si incorporation and duty cycle

Cr-Si-N thin films were successfully fabricated by a hybrid deposition system containing a high power impulse magnetron sputtering (HiPIMS) and a radio frequency (RF) magnetron in an Ar and N2 mixture. It can be found that the deposition rate of Cr-Si-N films increased with increasing power of RF and duty cycle of HiPIMS. Varying both HiPIMS duty cycle and RF power lead to a variation in Si content in the resulting Cr-Si-N films, indicating that the Si content in thin films is a crucial parameter. The Cr-Si-N film grown at a duty cycle of 2.5%, a repetition frequency of 1000 Hz, a HiPIMS average power of 500 W, and RF power of 450 W exhibits the highest Si content of 14.2 at.%, hardness of 31.5 GPa, elastic modulus of 292 GPa, the highest resistance to failure value of 0.1079, and the smallest grain size of 8 nm, average surface roughness of 0.7 nm and a wear rate of 0.50 × 10−6 mm3/N-m. The improved film properties can be attributed mainly to the incorporation of Si element. More importantly, the existence of Si atoms in CrN grains for forming solid solution (Cr,Si)N phase or extra Si atoms reacting with N atoms for forming amorphous Si3N4 (Si-N) phase segregated at the boundaries of the columnar CrN grains has strong influence on the microstructure and mechanical properties of thin films. The lower duty cycle of HiPIMS and higher Si content show synergistic effects on the grain refinement and enhanced mechanical properties of Cr-Si-N films in this work.

The effect of Ge content on the structure and properties of low temperature deposited infrared Ge100-xCx films on As40Se60 chalcogenide glass

In this work, amorphous Ge100-xCx films were deposited on As40Se60 chalcogenide glass by radio frequency magnetron co-sputtering (rf MS) with different Ge content. The deposition temperature rise, the structural, mechanical and optical properties of Ge100-xCx films as a function of Ge content was investigated by thermocouple, X-ray photoelectron spectroscopy (XPS), Raman Spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transformed Infrared Spectroscopy, Surface Profiler and Continuous Stiffness Measurement (CSM). The deposition temperature rise of Ge100-xCx films derived from radical ions and neutrals is mild (<140℃) and lower than the transition temperature of As40Se60 chalcogenide glass (185 ± 5℃). The results reveal that both sp3 CC and sp2 CC clusters within Ge100-xCx film are converted to sp3 C-Ge bonds and finally depleted as Ge content increases from 18% to 79%. The conversion of sp2 CC structure to sp3 C-Ge bonds is faster than sp3 CC structure. The olefinic chains and nc-graphite clusters of sp2 CC structure are preferentially consumed to construct the sp3 C-Ge bonds. The nanohardness of Ge100-xCx films increases from 6.86 GPa to 9.87 GPa and elastic modulus of Ge100-xCx films increases from 35.72 GPa to 62.42 GPa as Ge content increases from 18% to 79%. Elastic recovery parameter (ERP) of Ge100-xCx film increases from 33.79% to 35.01% and nanohardness/Elastic modulus (H/E) decreases from 0.192 to 0.158 as Ge content increases from 18% to 79%. Ge100-xCx (66% Ge) /DLC double layer promotes the longwave infrared band (8 μm ∼ 11 μm) mean transmittance of As40Se60 chacogenide glass from 61.3% to 66.4%.

New type Schottky diodes based on the heterostructure of transition metal oxides: p-La2/3Sr1/3VO3/n-TiO2

We make a new type of bipolar Schottky diodes using the p-type La2/3Sr1/3VO3 (LSVO)/n-TiO2 heterostructure. The p-type LSVO metal thin films are grown on various substrates using radio frequency magnetron co-sputtering deposition. We find that the LSVO film grown on anatase TiO2 layer produce the lowest resistivity of 0.28 mΩ cm. We discover that the resistivity decreases with decreasing LSVO film thickness for LSVO/TiO2/Si structures. Hall measurements are performed and the dielectric functions of LSVO films are measured. The effective mass of LSVO/TiO2/Si is determined to be 2.54 ± 0.05 m0. The current-voltage curves of the Schottky diodes of p-LSVO/n-TiO2 is measured and is explained using band alignment diagram. We identify a new type of Schottky diode, where both electrons in n-TiO2 and holes in p-LSVO can flow under bias.

Electrical and optical properties of annealed AlSnZnO films deposited using radio frequency magnetron cosputtering system

Abstract Using a dual aluminum zinc oxide (AZO) target and tin dioxide (SnO2) target, 200-nm-thick aluminum-tin-zinc-oxide (ATZO) films were deposited onto quartz substrates by a radio frequency magnetron cosputtering system. After measuring X-ray diffraction patterns, carrier concentration, carrier mobility, room-temperature photoluminescence spectra, and ultraviolet–visible–near infrared spectra of the ATZO films without and with thermal annealing treatment in an oxygen ambience for 10 min at various temperatures, the annealing effects were demonstrated. Correlations among crystalline structures, electrical properties, optical properties, and annealing temperatures were observed. As the annealing temperature increased from 200 °C to 300 °C, the atoms of ATZO films gained more kinetic energy and more surface mobility to occupy stable positions. However, by further increasing the annealing temperature to 400 °C, the bonds in ATZO films became broken rather than enabling the atoms to remain in their corresponding stable positions. Consequently, the best properties were obtained for ATZO films annealed at 300 °C.

Investigation on the improved electrical and optical properties of trivalent boron-doped Cu2O thin film and fabrication of Cu2O:B/c-Si heterojunction diode

Boron-doped cuprous oxide (Cu2O:B) thin films were deposited on glass and silicon substrates via radio frequency (rf) magnetron co-sputtering at room temperature using metallic copper and boron targets. The influence of B doping on the morphology of Cu2O was studied using X-ray diffraction and spectrometric techniques. Optical transparency and bandgap of the doped films were improved compared to intrinsic Cu2O thin film. X-ray photoelectron spectroscopy confirms that Cu is in + 1 valance state even after doping. Electrical characteristics suggest enhanced p-type conductivity and reduction in resistivity with boron doping, due to the increase in charge carriers. Cu2O:B/c-Si heterojunction shows good rectifying (~ 104) behavior, and the small ∆Ev and high ∆Ec obtained from the flat band diagram suggests its potential application as hole-selective layer in c-Si solar cell.

X-ray absorption study of the local structure of Mg in hydroxyapatites thin films deposited by RF magnetron Co-Sputtering

Mg-doped hydroxyapatite (HAp) were deposited on Ti–6Al–4V substrates by radiofrequency (RF) magnetron co-sputtering of HAp and Mg targets. The as-deposited films were amorphous. Therefore, they were annealed at 1000 °C in ambient air. After annealing, the crystal structure, local structure, coatings morphology, and composition were investigated by X-ray diffraction technique (XRD), X-ray absorption spectroscopy (XAS), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDX), respectively. The XRD results show the amorphous phase for as-deposited and the major phase of TiO2 with a few secondary phase. The Mg K-edge XANES spectra was examined in order to identify the local site of Mg in hydroxyapatite thin films, which is formed as MgO in as-deposited sample and as MgAl2O4 in annealed sample. The information on the locally determined structures were obtained and discussed. The surface morphologies show the spherical shape particles with uniform distribution on the surface and new agglomeration of particles of MgAl2O4 on the surface of as-deposited and annealed samples, respectively.

Performance improvement of Y-doped VOx microbolometers with nanomesh antireflection layer.

In the study, the yttrium (Y)-doped vanadium oxide (VOx:Y) films used as the sensitive layers of microbolometers were deposited using a radio frequency magnetron co-sputtering system. The temperature coefficient of resistance (TCR) of the VOx:Y films was enhanced from -1.88%/°C to -2.85%/°C in comparison with that of the VOx films. To further improve the performance of microbolometers, the nanomesh antireflection layer was placed on the top surface of the microbolometers to reduce the infrared reflection. The responsivity, thermal time constant, thermal conductivity, absorptance, and detectivity of the VOx:Y microbolometers with nanomesh antireflection layer were 931.89 ± 48 kV/W, 4.48 ms, 6.19×10-8 W/K, 74.41% and 2.20×108 cmHz0.5W-1, respectively.

GaTe-Sb2Te3 thin-films phase change characteristics.

A radio frequency magnetron co-sputtering technique exploiting GaTe and ${\rm Sb}_2 {\rm Te}_3$Sb2Te3 targets was used for the fabrication of Ga-Sb-Te thin films. Prepared layers cover broad region of chemical composition (${\sim}{10.0 {-} 26.3}\,\, {\rm at.}$∼10.0-26.3at. % of Ga, ${\sim}{19.9 {-} 34.4}\,\, {\rm at.}$∼19.9-34.4at. % of Sb) while keeping Te content fairly constant (53.8-55.6 at. % of Te). Upon crystallization induced by annealing, large variations in electrical contrast were found, reaching a sheet resistance ratio of ${{R}_{\rm annealed}}/{{R}_{\rm as - deposited}}\;\sim{2.2} \times {{10}^{ - 8}}$Rannealed/Ras-deposited∼2.2×10-8 for the ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 layer. Phase transition from the amorphous to crystalline state further leads to huge changes of optical functions demonstrated by optical contrast values up to $|\Delta n| + |\Delta k| = {4.20}$|Δn|+|Δk|=4.20 for ${{\rm Ga}_{26.3}}{{\rm Sb}_{19.9}}{{\rm Te}_{53.8}}$Ga26.3Sb19.9Te53.8 composition.

Statistical experimental design to optimize RF-sputtered NiTiO3 thin films

An original statistical approach was developed to improve the features of the as-grown photoactive semiconducting Nickel titanate (NiTiO3) thin films by radio frequency (rf) magnetron co-sputtering process. NiTiO3 deposition requires two metallic targets (Ni and Ti) targets with argon (Ar) and oxygen (O2) gas mixture. The key parameters for the film synthesis consist in the partial pressures of Ar and O2 gas inside the deposition chamber, the rf co-sputtering power levels related to metal targets, the deposition time and the substrate temperature. So undeniably, the above parameters require optimized values to achieve a thin film growth with controlled features such as the stoichiometry, microstructure, crystalline structure and surface morphology. Two successive statistical Design of Experiments (DoE) were carried out and precise evaluations of the effects of the various deposition parameters were obtained. The approach contributes to draw judiciously the best rf co-sputtering conditions for the synthesis of NiTiO3 thin films with the possibility to extend the approach to similar structures and compositions.

Influence of magentic annealing temperature on microstructure and magnetic properties of NiCu alloy film

In this paper, Ni&lt;sub&gt;88&lt;/sub&gt;Cu&lt;sub&gt;12&lt;/sub&gt; thin films are prepared on Si substrates by radio-frequency magnetron co-sputtering. The effects of film thickness and heat treatment on domain structure and magnetic properties are studied. The Ni&lt;sub&gt;88&lt;/sub&gt;Cu&lt;sub&gt;12&lt;/sub&gt; films with thickness less than 210 nm show weak in-plane anisotropy. After the vacuum magnetic field heat treatment, the crystal grains of all films grow, and the in-plane anisotropy extents of Ni&lt;sub&gt;88&lt;/sub&gt;Cu&lt;sub&gt;12&lt;/sub&gt; films with thickness less than 210 nm become weaker. The films have different morphological characteristics at different heat treatment temperatures. The surface of the film is very dense before heat treatment. After heat treatment at 300 °C, it forms island shape due to the solid solution between the grains. Compared with the grains on the surface of the heat-treated film at 300 °C, the grains grow further after being heat-treated at 400 °C. Grown grains cover the gaps between the grains, which makes the film surface flat. The results of in-plane normalized hysteresis loop of the films show that the critical thickness of the stripe domains decreases after heat treatment. The stripe domain structure appears in the 210-nm-thick films without being heat-treated. For the film with the heat treatment, its remanence ratio &lt;i&gt;M&lt;/i&gt;&lt;sub&gt;r&lt;/sub&gt;/&lt;i&gt;M&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; decreases, and the saturation field &lt;i&gt;H&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; increases, and thus leading the perpendicular anisotropy constant &lt;i&gt;K&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; to increase. Therefore, the thickness of the stripe domain in the film after being heat-treated decreases. Compared with the films after being heat-treated, the 105-nm-thick as-prepared Ni&lt;sub&gt;88&lt;/sub&gt;Cu&lt;sub&gt;12&lt;/sub&gt; film has a maximum natural resonance frequency of 2.1 GHz, which is attributed to the uniaxial anisotropy of the as-prepared Ni&lt;sub&gt;88&lt;/sub&gt;Cu&lt;sub&gt;12&lt;/sub&gt; film. The saturation magnetization of the 300 °C-treated 105-nm-thick film decreases to 3.01 × 10&lt;sup&gt;5&lt;/sup&gt; A/m. However, the saturation magnetization decreases to 5.9 × 10&lt;sup&gt;5&lt;/sup&gt; A/m after heat treatment at 400 °C. Moreover, the ferromagnetic resonance peak of the film narrows after being treated at 300 °C, and the resonance frequency decreases to 1.95 GHz.

Annealing dependence of structural and optical properties of Zr-doped ZnO films deposited by radio frequency magnetron co-sputtering

To examine the effects of annealing temperatures, Zr-doped ZnO (Zn1-xZrxO1+δ; ZZO) thin films with x = ~0.067 were deposited at room temperature by radio frequency co-sputtering on quartz substrates and annealed in air at 300 °C, 400 °C, 500 °C, respectively. Annealing dependence of ZZO films was investigated by using X-ray diffraction, atomic force microscope X-ray absorption fine structure (XAFS), ultraviolet-visible (UV–Vis) spectroscopy, and resistivity. The results show that ZZO films maintain a strong preferred orientation toward c-axis, but the size of crystallites increased and the surfaces of the ZZO films were roughened with increasing annealing temperature. The Zn atoms were in divalent state and slightly affected by annealing, but Zr atoms were tetravalent and the spectra were slightly different from that of ZrO2. The variance of the Zn-O distance distribution, probed by polarization-dependent K-edge XAFS, in the ab-plane was stronger than that of the c-axis. The optical transmission spectra at 200 ≤ λ ≤ 900 nm showed high transparency of ≥90%, decrease of optical band gap, and red-shift as temperature increased. The resistivity decreased with enormously with increasing temperature. These results are ascribed to the increase of grain size.