Direct Current Reactive Magnetron Sputtering Research Articles

Effects of substrate bias voltage on conductivity and internal stress of TiN films

In order to make the service life of microelectronic devices longer, titanium nitride electrode films need to meet the requirements of high electrical conductivity and low internal stress. In this paper, the effect of substrate bias voltage on the properties of titanium nitride films prepared by direct current (DC) reactive magnetron sputtering was studied systematically. The changes of titanium nitride films properties were investigated in detail from the aspects of resistivity, growth rate, crystal orientation, roughness and internal stress. The results show that the introduction of substrate bias voltage is conducive to the formation of dense titanium nitride films. Considering that the resistivity and internal stress of titanium nitride film vary with substrate bias voltage, the film deposited at substrate bias voltage of -100 V is selected as the electrode film material with the best performance (resistivity of 47.5 μΩ·cm, roughness of 1.1 nm and internal stress of -5.6 GPa).

Impact of blocking layers based on TiO2 and ZnO prepared via direct current reactive magnetron sputtering on DSSC solar cells

The optimization of dye-sensitized solar cells (DSSCs) technology towards suppressing charge recombination between the contact and the electron transport layer is a key factor in achieving high conversion efficiency and the successful commercialization of this type of product. An important aspect of the DSSC structure is the front blocking layer (BL): optimizing this component may increase the efficiency of photoelectron transfer from the dye to the semiconductor by reduction charge recombination at the TiO2/electrolyte and FTO/electrolyte interfaces. In this paper, a series of blocking layer variants, based on TiO2 and ZnO:TiO2, were obtained using the reactive magnetron sputtering method. Material composition, structure and layer thickness were referred to each process parameters. Complete DSSCs with structure FTO/BL/m-TiO2@N719/ EL-HSE/Pt/FTO were obtained on such bases. In the final results, verification of opto-electrical parameters of these cells were tested and used for the conclusions on the optimal blocking layer composition. As the conclusion, application of blocking layer consists of neat TiO2 resulted in improvement of device efficiency. It should be noted that for TiO2:ZnO/CuxO and TiO2/CuxO cells, higher efficiencies were also achieved when pure TiO2 was used as window layer. Additionally it was proven that the admixture of ZnO phase inspires Voc and FF growth, but is overall unfavorable compared to pristine TiO2 blocking layer and the reference cell, according to the final cell efficiency.

Durability enhancement of all-solid-state electrochromic devices by adjusting the charge density ratio between electrochromic and counter electrode layers

Owing to an increase in global warming, smart-window devices based on charge-balanced electrochromic devices (ECDs), which exhibit high potential to increase the thermal efficiency of buildings, have gained prominence. However, studies on the fabrication and cycling stability of charge-balanced ECDs are scarce. In this study, WO3 and NiOx films were deposited on indium–tin–oxide (ITO)-coated glass substrates by reactive direct-current magnetron sputtering, and the deposition time was varied to control the thickness and charge density of the thin films. Subsequently, the NiOx/ITO/glass and WO3/ITO/glass substrates were laminated with a Li-based polymeric electrolyte to fabricate all-solid-state ECDs comprising electrochromic (EC) and counter-electrode (CE) layers in charge-density ratios of 12.6, 6.4, 2.3, and 1.1. Changes in the electrochromic properties, device-layer microstructure, crystal structure, and elemental composition of the as-constructed ECDs before and after degradation were investigated to understand the influence of the charge-density ratio of the EC and CE layers on the long-term durability of ECDs. Increasing the charge-density ratio decreased the cycling stability of the device owing to changes in the microstructure and crystal structure of the NiOx layer in the microstructural deep-trap sites. Among all the ECDs, those comprising EC and CE layers with similar charge densities showed the most stable optical modulation and highest long-term durability. Finally, based on the aforementioned results, a degradation mechanism for charge-imbalanced all-solid-state ECDs was proposed. This study is expected to open new frontiers in designing optimal-performance electrochemical devices with a wide variety of potential applications.

Plasma emission spectroscopy and optical properties of reactive-sputtered silicon oxynitride films

Silicon oxynitride (SiO x N y ) thin films were synthesized via reactive direct current magnetron sputtering under different reactive gas mass flow ratios (O2:N2) and discharge powers. The process was monitored by optical emission spectroscopy (OES), while spectroscopic ellipsometry was used to characterize the optical properties of the thin films and deposition rates. In this work, the plasma generated under different deposition parameters is analyzed by monitoring the emission lines of different species (Si I, Ar I, O2, and N2) and these results are then correlated with the corresponding target poisoning process and the optical properties of the grown thin films. According to the spectral analysis, the emission lines proved to be sensitive to the synthesis process as it was possible to differentiate deposition variations when other parameters remained unchanged. Furthermore, similar plasma conditions determined via the emission of different species were found to produce consistent thin film optical properties and vice versa. OES showed to be an effective method of monitoring and controlling the deposition of SiO x N y thin films with specific compositions.

Band alignment engineering at ultra-wide bandgap GeO2/SiO2 heterointerfaces

Owing to the tremendous contribution for the carrier transport across the interface, the band alignment engineering in oxide semiconductor heterojunctions (OSHs) is of vital importance for developing oxide semiconductor optoelectronic devices. Here, we have deposited a series of ultra-wide bandgap GeO2 thin films on quartz substrates by the direct-current reactive magnetron sputtering method to construct the OSHs and described the effect of the flow rate ratios of O2 and Ar (O2:Ar) and substrate temperatures on the bandgap energies of GeO2 films and band alignments at the interface of OSHs. Based on the energy loss spectra of O 1 s peaks, the tunable bandgap energies ranging from 4.37 to 5.37 eV have been achieved for GeO2 films. An obvious variation of band alignments has been found in the OSHs, suggesting the dramatically influence of deposition conditions. The valence band offsets are determined to be ranging from 1.85 to 1.96 eV (from 1.88 to 1.95 eV) and the conduction band offsets are calculated to be ranging from 1.88 to 2.78 eV (from 1.74 to 2.19 eV) for the GeO2 films grown at different O2:Ar (substrate temperatures), respectively, due to the nonlocalization of the oxygen vacancies in valence band and the formation of single hexagonal phase in the GeO2 film. Our findings on the band alignment engineering in the GeO2/SiO2 heterointerfaces will open the way for developing GeO2-based optoelectronic devices.

Carbonaceous-TiO2 composite photocatalysts through reactive direct current magnetron sputtering on powdered graphene for environmental applications

An efficient photocatalytic composite material was produced by coating graphene powder with TiO2 using reactive pulsed direct-current magnetron sputtering. High-quality graphene powder with a thickness consisting of 6–10 layers was obtained by liquid-phase exfoliation of natural graphite. The process variables included the working pressure (0.7, 1.2, and 1.5 Pa), coating time (1, 2, 4, and 8 h), and graphene mass (0.1, 0.5, and 1.0 g). Raman spectroscopy, scanning electron microscopy coupled to energy dispersive spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the graphene-TiO2 nanocomposites. The results of the characterization showed efficient TiO2 deposition with anatase and rutile crystallographic structures on the powdered graphene. Additionally, it was verified that the graphene was not damaged during the coating process, thereby maintaining its unique conductive and mechanical properties. The produced material exhibited photocatalytic activity for methylene blue degradation and Escherichia coli inactivation under UV light.

Revisitation of reactive direct current magnetron sputtering discharge: Investigation of Mg–CF4, Mg–O2, and Ti–O2 discharges by probe measurements

The reactive direct current (DC) magnetron sputtering discharges of Mg–CF4, Mg–O2, and Ti–O2 were investigated using probe measurements as a function of reactive gas flow ratio. The emission spectroscopy, which was conducted before the probe measurements, demonstrates that all the three DC discharges transit from nonreactive to reactive discharge mode with increasing reactive gas flow ratio. The probe measurements show that the plasma potentials of the Mg–O2 and Ti–O2 DC discharges slightly increase or remain almost constant with increasing reactive gas flow ratio, whereas that of the Mg–CF4 DC discharge drastically decreases at the mode transition. For the same change in reactive gas flow ratio, the discharge voltage of the Mg–CF4 DC discharge slightly increases and that of the Mg–O2 DC discharge drastically increases at the mode transition, whereas that of the Ti–O2 DC discharge slightly decreases at the mode transition. The changes in the cathode sheath potential difference at the mode transition differ between the Mg–CF4 and Ti–O2 DC discharges and the Mg–O2 DC discharge because of the difference in the probability of secondary electron emission at the cathode surface; furthermore, the changes in the anode sheath potential difference at the mode transition differ between the Mg–CF4 DC discharge and the Mg–O2 and Ti–O2 DC discharges because of the difference in the probability of negative-ion formation in the plasma bulk. The most informative results obtained in this study were the differences in the potential differences at the cathode and anode sheaths among the Mg–CF4, Mg–O2, and Ti–O2 DC discharges. They well demonstrated the effects of the change in secondary-emitted species at the cathode surface and the change in reactive gas concentration in the plasma on the potential configuration.

Solar cells based on copper oxide and titanium dioxide prepared by reactive direct-current magnetron sputtering

Solar cells based on copper oxide and titanium dioxide prepared by reactive direct-current magnetron sputtering

Aluminum tantalum oxide thin films deposited at low temperature by pulsed direct current reactive magnetron sputtering for dielectric applications

This research aims at studying aluminum tantalum oxide thin films (AlxTayOz) deposited at low temperature for dielectric applications. These ternary oxide layers are synthesized at 180 °C by physical vapor deposition (PVD), specifically the mid-frequency pulsed direct current reactive magnetron sputtering. The deposition process uses targets made of a mixture of aluminum and tantalum in various proportions. Four target compositions are studied containing 95 at.%, 90 at.%, 80 at.%, and 70 at.% of aluminum, corresponding to 5 at.%, 10 at.%, 20 at.%, and 30 at.% of tantalum, respectively. The ternary oxide thin films of AlxTayOz are compared to aluminum oxide (AlxOz) and tantalum oxide (TayOz) layers produced in the same experimental conditions. The AlxTayOz thin films are dense, uniform, and amorphous regardless of the experimental conditions used in this study. Their chemical composition changes as a function of the target composition. The oxygen flow used during deposition also affects the chemical composition of the oxide layers and the deposition rate. The oxide thin films with tantalum are deposited at higher deposition rates and contain more oxygen. Tantalum also promotes the amorphization of the oxide layers. The highest dielectric strength is measured for the thin film containing a low amount of tantalum combined with a high amount of oxygen.

Insights into the oxidation resistance mechanism and tribological behaviors of multilayered TiSiN/CrVxN hard coatings

In the last decades, vanadium alloyed coatings have been introduced as potential candidates for self-lubrication due to their perfect tribological properties. In this work, the influence of V incorporation on the wear performance and oxidation resistance of TiSiN/CrN film coatings deposited by direct current (DC) reactive magnetron sputtering is investigated. The results show that vanadium incorporation significantly decreases the oxidation resistance of the coatings. In general, two layers are formed during the oxidation process: i) Ti(V)O2 on top, followed by a protective layer, which is subdivided into two layers, Cr2O3 and Si-O. ii) The diffusion of V controls the oxidation of V-containing coatings. The addition of vanadium improves the wear resistance of coatings, and the wear rate decreases with increasing V content in the coatings; however, the friction coefficient is independent of the chemical composition of the coatings. The wear of the V-containing coatings is driven by polishing wear.

Effect of Substrate Bias on the Microstructure and Properties of Non-Equimolar (AlCrSiTiZr)N Films with Different Cr/Zr Ratios Deposited Using Reactive Direct Current Magnetron Sputtering

To reduce the cost of tools operated in extreme environments, we developed films with excellent corrosion/oxidation resistance. Two high-entropy nitride films, (AlCrSi0.3TiZr)N and (AlCr1.5Si0.3TiZr0.5)N, were deposited using reactive DC magnetron sputtering under different substrate biases. The films exhibited a maximum hardness of 32.5 GPa ((AlCrSi0.3TiZr)N) and 35.3 GPa ((AlCr1.5Si0.3TiZr0.5)N) when deposited at −150 V, corresponding to 27 and 142% increases compared to those deposited at 0 V. This indicates that the bias strengthened (AlCr1.5Si0.3TiZr0.5)N (higher Cr/Zr ratio) more significantly. The enhancement of the mechanical properties was highly correlated with the interstitial point defects and densification of the film microstructures. The corrosion resistance of the films deposited on 6061 Al alloy substrate under different biases was tested in 0.1 M H2SO4. (AlCrSi0.3TiZr)N and (AlCr1.5Si0.3TiZr0.5)N displayed the lowest corrosion currents of 0.75 and 0.19 μA/cm2 when deposited at −100 and −150 V, respectively. These values are two orders of magnitude lower than that of the uncoated substrate. The (AlCr1.5Si0.3TiZr0.5)N film showed better oxidation resistance than the (AlCrSi0.3TiZr)N film and remained partially oxidized after heat treatment at 1000 °C. The (AlCr1.5Si0.3TiZr0.5)N film deposited at −150 V exhibits excellent mechanical properties and corrosion/oxidation resistances, making it suitable for protecting tools operating in harsh environments.

Improving the photoresponse of magnetron sputtered titania films by optimizing substrate and electrode configuration

Titania (TiO2) is a natural choice for photocatalysts and photodetectors due to its superior properties such as high stability and high photoelectric effect coupled with low cost fabrication routes. In this work we study the effect of substrate on the structural, morphological, and photoresponse behavior of sputtered titania thin films. We also compare the difference in photoresponse between parallel and series electrode configurations to understand the role of configuration on the design of photodetectors. TiO2 films of 50 nm thickness are sputtered onto three different substrates, namely quartz, fluorine-doped tin oxide (FTO), and silicon (Si) using direct current reactive magnetron sputtering. The structural and optical properties, along with photoresponse behavior, on these three different substrates are investigated. The sputtered TiO2 film crystallizes in the rutile structure with a uniform grain size distribution. Analysis of the transmittance data from UV–Vis spectra was used to derive the optical constants for the film. The sensitivity of TiO2 to photoresponse is highly dependent on the substrate. The response is better for Si substrate, when compared to FTO or quartz and this is due to the heterojunction formation at the TiO2/Si interface. Sensitivity, responsivity, and detectivity are also obtained for both parallel and series electrode configuration for Si substrate and better photoresponse is exhibited by the parallel configuration since carrier recombination in the bulk of the Si wafer is avoided. The photocurrent values in this work are an order of magnitude better than previous work on TiO2/Si, while the slightly slower response times maybe attributed to the strain-induced barrier reduction and band bending. Thus, this work showcases the tailoring of optoelectronic devices based on magnetron sputtered titania thin films by choosing appropriate substrates and electrode geometries.

Phase Composition and Thermoelectric Properties of Epitaxial CrMoVN Thin Films

Thin films of CrMoVN are deposited on c‐plane sapphire (Al2O3 (0001)) by direct current reactive magnetron sputtering, to investigate the effects of Mo and V addition to CrN‐based films. All films grow epitaxially, but Mo incorporation affects the crystal structure and nitrogen content. All films in the CrMoVN series are understoichiometric in nitrogen, but largely retain the NaCl B1 structure of stoichiometric CrN films. Addition of vanadium increases the phase‐stability range of the cubic phase, allowing for higher solubility of Mo than what has previously been reported for cubic CrN. The Seebeck coefficient and electrical resistivity are greatly affected by the alloying, showing a decrease of the Seebeck coefficient along with a decrease in resistivity. Cr0.83Mo0.11V0.06Nz shows a 70% increase in power factor (S2σ = 0.22 mW m−1 K−2) compared to the reference CrNz (S2σ = 0.13 mW m−1 K−2).

Microstructural and Electrical Resistivity of TiN Electrode Films Prepared by Direct Current (DC) Reactive Magnetron Sputtering

In this study, the crystal structure as well as electron transport of TiN thin films were evaluated. We used DC reactive magnetron sputtering to deposit a thin layer of polycrystalline titanium nitride (TiN) on a Si (100) substrate starting from elemental Ti in a nitrogen atmosphere. The influence of nitrogen flow rate on the crystal structure, surface morphology, and electron transport of TiN were investigated systematically. It was found that the preferred orientation and conductivity of TiN thin films exhibit strong nitrogen flow rate dependence. The preferred orientation changed from (111) to (200) initially and then changed back to (111) as the nitrogen flow rate increases. However, an increase in the (200) phase leads to higher conductivity and lower surface roughness. At the optimized deposition conditions, ultra-thin (around 30 nm) TiN thin films with a low resistivity of 101.8 μC·cm and a surface roughness of less than or equal to 0.51 nm were obtained. These superior performances, along with low running costs, suggest that TiN thin films have great potential for use as electrodes in microelectronic devices.

The role of the substrate on the structure of reactive sputtered Co3O4: From polycrystalline to highly oriented films

We report a systematic study of the substrate's influence on the structure of Co3O4 thin films grown by direct current reactive magnetron sputtering. Three different substrates have been simultaneously loaded to the deposition chamber and held at 620 K during growth: amorphous fused silica (a-SiO2), LaAlO3 (001), and α-Al2O3 (0001). Samples were characterized using atomic force microscopy, Raman spectroscopy, and high-resolution X-ray using synchrotron radiation (HR-XRD). Raman spectra showed bands corresponding to modes of Co3O4. The θ-2θ (HR-XRD) scans confirmed only the presence of the cubic spinel Co3O4 phase with its texture reliant on the sample substrate used. Rocking curves indicate that α-Al2O3 favors (111) Co3O4 film orientation (smaller mosaic spread). High-resolution 3-D Reciprocal Space Map analysis covering both (0006) α-Al2O3 and the (222) Co3O4 reflections have shown out-of-plane strain (0.1905%) and presented an in-plane isotropic intensity distribution of the film reciprocal lattice point, indicating no preferred mosaic direction. The substrate epitaxy governs the structure and morphology of the three samples, going from a rather flat, but polycrystalline textured Co3O4 film on a-SiO2, to a flat highly oriented strained film on α-Al2O3 and a rough highly textured and strained film on LaAlO3.

Effects of Oxygen Flow during Fabrication by Magnetron Sputtering on Structure and Performance of Zr-Doped HfO2 Thin Films.

Oxygen defects in Hafnium Oxide (HfO2)-based ferroelectric thin films not only are related to the cause of ferroelectricity but also affect the ferroelectric properties of the thin films. This paper, therefore, focuses on the fabrication of Zr:HfO2 thin films by RF (Radio Frequency) magnetron sputtering with Zr-doped HfO2 as the target and examines how oxygen flow impacts the oxygen vacancies and electrical properties thereof. Additionally, TiN thin-film electrodes were prepared by direct current (DC) magnetron reactive sputtering using nitrogen as the reaction gas, the influences of the substrate temperature on the film deposition rate and crystal phase structure were investigated, and the resultant thin-film electrodes with the lowest resistivity were obtained. Furthermore, the ferroelectric hysteresis loop and leakage current density of metal-insulator-metal (MIM) ferroelectric capacitors formed by annealing the 30 nm thick deposited Zr:HfO2 sandwiched between the top and bottom TiN electrodes were measured. The results demonstrate that varying oxygen flow has a considerable effect on oxygen vacancies and the Zr doping concentration of deposited Zr:HfO2 ferroelectric thin films. When the oxygen flow is set to 40 sccm (standard cubic centimeters per minute) and an external electric field strength of 2 mV/cm is applied, the remnant polarization reaches 18 μC/cm2, with a decrease in the leakage current density of 105-6 orders of magnitude.

High-quality c-axis oriented Al(Sc)N thin films prepared by magnetron sputtering

In order to adapt to the upgrading of wireless communication system, thin film bulk acoustic resonator (FBAR) has become one of the research hotspots in the communication field. The piezoelectric film, such as aluminum nitride (AlN), is the core functional layer of this device. However, previous reports have only focused on specific characteristics of the piezoelectric film, such as preferred orientation, piezoelectric coefficient, residual stress and so on. In this work, AlN and 6% scandium doped AlN films with (002) preferred orientation were deposited on (100) silicon wafers by direct-current magnetron reactive sputtering. We studied the crystallinity, roughness, element distribution, stress and additional characteristics of the films, and compared the quality changes of AlN thin films doped with Sc. Our results showed that all the deposited films had a uniform and dense structure with high crystallinity. But, the doping of Sc significantly reduced the nonuniformity, roughness, and stress of AlN films. Our research is of great significance for the preparation of high-quality piezoelectric thin films to improve the performance of FBAR filters, and ultimately improve the yield of devices.

Oxygen partial pressure dependent sputtered copper oxide films for visible photodetectors

In this study, metal-semiconductor-metal (MSM) structured visible photodetectors based on Cu2-xO thin films are fabricated onto a SiO2/Si substrate via direct current (DC) reactive magnetron sputtering. The dependence of oxygen partial pressure (pO2) on the visible photodetector performance of the deposited Cu2-xO films has been studied. Here, Cu2-xO film thickness is found to decrease from 229 nm to 202 nm with increasing pO2 from 2.0% to 8.0%. X-ray diffraction (XRD) analysis confirmed the cubic structure of the Cu2O phase. The compositional analysis confirms that 6.0% pO2 film has more copper vacancies than 2.0% pO2 film. As-deposited films have grain-like morphology with a uniform surface. The energy bandgap of deposited films decreases with the increase of pO2 from 2.0% to 6.0% and further increases at 8.0% pO2. Current-voltage (I-V) curves of the Au/Cu2-xO/Au test-device showed ohmic contact between the metal (Au) and semiconductor (Cu2-xO) due to the lower barrier height. Among different pO2 samples, the film grown at 6.0% pO2 exhibited a maximum photocurrent of 20.23 µA and also quick rise and fall times (100 ms and 90 ms) even at lower power density (0.1283 mW/cm2), which are superior to other reported copper oxide-based visible photodetectors. The obtained results indicated that MSM planar structured Cu2-xO photodetector is suitable to serve for future low-cost optoelectronic applications.

Growth of Nanocolumnar TiO2 Bilayer by Direct Current Reactive Magnetron Sputtering in Glancing-Angle Deposition Configuration for High-Quality Electron Transport Layer.

The electron transport layer (ETL) plays a crucial role in solar cell technology, particularly in perovskite solar cells (PSCs), where nanostructured TiO2 films have been investigated as superior ETLs compared to compact TiO2. In this study, we explored the nanocolumnar growth of TiO2 in the anatase phase for bilayer thin films by DC reactive magnetron sputtering (MS) technique and glancing-angle deposition (GLAD). For the growth of the compact TiO2 layer, it was found that the crystalline quality of the films is strongly dependent on the sputtering power, and the samples deposited at 120 and 140 W are those with the best crystalline quality. However, for the nanocolumnar layer, the reactive atmosphere composition determined the best crystalline properties. By optimizing the growth parameters, the formation of TiO2 nanocolumns with a cross-sectional diameter ranging from 50 to 75 nm was achieved. The average thickness of the films exceeded 12.71 ± 0.5 µm. All nanostructured films were grown at a constant GLAD angle of 70°, and after deposition, the measured inclination angle of the nanocolumns is very close to this, having values between 68 and 80°. Furthermore, a correlation was observed between the quality of the initial layer and the enhanced growth of the TiO2 nanocolumns. All bilayer films are highly transparent, allowing light to pass through up to 90%, and present a band gap with values between 3.7 and 3.8 eV. This article offers the experimental parameters for the fabrication of a nanocolumnar TiO2 using the magnetron sputtering technique and the glancing-angle deposition configuration.

Epitaxial growth of TiC on (0001) 4H-SiC substrate by reactive sputtering

Heteroepitaxial TiC films were grown on semi-insulating (0001) 4H-SiC substrates at high temperature by using direct current (DC) magnetron reactive sputtering. The effect of the CH4 flux ratio in Ar on the crystalline quality of the films was investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the deposited TiC films are heteroepitaxially grown on 4H-SiC substrates with the heteroepitaxial relationship between TiC and 4H-SiC in (111)TiC // (0001)4H-SiC and [11¯0]TiC // [112¯0]4H-SiC. The full width at half-maximum (FWHM) of X-ray rocking curve (XRC) of (111)TiC reflection can reach a minimum value of 0.039° and the resistivity of TiC film can be ∼ 80 μΩ⋅cm for deposition at 700 °C with 4% CH4 flow ratio. X-ray photoelectron spectroscopy (XPS) shows that the composition of TiC film is nearly in stoichiometry for 4% CH4 flow ratio. From the TEM results, it is observed that the TiC film is divided into a strained layer and a relaxed layer when the film thickness reaches a critical value over about 70 nm.