Silicon Carbide Thin Films Research Articles

Fatigue Life Properties and Availability of Proof Testing in Ceramics-Coated Glass

The long-term durability of high-performance ceramics-coated glass should be appropriately evaluated prior to their practical applications. Fatigue properties of such materials should be clarified to ensure the long-term durability. In this work, a borosilicate glass was coated with alumina or silicon carbide thin films by sputtering method. Fatigue tests of coated glass were conducted under three-point bending. It was clarified that the fatigue life was elongated by coating ceramic thin films on glass and the fatigue life distribution in glass coated with thicker films shifted toward longer life region. Proof testing was carried out for coated glass specimens to remove specimens having lower fatigue lives. It was suggested that proof testing for fatigue of ceramics-coated glass was effective as a screening procedure which can remove weaker specimens by static pre-loading before fatigue tests. In correlating average fatigue lives, fatigue resistance strength was introduced as the average bending strength divided by the applied maximum stress. It was revealed that the average fatigue lives of every coated glass, including average lives after proof testing, were well correlated by a power function of the fatigue resistance strength and its modified parameter, irrespective of film material and thickness and also applied stress level.

Wide bandgap semiconductor thin films for piezoelectric and piezoresistive MEMS sensors applied at high temperatures: an overview

The use of wide bandgap semiconductor thin films as sensing materials for micro-electrical---mechanical systems (MEMS) sensors has been the subject of much discussion in the academic and industrial communities. The motivation is that such materials are recognized as being suitable for extreme environment applications, namely: high temperatures, intense radiation and corrosive atmospheres. Among the wide bandgap semiconductor materials, aluminum nitride (AlN), zinc oxide (ZnO), diamond-like carbon (DLC) and silicon carbide (SiC) are highlighted due to their inherent sensing properties and compatibility with MEMS fabrication processes. Here we show an overview on the development technologies and applications of AlN, ZnO, DLC and SiC thin films in piezoelectric and piezoresistive MEMS sensors. Emphasis is placed on the influence of the temperature on the piezoelectric and piezoresistive properties of these films.

The Friction Characteristics and Microscopic Properties of Composite Electroplating Thin Films

The development of composite thin film materials bloomed with increasing demand and technical improvements. They have been used in various engineering areas, such as micro-conductor, sensors, and micro-electro-mechanical-system (MEMS) [1-. Nowadays, scientists were able to electroplate silicon carbide thin films directly on metal materials. Silicon carbide has many excellent mechanical properties, such as high Youngs modulus, high melting point, high hardness, and chemical inertness with resistance to high temperature oxidation and creep [4-7]. It is widely utilized in automotive and aerospace industry. Hence, it is very important to improve the durability and reliability of electroplated silicon carbide thin films.

High growth rate of a-SiC:H films using ethane carbon source by HW-CVD method

Hydrogenated amorphous silicon carbide (a-SiC:H) thin films were prepared using pure silane (SiH4) and ethane (C2H6), a novel carbon source, without hydrogen dilution using hot wire chemical vapour deposition (HW-CVD) method at low substrate temperature (200 °C) and at reasonably higher deposition rate (19·5 Å/s < r d < 3·2 Å/s). Formation of a-SiC:H films has been confirmed from FTIR, Raman and XPS analysis. Influence of deposition pressure on compositional, structural, optical and electrical properties has been investigated. FTIR spectroscopy analysis revealed that there is decrease in C–H and Si–H bond densities while, Si–C bond density increases with increase in deposition pressure. Total hydrogen content drops from 22·6 to 14·4 at.% when deposition pressure is increased. Raman spectra show increase in structural disorder with increase in deposition pressure. It also confirms the formation of nearly stoichiometric a-SiC:H films. Bandgap calculated using both Tauc’s formulation and absorption at 104 cm−1 shows decreasing trend with increase in deposition pressure. Decrease in refractive index and increase in Urbach energy suggests increase in structural disorder and microvoid density in the films. Finally, it has been concluded that C2H6 can be used as an effective carbon source in HW-CVD method to prepare stoichiometric a-SiC:H films.

Stoichiometric 6H-SiC thin films deposited at low substrate temperature by laser ablation

Silicon carbide thin films were grown by laser ablation on silicon substrates at different deposition temperatures using SiC powders as target material. The structural, morphological, compositional, and optical properties were studied as a function of the deposition temperature. The 6H-SiC crystalline phase was observed by Raman spectroscopy, x-ray diffraction, and transmission electron diffraction without the presence of any other polytype. In the room temperature photoluminescence spectra, a broad band was observed in the visible region which suggests that these films can have applications on silicon based optoelectronics.

Generation of periodic structures on SiC upon laser plasma XUV/NIR radiations

AbstractSurface periodic structures are generated upon irradiation of a silicon carbide (SiC) thin film by the plasma produced by 40 fs pulses from a Ti:Sapphire laser focused onto a thick low density polyethylene (LDPE) foil facing the SiC film. Independently of the number of laser pulses applied, these structures, with average regular periodicity of 710 nm, are evident throughout all irradiated areas. We attribute their formation to the efficient coupling of the unfocused femtosecond laser pulse with the incoherent extreme ultraviolet component of the laser-generated LDPE plasma.

Cyclic Indentation Behavior of Layered Nanocomposites: Viscoplastic Numerical Study

AbstractThe indentation behavior of layered metal/ceramic nanocomposites was studied. The primary objective was to examine the evolving plastic deformation in the ductile metal constrained by the hard ceramic layers, during indentation cycling with respect to fixed maximum and minimum indentation loads. The model consists of alternating aluminum and silicon carbide thin films on a silicon substrate, with the Al/SiC layered structure being indented by a diamond indenter. The rate-dependent viscoplastic response of Al was specifically taken into account in the numerical model. Plastic deformation in the ductile Al layers continued to occur during the unloading phase of the first cycle, in addition to during subsequent reload/unload processes. Cyclic plasticity resulted in an open load-displacement loop and the indenter continued to move deeper in accordance with each cycle. For the control model of a thick homogeneous Al layer, there was no hysteresis loop and the transient behavior approached stabilization...

Fabrication of silicon and carbon based wide-gap semiconductor thin films for high conversion efficiency

Nitrogen doped amorphous silicon carbide (N-doped a-SiC) thin films were fabricated by radio frequency plasma enhanced chemical vapor deposition (RF-PeCVD) method using mixed solution of tetramethylsilane (TES) and 1,1,1,3,3,3-hexamethyldisilazane (HMDS) as a liquid source. Chemical composition of N-doped a-SiC thin film was Si:C = 1:4 and sp2-bonded carbon ratio was 0.75. N-doped DLC were multi-phase structure including a-SiC phase, sp2 clusters and a-Si clusters. Optical gap and resistivity of the film were 1.68 eV and 4.32×104 Ω cm, respectively. From photocurrent measurement under UV exposure, it was clarified that the film functioned as n-type semiconductor materials with 4.87 % of quantum yield, which was on the same level as that obtained at anatase-type titanium oxide prepared by sol-gel method. To apply these films to solar cells, further improvements of optical gap and conductivity are necessary.

Growth of Hexagonal Columnar Nanograin Structured SiC Thin Films on Silicon Substrates with Graphene-Graphitic Carbon Nanoflakes Templates from Solid Carbon Sources.

We report a new method for growing hexagonal columnar nanograin structured silicon carbide (SiC) thin films on silicon substrates by using graphene–graphitic carbon nanoflakes (GGNs) templates from solid carbon sources. The growth was carried out in a conventional low pressure chemical vapor deposition system (LPCVD). The GGNs are small plates with lateral sizes of around 100 nm and overlap each other, and are made up of nanosized multilayer graphene and graphitic carbon matrix (GCM). Long and straight SiC nanograins with hexagonal shapes, and with lateral sizes of around 200–400 nm are synthesized on the GGNs, which form compact SiC thin films.

Mechanical Characterization of Polycrystalline and Amorphous Silicon Carbide Thin Films Using Bulge Test

This paper aims at determining the mechanical parameters such as Young's modulus, Poisson's ratio, and intrinsic stress of polycrystalline and amorphous silicon carbide thin films using the bulge test. A suitable method for the bulge test of highly compressive amorphous SiC films was devised by developing tensile composite layers involving a highly tensile substrate layer. A setup suitable for use in high temperatures was developed to hold membrane chips mechanically for applying pressure. The center deflection was measured with optical interferometry. The bulge test was done on square and rectangular membranes in order to ascertain the Poisson's ratio and the exact Young's modulus of the material. The tests in this paper were conducted at room temperature. The tensile polycrystalline SiC films were obtained by low-pressure chemical vapor deposition (LPCVD) at 825°C, using monomethylsilane as the precursor. The amorphous SiC (a-SiC) films were deposited by plasma enhanced chemical vapor deposition (PECVD) process at a temperature of 870°C with silane and acetylene as precursors. Test chips were pressurized from outside the membrane cavity, and membrane deflection was measured for each pressure step. The poly-SiC layers indicated a Young's modulus of 280 GPa with a Poisson's ratio of 0.237. The Young's modulus of a-SiC films was found to be 232 GPa, but the Poisson's ratio could not be determined as we used a composite layer. A comparison with the existing literature values of Young's modulus was also done.

Nanocrystalline SiC sputtered on porous silicon substrate after annealing

A novel technique for the fabrication of a nanocrystalline silicon carbide (SiC) thin film is introduced in this study. Thin layers of silicon carbide are successfully deposited on a porous silicon (PS) substrate via radio frequency magnetron sputtering. The PS skeleton acts as a template for the growth of SiC with the same morphology. To improve the PS stability as a template, an ultrathin layer of carbonized silicon is used to cover the entire PS surface via thermal carbonization. The structural results show that the annealing process at elevated temperatures induces crystallinity in amorphous as-deposited SiC. The optical results demonstrate an enhancement in porosity of the deposited SiC samples upon exposure to high annealing temperatures.

Amorphous Silicon Carbide Film Formation at Room Temperature by Monomethylsilane Gas

The silicon carbide thin film formation process, completely performed at room temperature, was developed by argon plasma and a chemical vapor deposition using monomethylsilane gas. Silicon-carbon bonds were found to exist in the obtained film, the surface of which could remain specular after exposure to hydrogen chloride gas at 800 oC. The silicon dangling bonds formed at the silicon surface by the argon plasma are considered to react with the monomethylsilane molecules at room temperature to produce the amorphous silicon carbide film.

Piezoresistivity and Electrical Conductivity of SiC Thin Films Deposited by High Temperature PECVD

We introduce a novel high temperature PECVD process and use it for the deposition of silicon carbide thin films on oxidized silicon wafers at 900°C substrate temperature. A variation of the atomic composition over a wide range is achieved by altering the flow ratio of the precursors silane (SiH4) and acetylene (C2H2). XPS analysis is performed to verify the silicon to carbon ratio in the deposited layers. The resistivity of the obtained thin films shows a strong dependence on the Si/C-ratio. Four point measurements show the resistivity ranging between 5•10-3Ωcm for C-rich layers and &gt;107Ωcm for near stoichiometric layers. We investigate the piezoresistivity of the SiC layers at room temperature under compressive and tensile strain using the four point bending method. The same method is used to analyze selected layers at elevated temperatures up to 600°C. Based on the results we evaluate the applicability of the obtained thin films for strain transducing in harsh environment MEMS sensors.

Identification and tackling of a parasitic surface compound in SiC and Si-rich carbide films

Abstract Silicon carbide and silicon rich carbide (SiC and SRC) thin films were prepared by PECVD and annealed at 1100 °C. Such a treatment, when applied to SiC/SRC multilayers, aimed at the formation of silicon nanocrystals, that have attracted considerable attention as tunable band-gap materials for photovoltaic applications. Optical and structural techniques (X-ray photoelectron spectroscopy, Reflectance and Transmittance, Fourier Transformed Infrared Spectroscopy) were used to evidence the formation, during the annealing treatment in nominally inert atmosphere, of a parasitic ternary SiO x C y surface compound, that consumed part of the originally deposited material and behaved as a preferential conductive path with respect to the nanocrystal layer in horizontal electrical conductivity measurements. The SiO x C y compound was HF-resistant, with composition dependent on the underlying matrix. It gave rise to a Si-O related vibration in FTIR analysis, that may be misinterpreted as due to silicon oxide. The compound, if neglected, can affect the structural and electrical characterization of the material. To overcome this problem, a procedure is analyzed, based on the deposition of a sacrificial capping a-Si:H layer that partially oxidizes, and is removed by tetra methyl ammonium hydroxide (TMAH) after annealing. XPS analysis revealed that the resulting surface is mainly made up of SiC regardless of the composition of the underlying SRC layer. Subsequent SF 6 :O 2 dry etching results in a porous SiC-rich surface layer. The proposed method is effective in controlling the SRC surface configuration, and allows the performance of reliable optical and electrical characterization.

Non-adiabatic ab initio molecular dynamics of supersonic beam epitaxy of silicon carbide at room temperature

In this work, we investigate the processes leading to the room-temperature growth of silicon carbide thin films by supersonic molecular beam epitaxy technique. We present experimental data showing that the collision of fullerene on a silicon surface induces strong chemical-physical perturbations and, for sufficient velocity, disruption of molecular bonds, and cage breaking with formation of nanostructures with different stoichiometric character. We show that in these out-of-equilibrium conditions, it is necessary to go beyond the standard implementations of density functional theory, as ab initio methods based on the Born-Oppenheimer approximation fail to capture the excited-state dynamics. In particular, we analyse the Si-C(60) collision within the non-adiabatic nuclear dynamics framework, where stochastic hops occur between adiabatic surfaces calculated with time-dependent density functional theory. This theoretical description of the C(60) impact on the Si surface is in good agreement with our experimental findings.

Hydrogenated amorphous silicon-carbide thin films with high photo-sensitivity prepared by layer-by-layer hydrogen annealing technique

Hydrogenated amorphous silicon carbide thin films with high photo-sensitivity were fabricated by using layer-by-layer hydrogen annealing technique in conventional plasma enhanced chemical vapor deposition system. It was found that the photo-conductivity is increased from 1.9×10−7 to 1.5×10−6S/cm after layer-by-layer hydrogen annealing. The photo-sensitivity can reach as high as 106 for sample with optical band gap of 2.11eV. The influence of the hydrogen annealing time on film quality and optical properties were investigated. It was demonstrated that the layer-by-layer hydrogen annealing technique can improve the film quality, which can be attributed to both the hydrogen chemical annealing and hydrogen passivation effect.

Deposition temperature effects on optical and structural properties of amorphous silicon carbide films

Hydrogenated amorphous silicon carbide thin films (a–SiC:H) were elaborated by DC magnetron sputtering technique by using 6H–SiC as target. The a–SiC:H films of 0.9–1.5 µm thicknesses were deposited at different temperatures of 250, 350, 450 and 550°C on p–type Si(100) and Corning glass 9075 substrates. The deposited films (a–SiC:H) were investigated by Infrared Spectroscopy (FTIR), spectrophotometry (UV–visible–NIR), Secondary Ion Mass Spectrometry (SIMS), and photoluminesence spectroscopy. The previous results of the FTIR measurements reveal the existence of a band located at 775 cm−1, which corresponds to Si–C stretching vibration of SiC amorphous, whereas the Si–C bonds of SiC crystalline is around 810 cm−1. The optical gap varies between 1.9 and 2.10 eV as a function of films' thicknesses and temperature. In addition, the PL spectra of the elaborated films show that the intensity increases when the deposition temperature increases.

Optical limiting effects in nanostructured silicon carbide thin films

We present the results of experiments on the interaction of nanosecond laser radiation at 532 and with nanostructured silicon carbide thin films of different polytypes. We have found the effect of optical intensity limiting at both wavelengths. The intensity of optical limiting at is shown to be an order of magnitude less than that at . We discuss the nature of the nonlinearity, leading to the optical limiting effect. We have proposed a method for determining the amount of linear and two-photon absorption in material media.

Silicon carbide nanowires as highly robust electrodes for micro-supercapacitors

The effectiveness of silicon carbide (SiC) nanowires (NW) as electrode material for micro-supercapacitors has been investigated. SiC NWs are grown on a SiC thin film coated with a thin Ni catalyst layer via a chemical vapor deposition route at 950 °C. A specific capacitance in the range of ∼240 μF cm−2 is demonstrated, which is comparable to the values recently reported for planar micro-supercapacitor electrodes. Charge–discharge studies demonstrate the SiC nanowires exhibit exceptional stability, with 95% capacitance retention after 2 × 105 charge/discharge cycles in an environmentally benign, aqueous electrolyte.

Chemical vapor deposition of amorphous silicon carbide thin films on metal surfaces using monomethylsilane gas at low temperatures

The low temperature chemical vapor deposition process of depositing silicon carbide on a metal surface, such as aluminum and stainless steel, was developed using monomethylsilane gas. In order to prepare the reactive substrate surface, two alternative methods were separately used. The first was the formation of a silicon interlayer containing silicon dimers. The other method was the argon plasma etching for producing dangling bonds. After the reactive surface preparation, the silicon carbide thin film was formed at room temperature using monomethylsilane gas. Because the silicon–carbon bond remained after the deposition, the silicon carbide coating technology is expected to be applicable for various metals.