SiOx Films Research Articles

Systematic Study of the SiOx Film with Different Stoichiometry by Plasma-Enhanced Atomic Layer Deposition and Its Application in SiOx/SiO₂ Super-Lattice.

Atomic scale control of the thickness of thin film makes atomic layer deposition highly advantageous in the preparation of high quality super-lattices. However, precisely controlling the film chemical stoichiometry is very challenging. In this study, we deposited SiOx film with different stoichiometry by plasma enhanced atomic layer deposition. After reviewing various deposition parameters like temperature, precursor pulse time, and gas flow, the silicon dioxides of stoichiometric (SiO2) and non-stoichiometric (SiO1.8 and SiO1.6) were successfully fabricated. X-ray photo-electron spectroscopy was first employed to analyze the element content and chemical bonding energy of these films. Then the morphology, structure, composition, and optical characteristics of SiOx film were systematically studied through atomic force microscope, transmission electron microscopy, X-ray reflection, and spectroscopic ellipsometry. The experimental results indicate that both the mass density and refractive index of SiO1.8 and SiO1.6 are less than SiO2 film. The energy band-gap is approved by spectroscopic ellipsometry data and X-ray photo-electron spectroscopy O 1s analysis. The results demonstrate that the energy band-gap decreases as the oxygen concentration decreases in SiOx film. After we obtained the Si-rich silicon oxide film deposition, the SiO1.6/SiO2 super-lattices was fabricated and its photoluminescence (PL) property was characterized by PL spectra. The weak PL intensity gives us greater awareness that more research is needed in order to decrease the x of SiOx film to a larger extent through further optimizing plasma-enhanced atomic layer deposition processes, and hence improve the photoluminescence properties of SiOx/SiO2 super-lattices.

Oxygen-Content Dependence of Cycle Performance and Morphology Changes in Amorphous-SiOx Thin-Film Negative Electrodes for Lithium-Ion Batteries

The silicon–oxygen binary system (SiOx) is a promising candidate as a negative electrode for next-generation lithium-ion batteries. Thin SiOx films of different oxygen contents were prepared by magnetron sputtering. Although almost all Si atoms in SiOx at low oxygen contents (x = 0.21 and 0.48) contributed to the reversible alloying/dealloying reactions, an irreversible fraction of Si in SiOx at high oxygen contents (x = 1.09 and 1.78) increased owing to the formation of Li4SiO4. In return for the decrease of reversible capacity, the capacity retention of heavily O-doped SiOx films improved owing to the buffer effect of Li4SiO4 matrix against volume changes. The addition of vinylene carbonate (VC) to the electrolyte further improved the cyclability of the SiOx films, especially those of higher oxygen contents. For the pure-Si film, a sponge-like porous structure appeared after cycling owing to repeated crack formation and inhomogeneous volume changes, and resulted in massive electrode swelling. The morphology change with cycling was suppressed by the presence of Li4SiO4 matrix and a homogeneous solid electrolyte interphase derived from VC, resulting in a superior cycle performance of the heavily O-doped SiOx negative electrodes.

Gd-Doped HfO2 Memristor Device, Evaluation Robustness by Image Noise Cancellation and Edge Detection Filter for Neuromorphic Computing

This paper estimates the robustness of non-volatile device (NVM) Gadolinium (Gd) doped Hafnium oxide (HfO2) nanoparticles (NPs) based memristor which was constructed using as-formed and annealed nanoparticles in 600 °C and 800 °C temperature, based on their performance in various basic image processing applications (i.e. edge detection filter and noise-canceling filter). A catalytic free glancing angle deposition technique (GLAD) is employed to grow Gd doped HfO2 nanoparticles (NPs) of 8 nm range on the thin film of Silicon oxide SiOx in 30 nm dimension. Annealing process is performed on Gd-doped HfO2 NPs and and the changes were demonstrated in its surface morphology. The elemental composition of the device was analyzed by Energy Dispersive X-ray (EDX). Photoluminescence (PL) analysis revealed that the topography and electrical characteristics of Gd-doped HfO2 alter swiftly after annealing process. A leakage current, interface state density (Dit) factor emphasizes that the device annealed at 600 °C portrayed significant improvement in the non-volatile characteristics in comparison with other devices. Additionally, the endurance of the device annealed at 600 °C was seen to possess more than decades of memory potential. The C-V and hysteresis curve measurement demonstrated maximal charge accumulation relative to other devices. Crossbar array is designed from both as-formed and annealed memristor devices.

Oxidation of ablated silicon during pulsed laser deposition in a background gas with different oxygen partial pressures

We have analysed changes in the oxidation state of SiOx films produced by pulsed laser deposition in a background gas with different partial pressures of oxygen. The optical properties of the films in IR range are shown to be close to those of SiO2 while the total oxidation degree is considerably less than 2. It is suggested that the film consists of oxidized and unoxidized regions due to preferential oxidation of the periphery of the silicon ablation plume during expansion. These regions are overlapping in the film if the laser beam is scanned on the target.

Reactive evaporation of SiOx films for passivation of GaN high-electron-mobility transistors

The surface passivation effects of silicon suboxide (SiOx) prepared by the reactive evaporation of silicon monoxide in oxygen atmosphere on the performance of AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) have been investigated. SiOx films with different oxygen contents (1.10 ≤ x ≤ 1.71) and root-mean-square (RMS) roughnesses (0.55 ≤ RMS ≤ 1.01 nm) were prepared under residual pressures from 1 × 10−6 to 6 × 10−4 Torr. Hall measurements revealed obvious increases in the product of sheet carrier concentration and electron mobility after the passivation. Accordingly, increases in drain current and transconductance were observed for all the SiOx passivated HEMTs. Both the gate and drain leakage currents first decreased and then increased with the increase of oxygen content. The lowest gate leakage current was observed in the devices with SiO1.23 passivation, and it was almost 20 times lower than that of the unpassivated devices. The same devices also exhibited the lowest current collapse and off-state drain current. The variations in leakage currents as a function of the residual pressure were found to correlate with the surface roughness of the passivation layer. Finally, the breakdown voltage of the SiO1.23 passivated HEMTs increased to 151 V, up from 99 V in unpassivated devices.

Mechanism of dense silicon dioxide films deposited under 100 °C via inductively coupled plasma chemical vapor deposition

High density of the inductively coupled plasma chemical vapor deposition (ICPCVD) enables growth of films on soft substrate such as polyethylene terephthalate (PET) that otherwise curls at temperatures higher than 100 °C. In this study, dense silicon oxide (SiOx) films are prepared on PET by ICPCVD. Intrusive optical emission spectroscopy is employed to monitor distribution of the plasma radicals during the deposition process. The study discovers a direct relationship between the dense structure of the deposited film and the CH/(CH + OH) plasma radical intensity ratio. The deposition plasma with the lowest CH radical ratio results in the SiOx film with the least CHx incorporation and densest film structure. The film exhibits the smallest etched area in hydrochloric acid etching tests and the minimal water-vapor transmission rate of about 1.5 × 10−1 g/m2/day.

Effect of dielectric and conductive targets on plasma jet behaviour and thin film properties

A double layer DBD plasma jet driven by a pulsed generator is used for SiOx thin film deposition. The effects of dielectric and conductive targets on discharge behavior and film properties are analyzed. Different fraction of N2 is added to the working gas (argon) to modulate film growth rate. The electrical property and optical emission of the plasma jet at different positions are characterized. Film surface morphology, composition and thickness are measured for different targets. The excitation temperature (Texc), vibrational temperature (Tvib) and rotational temperature (Trot) are calculated. The relationship between the discharge behavior and the film properties is studied. Results show that the relative optical emission intensities of Si, O, Ar and N2, as well as Texc, Tvib and Trot are higher for the PMMA target between the high voltage electrode and the grounded electrode (referred to as the H–G region). However, Tvib and Trot appear to be higher on the surface of the copper (conductive) target. The morphology of SiOx film is different: nanoparticles are formed on the PMMA (dielectric) target while dense amorphous film is formed on the copper target. With the same depositing parameters, the thickness of the SiOx film is higher on the copper target. The presence of PMMA at the downstream of the plasma can be considered as a small capacitor with a large resistance, which inhibits the current into the primary circuit passing through the H–G region. Although the presence of a dielectric target enhances the discharge in the H–G region, the charge accumulation on the PMMA surface limits the film growth. These results may contribute to the development of next-generation plasma surface modification technologies for diverse applications in electronics, material synthesis and other related areas.

Effect of substrate temperature on the properties of plasma deposited silicon oxide thin films

Silicon oxide (SiOx) films were obtained from SiH4/NO2/Ar by plasma-enhanced chemical vapors deposition (PECVD) technique. Effect of substrate temperature on the properties of the deposited films have been presented. The substrate temperature of the deposition process varied from 150 to 450°C at fixed working pressure of 1000 mTorr and RF power of 10 W. The films were investigated by atomic force and scanning electron microscopies as well as laser ellipsometry. The grain size, root-mean-square roughness and refractive index of the films were in the range of 20-250 nm, 0.2-2.4 nm and 1.5-2.0, respectively. The refractive indices and stoichiometry of SiOx films are discussed using the Lorentz-Lorenz formula.

Functional FAS-13/SiOx composite coatings for improved anticorrosion and hydrophobicity/oleophobicity on AZ91D magnesium alloys

The procedures of fabricating s functional composite coating with properties of anticorrosion, hydrophobicity, and oleophobicity on AZ91D magnesium alloy substrates are implemented. A SiOx anticorrosion layer is firstly fabricated by an atmospheric pressure plasma jet (APPJ) system with tetraethoxysilane as the precursor, and subsequently 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS-13) is coated on SiOx/AZ91D samples by a spin coater to alter the surface hydrophobicity. The APPJ-deposited SiOx film has a hydrophilic surface with a surface energy of 68.4 mN m−1, while the FAS-13 coating on the SiOx/AZ91D sample turns into the hydrophobic surface with a lower surface energy of 12.49 mN m−1, proving an improved anticorrosion performance by electrochemical impedance spectroscopy measurements. Tests of adhesion and oil contact angle also reveal the reliability of this coating. These results show the feasibility of the FAS-13/SiOx composite coating for improving the corrosion resistance and the surface properties with hydrophobicity and oleophobicity is practically achieved.

Down-Conversion Effect Created by SiOx Films Obtained by HFCVD and Applied over Pn-Junctions

A top coating film of silicon oxide off-stoichiometry (SiOx) was used on silicon solar cells to improve its electrical properties by the Down-conversion effect. The SiOx films were obtained by hot filament chemical vapor deposition (HFCVD) with different hydrogen flow (HF) and different distances: the wire-source distance and the source-substrate distance, and by consequence, with different temperatures. Transmittance spectra showed 0% of transmittance in the UV region. The amount of atomic silicon % in the SiOx films was changed with the variation of the mentioned parameters, as demonstrated with the Energy-Dispersive X-ray Spectroscopy (EDS) and the Fourier transform infrared spectroscopy (FTIR) results. The SiOx films showed a wide Photoluminescence (PL) between 400 nm and 900 nm when they were excited with UV light. The SiOx films were applied as a top coating on pn junctions of silicon substrate to develop silicon solar cells. The J-V measurements and the external quantum efficiency (EQE) of the solar cells were obtained, as well as the open circuit voltage (Voc), short-circuit current density (Jsc), the efficiency (η) and the fill factor (FF). The silicon solar cells with the SiOx top coatings, with the highest PL, showed the highest efficiency. The best figures of merit were η = 5.9%, Voc = 480 mV, Jsc = 27 mA/cm2, Pmax = 5.5 mW and FF = 0.4.

Effect of substrate bias and substrate/plasma generator distance on properties of a-C:H:SiOx films synthesized by PACVD

In this paper the a-C:H:SiOx films were synthesized on silicon (100) and glass substrates by plasma-assisted chemical vapor deposition combined with pulsed bipolar substrate bias from mixtures of argon and polyphenylmethylsiloxane vapor. The process of a-C:H:SiOx films formation was investigated by controlling processing conditions such as amplitude of negative pulse of substrate bias and the distance between the substrate and plasma generator. Physico-mechanical characteristics of a-C:H:SiOx films were studied by the nanoindentation technique, atomic force microscopy, Fourier transform infrared and Raman spectroscopy. The contact angle and surface free energy were determined by the sessile drop method using couple liquids (water and glycerin). It was found that the films' properties are interrelated with the density of the ion current on the substrate, which was measured using a guarded planar probe. The obtained results show that film prepared at the smaller substrate/plasma generator distance and optimal substrate biasing has a higher content of sp3 bonded carbon and, accordingly, has higher hardness, Young's modulus and resistance to plastic deformation. At the same time the a-C:H:SiOx films show large hydrophobicity with a contact angle for water of about 91° and small total surface free energy of about 17.9 mN/m.

Effect of precursor flow rate on physical and mechanical properties of a-C:H:SiOx films deposited by PACVD method

In this paper the deposition of a-C:H:SiOx films by plasma activated chemical vapour deposition in a mixture of argon and polyphenylmethylsiloxane (PPMS) vapor with the impulse bipolar bias voltage applied to the substrate is presented. The paper discusses the dependence of the physico-mechanical properties of the deposited films on the flow rate of the PPMS precursor. The structure of the deposited films was determined by Fourier transform infrared spectroscopy and Raman spectroscopy. Mechanical properties characterization of a-C:H:SiOx films (hardness and elastic modulus) was made using the nanoindentation method. Hardness and elastic modulus were used to evaluate the endurance capability (H/E) and resistance to plastic deformation (H3/E2). The elastic recovery was calculated based on loading and unloading curves. It is shown that with an increase in the PPMS flow rate in the range of 35-287 μl/min, the films deposition rate increases from 17 to 221 nm/min. At this films mechanical properties, such as hardness, elastic modulus and elastic recovery did not deteriorate. The maximum values of the endurance capability and resistance to plastic deformation are obtained at a flow rate of 175 μl/min and equal to 0.12 and 203 MPa, respectively.

Chemical and morphological characterization of photoactive SiOx films electrodeposited on Pt substrate

SiOx films electrodeposited on platinum (Pt) substrate were shown to exhibit n-type photoactivity while placed both in aqueous and organic solutions. The films were obtained via potentiostatic deposition at potential values ranging from −2.25 to −2.75V. The mechanism of the electrodeposition involved reactions with the used electrolyte and with traces of water as sources of oxygen and hydrogen, as interpreted from Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The photoactivity of the deposits deceased at potential −2.75V. The highest observed photocurrent was ca. 60μA/cm2 and it was registered in organic solution. The band gap energies determined by XPS technique were approximately 2.5, 2.3 and 3.7eV for films electrodeposited at −2.25, −2.5 and −2.75V, respectively. The depth profiles of Si, O and H in the films were registered by glow discharge optical emission spectroscopy (GD-OES), which showed that the film thickness was ca. 0.4μm. The n-type photoactivity was associated with oxygen evolution from the aqueous solution (0.1M HClO4, pH1), whereas the time instability as a function of time observed for the photocurrent was associated with morphological changes of the films as seen by scanning electron microscopy (SEM) and their oxidation detected by XPS and FTIR spectroscopies.

Effect of coating method on the structure and properties of a novel PbO2 anode for electrochemical oxidation of Amaranth dye

This study deals with the electrochemical degradation of Amaranth in aqueous solution by means of stainless steel (SS) electrodes coated with a SiOx interlayer deposited by Plasma Enhanced Chemical Vapour Deposition and a modified PbO2 top layer deposited by continuous galvanostatic electrodeposition. The morphological characterization of the PbO2 top-layer performed by Field Emission Scanning Electron Microscope put in evidence that the SiOx, interlayer allows obtaining a more integrated PbO2/SS electrode with a very homogeneous PbO2 film. The composition of the lead oxide layer was investigated by X-ray Diffractometry, showing that the β-PbO2/α-PbO2 ratio in the top layer deposited on the SiOx film was four times higher respect to the one deposited directly on the stainless steel surface. In addition, the electrochemical behaviour of SS/SiOx/PbO2 interfaces was studied by electrochemical impedance spectroscopy (EIS). The EIS results showed that the presence of SiOx favors electron transfer within the oxide layer which improves electro-oxidation capability. Moreover, bulk electrolysis showed that over 100% colour removal and 84% COD removal, using SS/SiOx/PbO2 at acidic pH were reached after 300 min. High Performance Liquid Chromatography analysis was used for the quantitative determinations of initial Amaranth dye molecule removal and to evaluate its specific degradation rate. In order to evaluate the phototoxicity of treated solution with different by-products, different tests of germination were performed and proved that the electrochemical treatment with modified PbO2 could be as an efficient technology for reducing hazardous wastewater toxicity and able to produce water available for reuse.

Spinodal decomposition versus nucleation and growth mechanism of phase separation in nonstoichiometric silicon oxide films during high temperature annealing

In this work, kinetic mechanisms of phase separation in nonstoichiometric Si oxide (SiOx) films during high temperature annealing are studied theoretically. Analysis of the composition dependence of the Gibbs free energy of SiOx phase is carried out to derive its binodal and spinodal characteristics. The ranges of the values of x corresponding to stability, metastability, and instability of nonstoichiometric Si oxide with respect to phase separation are determined as the functions of annealing temperature and SiOx elastic properties. The composition-temperature regions of the spinodal decomposition and the nucleation and growth mechanisms of phase separation are presented. Obtained results open a way to a development of the kinetic theory of phase separation in SiOx films and formation of Si quantum dots/SiO2 matrix composite structures.

Conductivity and Surface Passivation Properties of Boron‐Doped Poly‐Silicon Passivated Contacts for c‐Si Solar Cells

Passivating the contacts of crystalline silicon (c‐Si) solar cells with a poly‐crystalline silicon (poly Si) layer on top of a thin silicon oxide (SiOx) film are currently of growing interest to reduce recombination at the interface between the metal electrode and the c‐Si substrate. This study focuses on the development of boron‐doped poly‐Si/SiOx structure to obtain a hole selective passivated contact with a reduced recombination current density and a high photo‐voltage potential. The poly‐Si layer is obtained by depositing a hydrogen‐rich amorphous silicon layer by plasma enhanced chemical vapor deposition (PECVD) exposed then to an annealing step. Using the PECVD route enables to single side deposit the poly Si layer, however, a blistering of the layer appears due to its high hydrogen content, which leads to the degradation of the poly‐Si layer after annealing. In this study, the deposition temperature and gas flow ratio used during PECVD step are optimized to obtain blister‐free poly‐Si layer. The stability of the surface passivation properties over time is shown to depend on the blister density. The surface passivation properties are further improved thanks to a post process hydrogenation step. As a result, a mean implied photo‐voltage value of 714 mV is obtained.

Laser-Stimulated Phase Transformations in Thin Layers of SiOx and CNx –Ni

We demonstrate the possibility of laser-assisted phase transformations in thin layers of SiOx from the amorphous nonstoichiometric phase into a nanocomposite layer with Si nanocrystals embedded in the silicon-oxide matrix. The formation of Si nanoparticles (NPs) in SiOx films occurs due to their irradiation with nanosecond pulses of a Nd+3:YAG laser with base wavelength λ = 1.064 μm and the second harmonic λ = 0.532 μm. The nanostructurization of the surface in the form of nanoparticles with mean sizes varying within the range 5–85 nm was detected with the help of atomic force microscopy and optical transmission spectra. The sizes of nanoparticles and their surface distribution depend on the intensity of the laser and its wavelength λ. We determined the mechanism of formation of Si nanocrystals by laser-induced thermal shocks. By analyzing the results of atomic force microscopy, as well as the data of Raman and polarization-modulation spectroscopies, we detected the increase in the amount of single-crystal phase in the film of CNx–Ni nanocomposite with simultaneous increase in the sizes of CNx–Ni nanoparticles caused by the action of laser pulses. The mechanism of laser-stimulated nanocrystallization is proposed. This mechanism is based on the local annealing of the CNx shell as a result of laser heating of the metallic Ni core of CNx–Ni nanoparticles and a more intense sublimation of the amorphous phase of CNx–Ni due to the lower temperature of dissociation of the CNx shell as compared with the Ni core.

Ring Wrinkle Patterns with Continuously Changing Wavelength Produced Using a Controlled-Gradient Light Field.

We report a facile method to prepare gradient wrinkles using a controlled-gradient light field. Because of the gradient distance between the ultraviolet (UV) lamp and polydimethylsiloxane (PDMS) substrate during UV/ozone treatment, the irradiance reaching the substrate continuously changed, which was transferred into the resulting SiOx film with a varying thickness. Therefore, wrinkles with continuously changing wavelength were fabricated using this approach. It was found that the wrinkle wavelength decreased as the distance increased. We fabricated 1-D wrinkle patterns and ring wrinkles with a gradient wavelength. The ring wrinkles were prepared using radial stresses, which were achieved by pulling the center of a freely hanging PDMS film. The resulting wrinkles with changing wavelength can be used in fluid handling systems, biological templates, and optical devices.

IR Spectroscopy and Raman Spectroscopy for Controlling and Investigating Thin-Film Coatings

Vibrational spectroscopy is used to characterize inorganic solid, superhard, and anticorrosive thin-film coatings prepared via magnetron sputtering and surface chemical reactions. The most detailed and correct information on the parameters of the dielectric function of coatings can be obtained from the frequency angular spectra of phonon polaritons. Optical characteristics of coatings are considered using examples of SiOxNy and SiOx films grown on steel and silicon substrates.

High-quality surface passivation of crystalline silicon with chemical resistance and optical transparency by using catalytic chemical vapor deposition SiNx layers and an ultrathin SiOx film

We have developed high-quality surface passivation films for n-type crystalline silicon (c-Si) with an effective minority carrier lifetime (τeff) of more than 6 ms or a maximum surface recombination velocity (SRVmax) of less than 2 cm/s using two highly optically transparent silicon nitride (SiNx) layers and an ultrathin SiOx film. First, an ultrathin SiOx film is unintentionally formed on the surface of c-Si by annealing c-Si in N2 ambient at 350 °C. Then, on the SiOx film, two SiNx layers are sequentially formed at substrate temperatures (Tsub) of 100 and 250 °C by catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD. With the combination of the ultrathin SiOx film and the two SiNx layers, we can obtain a novel passivation structure with high-quality surface passivation, high optical transparency, and high chemical resistance for subsequent processes.