Radio Frequency Magnetron Sputtering Process Research Articles

Sputtered PbI2 with Post‐Processing for Perovskite Solar Cells

Conformal deposition of perovskite films on textured silicon surfaces using a dry process is crucial for producing high‐performance perovskite/silicon tandem solar cells. Herein, a radio frequency magnetron sputtering process is used with a PbI2 target to deposit precursor films. Iodination, thermal annealing, and dimethyl sulfoxide treatment are employed as posttreatment processes to improve the stoichiometry, crystallinity, and surface morphology of the PbI2 precursor. The precursor films are converted into perovskite using direct contact conversion process, and the interfacial and bulk properties are enhanced by methylamine vapor annealing to fabricate perovskite solar cells with a power conversion efficiency of 12.2%. Also, 18.3% efficiency is confirmed at a wider voltage sweep range, which suggests that further efficiency improvement is possible by removing defects inside the perovskite. Finally, uniform perovskite films are conformally deposited on a 25 cm2 textured silicon surface. With such high‐efficiency potential and conformality, the method of sputtering PbI2 can open a new way to fabricate perovskite/silicon tandem solar cells.

Study of dielectric parameters of hexagonal boron nitride thin film fabricated by RF magnetron sputtering method

We report the fabrication of hexagonal boron nitride (hBN) thin films over a sizable area (4 cm2) on a glass substrate by adjusting the deposition time during the radio frequency magnetron sputtering process. As-prepared hBN films were characterized using Raman spectroscopy, and we found the distinctive E2g vibration band at 1366 cm-1, which ensures the presence of hBN in its bulk form. AFM was used to examine how the deposition time affected the surface morphology. It has been found that the sputtered film is made up of large (about 1 μm) hBN flakes. Impedance measurements were made to determine the dielectric parameters of the hBN films. The specific capacitance of the hBN films is found to be 0.04 μF/cm2, and their resistances have been found to be as high as 105 Ω. This study shows that for an hBN film to have a high specific capacitance, less deposition time is needed during the sputtering process.

P‐83: Oxygen Ratio's Effect on the Photoluminescence Property of Zinc‐Oxide Thin‐Film Phosphor

ZnO thin films phosphor was fabricated using reducing annealing of deposited thin films. The effect of oxygen ratios on the structural and optical properties of ZnO films as well as nanostructures were investigated. The crystallinity of ZnO nanostructures was significantly improved depending on the oxygen ratios increasing during the radio frequency magnetron sputtering process. The photoluminescence property was enhanced with increasing the density of ZnO nanostructures which obtained from high oxygen ratio deposited thin film.

Characterization Analysis of Aluminum and Indium Codoping Zinc Oxide on Flexible Transparent Substrates by RF Magnetron Sputtering Process

Aluminum and indium codoping zinc oxide (AIZO) films have been deposited simultaneously on polyethylene terephthalate (PET) substrate by radio frequency (RF) magnetron sputtering technique at room temperature (from a ceramic target) prepared with a mixture of zinc oxide (ZnO), aluminum (Al), and indium oxide (In2O3) of varying RF power range from 50 to 100 W and working pressure range from 2.5 to 15 mTorr. In order to obtain an acceptable performance rate with high-quality conducting thin films, the effect of correlation between the electrical, optical, and microstructural properties was investigated. The electrical resistivity significantly declined, and the carrier concentration improved as a result of In2O3 and Al incorporation within the ZnO and the increasing RF power. In this case, the best optical and electrical results were deposited at the RF power of 100 W with the working pressure of 2.5 mTorr. We were practicable to fabricate AIZO/PET electrodes of the lowest resistivity ( $7.6\times 10^{-3}\,\Omega $ -cm), the highest mobility, carrier concentration ( $8.29\times 10^{3}$ cm2/vs and $9.8\times 10^{20}$ cm−3, respectively), and the maximum transmittance (83%–96%) along an energy bandgap range of 3.3–3.65 eV with a well crystalline structure showing a roughness surface of the AIZO films and a suitable Herzberg–Teller (HT). Thus, according to these expressions, we could be responsible for preparing AIZO/PET with improved electrical property and microstructure of great applications for flexible electronic devices.

Al2O3–TiO2 composite coatings with enhanced anticorrosion properties for 316L stainless steel

Abstract316L stainless steel is used as an important structural material in various industries. However, its service life is limited in the presence of chloride ions due to severe chemical corrosion. Herein, a facile radiofrequency magnetron sputtering process is reported for the synthesis of various Al2O3–TiO2 composite coatings as an anticorrosion layer for 316L stainless steel substrates. The enhanced chemical stability of Al2O3–TiO2 composite coatings was investigated by X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and X‐ray diffraction measurements. Moreover, the high specific surface area of Al2O3–TiO2 composite coatings displayed better hydrophobic property which can be confirmed by scanning electron microscopy and contact angle measurements. Finally, the direct characterization of anticorrosion properties was carried out using electrochemical tests. All of the above results exhibited the enhanced anticorrosion properties of Al2O3 coating after the incorporation of TiO2. Significantly, the Al2O3–TiO2 composite coatings with 15.56% Ti content provided the best corrosion resistance for 316L stainless steel.

Orienting high Curie point CaBi2Nb2O9 ferroelectric films on Si at 500 C

With the highest Curie temperature in all known ferroelectrics and a lead-free composition, CaBi2Nb2O9 (CBNO) has a good potential in electromechanical applications demanding a good temperature stability and environmental friendliness. However, due to its highly anisotropic crystalline lattice (a = 5.435 Å, b = 5.466 Å, c = 24.970 Å, Pa = Pb, Pc ≈ 0), a/b-axis oriented CaBi2Nb2O9 films with excellent ferroelectric and piezoelectric properties are difficult to grow on Si substrates (a ≈5.431 Å) at 500 °C or lower, temperatures compatible with the existing CMOS-Si technology. It is also difficult to grow them a/b-axis oriented on those commonly used semiconductor substrates (such as SrTiO3 and MgO), whose lattice parameters well match with the diagonal length of the CBNO (00l)-plane (a ≈4 Å ≈ aCBNO/√2). In this work, CaBi2Nb2O9 thin films with a SrRuO3 (a ≈3.96 Å) buffer layer, which promoted the growth of grains tilting away from the weakly polarized c-axis, were successfully prepared on platinum-coated (100)Si substrates at 500 °C via a radio-frequency magnetron sputtering process. These films exhibited a (117) texture with enhanced electrical properties, including a high dielectric constant (ɛr ∼ 480 @ 1 kHz), large electric polarizations (Pr ∼ 12 μC/cm2, Ps ∼ 63 μC/cm2 @ Emax = 1800 kV/cm), and a good transverse piezoelectric coefficient e31,f (∼1.25 C/m2). As a consequence of its high Curie temperature (>600 °C), the dielectric constant of the CBNO film showed a slow declination with temperature (∼0.1%/oC before 300 °C, and less than 0.03%/oC from 300 °C to 600 °C). Its dielectric loss is less than 5% at temperatures lower than 200 °C under a low working frequency (5 kHz/10 kHz), and it stays lower than 5% up to 500 °C when a high working frequency (500 kHz/1 MHz) is used. These enhanced electrical properties will greatly promote applications of CBNO thin films in lead-free ferroelectric devices, especially in those demanding a good high temperature stability.

Influence of annealing on the structural and optical properties of gallium oxide films deposited on c-sapphire substrate

The Ga2O3 films were grown on an Al2O3 (0001) substrate by a radio frequency magnetron sputtering process, the obtained samples were annealed at 800 °C for 30 min in air and vacuum atmosphere, respectively. The effects of annealing atmosphere on the crystal structure, microstructure, transmittance and band gap of Ga2O3 thin films were investigated in detail. It can be seen from the X-ray diffraction spectrum (XRD) that the film annealed showed better crystallinity with a monoclinic structure and the structure analysis revealed a clear out-of-plane orientation of β-Ga2O3 (2¯01) || Al2O3 (0001). The average transmittance of the films in the visible wavelength range exceeded 90% and the optical band gap of the films varied from 4.93 to 5.11 eV which were observed by spectrophotometer.

Treatment of a polycarbonate plate for a next-generation vehicle window by radio frequency magnetron plasma sputtering using a PVDF target

A polycarbonate (PC) plate was treated by a radio frequency magnetron sputtering process using a polyvinylidene difluoride target for a next-generation vehicle window. The treated PC surface resulted in a hydrophobic nature at higher sputtering pressures of 50 and 100 Pa, while hydrophilic at a low pressure of 2 Pa. These surfaces were examined with atomic force microscopy (AFM) images and X-ray photoelectron spectroscopy (XPS) analysis. It was found from AFM images that the surface of the films had a smooth structure with roughness Ra of 0.62–0.71 nm for the high pressure, whereas for the low pressure, had an irregular structure with Ra of 2.03 nm. The ratio of the F 1s component to all components of C 1s, O 1s and F 1s from XPS spectra for 100 Pa was approximately seven times higher than that for 2 Pa.

Micromorphology of sputtered aluminum thin films: A fractal analysis

Abstract In this article, the surface analyses of topography, microstructure and mechanical behavior of Al thin films sputtered on glass are presented to understand the influence of varying low substrate temperatures at high radio-frequency (RF) power. The films were prepared by RF magnetron sputtering process at different substrate temperatures of 55°C, 65°C, and 95°C and at a constant RF power of 350 W. The topography, microstructure and mechanical properties were characterized by atomic force microscope (AFM), field emission scanning electron microscope (FESEM) and nanoindentation method respectively. The results revealed that at a higher substrate temperature of 95°C the microstructure consists of dense and globular dominant aluminum structures and higher interface width (roughness) as compared to the other temperatures. Nanoindentation results showed that films deposited at 95°C exhibited the highest values of average hardness and elastic moduli and a lowest maximum depth of displacement. A fractal analysis on the topography and surface microstructure revealed a decrease of the fractal dimension with the increase in substrate temperature and that the films exhibited a mono-fractal behavior at all the substrate temperatures investigated in the present study. A description based on the sputtering theory for the monofractal nature of the aluminum films is provided.

Mechanical Property of Magnesium Alloy Surface with Dense Oxide

Low Al single-phase magnesium alloy surfaces with dense magnesium oxide films were uniformly formed. The films were deposited with a radio frequency magnetron sputtering process with a planar magnetron sputtering system. The thickness of deposited magnesium oxide thin films was around 240 nm. According to the XRD results, a magnesium oxide phase film was formed on the substrate. The surface was uniform, and no cracks or exfoliation were observed. The deposited magnesium oxide film did not have any cracks or pores, and the surface of the sample was covered by magnesium oxide. The hardness of the magnesium oxide-coated magnesium alloy reached around Hv200, while that of the uncoated Mg-alloy was around Hv80. Moreover, the Vickers indenter under a 10-mN load indented the magnesium alloy substrate coated with the magnesium oxide film to a depth of around 640 nm, while that for the uncoated magnesium alloy substrate was around 620 nm. Meanwhile, the elasticity value for the magnesium alloy substrate coated with magnesium oxide film was around 5.3×1010 Pa, while that of the uncoated magnesium alloy substrate was around 4.2×1010 Pa.

Plasma Polymerization Enabled Polymer/Metal–Oxide Hybrid Semiconductors for Wearable Electronics

A facile fabrication of polymer/metal-oxide hybrid semiconductors is introduced to overcome the intrinsically brittle nature of inorganic metal-oxide semiconductors. The fabrication of the hybrid semiconductors was enabled by plasma polymerization of polytetrafluoroethylene (PTFE) via radio frequency magnetron sputtering process which is highly compatible with metal-oxide semiconductor manufacturing facilities. Indium-gallium-zinc oxide (IGZO) and PTFE are cosputtered to fabricate PTFE-incorporated IGZO thin-film transistors (IGZO:PTFE TFTs) and they exhibit a field-effect mobility of 10.27 cm2 V-1 s-1, a subthreshold swing of 0.38 V dec-1, and an on/off ratio of 1.08 × 108. When compared with conventional IGZO TFTs, the IGZO:PTFE TFTs show improved stability results against various electrical, illumination, thermal, and moisture stresses. Furthermore, the IGZO:PTFE TFTs show stable electrical characteristics with a threshold voltage ( Vth) shift of 0.89 V after 10 000 tensile bending cycles at a radius of 5 mm.

Using Oxygen Plasma Pretreatment to Enhance the Properties of F-Doped ZnO Films Prepared on Polyimide Substrates

In this study, a radio frequency magnetron sputtering process was used to deposit F-doped ZnO (FZO) films on polyimide (PI) substrates. The thermal expansion effect of PI substrates induces distortion and bending, causing FZO films to peel and their electrical properties and crystallinity to deteriorate. To address these shortcomings, oxygen (O2) plasma was used to pretreat the surface of PI substrates using a plasma-enhanced chemical vapor deposition system before the FZO films were deposited. The effects of O2 plasma pretreatment time on the surface water contact angle, surface morphologies, and optical properties of the PI substrates were investigated. As the pretreatment time increased, so did the roughness of the PI substrates. After the FZO films had been deposited on the PI substrates, variations in the surface morphologies, crystalline structure, composition, electrical properties, and optical properties were investigated as a function of the O2 plasma pretreatment time. When this was 30 s, the FZO films had optimal optical and electrical properties. The resistivity was 3.153 × 10−3 Ω-cm, and the transmittance ratios of all films were greater than 90%. The X-ray photoelectron spectroscopy spectra of the FZO films, particularly the peaks for O1s, Zn 2p1/2, and Zn 2p3/2, were determined for films with O2 plasma pretreatment times of 0 and 30 s. Finally, a HCl solution was used to etch the surfaces of the deposited FZO films, and silicon-based thin-film solar cells were fabricated on the FZO/PI substrates. The effect of O2-plasma pretreatment time on the properties of the fabricated solar cells is thoroughly discussed.

Fabrication of ordered metallic glass nanotube arrays for label-free biosensing with diffractive reflectance

In this study, a photoresist template with well-defined contact hole array was fabricated, to which radio frequency magnetron sputtering process was then applied to deposit an alloyed Zr55Cu30Al10Ni5 target, and finally resulted in ordered metallic glass nanotube (MGNT) arrays after removal of the photoresist template. The thickness of the MGNT walls increased from 98 to 126nm upon increasing the deposition time from 225 to 675s. The wall thickness of the MGNT arrays also increased while the dimensions of MGNT reduced under the same deposition condition. The MGNT could be filled with biomacromolecules to change the effective refractive index. The air fraction of the medium layer were evaluated through static water contact angle measurements and, thereby, the effective refractive indices the transverse magnetic (TM) and transverse electric (TE) polarized modes were calculated. A standard biotin–streptavidin affinity model was tested using the MGNT arrays and the fundamental response of the system was investigated. Results show that filling the MGNT with streptavidin altered the effective refractive index of the layer, the angle of reflectance and color changes identified by an L*a*b* color space and color circle on an a*b* chromaticity diagram. The limit of detection (LOD) of the MGNT arrays for detection of streptavidin was estimated as 25nM, with a detection time of 10min. Thus, the MGNT arrays may be used as a versatile platform for high-sensitive label-free optical biosensing.

Hydrogen related crystallization in silicon carbide thin films

The present study reports on a detailed investigation on the transition from amorphous to nanocrystalline silicon carbide films grown by means of reactive radiofrequency magnetron sputtering process at low substrate temperatures Ts ranging from 200°C to 500°C. Fourier transform infrared spectroscopy (FTIR), optical transmission measurements and atomic force microscopy (AFM) images were used to study the structural and the optical properties of the films. The results clearly show that hydrogen atoms play a crucial role in the nanocrystal nucleation mechanism. The grown of the films is governed by the interactions between hydrogen atoms and SiC amorphous matrix. The FTIR analysis showed an abrupt structural transition from amorphous a-SiC:H to nc-SiC:H films occurred with increasing Ts from 250°C to 300°C. Upon increasing Ts, the extent of crystallization is substantial and reaches (70±2) % for films deposited at 500°C. In parallel, the total bonded hydrogen content decreases from 30 at.% to less than 6 at.%. The AFM observations confirm the structural changes in the films, and the average grain size reaches a value of about 60nm.

Room‐Temperature Fabricated Amorphous Ga2O3 High‐Response‐Speed Solar‐Blind Photodetector on Rigid and Flexible Substrates

A solution to the fabrication of amorphous Ga2O3 solar‐blind photodetectors on rigid and flexible substrates at room temperature is reported. A robust improvement in the response speed is achieved by delicately controlling the oxygen flux in the reactive radio frequency magnetron sputtering process. Temporal response measurements show that the detector on quartz has a fast decay time of 19.1 µs and a responsivity of 0.19 A W−1 as well, which are even better than those single crystal Ga2O3 counterparts prepared at high temperatures. X‐ray photoelectron spectroscopy and current–voltage tests suggest that the reduced oxygen vacancy concentration and the increased Schottky barrier height jointly contribute to the faster response speed. Amorphous Ga2O3 solar‐blind photodetector is further constructed on polyethylene naphthalate substrate. The flexible devices demonstrate similar photoresponse behavior as the rigid ones, and no significant degradation of the device performance is observed in bending states and fatigue tests. The results reveal the importance of finely tuned oxygen processing gas in promoting the device performance and the applicability of room‐temperature synthesized amorphous Ga2O3 in fabrication of flexible solar‐blind photodetectors.

H<sub>2</sub>S dosimeter with controllable percolation threshold based on semi-conducting copper oxide thin films

Abstract. Copper oxides, such as CuO and Cu2O, are promising materials for H2S detection because of the reversible reaction with H2S to copper sulfides (CuS, Cu2S). Along with the phase change, the electrical conductance increases by several orders of magnitude. On CuOx films the H2S reaction causes the formation of statistically distributed CuxS islands. Continuous exposition to H2S leads to island growth and eventually to the formation of an electrical highly conductive path traversing the entire system: the so-called percolation path. The associated CuOx ∕ CuxS conversion ratio is referred to as the percolation threshold. This pronounced threshold causes a gas concentration dependent switch-like behaviour of the film conductance. However, to utilize this effect for the preparation of CuO-based H2S sensors, a profound understanding of the operational and morphological parameters influencing the CuS path evolution is needed.Thus, this article is focused on basic features of H2S detection by copper oxide films and the influence of structural parameters on the percolation threshold and switching behaviour. In particular, two important factors, namely the stoichiometry of copper oxides (CuO, Cu2O and Cu4O3) and surface morphology, are investigated in detail. CuOx thin films were synthesized by a radio frequency magnetron sputtering process which allows modification of these parameters. It could be shown that, for instance, the impact on the switching behaviour is dominated by morphology rather than stoichiometry of copper oxide.

Transparent field-effect transistors based on AlN-gate dielectric and IGZO-channel semiconductor

The degradation of thin-film transistors (TFTs) caused by the self-heating effect constitutes a problem to be solved for the next generation of displays. Aluminum nitride (AlN) is a viable alternative for gate dielectric of TFTs due to its good thermal conductivity, matching coefficient of thermal expansion to indium–gallium–zinc-oxide, and excellent stability at high temperatures. Here, AlN thin films of different thicknesses were fabricated by a low temperature reactive radio-frequency magnetron sputtering process, using a low cost, metallic Al target. Their electrical properties have been thoroughly assessed. Furthermore, the 200nm and 500nm thick AlN layers have been integrated as gate-dielectric in transparent TFTs with indium–gallium–zinc-oxide as channel semiconductor. Our study emphasizes the potential of AlN thin films for transparent electronics, whilst the functionality of the fabricated field-effect transistors is explored and discussed.

Influence of ion bombardment on structure and properties of TiZrN thin film

The study is focused on the characterization of TiZrN thin film by controlling the behavior of ion bombardment. Thin films are grown using radio frequency magnetron sputtering process on Si wafer. The negative bias voltage ranging from −20V to −130V was applied to the substrate. The ion current density increases rapidly as substrate bias is lower than −60V, then slightly increases as the critical value about −60V is exceeded. At the substrate bias of −60V, the ion current density is close to 0.56mA/cm2. The resistivity measured by four-point probe decreases from conditions −20V to −60V and then increases for substrate bias increases from −60V to −130V. The resistivity of TiZrN films is contributed from the packing factor. The N/TiZr ratios about 1 were measured by Rutherford backscattering spectrometer, and the packing factors of TiZrN films can also be obtained by the results of RBS. Field Emission scanning electron microscope (FEG-SEM) is used to characterize the thickness and structure of the deposited TiZrN film. X-ray diffraction (XRD) is used to determine the preferred orientation and lattice parameter. The precursor results of XRD show that all the coating samples exhibited (111) preferred orientation, and the hardness values of TiZrN films were ranging from 20 to 40GPa. To sum up the precursor studies, the TiZrN films which can improve the properties from TiN and ZrN is a new ceramic material with higher potential. Following the advance process and analysis research, the structure and properties can be correlated and as a reference for industry application.

Detailed microstructure analysis of as-deposited and etched porous ZnO films

ZnO nanostructured materials in thin film forms are of particular interest for photovoltaic or photocatalysis processes but they suffer from a lack of simple methods for optimizing their microstructure. We have demonstrated that microporous ZnO thin films with optimized inter grain accessibility can be produce by radio frequency magnetron sputtering process and chemical etching with 2.75mM HCl solution for different duration. The as-deposited ZnO thin films were first characterized in terms of structure, grain size, inter grain space, open cavity depth and total thickness of the film by XRD, AFM, SEM, profilometry and optical measurements. A specific attention was dedicated to the determination of the surface enhancement factor (SEF) by using basic geometrical considerations and images treatments. In addition, the porous fraction and its distribution in the thickness have been estimated thanks to the optical simulation of the experimental UV–Visible–IR spectrums using the Bruggeman dielectric model and cross section SEM images analysis respectively. This study showed that the microstructure of the as-deposited films consists of a dense layer covered by a porous upper layer developing a SEF of 12–13m2m−2. This two layers architecture is not modified by the etching process. The etching process only affects the upper porous layer in which the overall porosity and the inter-grain space increase with the etching duration. Column diameter and total film thickness decrease at the same time when the films are soaked in the HCl bath. The microporous structure obtained after the etching process could generate a great interest for the interfaces electronic exchanges for solar cells, photocatalysis and gas sensors applications.

Sputtering condition effect on structure and properties of LiNbO3 films

Polycrystalline LiNbO3 films were grown on various substrates by the radio-frequency magnetron sputtering (RFMS) method and ion-beam sputtering (IBS) method at different sputtering conditions. Films formed on the substrates situated within erosion zone (plasma effect) manifested textured structure. When plasma effect became insignificant only LiNbO3 films with random size orientation were formed during the RFMS process and IBS process with an increase in the size of the crystallites. Reactive gas pressure as part of plasma effect has a profound effect on the films’ properties. When gas pressure was increased greatly, grain size declined two fold and the average surface roughness of the grown films doubled. At the higher gas pressure Li-poor phase LiNb3O8 appeared along with LiNbO3 during the growth process. As a result, the film texture disappeared. Single phase LiNbO3 films with two-axes (epitaxial) texture are formed on (111)Ag epitaxial film during the RFMS process at the ion assisted conditions.