Film Deposition Conditions Research Articles

Deposition phenomena of diamond-like carbon coating on inner surface of circular metal tube by nanopulse plasma chemical vapor deposition

A method of depositing a diamond-like carbon (DLC) film on the inner surface of a circular metal tube by chemical vapor deposition using a nanopulse power source was developed. Because the nanopulse power source can supply rapidly rising and falling high-voltage nanopulses of nanosecond order, a stable plasma can be obtained even in small-diameter tubes by applying a high gas pressure of more than 100 Pa. DLC films were successfully deposited on the inner surfaces of metal tubes of 14 mm diameter and 300 mm length (21% aspect ratio), and of 40 mm diameter and 300 mm length. To understand the plasma state inside the tubes to determine appropriate DLC film deposition conditions, wavelength- and time-resolved optical emission spectroscopy of the plasma generated inside the tubes and numerical simulation were performed. Results of these investigations and characterization clarified that one nanopulse power source introduced to tubes generates glow and after-glow discharges at μs time intervals. It was further clarified that these discharges in combination with high-repetition pulses, suggested together contribute to the effective ionization of gas. Thus, the high speed and high source gas yield of DLC film deposition inside the tubes were confirmed.

High Performance Predictable Quantum Efficient Detector Based on Induced-Junction Photodiodes Passivated with SiO2/SiNx.

We performed a systematic study involving simulation and experimental techniques to develop induced-junction silicon photodetectors passivated with thermally grown SiO2 and plasma-enhanced chemical vapor deposited (PECVD) SiNx thin films that show a record high quantum efficiency. We investigated PECVD SiNx passivation and optimized the film deposition conditions to minimize the recombination losses at the silicon–dielectric interface as well as optical losses. Depositions with varied process parameters were carried out on test samples, followed by measurements of minority carrier lifetime, fixed charge density, and optical absorbance and reflectance. Subsequently, the surface recombination velocity, which is the limiting factor for internal quantum deficiency (IQD), was obtained for different film depositions via 2D simulations where the measured effective lifetime, fixed charge density, and substrate parameters were used as input. The quantum deficiency of induced-junction photodiodes that would be fabricated with a surface passivation of given characteristics was then estimated using improved 3D simulation models. A batch of induced-junction photodiodes was fabricated based on the passivation optimizations performed on test samples and predictions of simulations. Photodiodes passivated with PECVD SiNx film as well as with a stack of thermally grown SiO2 and PECVD SiNx films were fabricated. The photodiodes were assembled as light-trap detector with 7-reflections and their efficiency was tested with respect to a reference Predictable Quantum Efficient Detector (PQED) of known external quantum deficiency. The preliminary measurement results show that PQEDs based on our improved photodiodes passivated with stack of SiO2/SiNx have negligible quantum deficiencies with IQDs down to 1 ppm within 30 ppm measurement uncertainty.

Hyperdoping of silicon films with titanium via nanosecond-laser melting: Structure evolution, impurity distribution, sub-bandgap formation, and doping mechanism

Hyperdoping of Si films with Ti was achieved via nanosecond (ns)-laser melting of Si/Ti composite films under different film deposition and laser treatment conditions. The structural evolution (from amorphous to nanocrystalline structure), Ti impurity distribution and concentration variation, and sub-bandgap (Ti impurity band) formation in the films, were carefully studied to optimize the hyperdoping process. The results show that the hyperdoping concentration and depth can be manipulated by controlling the Si and Ti co-evaporation speed ratio, Si/Ti composite film thickness together with a matched ns-laser fluence. Furthermore, Ti impurity bands were determined with two sub-bandgaps of energy 385–448 and 759 meV. In addition, the mechanism of ns-laser hyperdoping of Si films was clarified into the heat transfer, material ejection, partial ablation and redeposition, melting, and nanocrystallization (simultaneous hyperdoping) processes. Thus, hyperdoped nanocrystalline films up to the micron-level thickness with a crystallinity of ∼ 70%, an optical absorptance of ∼ 90% from the visible to the long-wavelength near-infrared spectrum, and good electronic transport properties were obtained. These hyperdoped Si films exhibit a high potential in the development of Si-based broad-spectrum tandem or thin film solar cells and room-temperature infrared photodetectors.

Growth Mechanisms and Morphology Engineering of Atomic Layer-Deposited WS2.

Transition-metal dichalcogenides (TMDs) have attracted intense research interest for a broad range of device applications. Atomic layer deposition (ALD), a CMOS compatible technique, can enable the preparation of high-quality TMD films on 8 to 12 in. wafers for large-scale circuit integration. However, the ALD growth mechanisms are still not fully understood. In this work, we systematically investigated the growth mechanisms for WS2 and found them to be strongly affected by nucleation density and film thickness. Transmission electron microscope imaging reveals the coexistence and competition of lateral and vertical growth mechanisms at different growth stages, and the critical thicknesses for each mechanism are obtained. The in-plane lateral growth mode dominates when the film thickness remains less than 5.6 nm (8 layers), while the vertical growth mode dominates when the thickness is greater than 20 nm. From the resulting understanding of these growth mechanisms, the conditions for film deposition were optimized and a maximum grain size of 108 nm was achieved. WS2-based field-effect transistors were fabricated with electron mobility and on/off current ratio up to 3.21 cm2 V-1 s-1 and 105, respectively. Particularly, this work proves the capability of synthesis of TMD films in a wafer scale with excellent controllability of thickness and morphology, enabling many potential applications other than transistors, such as nanowire- or nanosheet-based supercapacitors, batteries, sensors, and catalysis.

Impact of Ar:O2 gas flow ratios on microstructure and optical characteristics of CeO2-doped ZnO thin films by magnetron sputtering

In this study, a radio frequency magnetron sputtering technique was applied to deposit eminently oriented ZnO thin films on stainless steel (SS316L). The effect of different ratios (Ar:O2) of gas flow ((20:0), (15:5), (10:10), (5:15), (0:20)) on optical and structural properties of CeO2-doped ZnO thin films has been examined. The increase in grain size of thin films was observed with a partial increase in the Ar:O2 sputtering gas at substrate temperature of 673 K. The average surface roughness of the thin films has increased with sputtering gas. The photoluminescence peak exhibited a broad green-yellow band spiked at 467 nm for all the samples of CeO2-doped ZnO thin films and a wide band of visible light focused in the 500–600 nm range. Intensity reduction of deep level emission peaks of ZnO films was observed. The refractive index of undoped and CeO2-doped ZnO thin films with various sputtering gas ratios (Ar:O2) were also investigated. The optimized argon gas flow rate findings allow us to choose the deposition conditions for CeO2-doped ZnO thin films for solar thermal applications.

Installation of TOF-E telescope ERDA in UTTAC at the University of Tsukuba: Analysis of metal-nitride-based multi-layer coatings on glasses

We present the development of time-of-flight/energy (TOF-E) telescope for elastic recoil detection analysis (ERDA) in UTTAC at the University of Tsukuba. The designs of the TOF tube are introduced. The performance for the quantification and mass resolution for light elements is confirmed on a CaTaOxNy film deposited on a Si substrate. The results are cross-checked by the data taken by an existing ΔE-E telescope ERDA system, which was previously installed in MALT at The University of Tokyo. The newly developed system can be used to reveal the relationship between the film deposition condition and the contamination quantitatively on a Si-Al-N (SiAlN) film on a SiO2 substrate. Finally, the analysis of a triple-layered metal nitrides film on a soda glass substrate, in which each layer has a thickness of 10 to15 nm, is shown. From the analysis of the surface peak of oxygen, the time resolution corresponds to depth resolution of 2.1 nm at the surface. The overall practical depth resolution conservatively estimated as better than 10 nm, because the depth profiles of various elements show clear counters corresponding to the three layers.

Antiferromagnetic Oxide Thin Films for Spintronic Applications

Antiferromagnetic oxides have recently gained much attention because of the possibility to manipulate electrically and optically the Néel vectors in these materials. Their ultrafast spin dynamics, long spin diffusion length and immunity to large magnetic fields make them attractive candidates for spintronic applications. Additionally, there have been many studies on spin wave and magnon transport in single crystals of these oxides. However, the successful applications of the antiferromagnetic oxides will require similar spin transport properties in thin films. In this work, we systematically show the sputtering deposition method for two uniaxial antiferromagnetic oxides, namely Cr2O3 and α-Fe2O3, on A-plane sapphire substrates, and identify the optimized deposition conditions for epitaxial films with low surface roughness. We also confirm the antiferromagnetic properties of the thin films. The deposition method developed in this article will be important for studying the magnon transport in these epitaxial antiferromagnetic thin films.

Piezoelectric P(VDF-TrFE) film inkjet printed on silicon for high-frequency ultrasound applications

We investigated the innovative processing of poly(vinylidene fluoride-trifluoroethylene) P(VDFx-TrFE1-x) (x = 83 mol. %) by inkjet printing to deliver uniform and thickness-controlled layers on silicon substrates. Here, we provide detailed processing steps and optimize film deposition conditions. The thickness coupling factor for a P(VDF-TrFE) film around 11 μm thick was 22%, demonstrating good electromechanical performance after poling. These multilayer structures were specifically for high-frequency, single-element ultrasonic transducer applications. The measurements of electro-acoustic responses were in water. The maximal frequency was centered at 33.2 MHz and had a fine axial resolution at 22 μm, corresponding to a fractional bandwidth at −6 dB of 100%. In the context of technological evolutions aimed at miniaturized devices and integrated electronics, these results allow for the consideration of complex structures such as multi-element transducers for high-frequency imaging applications.

Evaluation of correlation between fill factor and high mobility transparent conductive oxide film deposition temperature in the silicon heterojunction solar cells

We investigated the degradation factor of the conversion efficiency of the silicon heterojunction solar cells. In particular, we clarified the effect of the transparent conductive oxide film deposition conditions on the film quality and interface states, and the relationship between these factors and the conversion efficiency. Heat process causes a decrease in carrier mobility due to a decrease in the grain size of the TCO film, but has an effect of improving the TCO/a-Si:H(p) interface states. In particular, the silicon oxide layer between the TCO film and a-Si:H(p) increases the series resistance and moderates the band bending at the TCO/a-Si:H(p) interface, leading to FF degradation. Since In2O3:H film easily forms a silicon oxide layer at the TCO/a-Si:H(p) interface, the interface treatment is important factor in the cell manufacturing process.

Structural and optical characteristics determined by the sputtering deposition conditions of oxide thin films.

The influence of film thickness on the structural and optical properties of silicon dioxide (SiO2) and zinc oxide (ZnO) thin films deposited by radio frequency magnetron sputtering on quartz substrates was investigated. The deposition conditions were optimized to achieve stoichiometric thin films. The orientation of crystallites, structure, and composition were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while the surface topography of the samples was analyzed using scanning electron microscopy (SEM). The optical characteristics were measured for samples with the same composition but obtained with different deposition parameters, such as increasing thickness. The optical constants (i.e., the refractive index n, the extinction coefficient k, and the absorption coefficient α) of the SiO2 and ZnO oxide films were determined from the transmission spectra recorded in the range of 190–2500 nm by using the Swanepoel method, while the energy bandgap was calculated from the absorption spectra. The influence of thickness on the structural and optical properties of the oxide films was investigated. Good optical quality and performance were noticed, which makes these thin films worthy of integration into metamaterial structures.

Chemical stability diagrams as a powerful tool to the synthesis of Cu2SnS3 thin films by chemical bath deposition

Cu2SnS3 films are produced by chemical bath method employing low toxicity citrate precursor taking advantage of the strong complexes formed with Cu(II) and Sn(II). The deposition conditions for Cu2SnS3 thin films were obtained through a thermodynamic analysis of the effect of tin concentration on Cu(II)–Sn(II)-Citrate complexes and Cu(II)–Sn(II)-Citrate-Thiourea system using a species distribution and potential–pH (Eh-pH) analysis. Theoretical analysis of the speciation fraction of Cu(II) and Sn(II) shown that the predominant species at pH equal to 4.5 at 90 °C are [Cu2(Cit)2OH]3− and [Sn2(Cit)2]2−. For the Cu(II)–Sn(II)-Citrate-Thiourea system at 90 °C, the Eh-pH diagrams established that binary precursors, Cu2S and SnS2, would be obtained under basic pH conditions. Subsequently, Cu2SnS3 films were synthetized at 90 °C at pH equal to 8 by keeping fixed the molar relationships complexing agent-metal and sulfur-metal. The redox potentials were measured in solution and chemical equilibrium diagrams were constructed, confirming the existence of binary precursors under reductive conditions. Characterization of structural, electronic and transport properties indicated that Cu2SnS3 fabricated by chemical bath deposition have monoclinic crystal structure, a direct band gap energy of 1.70 eV and p-type conductivity.

Critical role of additive-induced molecular interaction on the operational stability of perovskite light-emitting diodes

Summary Despite rapid improvements in efficiency and brightness of perovskite light-emitting diodes (PeLEDs), the poor operational stability remains a critical challenge hindering their practical applications. Here, we demonstrate greatly improved operational stability of high-efficiency PeLEDs, enabled by incorporating dicarboxylic acids into the precursor for perovskite depositions. We reveal that the dicarboxylic acids efficiently eliminate reactive organic ingredients in perovskite emissive layers through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate. The formed stable amides prohibit detrimental reactions between the perovskites and the charge injection layer underneath, stabilizing the perovskites and the interfacial contacts and ensuring the excellent operational stability of the resulting PeLEDs. Through rationally optimizing the amidation reaction in the perovskite emissive layers, we achieve efficient PeLEDs with a peak external quantum efficiency of 18.6% and a long half-life time of 682 h at 20 mA cm−2, presenting an important breakthrough in PeLEDs.

Study of the Correlation between the Amorphous Indium-Gallium-Zinc Oxide Film Quality and the Thin-Film Transistor Performance.

In this work, we performed a systematic study of the physical properties of amorphous Indium–Gallium–Zinc Oxide (a-IGZO) films prepared under various deposition pressures, O/(Ar+O) flow ratios, and annealing temperatures. X-ray reflectivity (XRR) and microwave photoconductivity decay (-PCD) measurements were conducted to evaluate the quality of a-IGZO films. The results showed that the process conditions have a substantial impact on the film densities and defect states, which in turn affect the performance of the final thin-film transistors (TFT) device. By optimizing the IGZO film deposition conditions, high-performance TFT was able to be demonstrated, with a saturation mobility of 8.4 cm/Vs, a threshold voltage of 0.9 V, and a subthreshold swing of 0.16 V/dec.

Stress-Assisted Thermal Diffusion Barrier Breakdown in Ion Beam Deposited Cu/W Nano-Multilayers on Si Substrate Observed by in Situ GISAXS and Transmission EDX.

The thermal stability of Cu/W nano-multilayers deposited on a Si substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX—a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems.

Investigation of Deposition Conditions of Thin Copper Films from Electrode Destruction Products of Overvoltage High-voltage Discharge in High Pressure Argon

Investigation of Deposition Conditions of Thin Copper Films from Electrode Destruction Products of Overvoltage High-voltage Discharge in High Pressure Argon

Laser Assisted Fabrication of Surface Oxide Nanostructures for Photovoltaic Applications

The paper discusses the application of laser-assisted processes for synthesis of oxides nanoparticles (NPs) and their assembling into the nanostructured thin films. The study of the laser parameters influence on the NPs formation and thin film deposition conditions allowed to find optimal conditions for the formation of ZnO, CuO colloidal NPs as well as ZnO/CuO nanostructured thin films suitable for practical applications. The morphology, structure, as well as electronic and optical characteristics of the formed oxide nanostructures were studied and their potential optoelectronic and photovoltaic applications are discussed.

The role of substrate temperature on the performance of humidity sensors manufactured from cerium oxide thin films

Cerium oxide (CeO2) thin films as humidity sensors are obtained by pulsed laser deposition (PLD) grown on Si (100) substrate. CeO2 nanoparticles were taken as target materials for PLD technique. The effect of film deposition condition, such as deposition temperature on performance sensor, was explored. The substrate temperature ranges varied from 300 to 700 °C. The structural and surface morphologies were examined by X-ray diffractometer (XRD) and scanning electronic microscopy (SEM), respectively. The capacitance and resistance of the sensors were tested. The sensor utilizing CeO2 films exhibited high sensitivity, and the increase in humidity led to a gradual increase in sensitivity and decreased resistance. The sensor performance is highly dependent on morphology and surface, which in turn is affected by the change in electrical properties of the film.

Improvement of drilling performance by overcoating diamond-like carbon films on diamond-coated drills for carbon fiber reinforced plastics processing

The hardness and hydrogen content of diamond-like carbon (DLC) films vary depending on the film deposition methods and conditions. Carbon fiber reinforced plastics (CFRP), known as hard-to-machine materials, have been widely used for industrial aircrafts that require structural materials. In this study, the effects of the hardness and hydrogen content in DLC films on the drilling performance of CFRP drills were investigated. Various DLC films, prepared using the T-shaped filtered arc deposition method, were used to coat diamond-coated drills for CFRP processing. The drilling test of the CFRP plates revealed that the occurrence of burrs was suppressed using the drill coated with a hard DLC film containing small amounts of hydrogen, classified as a hydrogenated tetrahedral amorphous carbon (ta-C:H) film. The spherical polishing test of the CFRP plate using DLC-coated balls demonstrated that the DLC films containing hydrogen suppressed the adhesion of the resin material constituting the CFRP. The coating of hard DLC films containing small amounts of hydrogen, such as a ta-C:H film, significantly improved the drilling performance of diamond-coated drills for CFRP processing. The performance improvement of CFRP drills expands the range of CFRP processing conditions.

PECVD SiNx passivation for AlGaN/GaN HFETs with ultra-thin AlGaN barrier

We have investigated the effects of a silicon nitride (SiNx) passivation process using plasma-enhanced chemical vapor deposition (PECVD) on a ultra-thin-barrier AlGaN/GaN heterostructure field-effect transistors (HFETs). The bulk charge characteristics of the PECVD SiNx films were dependent on the film deposition conditions, which strongly influenced the sheet resistance (Rsh) and flat-band voltage characteristics of AlGaN/GaN HFETs. The reduction in Rsh is a strong function of the amount of positive bulk charges in the SiNx passivation film. An optimized PECVD SiNx process was used to drastically decrease the Rsh from 45,450 Ω/sq to 732 Ω/sq. A Mo/Au Schottky-gate device fabricated with PECVD SiNx passivation exhibited a maximum drain current density of 172 mA/mm, quasi-normally-off operation, and breakdown voltage of > 1100 V

Direct Exposure of Dry Enzymes to Atmospheric Pressure Non-Equilibrium Plasmas: The Case of Tyrosinase.

The direct interaction of atmospheric pressure non-equilibrium plasmas with tyrosinase (Tyr) was investigated under typical conditions used in surface processing. Specifically, Tyr dry deposits were exposed to dielectric barrier discharges (DBDs) fed with helium, helium/oxygen, and helium/ethylene mixtures, and effects on enzyme functionality were evaluated. First of all, results show that DBDs have a measurable impact on Tyr only when experiments were carried out using very low enzyme amounts. An appreciable decrease in Tyr activity was observed upon exposure to oxygen-containing DBD. Nevertheless, the combined use of X-ray photoelectron spectroscopy and white-light vertical scanning interferometry revealed that, in this reactive environment, Tyr deposits displayed remarkable etching resistance, reasonably conferred by plasma-induced changes in their surface chemical composition as well as by their coffee-ring structure. Ethylene-containing DBDs were used to coat tyrosinase with a hydrocarbon polymer film, in order to obtain its immobilization. In particular, it was found that Tyr activity can be fully retained by properly adjusting thin film deposition conditions. All these findings enlighten a high stability of dry enzymes in various plasma environments and open new opportunities for the use of atmospheric pressure non-equilibrium plasmas in enzyme immobilization strategies.